Titanium-based alloy composition

Abstract

The present invention relates to a titanium alloy composition suitable for manufacturing a component by additive manufacturing, the resulting component exhibiting a relatively small primary beta grain size. The titanium alloy composition comprises 2 wt% to 7 wt% of Al, 1.5 wt% to 6 wt% of Mo, 0.25 wt% to 1.5 wt% of Bi, unavoidable impurities and the balance Ti, the balance Ti enables the sum of the total content of the components in the titanium alloy composition to be 100 wt%, and the weight percentage is based on the total mass of the titanium alloy composition.

Description

TECHNICAL FIELD

[0001] The present invention relates to titanium alloy compositions suitable for manufacturing components by additive manufacturing, the resulting components exhibiting relatively small as-beta grain size components. BACKGROUND

[0002] Structured metal components made from titanium or titanium alloys have traditionally been made from billets by casting, forging, or machining. These techniques have several drawbacks, such as high material usage of expensive titanium metal and long manufacturing cycle times for the metal components. Casting, which can be used to produce potentially near-net shape components, generally has reduced material quality due to lack of control over solidification and cooling rates. Tooling costs and inability to make components with complex shapes are additional drawbacks of traditional methods.

[0003] Fully dense solid components can be manufactured by additive manufacturing, a manufacturing technique also known as rapid prototyping, rapid manufacturing, freeform fabrication, and layer additive manufacturing. Additive manufacturing produces near-net shape products by continuously stacking material one layer at a time to form a three-dimensional component. This is in contrast to subtractive manufacturing, where a billet or block of material is machined to produce the final product by removing material.

[0004] Achieving material properties realized by conventional thermomechanical processing methods, such as forging, is desirable in additive manufacturing. In thermomechanical processing, the material properties are, in most cases, a result of a refined grain structure achieved by plastic deformation induced recrystallization during the mechanical shaping step. This mechanism is not available in typical additive manufacturing processes, where molten material is added layer by layer, solidified, and cooled without any mechanical shaping. This typically results in a coarse as-solidified grain structure. In many alloys, the resulting structure will also be elongated with high aspect ratios. This is due to directional heat extraction provided by the relatively cooler workpiece when superheated molten metal is added. Solidification starts from the previously deposited layer and propagates upwards into the deposited material as it cools. In many cases, the solidification structure will extend across several layers, up to several centimeters in size. These characteristics are generally detrimental to mechanical properties, resulting in reduced and / or anisotropic strength, elongation, and fatigue performance.

[0005] Existing techniques to improve as-deposited grain structure include, for example, the use of hybrid processes in which each deposited layer is plastically deformed to obtain a recrystallized grain structure, which has been applied to reduce deformation and improve mechanical properties (see U.S. Patent Application Publication No. US2015 / 0360289, Liou et al., 2015). However, this intermediate forming step reduces the effective deposition rate (having a negative impact on productivity) and can limit the freedom of fabrication in terms of the ability to form complex shapes. Other techniques include inter-layer laser peening and ultrasonic impact treatment, such as described in International Patent Application WO 2013140147 Al (Wescott et al., 2013); and inter-layer cold rolling, such as described in European Patent Application Publication EP2962788 Al (Liou et al., 2016). And forced cooling of the solidified layers during the cooling process of the solidified metal to prepare for laser or ultrasonic impact treatment to reduce thermal deformation and refine the grain structure by recrystallization (see U.S. Patent Application Publication No. US2015 / 0041025, Wescott et al., 2015). Physical machining of the solidified surface of the work product has met with varying degrees of success and can be complex and expensive due to the need for special equipment. Furthermore, for methods that physically machine the deposited layers, contamination from the tooling would be an issue as any contamination can be trapped between the layers of the final product in the additive manufacturing process. Physically machining the product also adds processing time, thereby reducing productivity.

[0006] Other techniques for refining metals to achieve grain refinement include imparting high frequency vibrations to the body of molten material, such as by applying mechanical vibrations (see, for example, U.S. Patent No. 3,363,668, Petit et al., 1968), acoustic energy (U.S. Patent Application Publication No. 2014 / 0255620, Shuck et al., 2014), or oscillating electromagnetic fields (International Patent Application WO2015028065 Al, Jarvis et al., 2015). In addition to potentially prohibitive costs and lack of practical implementation methods, the effectiveness of the general principle of molten pool stirring is very limited on many relevant metal alloys. Specifically, it requires a region of partially solidified material at the extended solidification front to be able to disrupt the front by fragmentation. Many alloys suitable for additive manufacturing, such as many titanium alloys, and in particular the primary titanium alloy Ti-6Al-4V, are characterized by a narrow solidification interval, which makes them very resistant to fragmentation of the solidification front by techniques using vibrational mechanisms, such as acoustic, electromagnetic, or mechanical vibration mechanisms.

[0007] US 2013 / 0174944 A1 discloses titanium alloys designed for additive manufacturing, the titanium alloys being designed to achieve an equiaxed grain structure, comprising about 3.0% to about 6.0% by weight aluminum, 0% to about 1.5% tin, about 2.0% to about 4.0% vanadium, about 0.5% to about 4.5% molybdenum, about 1.0% to about 2.5% chromium, about 0.20% to about 0.55% iron, 0% to about 0.35% oxygen, 0% to about 0.007% boron, and 0% to about 0.60% other incidental elements and impurities.

[0008] US 2021 / 0238712 A1 discloses titanium alloys with 2-20 wt% of Fe, Ni and / or Cu to achieve an equiaxed grain structure.

