Methods of obtaining full-density and fine grain sintered titanium components

Abstract

A method (100) of obtaining a full-density sintered titanium component can include providing (110) a titanium component having a starting density of 92% or less. The titanium component can be heated to and held at a sintering temperature (120) under a sintering atmosphere containing hydrogen with a pressure during sintering less than 0.2 MPa. This can sinter (130) the titanium component to greater than 92% theoretical density forming a sintered component. The sintered component can be held (140) at a densification temperature while applying a gaseous pressure of 0.2 MPa to 100 MPa with a densification atmosphere, to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component.

Description

[0001] METHODS OF OBTAINING FULL-DENSITY AND FINE GRAIN SINTERED TITANIUM COMPONENTS

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003] This application claims priority to U.S. Provisional Patent Application No. 63 / 671,911, filed on July 16, 2024, which is hereby incorporated herein by reference.

[0004] BACKGROUND

[0005] Titanium (Ti)-based materials can be made using powder metallurgy processes. A key step of the powder metallurgy process is sintering, whereby metal powder particles are bonded to form a nearly fully densified solid material. A common issue, however, is that there can be a small but critical amount of porosity in the sintered parts. Typical porosity ranges from 1.0 to 5.0% by volume. In other words, the sintered materials typically have a relative density of approximately 95.0 to 99.0%, depending on the specific materials, conditions, and processing steps. The existence of pores in the sintered metallic materials limits these materials from being used in demanding applications. Such limitation is especially an acute problem for titanium alloys.

[0006] Powder metallurgy (PM) has been regarded as a viable and promising approach for reducing the cost of Ti fabrication because of its near-net-shape capability and the potentially melt-less nature of the process. There are generally two kinds of powder metallurgy approaches for making PM titanium products: the blended elemental (BE) method and the pre-alloyed (PA) method. The BE method, in general, refers to the pressing and sintering of blended elemental powders. Sintering is generally carried out under vacuum. The PA method refers to sintering pre-alloyed powders, which are typically produced using gas atomization or plasma rotating electrode techniques. Pre-alloyed powders have high hardness and, therefore, poor press-ability when compacted using conventional, uni-axial, cold pressing methods.

[0007] Pore-free sintered materials can be obtained by using a pressure-assisted sintering and consolidation process, including hot pressing, hot isostatic pressing (HIP), and / or other high-pressure thermomechanical processes. HIPing is a superior process because it can be used to produce near-net-shaped parts, while the hot pressing and thermomechanical working are limited in that regard. However, as explained in the next section, conventional HIP is an expensive and cost-prohibitive process, which is why it is not widely used except for niche high end applications where the high cost of HIPing can be tolerated.

[0008] HIPing has been used to consolidate powder or close porosity of components for many years. Components can be made by putting powder in an evacuated and sealed can and then subjecting the can to HIPing. Components can also be made by first sintering the components using pressure-less processes, such as sintering in a variety of atmospheres, including vacuum, Ar, or other inert atmospheres. However, the conventional HIPing is done at very high pressures, typically 100 -300 MPa. The capital cost for HIPing with such high pressure is very high so HIPing adds significantly to the total manufacturing cost.

[0009] Overall, considering the need to obtain full density and fine grain microstructure in a sintered material without the cost of a traditional high pressure hot isostatic pressing (HIP), it is highly desirable to develop a process that would deliver fully dense, i.e., greater than 99.5% relative density with a refined microstructure in one furnace cycle at a moderate pressure level.

[0010] SUMMARY

[0011] An example method of obtaining a full-density sintered titanium component can include providing a titanium component having a starting density of 92% or less. The titanium component can be heated to, and held at, a sintering temperature under a sintering atmosphere containing hydrogen with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density, thus forming a sintered component. The sintered component can be held at a densification temperature, while applying gaseous pressure of 0.2 MPa to 100 MPa with a densification atmosphere, to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component.

[0012] Another example method of obtaining a sintered titanium component can include providing a titanium component having a starting density. The titanium component can be either a green compact or a pre-sintered part. If the titanium component is a green compact that includes a polymeric binder, the green compact can be heated in the presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder, thus forming a debinded compact. The titanium component can then be heated, whether as a debinded compact or as a pre-sintered part, to a sintering temperature and held at the sintering temperature under a sintering atmosphere with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density, thus forming a sintered component. The sintered component can be held at a densification temperature while applying a gaseous pressure of 0.2 MPa to 100 MPa under a densification atmosphere, to hot isostatically press (HIP) the sintered component to near full density. The sintered component can also be cooled to room temperature in a cooling atmosphere. At least one of the sintering atmosphere, the densification atmosphere, and the cooling atmosphere can include hydrogen.

[0013] There has thus been outlined, rather broadly, the features of embodiments of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying drawings and claims, or may be learned by the practice of the invention.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a flowchart illustrating an example method of obtaining a full-density sintered titanium component, in accordance with the present technology.

[0016] FIG. 2A is a graph of temperature and pressure over time for an example method in accordance with the present technology.

[0017] FIG. 2B is a graph of temperature and pressure overtime for another example method in accordance with the present technology.

[0018] FIG. 3 is a flowchart illustrating an example method of obtaining a sintered titanium component, in accordance with an example of the present technology.

[0019] FIG. 4 shows scanning electron micrograph (SEM) images of a titanium material made using a method as described herein. The left image shows the material before the HIP operation, and the right image shows the material after HIP. The material was formed from deoxygenated angular powder. Before HIP, the material had a density of 95.6% and an oxygen content of 0.22%. FIG. 5 shows SEM images of another titanium material before and after HIP. The material was made from commercial titanium hydride powder. Before HIP, the material had a density of 98.5%.

[0020] FIGs. 6 is an SEM image of another titanium component after being HIP processed. FIGs. 7 is an SEM image of another titanium component after being HIP processed. FIGs. 8 is an SEM image of another titanium component after being HIP processed. These drawings are provided to illustrate various aspects of the invention and are not intended to be limiting of the scope in terms of dimensions, materials, configurations, arrangements or proportions unless otherwise limited by the claims.

[0021] DETAILED DESCRIPTION

[0022] While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. Thus, the following more detailed description of the embodiments of the present invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the present invention, to set forth the best mode of operation of the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the present invention is to be defined solely by the appended claims.

[0023] Definitions

[0024] In describing and claiming the present invention, the following terminology will be used.

[0025] As used herein, “hydrogen-containing atmosphere” refers to an atmosphere which contains a non-zero percentage of hydrogen gas, where the hydrogen gas is externally introduced rather than liberated or produced from the feedstock, sintered or densified materials.

[0026] As used herein, “fine and ultrafine” refer to grain sizes which range from about 5 pm to about 20 pm for fine grains, and about 0.1 pm to about 5 pm for ultrafine grains. Most often grains sizes can be about 0.1 pm to about 3 pm. As used herein, the terms “dynamically controlled hydrogen atmosphere” or “dynamically controlled H2 partial pressure” are used to mean that the H2 partial pressure can be held constant or varied as a function of time during each step in the thermal cycle. In any embodiment, H2 partial pressure is dynamically controlled during sintering and phase transformations including eutectoid decomposition as a function of time and temperature in order to precisely control the microstructure of the as-sintered Ti or Ti alloy. The H2 partial pressure is controlled by the addition or removal of H2 from the atmosphere using mass flow controllers or pressure controllers. When hydrogenated titanium is used as all or part of the particulate feedstock material, H2 will be naturally evolved during heating of the material. However, for this invention, it is important that the level of hydrogen be dynamically controlled beyond this natural occurrence by the addition or removal of additional H2 gas. The degree of grain refinement due to phase transformations including eutectoid decomposition and dehydrogenation results from the changing phase equilibria between a, ci2, P, and 8 phases of Ti and Ti alloys during processing. These phase equilibria change with temperature and with equilibrium hydrogen concentration, which varies as a function of temperature and H2 partial pressure. Therefore, by dynamically controlling partial pressure of H2 as well as temperature, phase evolution and, therefore, microstructure can be precisely controlled at each step of the process. The dynamically controlled hydrogen atmosphere can have, for example, partial pressures of H2 between 0.01 MPa and 100 MPa, which are achieved by a mixture of H2 and an inert gas at approximately 0.01 MPa to 100 MPa total pressure, pure H2 at pressures approximately between 0.01 MPa and 100 MPa, or a fixed mixture of H2 and inert gas at pressures between 0.01 and 200 MPa. Therefore, partial pressure of H2 is dynamically controlled by dynamically varying the gas ratio in the former example, or the absolute system pressure in the latter two. The partial pressure of H2 can be controlled independently of any H2 that is produced from the evolution of H2 gas from hydrogenated titanium during sintering. Different H2 partial pressure profiles can be used to tailor the mechanical properties of the as-sintered material by controlling the as-sintered microstructure.

[0027] As used herein, the term “near full density” refers to a minimization of porosity in the material, such that if full density were achieved, the density of the bulk material would be equal to 99.6% or more of the theoretical density of the material. Densities can be measured by the Archimedes method or any other method that produces equivalent results. As used herein, near full density refers to the material having a relative density of greater than 95.0% relative density. As used herein, “full density” refers to the material having a relative density of greater than 99.5% relative density. According to some embodiments of the invention, the titanium metal or the titanium metal alloy achieves a relative density greater than 97.0%. In other embodiments, the titanium metal or the titanium metal alloy has a near full density. In other embodiments, the titanium metal or the titanium metal alloy has a full density.

[0028] As used herein, the term “a-phase” refers to a hexagonal close-packed (HCP) of Ti, which may or may not contain alloying elements. The term P-phase refers to a body-centered cubic (BCC) Ti, which may or may not also contain alloying elements. The term 5-phase refers to a face-centered cubic (FCC) hydrogenated titanium or Ti hydride, TiHx, where x varies from 1.5 to 2, at room temperature. The term a.2 refers to TfAl phase which is an ordered hexagonal structure in a phase with DO 19 crystal structure. The definitions of the phases are further illustrated by the phase diagrams of Ti-H, and Ti-6A1-4V-H (ASM Handbook, Vol 3, p238, 1992). It should be noted that the phase diagrams of titanium alloys with hydrogen vary considerably within the scientific literature and are not yet completely characterized. Therefore, the exact temperatures and time of sintering, isothermal holding for eutectoid transformation, and dehydrogenation may all vary accordingly.