[0009] US 2004 / 0136859 discloses a titanium alloy comprising 0.01-5 wt%, preferably 0.1-3 wt% of bismuth, based on the weight of the bismuth and the titanium alloy, suitable for manufacturing dental castings or medical implants by casting.

[0010] JP H05279773 discloses adding 0.1 wt% to 0.8 wt% of O and 0.001 wt% to 0.5 wt% of one or more of P, As, Sb, Bi, S, Se, Te and B to titanium alloys of the alpha, alpha+beta and beta types, the alloy having an improved strength uniform fine structure at room temperature and high temperature.

[0011] From US 2004 / 136859 A1 it is known to improve castability of a titanium alloy by introducing 0.01 wt% - 5 wt%, preferably 0.1 wt% - 3 wt% of bismuth, the bismuth being introduced into the titanium alloy, based on the weight of the bismuth and the titanium alloy. The titanium alloy is suitable for manufacturing dental castings or medical implants by casting. In one embodiment, the document discloses that the castability of a Ti-6Al-4V alloy can be improved almost 30% by adding 1 wt% of Bi in the alloy compared to the undoped Ti. The document further teaches a biocompatible titanium alloy composition having good castability, comprising (a) about 0.01 wt% - 5 wt% of Bi, (b) at least one alloying element selected from the group consisting of Mo, Nb, Ta, Zr and Hf; (c) the balance being Ti and at least one eutectoid beta stabilizing element selected from Fe, Cr, Mn, Co, Ni, Cu, Ag, Au, Pd, Si and Sn.

[0012] US 2017326868 A1 discloses a welding wire for electron beam or plasma arc additive manufacturing of titanium alloys. The welding wire has a first portion comprising a first material and a second portion comprising a second material. The combination of the first material and the second material results in a titanium alloy product having a suitable composition.

[0013] It is common for many alloy compositions that they are less suitable for high energy input, high deposition rate additive manufacturing processes due to insufficient level of grain refinement or excessive segregation of solute elements. Therefore, there is a need in the art for an economic method to produce metal products made of titanium with finer solidification grain structure, in particular with more equiaxed primary beta grains formed during solidification, for metal additive manufacturing at increased metal deposition rates in additive manufacturing systems compared to what is achieved in conventional additive manufacturing processes.

[0014] Object of the present invention

[0015] It is a main object of the present invention to provide a titanium alloy suitable for the additive manufacturing of components with isotropic high strength mechanical properties.

[0016] It is a further object of the present invention to provide an additive manufacturing method for producing titanium components with isotropic high strength mechanical properties. SUMMARY

[0017] The present invention is based on the finding considered to be novel that an aluminum and molybdenum based titanium alloy obtains a significant grain refinement effect of the as-solidified grain structure with the addition of bismuth, making this titanium alloy particularly suitable for the additive manufacturing of components with high mechanical strength.

[0018] Thus, in a first aspect, the present invention relates to a titanium alloy, wherein the composition of the titanium alloy is: a first alloy composition characterized in comprising: - from 2 wt% to 7 wt% of Al, - from 1.5 wt% to 6 wt% of Mo, - from 0.25 wt% to 1.5 wt% of Bi, - optionally from 0 to 1 wt% of V, and - the balance of wt% Ti such that the sum of the total content of the ingredients in the titanium alloy composition is 100 wt%, wherein the weight percentages are based on the total mass of the titanium alloy composition, or: a second alloy composition characterized in comprising: - from 2 wt% to 7 wt% of Al, - one or more of Mo and V in a total amount from 1.5 wt% to 6 wt%, - Bi from 0.25 wt% to 1.5 wt%, - one or more elements selected from the group of β eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B and Si, in a total amount from 0.3 wt% to 1.5 wt%, and - Ti for the balance of the wt%, such that the sum of the total contents of the constituents in the titanium alloy composition is 100 wt%, wherein the weight percentages are based on the total mass of the titanium alloy composition, or: a third alloy composition, characterized in that it comprises: - Al from 2 wt% to 7 wt%, - V from 1.5 wt% to 6 wt%, - Bi from 0.25 wt% to 1.5 wt%, - one or more elements selected from the group of β eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B and Si, in a total amount from 0.3 wt% to 1.5 wt%, and - Ti for the balance of the wt%, such that the sum of the total contents of the constituents in the titanium alloy composition is 100 wt%, wherein the weight percentages are based on the total mass of the titanium alloy composition.

[0019] Alternatively, in a first aspect, the present invention relates to a titanium alloy, wherein the titanium alloy is: a first alloy composition, characterized in that it consists of: - Al from 2 wt% to 7 wt%, - Mo from 1.5 wt% to 6 wt%, - Bi from 0.25 wt% to 1.5 wt%, - optionally V from 0 to 1 wt%, and - for the balance Ti and unavoidable impurities, wherein the weight percentages are based on the total mass of the titanium alloy composition, or: a second alloy composition, characterized in that it consists of: - Al from 2 wt% to 7 wt%, - one or more of Mo and V in a total amount from 1.5 wt% to 6 wt%, - Bi from 0.25 wt% to 1.5 wt%, - the balance being Ti and unavoidable impurities, - the balance being Ti and unavoidable impurities, wherein the weight percentages are based on the total mass of the titanium alloy composition, or: A third alloy composition, characterized in that it consists of: - from 2 wt% to 7 wt% of Al, - from 1.5 wt% to 6 wt% of V, - from 0.25 wt% to 1.5 wt% of Bi, - the balance being Ti and unavoidable impurities, - the balance being Ti and unavoidable impurities, wherein the weight percentages are based on the total mass of the titanium alloy composition.

[0020] As used herein, the term "one or more of element A, element B and element C" is to be understood as encompassing alloys comprising only one of these elements A, B or C and any other possible combination of the specified elements. For example, in the case of "one or more of A, B and C", the alloy can comprise any one of the following: A (alone), B (alone), C (alone), A+B, A+C, B+C and A+B+C. Furthermore, the term "one or more of element A, element B and element C in a total amount from x to y wt%" as used herein means that any combination of elements A, B and C is applied in the alloy, the content of this combination of elements should be in the range from x to y wt% based on the total mass of the titanium alloy composition.

[0021] As used herein, the term "the balance of Ti" means that the amount of titanium in the alloy composition is determined from the content of the other ingredients in the composition so that the total content of the ingredients amounts to 100 wt%. That is, the content of titanium in the composition fills the "available space" in the composition left by the other components. For example, if an alloy composition according to the present application comprises 6 wt% of Al, 3 wt% of Mo, 1 wt% of Bi, 1 wt% of impurities, and 3 wt% of optional alloying elements, the content of Ti including unavoidable impurities is 86 wt% because the total content of the other ingredients amounts to 14 wt%.

[0022] Accordingly, the example embodiments are directed to refining the solidification structure in additive manufacturing by providing a weldable titanium alloy wire made of an Al and Mo containing Ti alloy, which includes a small addition of the low surface tension metal Bi. Experience suggests that the addition of a surface active element such as Bi in such titanium alloys for additive manufacturing to promote grain nucleation, presumably due to a reduction in the liquid-solid interfacial energy, which can result in a reduction in the potential barrier for nucleation and growth, along with an enhancement of the surface tension driven melt pool flow.

[0023] In one embodiment, the content of aluminum in the first, second or third alloy composition according to the first aspect of the application can be from 3 wt% to 6.75 wt%, preferably from 4 wt% to 6.5 wt%, more preferably from 5 wt% to 6.25 wt%, and most preferably from 5.9 wt% to 6.1 wt%, based on the total mass of the titanium alloy composition.

[0024] In one embodiment, the content of molybdenum in the first alloy composition of the first aspect of the application can be from 1.75 wt% to 5.5 wt%, preferably from 2 wt% to 5 wt%, more preferably from 2.25 wt% to 4 wt%, more preferably from 2.5 wt% to 3.5 wt%, most preferably from 2.9 wt% to 3.1 wt%, and / or the total content of molybdenum and vanadium in the second alloy composition can be from 2 wt% to 5.5 wt%, preferably from 2.5 wt% to 5 wt%, more preferably from 3 wt% to 4.5 wt%, more preferably from 3.25 wt% to 4.0 wt%, and most preferably from 3.4 wt% to 3.6 wt%, and wherein the weight percentages are based on the total mass of the titanium alloy composition.

[0025] In one embodiment, the content of bismuth in the first, second or third alloy composition according to the first aspect of the application can be from 0.3 wt% to 1.4 wt%, preferably from 0.35 wt% to 1.3 wt%, more preferably from 0.4 wt% to 1.2 wt%, more preferably from 0.45 wt% to 1.1 wt%, more preferably from 0.5 wt% to 1 wt%, more preferably from 0.6 wt% to 0.9 wt%, and most preferably from 0.7 wt% to 0.8 wt%, based on the total mass of the titanium alloy composition.

[0026] In one embodiment, the total content of one or more elements selected from the group of beta eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si in the second or third alloy composition according to the first aspect of the application can range from 0.4 wt% to 1.4 wt%, preferably from 0.5 wt% to 1.3 wt%, more preferably from 0.6 wt% to 1.2 wt%, more preferably from 0.7 wt% to 1.1 wt%, and most preferably from 0.8 wt% to 1.0 wt%, based on the total mass of the titanium alloy composition. Experience has shown that the combination of Bi with one or more of the above-mentioned range-extending elements results in a significant refinement of the primary beta grain size.

[0027] In one embodiment, the oxygen content in the first, second or third alloy composition according to the first aspect of the application can comprise less than 0.5 wt%, preferably less than 0.4 wt%, more preferably less than 0.3 wt%, more preferably less than 0.2 wt%, and most preferably between 0.06 wt% and 0.18 wt%, based on the total mass of the alloy composition.

[0028] In one particularly preferred embodiment, the titanium alloy composition comprises or consists of 6 wt% Al, 3 wt% Mo, 0.6 wt% Bi, and 0.6 wt% Fe, with the remainder being Ti and unavoidable impurities, wherein the weight percentages are based on the total mass of the titanium alloy composition.

[0029] In one embodiment, the first and / or second and / or third alloy composition according to the first aspect of the application can further comprise Sn in a total amount of from 0.1 wt% to 5.0 wt% and / or Zr in a total amount of from 0.1 wt% to 6.0 wt%, based on the total mass of the titanium alloy composition.

[0030] As used herein, the term “unavoidable impurities” refers to any undesired constituents and / or elements present in the alloy composition, typically originating from upstream processing and / or raw materials used to manufacture titanium and / or alloy constituents of the alloy composition.

[0031] The alloy compositions provided herein allow for the refinement of these solidification structures in a metal additive manufacturing process to obtain a product with improved material quality, in particular with a more equiaxed as-solidified grain structure. These refined grain structures can result in increased strength, fatigue resistance, ductility, and isotropic properties of the additively manufactured parts.