[0029] As used herein with respect to an identified property or circumstance, “substantially” refers to a degree of deviation that is sufficiently small so as to not measurably detract from the identified property or circumstance. The exact degree of deviation allowable may in some cases depend on the specific context.

[0030] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.

[0031] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (z. ?., meaning “including, but not limited to,”) unless otherwise noted. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Additionally, the phrase “consisting essentially of’ will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed invention. The phrase “consisting of’ excludes any element not specifically specified.

[0032] The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0033] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0034] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

[0035] Any steps recited in any method or process claims may be executed in any order and are not limited to the order presented in the claims. Means-plus-function or step-plus- function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; and b) a corresponding function is expressly recited. The structure, material or acts that support the means-plus function are expressly recited in the description herein. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents, rather than by the descriptions and examples given herein.

[0036] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

[0037] Methods of Obtaining Full-density Sintered Titanium Components

[0038] Methods of obtaining full-density sintered titanium components are described herein. In one example, a method of obtaining a full-density sintered titanium component can include providing a titanium component having a starting density. In certain examples, the starting density can be 92% or less. In some examples, the titanium component can be either a green compact or a pre-sintered part. The green compact can be heated in the presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder forming a debinded compact. The debinded compact or pre-sintered part can be heated to, and held at, a sintering temperature under a sintering atmosphere containing hydrogen with a pressure during sintering less than 0.2 MPa to sinter the titanium component to greater than 92% theoretical density, forming a sintered component. The sintering atmosphere can be a mixture of hydrogen with an inert gas, such as argon. The partial pressure of hydrogen can be dynamically controlled to control the hydrogen content in Ti. As a general guideline, for embodiments using hydrogen during the sintering step, the fraction of hydrogen in the Ar+H2 mixture during lower pressure sintering may vary from 5 % to 100%, and in some cases 50 to 100%.

[0039] The sintered component can be held at a densification temperature, while applying a gaseous pressure greater than the pressure of the lower pressure sintering step to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component, up to about 100%. In some cases, the relative density can be greater than 99.7%, and in other cases greater than 99.9%. The HIPing step can be carried out in a densification atmosphere, which may be an inert atmosphere or an atmosphere that includes hydrogen. As a general guideline, for embodiments using hydrogen during the HIPing step, the fraction of hydrogen in the Ar+H2 mixture during lower pressure sintering may vary from 1 % to 100%, in some cases 2% to 50%, and in other cases 5% to 20% or 4% to 10%.

[0040] After the HIPing step, the sinter-HIPed components can be cooled under a dynamically controlled atmosphere. The cooling step can be carried out in an inert atmosphere or in an atmosphere containing hydrogen. The use of hydrogen during cooling is particularly useful when the HIPing step does not include a hydrogen-containing atmosphere. The sintered and HIPed material can be cooled to below the a-P transus temperature and then held at a temperature between 500 and 800 °C to allow phase transformations to reach an equilibrium before cooling further to room temperature. During cooling, phase transformations can continue to occur and yield a refined microstructure. The methods can also include a further step, which can include dehydrogenating the sinter-HIPed part according to the procedures described herein.

[0041] In further detail, the present disclosure describes methods of obtaining full-density titanium components using a sinter-HIP process of sintering and consolidation of solid metals, Ti alloy in particular, to achieve fully densified Ti alloy material and components. Sinter-HIP, meaning "sinter" first, then HIP, i.e. two steps in one furnace cycle.

[0042] These methods can produce Ti alloys from Ti alloy powders, either pre-alloyed or blended elemental powders, by sintering the powder and then hot-isostatically pressing the material in one furnace cycle with two or more phases.

[0043] Atmosphere for the sintering portion of the sinter-HIP method can be an inert atmosphere or a hydrogen-containing atmosphere. A mixture of Ar and H2 is used in some embodiments. The fraction of H2 in the Ar / Fh mixture can generally be dynamically controlled to achieve a desire hydrogen content in Ti parts. For embodiments using hydrogen during the sintering step, the fraction of hydrogen in the Ar+H2 mixture during lower pressure sintering may vary from 5 % to 100%, and in some cases 50% to 100%. For example, the mixture can be 50%Ar-50%H2. Note that sintering is not done at pressures above 0.2 MPa before the density reaches above 92% because the pores would be connected and open to the surfaces of a component when the relative density is less than 92%. In other words, gas in the pores can become trapped, preventing the pores from closing even if pressure is applied later. The sintering step of the sinter-HIP run can be done in a vacuum, but sometimes a slight positive pressure can be used to prevent the backflow of air into the furnace. In any case, the pressure during the sintering step of the sinter-HIP process can generally be sufficiently low, e g., lower than 0.2MPa.

[0044] For the HIPing portion of the sinter-HIP process, an inert atmosphere or a hydrogencontaining atmosphere can be used. In one example, the HIPing step is carried out in the presence of hydrogen. In such cases, the fraction of hydrogen in the Ar+H2 mixture during lower pressure sintering may vary from 0.1 % to 100%, in some cases 2% to 50%, and in other cases 5% to 20% or 4% to 10%. As an example, the partial pressure of H2 can be less than 5 bar.

[0045] Pressure for hot-isostatic-pressing can be less than 10 MPa in some examples (e g. 0.2 MPa to 10 MPa), although higher pressures are usually more beneficial subject to the constraint of costs. In some examples, the pressure during HIPing can be 1 MPa to 20 MPa, or 2 MPa to 10 MPa, or 2 MPa to 6 MPa. In further examples, the pressure during HIPing can be from 0.2 MPa to 100 MPa.

[0046] As a general guideline, the temperatures can vary from 1000 °C to 1400 °C for both the sintering and the HIP portion of the cycle. The temperatures during the sintering step and the HIPing step can be the same or different. The average temperature during the sintering step can vary from 1000 °C to 1400 °C and in some cases 1150 °C to 1250 °C, such as about 1200 °C. The average temperature during the HIPing can vary from 800 °C to 1400 °C and in some cases 850 °C to 1200 °C.

[0047] During the HIP stage, pores in sintered Ti alloy with >92% density can be closed by hot isostatic pressing under inert gas or hydrogen-containing atmosphere (e.g. lOMPa Ar or Ar containing hydrogen), because the strength of Ti alloy at high temperatures (1000 to 1400 °C) is sufficiently low. Advantageously, the sintering temperature-time (T-t) profdes described herein can achieve an ultrafine microstructure while securing near full density and full density sintered components. More specifically, embodiments of these methods can produce ultrafine Ti alloys with full density while using moderate HIP pressure and a small partial pressure of H2 which can allow for reduced equipment and operating costs.

[0048] Because moderate HIP pressure and a small fraction of H2 may be used, the disclosed process can be cost-competitive compared to many other processes for making sintered titanium components. For example, other vacuum or low-pressure sintering processes cannot produce fully dense Ti materials and components by sintering. Additionally, many widely- used HIP processes use very high pressures from 100 to 350 MPa, which makes these processes cost prohibitive to most industrial applications. These processes often produce Ti alloys with a coarse microstructure, which is not satisfactory for most industrial applications. Additionally, many processes utilize separate steps for sintering and HIPing, which drives up costs. The methods described herein address these issues by performing sintering and HIP at a relatively low pressure in a single furnace cycle.

[0049] With this general description in mind, FIG. 1 is a flowchart illustration of one example method 100 of obtaining a full-density sintered titanium component. This method includes: providing a titanium component having a starting density of 92% or less, wherein the titanium component is either a green compact or a pre-sintered part 110; heating the green compact in the presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder forming a debinded compact 120; heating the titanium component as the debinded compact or as the pre-sintered part to, and holding at, a sintering temperature under a sintering atmosphere containing hydrogen with a sintering pressure of less than 0.2 MPa, such as about one atmosphere, or 0.1 MPa, or lower than one atmosphere, to sinter the titanium component to greater than 92% theoretical density forming a sintered component 130; and holding the sintered component at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa with a densification atmosphere that may contain an inert gas and hydrogen, to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component 140. The gaseous pressure during the HlPing step can be maintained above the pressure during sintering. Thus, as an example, with a pressure during sintering of 0.15 MPa, then the gaseous pressure would be greater than 0.15 MPa.

[0050] In some examples, the titanium component can be a green part. In some cases, the green part also contains a polymeric binder. The debinding process can be used for such green parts to remove the polymeric binder. In some cases, the polymeric binder can be a single polymer, but in other cases can include one or more thermoplastic polymers in combination. The multiple polymer components can have different melting or vaporizing temperatures. Some polymer binders will vaporize at a lower temperature, while others melt or vaporize at higher temperatures. In such cases, the debinding can be done by holding the green compact at multiple different temperatures for distinct binding times sufficient to vaporize the binders one component at a time.

[0051] In other examples, the titanium component can be a pre-sintered part. As used herein, pre-sintered part can mean a green part that was subjected to debinding and sintering at a temperature higher than the debinding temperature, to a density that is less than the desired final density. In certain examples, a pre-sintered part can have a density up to 85% of theoretical density so that the part is strong enough to be handled for additional processing steps. Pre-sintering is sometimes used as an intermediate step between debinding and sintering due to practical challenges such as insufficient capacity of sintering furnaces, etc.