[0032] Exemplary embodiments of the alloy composition according to the first aspect of the invention can provide grain refinement in titanium metal articles produced by additive manufacturing without modification of the manufacturing process. The resulting grain structure of the deposited material can have an aspect ratio and homogeneity comparable to that of mechanically machined titanium alloys. Some embodiments can exhibit a significantly reduced average grain size compared to typical cast or additively manufactured materials. The reduced barrier to grain formation provided by the Bi addition, optionally in combination with one or more of the solidification interval extending elements Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si, can result in solidification structure refinement by simply applying the alloy composition in an additive manufacturing process involving melting and subsequent layered metal deposition of the alloy. In particularly preferred embodiments, the alloy composition according to the first aspect of the invention is provided in the form of a welding wire.

[0033] Exemplary alloy compositions in the form of weldable welding wires can provide a practical means to achieve significant refinement of the metal structure of titanium alloy parts made by metal additive manufacturing, resulting in grains that in most cases can be similar to or slightly coarser than typical mechanically machined titanium metals and can have comparable aspect ratios and homogeneity.

[0034] Embodiments of the alloy composition can achieve solidification refinement without negatively affecting deposition productivity. The alloy composition according to the first aspect of the invention can be used with most melting tools. In embodiments, the alloy composition can preferably be used with plasma arc torches and inert gas atmospheres due to the evaporation and volatility associated with low melting point additives in high intensity laser processes and electron beam processes performed in a vacuum. The alloy composition according to the first aspect of the invention can be used with any metal additive manufacturing process, including plasma and wire-based processes, as well as electron beam and laser systems, and combinations thereof. Exemplary embodiments in the form of welding wires can be particularly suitable for high deposition rate processes where the solidification grain structure can be very coarse.

[0035] There is provided feedstock for metal additive manufacturing, wherein the feedstock is a titanium alloy comprising the low surface tension element Bi, optionally in combination with one or more elements that increase the solidification interval. The feedstock can be in the form of a titanium alloy powder or a titanium alloy welding wire.

[0036] Accordingly, in a second aspect, the invention relates to a welding wire made of a titanium alloy composition according to the first aspect of the invention. In one embodiment, the welding wire can have a nominal diameter in the range from 0.5 to 10.0 mm, preferably from 0.7 to 5.0 mm, more preferably from 0.8 to 2.5 mm, more preferably from 0.9 to 2.0 mm, more preferably from 1.0 to 1.8 mm, and most preferably from 1.2 to 1.6 mm.

[0037] The welding wire can be produced using any conventional method. One method can include the production of a rod or billet. The rod or billet can be rolled to a diameter typically less than about 10 mm to 15 mm. The rolled rod or billet can be drawn to a final size having a target diameter for use in the additive manufacturing process. An alternative method of producing a titanium welding wire can include production by a solid state process. For example, the method can include powder compaction and sintering prior to hot working without intermediate melting of the titanium sponge. The weldable titanium wire can be produced from a titanium sponge by processing only in the solid state without any melting of the components at any time during processing.

[0038] In a third aspect, the present application relates to a powder made of the titanium alloy composition according to the first aspect of the present application.

[0039] The titanium alloy powder can be produced using any known method. For example, the titanium alloy powder can be produced by gas atomization, water atomization, plasma atomization, centrifugal atomization, plasma rotating electrode process, or any combination thereof. Depending on the method chosen, the resulting titanium alloy powder can have an irregular shape or can be spherical or a combination thereof. The titanium alloy powder grains can have a smooth or rough surface. In one embodiment, the grains of the titanium alloy powder can have a nominal particle size distribution from 15 pm to 200 pm, as determined by laser diffraction analysis according to standard ISO 13320:2020.

[0040] In a fourth aspect, the present application relates to a method for manufacturing a three-dimensional part made of a titanium alloy, characterized in that the method comprises forming the three-dimensional part by applying an additive manufacturing process of the titanium alloy according to the first aspect of the present application.

[0041] In one embodiment, the additive manufacturing method can advantageously comprise: - building the three-dimensional part by fusing together successive deposits of the titanium alloy on a base material by: - using a melting tool to heat and melt feedstock of the titanium alloy and deposit the molten feedstock onto a deposition area of the base material, and a) moving the position of the base material relative to the first melting tool according to a predetermined path, so that the successively deposited molten feedstock solidifies and forms the three-dimensional part, or: b) moving the first melting tool relative to the base material according to a predetermined path, so that the successively deposited molten feedstock solidifies and forms the three-dimensional part.

[0042] In one embodiment, the method according to the application can advantageously further comprise the use of two melting tools, a first melting tool to pre-heat at least a portion of the surface of the base material; and a second melting tool for heating and melting the weldable wire according to the second aspect of the application, such that molten titanium alloy material is deposited onto the pre-heated area of the base material, thereby forming a liquid puddle. The base material can be moved in a predetermined path relative to the position of the first and second heating devices, such that successive deposits of molten titanium alloy material solidify and form a three-dimensional part.

[0043] In one embodiment, the feedstock can be a wire according to the second aspect of the application, and the second melting tool can be a plasma transferred arc torch (PTA) applied to heat and melt the wire above the deposition area of the base material.