[0052] The titanium component can be a green compact that includes titanium powder in some cases. In other cases, the titanium component can be a pre-sintered part that was formed from a green compact. In either case, the original green compact can include titanium powder. In certain examples, the green compact can also include at least one alloying metal powder in the form of a pre-alloyed powder or blend of individual components. Pre-alloyed powder can refer to powder that includes individual particles having both titanium and one or more alloying elements alloyed together within the individual particle. A blend of individual components can refer to powder that includes particles of different metals, where the particles are physically blended together. In such a blend, some particles can be titanium metal particles, while other particles can be made of one or more alloying elements. In some examples, each individual particle in the blend can be made of a single element. The particles of titanium and any alloying elements can be blended together in a ratio to provide a desired composition of the final titanium alloy. In certain examples, alloying elements can include one or more of Al, Cr, V, Fe, Mo, Ni, Cu, Mn, Zr, W, Ta, Nb, Hf, Ag, and Au. For example, in some embodiments the mixture can have the composition of Ti-6A1-4V alloy.

[0053] In further examples, the titanium component can consist of particulate titanium and / or hydrogenated titanium that has or has not been previously alloyed with the elements for the alloy (e.g. aluminum and vanadium for Ti-6A1-4V) as well as particulate alloying elements that are in the form of individual powders or pre-alloyed “master alloys” (e.g. 60A1 / 40V master alloy for Ti-6A1-4V). The particulate titanium and alloying element feed materials may be provided in commercially available powders that are produced from virgin metal using any of the extractive process used in commercial titanium production including, but not limited to, the Kroll Process, the Armstrong Process, the Hunter Process, etc. The particulate titanium and alloying element feed materials may come from materials that are traditionally considered by-products of commercial titanium production processes, such as “sponge fines” from the Kroll Process. The particulate titanium and alloying element feed materials may come from scrap that is produced during milling, machining, or recycling of metals. The particulate titanium and alloying element feed materials may come from a combination of the aforementioned sources. In one embodiment, the particulate titanium and alloying element feed materials can be produced by hydrogenating Ti-6A1-4V machine turning and ball milling to an appropriate size and morphology for compaction and sintering.

[0054] The green compact can have an initial starting density before the debinding, sintering, and hot isostatic pressing. In some examples, the starting density can be from 40% to 90%, and most often from 40% to 80% relative density.

[0055] When the titanium component is initially a pre-sintered part, the pre-sintered part can be a titanium component which is at least partially sintered and has a density less than 92%. Pre-sintered parts can have a density higher than a corresponding green compact. In some examples, the density of the pre-sintered part can be from 60% to 92%, and in some cases 70% to 92%.

[0056] In some examples, the green compact can be formed of powders having a D50 particle size greater than 1 micron. In certain examples, the powders in the green compact can have a D50 particle size from 1 micron to 1,000 microns, or from 1 micron to 500 microns, or from 1 micron to 300 microns, or from 1 micron to 200 microns, or from 1 micron to 100 microns, or from 1 micron to 50 microns, or from 1 micron to 20 microns, or from 20 microns to 1,000 microns, or from 20 microns to 500 microns, or from 20 microns to 300 microns, or from 20 microns to 200 microns, or from 20 microns to 100 microns, or from 20 microns to 50 microns, or from 50 microns to 1,000 microns, or from 50 microns to 500 microns, or from 50 microns to 300 microns, or from 50 microns to 200 microns, or from 50 microns to 100 microns, or from 100 microns to 1,000 microns, or from 100 microns to 500 microns, or from 100 microns to 300 microns, or from 100 microns to 200 microns, or from 200 microns to 1,000 microns, or from 200 microns to 500 microns, or from 200 microns to 300 microns, or from 300 microns to 1,000 microns, or from 300 microns to 500 microns, or from 500 microns to 1,000 microns.

[0057] In one embodiment, the powder can have an average size from about -20 mesh to about +1200 mesh (or 841 to 12 micrometers). In another embodiment, the powder can have a size of from about 100 mesh to about 325 mesh (or 149 to 44 micrometers). In another embodiment, the powder can have a size of about 200 mesh to about 325 mesh (or 74 to 44 micrometers). In another embodiment, the powder can have a size of about 400 mesh. In another embodiment, the powder can have a size of from about 325 mesh to about 450 mesh (or 44 to 32 micrometers), and in another case to about 400 mesh. In another embodiment, the powder can have a size of from about 325 mesh to about 635 mesh (or 44 to 20 micrometers). In another embodiment, the powder can have a size of from about 325 mesh to about 1200 mesh (or 44 to 10 micrometers). In another embodiment, the powder can have a size of from about 450 mesh to about 635 mesh (or 32 to 20 micrometers). In another embodiment, the powder can have a size of from about 400 mesh to about 1200 mesh (or 37 to 10 micrometers). In one optional embodiment, the powder can be prepared by combining corresponding powders with average particle sizes greater than 20 pm with a non-volatile liquid to form a slurry. The slurry mixture can be subjected to size reduction processing (e.g. mechanical or other techniques) to produce powders with average particle sizes less than 20 pm, such as submicron to 20 pm. After the size reduction processing, the slurry can be dried or drained to remove excess liquid and powder particles of which the surface is coated by the non-volatile liquid and isolated from surrounding air or other gaseous atmosphere are collected. In order to reduce residual porosity to lower levels and minimize the size of the residual pores in produced materials, a finer starting powder size may be desirable, while retaining low oxygen levels. In one embodiment, powders of hydrogenated titanium or Ti hydride, optionally with titanium and other alloying elements, can be milled to finer sizes with a protective coating of a non-volatile liquid. Suitable non-volatile milling liquid can substantially coat the powders to prevent oxidizing during milling. This non-volatile liquid can be an organic liquid such as a natural or synthetic oil such as mineral oils, an ionic liquid, or a mixture of these liquids. In this procedure, the powders are mixed with a selected nonvolatile liquid between l / 20thand 20 times the volume of the powder, and then subjected to a particle size reduction process. For example, the powder can be milled in any of a range of milling devices, including but not limited to: drum mills, roller mills, hammer mills, vibration mills, jet mills, attritor mills, or planetary mills. The powder and liquid mixture may or may not be under a protective cover gas of argon or other inert gas. The milled powder slurry can be dried or drained to remove excess liquid. Powder particles of which the surfaces are coated by the non-volatile liquid and isolated from the air or other gaseous atmosphere can then be collected for subsequent processing.

[0058] In another aspect of the present technology, a material is provided that includes any of the titanium metal or titanium metal alloys produced by any of the above processes. The material can be a commercially pure titanium (CP-Ti). CP-Ti is a term that is widely used in the art. CP-Ti is classified on scale of Grade 1 to 4, each level of the scale being based upon the oxygen content and / or alloying according to industry standards. Alternatively, the material can be a commercial alloy of Ti. In one embodiment, the material can be Ti-6A1- 4V. In further examples, the titanium powder can include titanium hydride. In certain examples, the green compact can include titanium metal powder blended with 6A1-4V powder. Titanium hydride can also be included in addition to the titanium metal powder or instead of the titanium metal powder.

[0059] The initial powders can have any suitable shape. In certain examples, the powder can have spherical shaped particles, angular shaped particles, or a combination thereof. In further examples, spherical particles can have an average aspect ratio from 1 to 1.2, or from 1 to 1.1, or from 1 to 1.05. The aspect ratio can be defined as the ratio from the longest dimension of a particle to the shortest dimension of the particle. In more detail regarding the formation of the initial titanium component, in some examples a titanium feed material and alloying additive powders can be formed into a compact in the approximate shape of the final sintered part. First, the powders can be intimately mixed by blending or powder milling. Then the powders can be formed into a powder compact. In one embodiment, this can be done using a cold isostatic press. Powders can be cold isostatically pressed at a sufficient pressure to form a powder compact of the desired shape that can subsequently be sintered. The press can use a compacting pressure ranging from 100 MPa to 500 MPa. In one embodiment, the compacting pressure can be about 350 MPa. In another embodiment, powders can be pressed in a uniaxial die press to form a powder compact of the desired shape that can be subsequently sintered. The press can use a compacting pressure ranging from 100 MPa to 1 GPa. In one embodiment, the compacting pressure can be about 350 MPa. In another embodiment, powder compacts can be manufactured using injection molding by mixing the powders with 10% to 60% binder by volume, heating to an appropriate temperature to sufficiently melt the binder, and injecting into a die of the desired geometry. After injection molding, the compact can be extracted from the die and the binder removed before sintering. The binder may be removed by submersing the compact in a suitable solvent to dissolve the binder, heating to a sufficient temperature to evaporate or thermally decompose the binder along with any residual milling liquids, or a combination of both methods. Suitable binders can consist of a mixture of one or more of a polymer component and / or a wax component. In one embodiment, a 1 : 1 ratio by volume of polyethylene glycol and paraffin wax can be used as the binder. In another embodiment, powders can be formed into the desired shape for sintering without the use of compaction. This method consists of filling a refractory ceramic or metallic mold of the desired geometry with loose powder, tapping or vibrating the mold until the powder settles to at or near its tap density, and loading the mold into a furnace for sintering. If the morphology of the powder is such that reasonable particle-to-particle contact is achievable at tap density, the rapid diffusion of titanium in the presence of hydrogen results in greater than 99% density without pressure-assisted compaction.

[0060] As generally shown in FIG. 2A, green compacts can be held at one or more debinding temperatures (T1 and T2) in the presence of a debinding atmosphere to remove different components of the polymeric binder. In some examples, the debinding atmosphere can be an inert atmosphere, a hydrogen atmosphere, a vacuum, or a combination thereof. Inert atmospheres can include helium, argon, or a combination thereof. For example, a mixture of helium and argon can be used in certain examples. In various examples, the debinding temperatures can be from 400 °C to 1000 °C, or from 400 °C to 800 °C, or from 400 °C to 700 °C, or from 400 °C to 600 °C, or from 400 °C to 500 °C, or from 500 °C to 1000 °C, or from 500 °C to 800 °C, or from 500 °C to 700 °C, or from 500 °C to 600 °C, or from 600 °C to 1000 °C, or from 600 °C to 800 °C, or from 600 °C to 700 °C, or from 700 °C to 1000 °C, or from 700 °C to 800 °C, or from 800 °C to 1000 °C. The green compact can be held at one or more temperatures in these ranges for a sufficient time to remove one or more polymeric binder components in the green compact.