[0044] In one embodiment, both the first and second melting tools are plasma transferred arc torches (PTA). In Figure 6 An exemplary embodiment applying two melting tools is schematically shown in Fig. 1. The figure shows a carrier substrate 1, e.g. made of Ti-6Al-4V alloy, on which a three-dimensional object is formed by solid freeform fabrication. The figure shows an initial portion of the deposition process, in which a first bead 2 of titanium alloy is being shaped.

[0045] A wire 3 made of titanium alloy according to the first aspect of the application is continuously supplied from a wire feeder 4, which positions the wire 3 such that its distal end is located above a puddle 5 at the deposition area on the carrier substrate 1. The wire 3 is imparted with a speed, indicated by the upper arrow in the figure, which corresponds to the rate of heating and melting of the distal end, such that droplets 6 of molten wire are continuously supplied to the puddle 5.

[0046] A first plasma transferred arc 7 is formed by a first melting tool, a PTA torch 8, which is electrically connected with a DC power source 9, such that the electrode 10 of the PTA torch becomes the cathode, while the carrier substrate 1 becomes the anode. The first plasma transferred arc 7 heats the deposition area and contributes to the formation of the puddle 5. The PTA torch 8 can be a gas tungsten arc welding (GTAW) torch equipped with a magnetic arc deflector (not shown) to control the size and position of the arc 8.

[0047] A second plasma transferred arc 11 is formed by a second melting tool (PTA torch 12) that is electrically connected to a DC power source 13 such that the electrode 14 of the PTA torch 12 becomes the cathode and the advancing wire 3 becomes the anode. The plasma transferred arc 11 is continuous and is directed to heat and melt the distal end of the wire 3. The action of the DC power source 13 can advantageously be regulated to maintain a heating and melting rate in accordance with the feed rate of the wire 3 such that the timing of the formation of the droplets 6 is controlled to maintain a continuous dripping of molten wire into the melt pool 5.

[0048] Methods for minimizing columnar growth in titanium alloy three-dimensional parts produced by additive manufacturing and methods for solidification refinement are also provided. Surface active elements can lower the liquid-solid interface energy and thus lower the barrier to grain nucleation and growth during solidification. The surface active elements can enhance surface tension driven flow in the melt pool by affecting the thermal gradients in the melt and at the solid-liquid interface, which flow affects solidification. Surface active elements can promote fragmentation in the partially solidified mushy zone. Surface active elements can help increase constitutional undercooling due to the expansion of the solidification interval to provide an increased growth restriction factor.

[0049] The method can also include the step of including in the weldable wire an element that promotes additional constitutional undercooling by expanding the freezing interval of the alloy. This can further increase the tendency for grain nucleation and refinement. It is important to limit such additions to avoid deleterious segregation and solidification flaws in the final product. Combinations with Bi allow for significant grain refinement without such deleterious effects. Elements that promote constitutional undercooling can be selected from the group classified as eutectoid beta stabilizing solutes. Relevant elements from this group consist of Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si. The method can also include the step of including in the weldable wire an element that promotes alpha stabilization. An exemplary element that promotes alpha stabilization is Al. Elements in this group also help increase strength due to solid solution hardening. Another element that can be included to provide further solid solution strengthening is Si. The methods provided herein can produce three-dimensional parts with an average grain size that is reduced by at least a factor of 2, and preferably at least a factor of 5, compared to the grain size of three-dimensional parts made from the alloy Ti-6Al-4V or other conventional weldable alpha-beta titanium alloys (excluding surface active elements) using the titanium alloy feedstock in an additive manufacturing process.

[0050] Finally, in a fifth aspect, the present invention can relate to the use of a titanium alloy according to the first aspect of the present invention in an additive manufacturing process, which can preferably be in the form of a wire according to the second aspect of the present invention or a powder according to the fourth aspect of the present invention in further embodiments.

[0051] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present application as claimed.

[0052] Additional features will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. The purposes and other advantages of the exemplary embodiments will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0053] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application.

[0054] In the drawings: Figure 1A is an illustration of a cross-section of a wall deposit as it is layer-by-layer fused in conventional prior art additive manufacturing.

[0055] Figure 1B is an illustration of a cross-section of a wall deposit layer-by-layer fused in additive manufacturing using a weldable titanium alloy welding wire or titanium alloy powder containing surface active elements. These surface active elements can reduce surface tension and interfacial energy. Reduced surface tension can reduce the potential barrier to grain nucleation and growth. This can result in solidification refinement. In exemplary embodiments, this can result in minimized columnar grain growth.

[0056] Figure 2A is a macrograph of a cross-section of a columnar deposit of an additively manufactured Ti5,5Al-3Mo metal component additionally containing 0.58 wt% Bi. Solidification grain size is reduced by the addition of Bi. Columnar grains are greatly eliminated and more equiaxed grains are produced. The addition of Bi results in solidification refinement. The deposit is composed of about 7-8 deposited layers.

[0057] Figure 2B is a macrograph of a cross-section of a wall deposit of a comparative Ti5,5Al-3Mo metal component additively manufactured, without the addition of Bi, to serve as a reference to exhibit a typical columnar macrostructure. The deposit is composed of about 7-8 deposited layers.

[0058] Figure 2C is a macrograph of a cross-section of a wall deposit of a comparative Ti5,5Al-3Mo metal component additively manufactured containing 0.57 wt% Bi and additionally 0.73 wt% Fe. The deposit is composed of about 4-5 deposited layers. Solidification grain size is further reduced due to the effect of the addition of Fe on the alloy's freezing range and the associated tendency of compositional undercooling to further promote grain nucleation.

[0059] Figure 3A It comes from and Figure 2A Images composed of stitched micrographs of the same cross-section. Here, the solidified grain structure is outlined for most samples to clearly show the primary β-grain size. Each outlined seed grain was measured, and the average grain size is 0.60 mm².

[0060] Figure 3B It comes from and Figure 2B Images composed of stitched micrographs of the same cross-section. Here, the solidified grain structure is outlined for most samples to clearly show the primary β-grain size. Measurements were taken for each outlined grain, and the average grain size is 8.76 mm².

[0061] Figure 3C It comes from and Figure 2C Images composed of stitched micrographs of the same cross-section. Here, the solidified grain structure is outlined for most samples to clearly show the primary β-grain size. Each delineated grain was measured, and the average grain size is 0.10 mm².

[0062] Figure 4A This is a macroscopic cross-sectional view of the wall deposits of an additively manufactured comparative titanium alloy metal part, comprising Ti-6Al-4V and additionally containing 0.67 wt% Bi. For most samples, the solidified grain structure is delineated to clearly show the grain size. The average grain size is 0.91 mm. 2 .

[0063] Figure 4B This is a macroscopic cross-sectional view of the wall deposits of a comparative titanium alloy metal part manufactured by additive manufacturing with the same Ti-6Al-4V base composition, but alternatively containing 0.57 wt% Fe and excluding Bi. For most samples, the solidified grain structure is delineated to clearly show the grain size. The average grain size is 2.49 mm. 2 .

[0064] Figure 5 It is a histogram summarizing the average grain size obtained in a series of comparative tests, wherein components are constructed in titanium alloys that fall into and do not include the titanium alloy composition of the present invention.

[0065] Figure 6 The diagram schematically illustrates an embodiment of the method according to the fourth aspect of the present invention. Detailed Implementation

[0066] Reference will now be made in detail to embodiments of the present invention, examples of which are shown in the accompanying drawings.

[0067] A. Definitions

[0068] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art to which this application belongs. All patents, patent applications, published applications and publications, websites and other published materials referred to throughout the entire disclosure herein, unless otherwise indicated, are hereby incorporated by reference in their entirety. In the event that there is a plurality of definitions for a term herein, those in this section prevail.

[0069] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0070] As used herein, ranges and amounts can be expressed as "about" a particular value or range. About also includes the exact amount. Hence "about 5%" means "about 5%" but also "5%." About means within typical experimental error for the application or purpose intended.

[0071] As used herein, "wt%" refers to weight percent, sometimes referred to as w / w, and is the percentage of the total mass of a composition that is a component. Weight percent can also be expressed as 100 times the fractional weight of a component in a composition. The sum of the wt% of all components in a composition equals 100.

[0072] As used herein, "optional" or "optionally" means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. For example, an optional component in a system means that the component can or can not be present in the system.

[0073] As used herein, the terms "comprising," "including," and "containing" are synonymous and are inclusive or open-ended. Each term indicates that additional, unlisted elements or method steps can optionally be included.

[0074] As used herein, “and / or” means “any or all” of the enumerated items so conjoined, i.e., one or more items in some cases, and in other cases, all of the items. Multiple elements listed with “and / or” should be construed in the same fashion as if each item in the list were individually preceded by “one or more” followed by a listing of the elements. Other elements can optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. As a non-limiting example, a reference to “A and / or B” when used in conjunction with open-ended language such as “comprising” can refer, in one implementation, to only A, in another implementation, to only B, in yet another implementation, to both A and B, and in yet another implementation, to both A and B and one or more elements in addition to A and B. As used herein in the context of describing various structures, configurations, components, elements, items, etc., the phrase “at least one of’ means “one or more of’ and “one or more selected from the group consisting of’.

[0075] As used herein, “combination” refers to any association between two items or more than two items. The association can be spatial or refer to the use of two or more items for a common purpose.

[0076] As used herein, “additive manufacturing” is also known as “additive shaping” and “additive layer manufacturing” and refers to an additive process that enables the layer-by-layer manufacturing of a part. The part can be manufactured from 3D model data. A titanium alloy source, such as a welding wire or powder, can be used. An energy source, such as a plasma arc, laser, electron beam, or a combination thereof, can be used to melt the titanium alloy source.

[0077] As used herein, “additive manufacturing system” refers to a machine used for additive manufacturing.

[0078] As used herein, “weldable welding wire” refers to a welding wire of a titanium alloy material to be melted under additive manufacturing conditions to form a designed part. The weldable welding wire can be a long, narrow, wire-like structure. The weldable welding wire can be provided as a coil wound around a spool. The weldable welding wire can be a shorter, generally linear structure. They can be provided as a welding rod or electrode. The weldable welding wire can be in the form of a narrow, elongated welding wire that can have a nominal diameter in the range from 0.025 inch to 0.5 inch. It can have a length of at least 10 feet. For example, the welding wires can have a nominal diameter selected from 1 / 32, 1 / 16, , ¼, and ½ inch, or a nominal diameter from about 0.5 mm to 15 mm. Such welding wires can have a length of at least 10 feet, at least 20 feet, at least 100 feet, or at least 1000 feet. They can be wound. In the case of a larger diameter rod, e.g., 5-15 mm in diameter, the total length can be only a few inches, e.g., a length of about 3 inches to 1 foot.