[0061] Notably, although FIG. 2A illustrates multiple stages where temperatures are held constant for a time, heating and cooling steps can also be performed in a continuous manner (i.e. without holding temperature constant). In these cases, temperatures can be ramped up at a rate that allows for complete debinding before arriving at a corresponding sintering temperature or HIPing temperature. FIG. 2B illustrates an initial debinding stage where debinding temperature is continuously increased without holding at a constant intermediate temperatures such as those shown in FIG. 2A (T1 and T2). In cases of continuous heating during debinding, the rate of heating can be controlled such that polymeric binder is fully removed through volatilization and / or degradation by the time a sintering temperature is reached.

[0062] The sintering operation can be performed by heating the debinded compact or presintered part to a sintering temperature and holding at the sintering temperature under a sintering atmosphere as generally illustrated by FIG. 2 A at T3. The sintering temperature can be from 1000 °C to 1400 °C, or from 1100 °C to 1400 °C, or from 1200 °C to 1400 °C, or from 1300 °C to 1400 °C, or from 1000 °C to 1300 °C, or from 1100 °C to 1300 °C, or from 1200 °C to 1300 °C, or from 1000 °C to 1200 °C, or from 1100 °C to 1200 °C, or from 1000 °C to 1100 °C, in some examples. In certain examples, the sintering temperature can be about 1200 °C.

[0063] Both FIG. 2A and 2B show that pressure can be maintained at relatively low pressures during debinding and sintering. In each of these cases, the pressure during debinding and sintering is maintained constant at vacuum or low pressure. However, in some cases, pressures can vary during these stages. In some examples, the atmosphere pressure during sintering can be 10'4torr to 0.2 MPa atm. In further examples, the pressure during sintering can be 10’4torr to 1.5 atm, 10’4torr to 1 atm, 10’4torr to 0.5 atm, or 10’4torr to 0.2 atm. In some cases, the pressure during sintering can be above vacuum pressure. In other examples, the pressure during sintering can be substantially vacuum. In certain examples, the sintering atmosphere can be an inert atmosphere, a hydrogen atmosphere, vacuum, or a combination thereof. When the sintering atmosphere includes hydrogen. In some examples, the sintering atmosphere and the debinding atmosphere can be the same composition, while in other examples these atmospheres can be different.

[0064] The sintering atmosphere and sintering temperature can be sufficient to form the sintered titanium component having a majority beta-phase of the sintered titanium. In one example, the sintering temperature can be above a beta transus temperature and below a melting point of the compact. The beta transus temperature refers to the starting temperature of the alpha to beta phase transformation. The majority beta-phase can be a substantially homogeneous beta-phase titanium material in some examples. Regardless of the starting titanium component, the sintering temperature and time can be sufficient to achieve a theoretical density greater than 92% to form a sintered component. In this case, the void spaces are sufficiently densified and closed so as to close off channels which allow gases to flow from an exterior surface of the sintered component into a center or core portion of the sintered component. In other words, void spaces within an interior of the sintered titanium component are fluidly isolated from the exterior surfaces so as to allow subsequent HIP steps to further densify the component. As a general guideline, it can be useful to note that higher pressures during sintering can allow use of lower temperatures. This can be particularly useful when forming fragile parts or parts which involve very tight dimensional tolerances (i.e. where very low or no deformation is desirable).

[0065] The sintered titanium component can then be densified to full density by HIP by holding the sintered titanium component at a densification temperature (See FIG. 2A and FIG. 2B T4 as an example) while applying gaseous pressure with an inert gas optionally with hydrogen. The densification temperature can be from 800 °C to 1400 °C, and in some cases 850 °C to 1200 °C. The densification temperature can be high enough so that the metal will be soft enough to deform under the applied pressure. In some cases, the sinter-HIP cycle may work even if the temperature for HIPing is below the beta-transus temperature, especially if the pressure is between 10 MPa and 100 MPa. However, the cost of a higher-pressure furnace would be much higher than if the pressure is less than about 10 MPa.

[0066] The gaseous pressure used during the HIP operation can be from 0.2 MPa to lOOMPa in some examples. In further examples, the gaseous pressure can be from 0.2 MPa to 50 MPa or from 1 MPa to lOMPa. In other examples, the gaseous pressure can be from 0.2 MPa to 1 MPa, 2 MPa to 10 MPa, or from 1 MPa to 8 MPa, or from 3 MPa to 10 MPa, or from 5 MPa to 10 MPa, or from 8 MPa to 10 MPa, or from 10 MPa to 20 MPa, or from 10 MPa to 50 MPa. The inert gas used to apply the gaseous pressure during HIP can be argon gas, or a mixture of argon and hydrogen. When the gas for HIPing contains hydrogen, the partial pressure of hydrogen may range from 0.1 to 50MPa, in some cases 0.2 MPa to 10 MPa, and in some cases 2 MPa to 10 MPa.

[0067] The HIP operation can provide a full-density sintered titanium component with a density greater than 99.5% to 100%.

[0068] In some cases, the methods described herein can also include additional operations to refine the microstructure of the titanium component. In one example, refining the microstructure can be performed by cooling the sintered titanium component under a hydrogen-containing atmosphere from the sintering temperature to a phase transformation temperature below the beta-transus temperature and above about 400° C; holding the sintered titanium component at the phase transformation temperature for a phase transformation time and at a phase transformation pressure to produce a transformed titanium material having alpha-phase regions; and holding the transformed titanium material under a substantially hydrogen-free atmosphere or vacuum at a dehydrogenation temperature below the beta- transus temperature and above about a delta-phase decomposition temperature to remove hydrogen from the transformed titanium material to form a dehydrogenated titanium material. The phase transformation and refinement temperature can generally range from 400 °C to 800 °C, and in some cases 600 °C to 675 °C, such as about 650 °C. These refinement temperatures can be held for a refinement time of 15 minutes to 24 hours, and in some cases 30 minutes to 1 hour. The above operations used to refine the microstructure of the titanium component can be performed before the HIP operation. In other examples, the refining of the microstructure can be performed after the HIP operation.

[0069] In further examples, the transformed titanium material can have a density greater than 99.5%. In certain examples, the HIP operation can be performed before the phase transformation, and the density can remain unchanged from before the phase transformation to after the phase transformation. In further examples, the oxygen content of the transformed titanium material can be less than 0.2% or less than 0.15%.

[0070] In some examples, the steps of heating and holding can be performed in a common furnace. The common furnace can be a sinter-HIP furnace adapted for sintering at up to 1400 °C, 10 MPa, and in a hydrogen-containing atmosphere.

[0071] One of the issues with sintered Ti is the grain microstructure. Conventional vacuum or pressure-less sintering of Ti would result in coarse microstructure. The sinter-HIP process described herein does not directly address that issue unless additional steps are taken in combination with the sinter-HIP process. Accordingly, one or more of the sintering, densification and microstructure refinement including eutectoid decomposition steps can be performed under a dynamically controlled hydrogen atmosphere to refine the microstructure. The dynamically controlled hydrogen atmosphere contains primarily hydrogen that was not produced from the particulate titanium feed material. Hydrogen gas can often be liberated from the titanium material during sintering at a high temperature. When sintering is performed under a vacuum, the titanium material can often be completely dehydrogenated during the sintering process. In such a process, the atmosphere surrounding the titanium part during sintering is a near-vacuum with only a small pressure of hydrogen as the hydrogen is driven off from the titanium. In processes according to the present technology, however, the sintering step can be performed under a dynamically controlled hydrogen atmosphere that primarily includes hydrogen from an external source. This dynamically controlled hydrogen atmosphere can be used to control the concentration of hydrogen in the titanium material during sintering, equilibrating, densification, and phase transformations.

[0072] Controlling the hydrogen pressure during sintering, equilibration, densification, and phase transformations including eutectoid decomposition can allow for high sintered densities and fine grain sizes in the final titanium material. In some embodiments of the present technology, the sintering can be performed under an atmosphere with an appropriate pressure of hydrogen such that the titanium material remains in a P-Ti(H) solid solution phase region during sintering. In such embodiments, the material is a solid solution of -phase titanium with hydrogen at the sintering temperature, rather than a pure titanium metal as would be the case under a vacuum. It has been found that titanium can be sintered to very high density at high temperatures, e.g. in the 0-phase region, under controlled hydrogen partial pressure with significant hydrogen content in the metal. Without being limited to one particular mechanism, it is believed that self-diffusion of the titanium in the P-Ti phase is significantly faster than in the a-Ti phase, and a solid solution of hydrogen atoms in titanium can reduce the activation energy of Ti self-diffusion due to the presence of Ti-H bonds, which have a significantly decreased bond strength in relation to Ti-Ti bonds. It is believed that each of these effects helps to achieve full densifi cation during P-Ti(H) sintering.

[0073] Conventionally, titanium is sintered in vacuum in order to achieve high density and low oxygen. Sintering of titanium under argon atmosphere often produces a product with unacceptable residual porosity and oxygen levels. In addition to allowing for improved microstructure and mechanical properties, sintering titanium in a partial hydrogen atmosphere can also allow for continuous production of powder metallurgy titanium parts, as opposed to batch processing as is often used in conventional vacuum sintering. However, the present process is not limited to continuous processing. Additionally, it may be advantageous to employ this process as a batch process to allow for minimal capital expenses or the ability to change temperature and hydrogen partial pressure profdes between batches.