[0079] As used herein, "plasma arc welding torch" or "PAW torch" refers to a welding torch that can be used for plasma arc welding. The torch can be designed such that a gas can be heated to a high temperature to form a plasma and can become electrically conductive. The plasma can then transfer an electric arc to a workpiece. The intense heat of the arc can melt metal and / or fuse two pieces of metal together. The PAW torch can include a nozzle for compressing the arc, thereby increasing the power density of the arc. The plasma gas can be a noble gas. The plasma gas can be argon. The PAW torch can have an outer nozzle for providing a shielding gas. The shielding gas can be argon, helium, or a combination thereof. The shielding gas can help reduce oxidation of the molten metal. The PAW torch can include a plasma transferred arc torch.

[0080] As used interchangeably herein, the term "plasma transferred arc torch" or "PTA torch" refers to any device capable of heating and exciting a stream of inert gas to a plasma by an electric arc discharge, and then transferring the stream of plasma gas (including the arc) out through an orifice (such as a nozzle) to form a constricted plume extending out of the orifice and to deliver the intense heat of the arc to a target area. The plasma gas can be fed along an electrode and ionized and accelerated near a cathode. The arc can be directed toward the workpiece and is more stable than a free-burning arc (such as in a TIG torch). The current typically rises to 400 A, and the voltage typically ranges from about 25-35 V.

[0081] As used herein, the term "substrate material" refers to a target material for heat from a melting tool, and a molten pool can be formed on the target material. The melting tool can be a PAW torch, a PTA torch, a laser device, an electron beam, or any combination thereof. The substrate material can be a carrier substrate when depositing a first layer of titanium alloy material. The substrate material can be an upper layer of deposited titanium alloy material when one or more layers of titanium alloy material have been deposited onto the carrier substrate.

[0082] As used herein, the term "workpiece" refers to a metallic body made of a titanium alloy according to the present application produced using solid freeform fabrication manufacturing.

[0083] The terms "design model" or "computer-aided design model" or "CAD model" as used interchangeably herein refer to any known or conceivable virtual vectorized layered three-dimensional representation of a part to be formed by an additive manufacturing process. For example, a model can be obtained by forming a virtual vectorized layered model of a three-dimensional part by first dividing the part into a set of virtual parallel layers, and then dividing each parallel layer into a set of virtual quasi-one-dimensional slices that can be used by a controller of an additive manufacturing system to form the part by depositing or fusing layers of metal according to the virtual parallel layers.

[0084] As used herein, "controller" refers to any logic circuitry and / or processing element that is involved in communicating with and / or controlling one or more components of an additive manufacturing system and related software or programs of the additive manufacturing system components. The controller can include a computer and / or computer memory.

[0085] As used herein, "computer" can include, but is not limited to, hardware and / or software that can capture and / or store data, and any program that can be programmed to communicate with and / or control one or more electronic devices or software that controls a mechanical device. The computer can include a non-transitory computer readable medium, which can include, but is not limited to, a CD-ROM, a removable flash memory card, a hard disk drive, or a magnetic tape.

[0086] As used herein, "computer memory" refers to a configurable storage element capable of storing digital data or information that can be accessed and processed by a computer.

[0087] As used herein, "inert atmosphere" refers to any known or conceivable gas or mixture of gases containing less than 1% oxygen to reduce or prevent oxidation. The inert atmosphere can be non-reactive. The inert atmosphere can be non-oxidizing. The inert atmosphere can protect components from exposure to oxygen or from undergoing oxidation or other undesirable chemical action from the ambient atmosphere. Exemplary inert atmospheres include one or more noble gases. The inert atmosphere can include argon, helium, neon, xenon, or combinations thereof.

[0088] As used herein, "pasty zone" refers to the region adjacent to the liquid-solid interface where the liquid and solid phases coexist during solidification.

[0089] As used herein, "microstructure" refers to the internal crystalline structure of an alloy over distances of about 1 micron to about 1 mm, which can include the location, shape, size, and relative amounts of grains and metallurgical phases in the metal. It can include the three-dimensional arrangement of grains or metallurgical phases.

[0090] As used herein, "macrostructure" refers to the internal grain structure of an alloy over distances of from about greater than 0.5 mm to about 100 mm, or a plurality of crystallographically related microstructural elements, which can include the location, shape, size, and relative amounts of elements that make up the internal structure of the material at a macroscopic scale. For titanium alloys, the macrostructure, which is typically present in materials that are cast, welded, or additively manufactured, consists of so-called primary beta grains. This refers to discrete regions that can be identified by observing the pattern in the microstructure, which reflects the crystallographically related microstructure (in addition to the elongated continuous grain of the boundaries that exist between most primary beta grains).

[0091] As used herein, "surface active" refers to a chemical element that reduces the surface tension (or interfacial tension) between a gas and a liquid or between a liquid and a solid.

[0092] For any range recited herein, unless otherwise stated, the range is intended to include all values and sub-ranges within the range. For example, if a range of 1 to 10 is recited, the range includes 1 and 10, as well as any and all sub-ranges between (and inclusive of) the

[0093] B. Metal feedstock composition

[0094] Provided herein are Ti alloy compositions that can exhibit refined solidification structures when used to manufacture components using a melt and fusion based additive manufacturing process. The Ti alloy feedstock composition can be in the form of a powder, a welding wire, a rod, a ribbon, or a combination thereof. The Ti alloy feedstock composition can be a weldable welding wire. The addition of a surface active element or a combination thereof can reduce the interfacial energy barrier to nucleation during solidification of the deposited Ti alloy material. In an embodiment, the Ti alloy composition can include a combination of the surface active element Bi and one or more elements selected from the group of beta eutectoid stabilizers that increase the solidification interval, selected from the group consisting of Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si. An exemplary composition includes titanium or a titanium-based alloy and about 0.05 wt% to about 1.5 wt% Bi and 0.3 wt% to 1.5 wt% Fe.