[0074] The dynamically controlled hydrogen atmosphere can include pure hydrogen or a mixture of hydrogen and an inert gas, such as helium, argon, or xenon. The partial pressure of hydrogen can typically be between 0.01 atm and 10 atm. In some embodiments, the dynamically controlled hydrogen atmosphere has a hydrogen to inert gas ratio from about 1 : 100 to about 1 :0. The total pressure of hydrogen with the inert gas can be any pressure, but in many embodiments the total pressure can be between about 0.01 atm and 10 atm of absolute pressure. In one example, the hydrogen atmosphere can include Ar with 5%H2, which at lOMPa gives a partial pressure of H2 at 0.5 MPa, which is approximately 5 atm. pressure. As a general guideline, from about 0.5% to 5% H2, and in some cases 1% to about 3% H2 can be used with an overall Ar+xH2 gas pressure of 1 to 10 MPa. Therefore, the partial pressure of hydrogen may be controlled by, but not limited to, one of several methods. In one method, the absolute pressure of the system is constant and the partial pressure of hydrogen is controlled using two programmable gas mass flow controllers; one being connected to a supply of hydrogen and the other to a supply of inert gas. The partial pressure of hydrogen is increased by increasing the volume fraction of hydrogen flowing into the system and vice versa. In another method, the partial pressure of hydrogen is controlled by controlling the absolute pressure of the system using a programmable pressure controller with an inlet valve to increase absolute pressure and an exhaust valve to decrease absolute pressure. The inlet valve of the pressure controller is connected to a supply of either pure hydrogen or a mixture of hydrogen and inert gas with a fixed ratio. Additionally, a hybrid method may be used where the volume fraction of hydrogen on the inlet valve of the pressure controller is controlled using two programmable gas mass flow controllers. In any method, the partial pressure of hydrogen is equal to the product of the absolute pressure of the system and the overall volume fraction of hydrogen in the system. In some embodiments, the absolute pressure of the system can be maintained at a substantially constant controlled absolute pressure. However, controlling the pressure can involve merely maintaining pressure within the desired hydrogen partial pressure ranges. Under conditions using pure hydrogen (i.e. the hydrogen atmosphere consists essentially of hydrogen), the corresponding process pressure can be at a controlled absolute pressure corresponding to the above recited hydrogen partial pressures. Specifically, pure hydrogen can generally be from 0.01 atm to 10 atm, and in some cases 0.01 atm to less than 1 atm.

[0075] In some embodiments, the dynamically controlled hydrogen atmosphere can be varied throughout the sintering, equilibrating, densification, and phase transformation steps to offer further microstructural control. Exact hydrogen pressure can be selected based on the equilibrium pressure as a function of the temperature and the desired hydrogen content necessary to produce a particular microstructure. More specifically, as temperature decreases, equilibrium pressure of hydrogen gas over the surface of titanium with a given concentration of dissolved hydrogen decreases. Therefore, the sintered material will absorb additional hydrogen at lower temperatures given a constant partial pressure of hydrogen. As such, the dynamically controlled hydrogen atmosphere can include a hydrogen partial pressure which is varied during the process in order to achieve a target hydrogen concentration within the sintered titanium material as a function of time. For example, if a constant hydrogen content is desired then as temperature decreases, the partial pressure of hydrogen would also be decreased commensurate with the equilibrium pressure. Alternatively, the hydrogen content can be varied as a function of time throughout the process to achieve the desired microstructure. In one embodiment, the hydrogen partial pressure is kept at 1 atm during the sintering step to maintain elevated levels of hydrogen within the titanium during sintering, the atmosphere is then gradually changed to 0.5 atm of hydrogen as the sample cools to the phase transformations including eutectoid decomposition temperature to prevent excessive absorption of hydrogen. In any embodiment, if the equilibrium pressure of the titanium-hydrogen system, which is a function of temperature and hydrogen content of the titanium, is different than partial pressure of hydrogen in the atmosphere, hydrogen evolution or absorption will occur. Therefore, one of the methods described above, or a similar method, can be used to control the partial pressure of hydrogen throughout the process to prevent excessive evolution or absorption. Using Ti-6A1-4V as an example, under a partial hydrogen pressure, blended powder can be sintered to near full density with a microstructure having one, two, three, or four phases including alpha (a), alpha-2 (a ), delta (8) and beta (0) phases after cooling to room temperature.

[0076] After the sintering step, the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition can also be performed under a dynamically controlled hydrogen atmosphere containing hydrogen. Controlling the hydrogen content in the titanium material during alpha and alpha-2 precipitation in 0 and during the eutectoid phase transformation from 0-phase to a-, and 8-phases can allow for titanium materials with very fine microstructure without resorting to thermo mechanical working that relies on recrystallization to control grain sizes. The equilibrium transformation temperature decreases and the kinetics of the transformation reaction slow with increasing hydrogen concentration. Additionally, the hydrogen concentration is a function of temperature and partial pressure of hydrogen in the atmosphere. Therefore, the thermodynamics and kinetics of the phase transformations are dependent not only on temperature (as is the case with most metallurgical processes), but also on the partial pressure of hydrogen in the atmosphere. In some embodiments, the partial pressure of hydrogen used during sintering could result in excessive uptake of hydrogen at the decomposition temperature, which would result in reduced undercooling and slowed kinetics. Conversely, in these embodiments, a simultaneous decrease of hydrogen partial pressure during cooling can prevent an inordinate uptake of hydrogen. Decreasing the partial pressure could result in a greater degree of undercooling and faster kinetics at the decomposition temperature, which would, in turn, result in a finer microstructure due to more homogenous nucleation and a greater degree of reaction completion per unit time. This phenomenon gives the process another parametric degree of freedom and, therefore, greater control over microstructural evolution. In one embodiment, the hydrogen partial pressure can gradually decrease from 1 atm of pure hydrogen at the sintering temperature to 0.5 atm hydrogen and 0.5 atm of inert gas at the decomposition temperature. The atmosphere can then be abruptly changed to 1 atm of inert gas with no hydrogen immediately before cooling to prevent excessive absorption of hydrogen.

[0077] In some embodiments, the partial pressure of hydrogen in the dynamically controlled hydrogen atmosphere can change with each step. For example, in one embodiment the process can include sintering blended powders of TiFF and alloying powders in a dynamically controlled hydrogen atmosphere with a first partial pressure of hydrogen, cooling and holding for phase transformations including eutectoid decomposition under a second partial pressure of hydrogen, and then switching the atmosphere condition to vacuum, inert gas, or a combination of both to dehydrogenate the material. In other embodiments, a single partial pressure of hydrogen can be used throughout the sintering, equilibrating, and phase transformations including eutectoid decomposition steps. Furthermore, the partial pressure of hydrogen can be changed multiple times within a single step, or the partial pressure can be gradually ramped up or down over the duration of a step.

[0078] The elevated sintering temperature can be any temperature that corresponds to the P- phase region with a given hydrogen content. One of skill in the art will appreciate that the temperatures and compositions that fall within the 0-phase region can be different for pure titanium and various alloys of titanium with other metals. In one embodiment, the sintering process consists of three steps: (1) -Ti(H) sintering, (2) phase transformations including eutectoid decomposition, and (3) dehydrogenation in vacuum, an inert gas such as Ar, or a combination of vacuum and an inert gas. Note that the steps can be completely separated as separate processes conducted in different runs, or as a single integrated continuous run. Without being bound by theory, the following steps describe what are believed to be the phase transitions that occur to produce titanium and titanium alloys having fine grain size.

[0079] In the first step of -Ti(H) sintering, by controlling the H2 atmosphere, the process maintains sintering in P-Ti phase region. Self-diffusion of the titanium in the p-Ti phase is significantly faster than in the a-Ti phase, and a solid solution of hydrogen atoms in titanium can reduce the activation energy of Ti self-diffusion due to the decrease of bonding strength due to the presence of comparatively weak Ti-H bonds. It is believed that each of these effects helps to achieve full densification during -Ti(H) sintering.

[0080] In one exemplary embodiment, the sintered titanium material can be Ti-6A1-4V alloy. Under the partial hydrogen pressure, a blended powder can be sintered to near full density with a microstructure having one, two, three, or four phases including alpha (oc), alpha-2 (012), delta (5) and beta (P) phases after cooling to room temperature. The elevated temperature at which sintering occurs can be from about 1000°C to about 1500°C. In one particular embodiment the elevated temperature can be about 1200°C. The sintering is also conducted for a time period sufficient to gain near full density. For example, the material can be held at the elevated temperature from about 1 hour to about 24 hours. In some embodiments, the sintering time can vary from about 30 minutes to about 30 hours. In other embodiments, the sintering can be performed from about 1 hour to 24 hours. In one particular embodiment, the sintering time can be about 2 hours.

[0081] The sintering can be conducted in any chamber in which the temperature and atmosphere can be controlled. For example, the sintering can be conducted in a furnace which is capable of attaining a working temperature of up to 1500°C or even higher, is capable of being used under vacuum, and is capable of using gases such as hydrogen, argon, nitrogen, and the like, or a mixture of any two or more such gases. In one particular embodiment, the furnace can be an alumina tube furnace. In another embodiment, the furnace can be a refractory metal alloy including, but not limited to, a Fe-Cr-Al alloy. The heating elements of the furnace can be made of such materials as are known in the art, including, but not limited to, tungsten or molybdenum mesh, silicon carbide, or MoSi2.

[0082] After sintering, an optional intermediate equilibration step can be introduced in order to allow hydrogen partial pressure to be adjusted dynamically to facilitate the following phase transformations including eutectoid decomposition step. In some embodiments this equilibrating step can include holding the sintered titanium material at a temperature above the P-transus prior to phase transformations including eutectoid decomposition to allow hydrogen within the sample to reach the required equilibrium concentration necessary for a desired phase evolution during phase transformations including eutectoid decomposition. The equilibration temperature can be below the sintering temperature and above the phase transformations including eutectoid decomposition temperature. The equilibration temperature can vary between about 300 °C and about 1000 °C. Typically, the equilibration temperature for Ti-6A1-4V alloy can be from about 870 °C to about 900 °C. The equilibration temperature can vary from one alloy composition to another. The temperature can be held constant, or nearly constant, during this step for from about 10 minutes to about 12 hours. The equilibration time can be sufficient for the hydrogen within the sample to reach equilibrium with the dynamically controlled hydrogen atmosphere and homogenize the sintered titanium material.

[0083] Optionally, an additional cooling step can be performed in which the sintered titanium material is cooled from the elevated sintering temperature to the equilibration temperature at a non-uniform rate. Another optional step prior to the phase transformations including eutectoid decomposition step can be performed in which the sintered titanium material is cooled from the equilibration temperature to the phase transformations including eutectoid decomposition hold temperature at a non-uniform rate. In one embodiment, the material can be cooled from the sintering temperature to the equilibration temperature at a rate of 10 °C / min. After a sufficient amount of time for equilibration to a desired hydrogen content, the material can be cooled from the equilibration temperature to the decomposition temperature at a non-uniform rate, beginning at 10 °C / min and decreasing to about 1 °C / min as the target temperature is approached. A non-uniform temperature change rate can allow for increased microstructural control due to the diffusion of hydrogen that is being absorbed during temperature change as well diffusion of alloying elements being segregated to their respective phases during phase transformation.

[0084] The phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step can be performed by holding the sintered titanium material at a hold temperature and a hold time sufficient for phase transformations including alpha and alpha- 2 precipitation and eutectoid decomposition of the sintered titanium material. In some embodiments, the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step is conducted at a temperature from about 200°C to about 900°C. The temperature can be below the P-phase transition temperature for whatever particular composition of Ti, H, and other alloying additives is being used. In some embodiments, the material can be held at the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition hold temperature for a hold time from about 10 minutes to about 120 hours.

[0085] The phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step can be between the sintering step and the dehydrogenation step. The sintered material can be cooled in the dynamically controlled H2 atmosphere to a phase transformation including alpha and alpha-2 precipitation and eutectoid decomposition temperature below the P-transus. The material can then be held at this temperature for a period of time to complete the phase transformations. As used herein, the term “eutectoid reaction” refers to the formation of new phases (a-Ti(H) + 8-TiHx) that precipitate in the interior of P-Ti(H) grains in the sintered material. As a result, the coarse P-Ti(H) grains break into finely dispersed (a-Ti(H) + a + P-Ti(H) + 8-TiHx) grains, thereby refining the microstructure.

[0086] The holding temperature and holding time for the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step can be sufficient to allow phase transformations to take place and form a eutectoid decomposed material. For example, the temperature can range from about 150 °C to about 900°C depending on exact alloy compositions. In some embodiments, the temperature can range from about 400°C to about 800°C for Ti-6A1-4V alloy and about 150°C to about 400°C for commercially pure titanium. The time period for phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition can be sufficient for the process to proceed sufficiently toward completion. For example, the temperature can be held constant, or nearly constant, from about 10 minutes to about 120 hours. In other embodiments, the temperature can be held constant, or nearly constant, from about 10 minutes to about 12 hours, from about 30 minutes to about 6 hours, from about 1 hour to about 24 hours, or from about 1 hour to about 12 hours. After the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step, the sintered titanium material can be re-heated under vacuum or inert gas to dehydrogenate. The dehydrogenation temperature can be below the sintering temperature. The temperature for dehydrogenation in vacuum or inert gas can typically be from about 400 °C to about 900 °C, below the -phase transition temperature. The sintered titanium material can be held at the dehydrogenation temperature from about 2 hours to about 100 hours depending on the size of the components.

[0087] The dehydrogenation step can be after the phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition step. During the step of dehydrogenation in vacuum and / or an inert atmosphere, the hydrogen atoms in the titanium are removed. The phase transformations during dehydrogenation further refine and modify the microstructure. The final fine grain microstructure can be formed during this step. According to various embodiments, if the material is a Ti-6A1-4V alloy, such fine grain microstructure includes both oc-phases and 0-phases. Without being bound by theory, the dehydrogenation process is believed to decompose the 8- phase and release the hydrogen in the material. During the dehydrogenation process, the 6- phase transforms to a oc+P phase mixture. Hydrogen then diffuses through the material to the surface, where it escapes as hydrogen gas.

[0088] The re-heating of the material can be conducted for a time period sufficient to reduce hydrogen content in materials to less than 150 ppm. Generally, hydrogen can be removed to a level much lower than allowable levels according to ASTM standards (150 ppm). For example, the residual hydrogen content after conventional vacuum sintering of TiH2 or thermohydrogen processing (THP) can be as low as 10 ppm, which is not detrimental to the mechanical properties of titanium materials. The hydrogen content of materials prepared using the processes of the present invention can be nearly as low. For example, in one embodiment the hydrogen present after performing the present process using vacuum during dehydrogenation has been measured at or below 30 ppm, and at or below 60 ppm when using Ar atmosphere during dehydrogenation. These are both well below the ASTM standard of 150 ppm. The time for dehydrogenation can vary depending on the size of the part being formed or the components used. The dehydrogenation step can be conducted by holding the material at the dehydrogenation temperature for from about 1 hour to about 100 hours. The actual time required is governed by the law of diffusion. According to some embodiments, dehydrogenation can be performed from about 10 to about 24 hours. In other embodiments, the dehydrogenation time can be from about 1 to about 20 hours. The dehydrogenation can be conducted in the same chamber as the initial sintering, or in a separate furnace chamber in which the temperature and atmospheric pressure and composition can be controlled.

[0089] The steps of sintering in the dynamically controlled hydrogen atmosphere, phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition in the dynamically controlled hydrogen atmosphere, and the dehydrogenation under vacuum, inert gas, or a combination of both, can be three separate processes, or they can be integrated in a single process. Alternatively, the sintering and phase transformations including alpha and alpha-2 precipitation and eutectoid decomposition steps can be processed in sequence with the dehydrogenation step following later, or just the sintering step can be completed with the phase transformations including eutectoid decomposition and dehydrogenation steps being processed together later. In one embodiment, a single, integrated process of all three steps can be performed. This embodiment can include sintering blended powders of TiH? and alloying powders in a dynamically controlled hydrogen atmosphere with a partial pressure of hydrogen (H2) gas, cooling and holding for phase transformations including eutectoid decomposition under the same or different partial pressure of H2, and then switching the atmosphere condition to vacuum, inert gas, or a combination of both at certain temperatures to perform the dehydrogenation step. In another embodiment, after the sintering step, the parts are subjected to the dehydrogenation step directly without specifically holding for phase transformations. The parts may be cooled to room temperature before heating up to the dehydrogenation temperature, or the parts may be cooled from the sintering temperature to the dehydrogenation temperature directly without interruptions.

[0090] Consistent with these principles, methods of forming sintered titanium components having near full density or full density can be performed at least partially under a hydrogencontaining atmosphere. As generally described in connection with FIG. 3, a hydrogencontaining atmosphere can be maintained during at least one of sintering, HIPing, and cooling. In some examples, the hydrogen-containing atmosphere can be maintained only one of these stages, during two or more of these stages, or during all three stages. The hydrogencontaining atmosphere can also have a hydrogen content from greater than zero to 100%. Thus, in some cases a mixture of hydrogen and inert gas can be used. Furthermore, the described features, structures, or characteristics associated with descriptions throughout (e g. FIG. 1 through 2B may be combined in any suitable manner with the methods described under FIG. 3. In the preceding description, numerous specific details were provided, such as examples of various configurations, temperatures, compositions, etc. to provide a thorough understanding of examples of the described technology. It will be recognized, however, that the methods of FIG. 3 may be practiced with or without one or more of the specific details, or with other methods.

[0091] As shown in FIG. 3, a method 300 of obtaining a sintered titanium component can comprise providing a titanium component 310 having a starting density, wherein the titanium component is either a green compact or a pre-sintered part. The green compact which includes a polymeric binder can be heated 320 in presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder forming a debinded compact. The titanium component as the debinded compact or as the pre-sintered part can be heated 330 to, and held at, a sintering temperature under a sintering atmosphere with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density forming a sintered component. The sintered component can be held 340 at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa under a densification atmosphere, to hot isostatically press (HIP) the sintered component to near full density. The sintered component can be cooled 350 to room temperature in a cooling atmosphere. In this approach, at least one of the sintering atmosphere, the densification atmosphere, and the cooling atmosphere includes hydrogen. In this approach, all of the guidelines provided previously can be used together or in combination in the same manner.

[0092] In one example, both the sintering atmosphere and the densification atmosphere includes hydrogen. As a general rule, when a hydrogen-containing atmosphere is included in both the sintering and HIPing stages, an additional microstructure refinement step may not be necessary. In one more specific example, both the sintering atmosphere and the densification atmosphere further includes an inert gas. In cases where a mixture of hydrogen and inert gas is used, the sintering atmosphere, the densification atmosphere and / or the cooling atmosphere may have a hydrogen content from greater than 0% to 99%, in some cases 5% to 25%, in other cases 0.5% to 10%, and in still other cases 3% to 6%. In one example, at least one of the sintering atmosphere and the densification atmosphere has a hydrogen content of 100%, and in another case both have a hydrogen content of 100%. In still another example, the sintering atmosphere can comprise hydrogen (i.e. solely hydrogen or a mixture of hydrogen and inert gas), and the densification atmosphere consists of inert gas (e.g. no hydrogen). In another related example, the sintering atmosphere consists of inert gas while and the densification atmosphere comprises hydrogen (i.e. solely hydrogen or a mixture of hydrogen and inert gas). In another case, both the sintering atmosphere and the densification atmosphere consists of inert gas, while the cooling atmosphere comprises hydrogen (i.e. solely hydrogen or a mixture of hydrogen and inert gas). In another variation, each of the sintering atmosphere, the densification atmosphere, and the cooling atmosphere comprises hydrogen (i.e. solely hydrogen or a mixture of hydrogen and inert gas). Regardless of the stage at which hydrogen is introduced (i.e. sintering, HIPing, and / or cooling, the hydrogen content can be static or dynamically controlled as described herein.

[0093] According to this method, the HIPing stage can be performed to achieve near full density (e.g. greater than 97%). However, in some examples, the HIPing is performed such that the sintered component is full density.

[0094] In any of the above embodiments, the process can be void of mechanical processing steps after sintering and densification. As used herein, the term “mechanical processing steps” refers to forging, rolling, extrusion, drawing, swaging, and the like as known in the art. Mechanical processing steps are those steps where the material is deliberately deformed plastically at either elevated (thermomechanical or hot working) or room temperatures (cold working). In a conventional process including mechanical processing steps, after the plastic deformation of cold working, or during hot working the microstructure of the material can be transformed at elevated temperatures via recrystallization to achieve a desired microstructure. In the processes of the present invention, the desired fine grain microstructure is formed in situ during the integrated sintering-phase transformations including eutectoid decomposition-dehydrogenation process. In some cases, thermal mechanical working can be done after the process to further enhance the properties. However, by using the processes of the present invention, strong titanium materials with fine microstructures can be produced without the need for further mechanical processing steps after sintering. The titanium metal or titanium metal alloys obtained from the process can have a fine or ultrafine grain size (i.e. average grain size). Such ultrafine grain sizes on the microscopic scale provide for high strength and ductility in the macro scale materials. The use of coarse powders in the process does not lead to coarse final grain microstructure because of the controlled stages of densification and phase transformation. The grain sizes of the final material do not depend as much on the initial particle size of the powder as does the titanium metal powder, but rather the grain size is primarily a function of the kinetics of phase transformation and the temperature versus time profiles as well as partial pressure of H2 versus time profiles during the sintering, phase transformations including eutectoid decomposition, and dehydrogenation steps. In any of the above embodiments, the titanium metal or the titanium metal alloy obtained from the process can have a grain size of less than 100 pm. In some embodiments, the titanium metal or titanium metal alloy prepared using the above process can have a grain size of less than 10 pm. In some embodiments, the titanium metal or titanium metal alloy prepared using the above process can have a grain size of less than 20 pm and in some cases less 5 pm. In other embodiments, the titanium metal or the titanium metal alloy can have a grain size of from about 10 nm to about 10 pm. In other embodiments, the titanium metal or the titanium metal alloy can have a grain size of from about 10 pm to about 100 pm. These grain sizes and other properties recited herein are typically obtained directly from the process without further post-processing (i.e. as-sintered). Note the term as-sintered can be used to encompass the step of sintering at the high temperatures in hydrogen or all three steps of the process including sintering in hydrogen, phase transformations, and dehydrogenation. Accordingly, in some cases the process can consist essentially of sintering, holding to cause eutectoid decomposition, and heating to cause dehydrogenation.

[0095] The materials prepared by the above processes can be achieved at lower cost because of the high yield of the processes, fewer processing steps, and lower energy consumption, compared to materials produced by traditional wrought alloy methods. The traditional wrought alloy methods refer to the manufacturing process by melting, casting, hot working, cold working and machining. The materials prepared by the presently described processes have fine grain sizes, and thus exhibit equivalent or superior mechanical properties to traditionally wrought alloys. The titanium metal or titanium metal alloy materials above can find utility in any of a number of applications where titanium and its alloys are currently used, or will be used. For example, the materials can be used in, but not limited to, automobile parts, biomedical implants, medical surgical tools, aircraft equipment, diving equipment, oil field equipment, sports equipment, chemical equipment, food processing equipment, among others.

[0096] The present technology, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting.

[0097] Examples of the invention: SinterHIP without hydrogen

[0098] FIG. 4 shows scanning electron micrograph (SEM) images of a titanium material made using a method as described herein. The left image shows the material after being sintered but before the HIP operation, and the right image shows the material after HIP. The material was sintered from blended TiH2 and 60A140V powders. The HIP was conducted at 1200 C for 1 hour under Ar with a pressure of lOMPa. Before HIP, the material had a density of 95.6%. After HIP, the material had a density of 99.9%.

[0099] FIG. 5 shows SEM images of another titanium material before and after HIP. The material was sintered from blended TiH? and 60A140V powders. Before HIP, the material had a density of 98.5%. After HIP at 1200 C for 1 hour under 10 MPa Ar, the material had a density of 99.9%.

[0100] Examples of the invention: SinterHIP with Hydrogen

[0101] A series of titanium components were made using different temperature and pressure profiles for the HIP process, in order to determine which temperatures and pressures were effective. In this HIP process, the initial titanium component was pre-sintered using a hydrogen sintering and phase transformation process by sintering at 1200 °C for 4 hours under hydrogen.

[0102] FIG. 6 shows an SEM image of the titanium material after HIP. Before HIP, the material had a density of 96.4%. After HIP at 1100 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 10 MPa, the material had a density of 99.7%. Another presintered titanium component was HIP at 1100 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 5 MPa, the material had a density of 99.6%. FIG. 7 shows SEM images of the titanium material after HIP. Before HIP, the material had a density of 98.3%. After HIP at 1000 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 10 MPa, the material had a density of 99.7%. Another presintered titanium component was HIP at 1000 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 5 MPa, the material had a density of 99.6%.

[0103] FIG. 8 shows an SEM image of the titanium material after HIP. Before HIP, the material had a density of 98.3%. After HIP at 950 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 10 MPa, the material had a density of 99.7%. Another presintered titanium component was HIP at 1000 C for 1 hour under 5% H2 balanced with 95% Ar with the pressure of 5 MPa, the material had a density of 99.3%.

[0104] Additional Examples

[0105] The technology described herein can also include the following enumerated examples:

[0106] 1. A method of obtaining a full-density sintered titanium component comprising: providing a titanium component having a starting density of 92% or less; heating the titanium component to, and holding at, a sintering temperature under a sintering atmosphere containing hydrogen with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density forming a sintered component; and holding the sintered component at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa with a densification atmosphere, to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component.

[0107] 2. The method of any of examples 1-44, wherein the titanium component is a green compact including titanium powder and a polymeric binder.

[0108] 3. The method of any of examples 1-44, wherein the green compact further includes at least one alloying metal powder in the form of a pre-alloyed powder or blend of individual components. 4. The method of any of examples 1 -44, wherein the at least one alloying metal powder includes one or more of Al, Cr, V, Fe, Mo, Ni, Cu, Mn, Zr, W, Ta, Nb, Hf, Ag, and Au.

[0109] 5. The method of any of examples 1-44, wherein the green compact has the starting density of 40-90%.

[0110] 6. The method of any of examples 1-44, wherein the green compact is formed of powders having a D50 particle size range greater than 1 micron.

[0111] 7. The method of any of examples 1-44, wherein the titanium powder is at least one of commercially pure titanium and titanium hydride.

[0112] 8. The method of any of examples 1-44, wherein the titanium powder is at least one of spherical and angular shaped powder.

[0113] 9. The method of any of examples 1-44, further comprising heating the green compact in the presence of a debinding atmosphere to at least one debinding temperature below the sintering temperature sufficient to debind a component of the polymeric binder, before the sintering.

[0114] 10. The method of any of examples 1-44, wherein the debinding atmosphere is one of an inert atmosphere, a hydrogen atmosphere, and a vacuum.

[0115] 11. The method of any of examples 1-44, wherein the inert atmosphere includes helium, argon or both.

[0116] 12. The method of any of examples 1-44, wherein the hydrogen atmosphere is an argonhydrogen mixture.

[0117] 13. The method of any of examples 1-44, wherein the debinding atmosphere and the sintering atmosphere are compositionally common atmospheres. 14. The method of any of examples 1-44, wherein the titanium component is a pre-sintered part having a starting density less than 92%.

[0118] 15. The method of any of examples 1-44, wherein the sintering temperature is 1000 °C to 1400 °C.

[0119] 16. The method of any of examples 1-44, wherein the sintering temperature is about 1200 °C.

[0120] 17. The method of any of examples 1-44, wherein the pressure during sintering is 1 atm or less, not including vacuum.

[0121] 18. The method of any of examples 1-44, wherein the sintering atmosphere comprises hydrogen at a partial pressure of about 5% or less.

[0122] 19. The method of any of examples 1-44, wherein the sintering atmosphere is sufficient to form the sintered component having a majority of a beta-phase, wherein the sintering temperature is above a beta transus temperature and below a melting point of the sintered component.

[0123] 20. The method of any of examples 1-44, wherein the sintered component has a majority of a beta-phase at the sintering temperature which is a substantially homogenous beta-phase titanium material.

[0124] 21. The method of any of examples 1-44, wherein the densification temperature is 800 °C to 1400 °C.

[0125] 22. The method of any of examples 1-44, wherein the densification temperature is 900 °C to 1200 °C. 23. The method of any of examples 1 -44, wherein the densification temperature is 1000 °C to 1100 °C.

[0126] 24. The method of any of examples 1-44, wherein the gaseous pressure is 0.2 MPa to 50MPa.

[0127] 25. The method of any of examples 1-44, wherein the gaseous pressure is 1 MPa to lOMPa.

[0128] 26. The method of any of examples 1-44, wherein the densification atmosphere comprises argon gas.

[0129] 27. The method of any of examples 1-44, wherein the densification atmosphere comprises hydrogen gas.

[0130] 28. The method of any of examples 1-44, wherein the hydrogen gas is present at a concentration of about 5 vol% or less.

[0131] 29. The method of any of examples 1-44, further comprising refining a microstructure of the full-density sintered titanium component by: cooling the full-density sintered titanium component under an atmosphere containing hydrogen from the sintering temperature to a phase transformation temperature below an a- -transus temperature of the full-density sintered titanium component and above about 400° C; holding the full-density sintered titanium component at the phase transformation temperature for a phase transformation time to produce a transformed full-density sintered titanium component having a fine or ultrafine microstructure; and cooling the transformed full -density sintered titanium component to room temperature in an inert atmosphere.

[0132] 30. The method of any of examples 1-44, further comprising holding the transformed fulldensity titanium component under a substantially hydrogen-free atmosphere or vacuum at a dehydrogenation temperature below the a-P -transus temperature and above about a deltaphase decomposition temperature to remove hydrogen from the transformed full-density titanium component to form a dehydrogenated titanium component.

[0133] 31. The method of any of examples 1-44, wherein the transformed titanium component has a density of greater than 99.5%.

[0134] 32. The method of any of examples 1-44, wherein the transformed titanium component has an oxygen content less than 0.2% or less than 0.15%.

[0135] 33. The method of any of examples 1-44, wherein the fine or ultrafine microstructure has a fine grain size of 5 pm to 20 pm or an ultrafine grain size of 0.1 pm to 5 pm.

[0136] 34. The method of any of examples 1 -44, wherein the steps of heating and holding are performed in a common furnace and the common furnace is a sinter-HIP furnace adapted for sintering at up to 1400 °C, 10 MPa, and in a hydrogen-containing atmosphere.

[0137] 35. A method of obtaining a sintered titanium component comprising: providing a titanium component having a starting density, wherein the titanium component is either a green compact or a pre-sintered part; heating the green compact which includes a polymeric binder in presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder forming a debinded compact; heating the titanium component as the debinded compact or as the pre-sintered part to, and holding at, a sintering temperature under a sintering atmosphere with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density forming a sintered component; holding the sintered component at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa under a densification atmosphere, to hot isostatically press (HIP) the sintered component to near full density; and cooling the sintered component to room temperature in a cooling atmosphere, wherein at least one of the sintering atmosphere, the densification atmosphere, and the cooling atmosphere includes hydrogen.

[0138] 36. The method of any of examples 1-44, wherein the sintering atmosphere and the densification atmosphere includes hydrogen.

[0139] 37. The method of any of examples 1-44, wherein the sintering atmosphere and the densification atmosphere further includes an inert gas.

[0140] 38. The method of any of examples 1-44, wherein the sintering atmosphere has a hydrogen content from 5% to 99%, and the densification atmosphere has a hydrogen content of 5% to 99%.

[0141] 39. The method of any of examples 1 -44, wherein at least one of the sintering atmosphere and the densification atmosphere has a hydrogen content of 100%.

[0142] 40. The method of any of examples 1-44, wherein the sintering atmosphere comprises hydrogen and the densification atmosphere consists of inert gas.

[0143] 41. The method of any of examples 1-44, wherein the sintering atmosphere consists of inert gas and the densification atmosphere comprises hydrogen.

[0144] 42. The method of any of examples 1-44, wherein the sintering atmosphere and the densification atmosphere consists of inert gas, and the cooling atmosphere comprises hydrogen.

[0145] 43. The method of any of examples 1-44, wherein the sintering atmosphere, the densification atmosphere, and the cooling atmosphere comprises hydrogen.

[0146] 44. The method of any of examples 1-44, wherein the holding is performed such that the sintered component is full density. Reference was made to the examples illustrated in the drawings and specific language was used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the technology is thereby intended. Alterations and further modifications of the features illustrated herein and additional applications of the examples as illustrated herein are to be considered within the scope of the description.

[0147] Although the subject matter has been described in language specific to structural features and / or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements may be devised without departing from the spirit and scope of the described technology.

Claims

CLAIMSWhat is claimed is:

1. A method of obtaining a full-density sintered titanium component comprising: providing a titanium component having a starting density of 92% or less; heating the titanium component to, and holding at, a sintering temperature under a sintering atmosphere containing hydrogen with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density forming a sintered component; and holding the sintered component at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa with a densification atmosphere, to hot isostatically press (HIP) the sintered component to full density having greater than 99.5% relative density to form the full-density sintered titanium component.

2. The method of claim 1, wherein the titanium component is a green compact including titanium powder and a polymeric binder.

3. The method of claim 2, wherein the green compact further includes at least one alloying metal powder in the form of a pre-alloyed powder or blend of individual components.

4. The method of claim 3, wherein the at least one alloying metal powder includes one or more of Al, Cr, V, Fe, Mo, Ni, Cu, Mn, Zr, W, Ta, Nb, Hf, Ag, and Au.

5. The method of claim 2, wherein the green compact has the starting density of 40-90%.

6. The method of claim 2, wherein the green compact is formed of powders having a D50 particle size range greater than 1 micron.

7. The method of claim 2, wherein the titanium powder is at least one of commercially pure titanium and titanium hydride.

8. The method of claim 2, wherein the titanium powder is at least one of spherical and angular shaped powder.

9. The method of claim 2, further comprising heating the green compact in presence of a debinding atmosphere to at least one debinding temperature below the sintering temperature sufficient to debind a component of the polymeric binder, before the sintering.

10. The method of claim 9, wherein the debinding atmosphere is one of an inert atmosphere, a hydrogen atmosphere, and a vacuum.

11. The method of claim 10, wherein the inert atmosphere includes helium, argon or both.

12. The method of claim 10, wherein the hydrogen atmosphere is an argon-hydrogen mixture.

13. The method of claim 9, wherein the debinding atmosphere and the sintering atmosphere are compositionally common atmospheres.

14. The method of claim 1, wherein the titanium component is a pre-sintered part having a starting density less than 92%.

15. The method of claim 1, wherein the sintering temperature is 1000 °C to 1400 °C.

16. The method of claim 1, wherein the sintering temperature is about 1200 °C.

17. The method of claim 1, wherein the pressure during sintering is 1 atm or less, not including vacuum.

18. The method of claim 1, wherein the sintering atmosphere comprises hydrogen at a partial pressure of about 5% or less.

19. The method of claim 1 , wherein the sintering atmosphere is sufficient to form the sintered component having a majority of a beta-phase, wherein the sintering temperature is above a beta transus temperature and below a melting point of the sintered component.

20. The method of claim 1, wherein the sintered component has a majority of a beta-phase at the sintering temperature which is a substantially homogenous beta-phase titanium material.

21. The method of claim 1, wherein the densification temperature is 800 °C to 1400 °C.

22. The method of claim 1, wherein the densification temperature is 900 °C to 1200 °C.

23. The method of claim 1, wherein the densification temperature is 1000 °C to 1100 °C.

24. The method of claim 1, wherein the gaseous pressure is 0.2 MPa to 50MPa.

25. The method of claim 1, wherein the gaseous pressure is 1 MPa to lOMPa.

26. The method of claim 1, wherein the densification atmosphere comprises argon gas.

27. The method of claim 1, wherein the densification atmosphere comprises hydrogen gas.

28. The method of claim 27, wherein the hydrogen gas is present at a concentration of about 5 vol% or less.

29. The method of claim 1, further comprising refining a microstructure of the full-density sintered titanium component by: cooling the full-density sintered titanium component under an atmosphere containing hydrogen from the sintering temperature to a phase transformation temperature below an a- -transus temperature of the full-density sintered titanium component and above about 400° C;holding the full-density sintered titanium component at the phase transformation temperature for a phase transformation time to produce a transformed full-density sintered titanium component having a fine or ultrafine microstructure; and cooling the transformed full-density sintered titanium component to room temperature in an inert atmosphere.

30. The method of claim 29, further comprising holding the transformed full-density titanium component under a substantially hydrogen-free atmosphere or vacuum at a dehydrogenation temperature below the a-P -transus temperature and above about a deltaphase decomposition temperature to remove hydrogen from the transformed full-density titanium component to form a dehydrogenated titanium component.

31. The method of claim 29, wherein the transformed titanium component has a density of greater than 99.5%.

32. The method of claim 29, wherein the transformed titanium component has an oxygen content less than 0.2% or less than 0.15%.

33. The method of claim 29, wherein the fine or ultrafine microstructure has a fine grain size of 5 pm to 20 pm or an ultrafine grain size of 0.1 pm to 5 pm.

34. The method of claim 1, wherein the heating and the holding are performed in a common furnace and the common furnace is a sinter-HIP furnace adapted for sintering at up to 1400 °C, 10 MPa, and in a hydrogen-containing atmosphere.

35. A method of obtaining a sintered titanium component comprising: providing a titanium component having a starting density, wherein the titanium component is either a green compact or a pre-sintered part; heating the green compact which includes a polymeric binder in presence of a debinding atmosphere up to at least one debinding temperature sufficient to debind different components of the polymeric binder forming a debinded compact;heating the titanium component as the debinded compact or as the pre-sintered part to, and holding at, a sintering temperature under a sintering atmosphere with a pressure during sintering less than 0.2 MPa, to sinter the titanium component to greater than 92% theoretical density forming a sintered component; holding the sintered component at a densification temperature, while applying a gaseous pressure of 0.2 MPa to 100 MPa under a densification atmosphere, to hot isostatically press (HIP) the sintered component to near full density; and cooling the sintered component to room temperature in a cooling atmosphere, wherein at least one of the sintering atmosphere, the densification atmosphere, and the cooling atmosphere includes hydrogen.

36. The method of claim 35, wherein the sintering atmosphere and the densification atmosphere includes hydrogen.

37. The method of claim 36, wherein the sintering atmosphere and the densification atmosphere further includes an inert gas.

38. The method of claim 37, wherein the sintering atmosphere has a hydrogen content from 5% to 99%, and the densification atmosphere has a hydrogen content of 5% to 99%.

39. The method of claim 35, wherein at least one of the sintering atmosphere and the densification atmosphere has a hydrogen content of 100%.

40. The method of claim 35, wherein the sintering atmosphere comprises hydrogen and the densification atmosphere consists of inert gas.

41. The method of claim 35, wherein the sintering atmosphere consists of inert gas and the densification atmosphere comprises hydrogen.

42. The method of claim 35, wherein the sintering atmosphere and the densification atmosphere consists of inert gas, and the cooling atmosphere comprises hydrogen.

43. The method of claim 35, wherein the sintering atmosphere, the densification atmosphere, and the cooling atmosphere comprises hydrogen.

44. The method of claim 35, wherein the holding is performed such that the sintered component is full density.

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