[0095] Titanium melts have a high surface tension. This high surface tension can be a barrier to nucleating grains. This can result in a strong tendency for epitaxial and columnar solidification, as the interfacial energy barrier is circumvented when solidification proceeds from a prior grain. This is schematically shown in Figure 1A The schematic shows the typical epitaxial growth exhibited by many conventional alloys when applied in additive manufacturing. It is preferred that solidification continue on partially remelted grains in the previous layer, rather than forming new nuclei that are separate from the expanding solidification front. Nucleation resistance is related to the surface energy associated with forming a new liquid-solid interface in the melt pool.

[0096] In embodiments, it has been found that a small addition of Bi to titanium alloys breaks the characteristic epitaxial and columnar grain growth when multiple layers are fused. This can promote grain nucleation in the melt (homogeneous nucleation) during solidification. The addition of Bi can result in solidification refinement and can reduce columnar grain growth. This is shown in Figure 1B .

[0097] In some embodiments, it has also been found that by reducing the surface tension and including elements that increase the solidification interval, the addition of Bi in combination with a small amount of one or more elements selected from the group of beta eutectic stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si; can achieve substantially more significant solidification refinement. For example, the addition of as little as 0.58 wt% Bi to a metallic composition comprising Ti, Al, V, and Mo reduces the average grain size in the deposited metal by more than a factor of 10 when melted during an additive manufacturing process.

[0098] Without wishing to be bound to any particular theory, it is believed that solidification refinement occurs in the presence of Bi because this element can lower the liquid- solid interface energy and thus the barrier to grain nucleation and growth during solidification. In the mechanism proposed here, Bi acts as a surface active element. In some embodiments, Bi can enhance surface tension driven flow in the melt pool by affecting the thermal gradients in the melt and at the solid-liquid interface, which affects solidification. Bi can potentially contribute to refinement through fragmentation in the partially solidified mushy zone.

[0099] In some embodiments, Bi can increase the tendency for constitutional undercooling due to the expansion of the solidification interval, but it is expected that Bi contributes less to this mechanism than elements such as Fe, Ni, or Cu based on solute partitioning shown in established binary phase diagrams. The constitutional undercooling of a composition can be initiated and increased by one or more surface active elements in combination with other elements that specifically include increasing the solidification interval and providing increased grain growth restriction. The presence of these other elements that increase the solidification interval can result in a greater proportion of solid clusters to overcome the nucleation barrier. The partitioning of elements can occur during solidification, which can increase or decrease the amount of an element in the liquid adjacent to the solid. The accumulation of solute at the solid-liquid interface can cause constitutional undercooling and contribute to nucleation at multiple sites rather than continuous columnar grain growth. The degree of partitioning can be approximately proportional to the grain growth restriction. Examples of elements that increase the solidification interval and provide increased grain growth restriction are Fe, Ni, and Cu. Particular care must be taken with such additions to avoid excessive segregation that can lead to material defects. Therefore, it is preferred that the refinement not be achieved solely by this mechanism because it requires greater addition amounts, typically higher than 1.5 wt%. It is therefore beneficial to combine the surface active addition of Bi to increase the effectiveness of such solutes (such as Fe, Ni, and Cu).

[0100] The addition of a surface active element (e.g., Bi) in combination with one or more elements selected from the group of β eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si can result in a metal wire feedstock that when melted in an additive manufacturing process can result in a refinement of the solidification structure that substantially eliminates one or more problems resulting from the limitations and shortcomings of additive manufacturing using conventional alloys. In embodiments, the resulting product can have a more equiaxed as-solidified grain structure. The finished product having these refined grain structures can exhibit increased strength, fatigue resistance, ductility, or a combination thereof. Exemplary metal compositions containing Bi in combination with one or more elements selected from the group of β eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si can result in a metal layer having a grain structure deposited during an additive manufacturing process that has an aspect ratio and uniformity comparable to that typically found in a machined metal and a substantially reduced average grain size compared to typical cast or additive manufactured materials.

[0101] Exemplary metal compositions containing Bi in combination with one or more elements selected from the group of β eutectoid stabilizers; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si can be provided in the form of a weldable wire.

[0102] When used in an additive manufacturing process, exemplary metal compositions can result in a deposited metal layer that can include an α-β titanium alloy that exhibits a substantially refined solidification structure primarily due to the addition of Bi. The total amount of Bi that can be present in the titanium alloy composition can be from 0.3 wt% to 1.4 wt%, preferably from 0.35 wt% to 1.3 wt%, more preferably from 0.4 wt% to 1.2 wt%, more preferably from 0.45 wt% to 1.1 wt%, more preferably from 0.5 wt% to 1 wt%, more preferably from 0.6 wt% to 0.9 wt%, and most preferably from 0.7 wt% to 0.8 wt%.

[0103] In addition to Bi, embodiments of the titanium alloy composition can include one or more elements known to increase the solidification range, typically belonging to the group of β eutectoid stabilizing elements, selected from the following: Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si. The total amount of the combination of one or two or more β stabilizing elements that can be present in the titanium alloy composition can be from 0.4 wt% to 1.4 wt%, preferably from 0.5 wt% to 1.3 wt%, more preferably from 0.6 wt% to 1.2 wt%, more preferably from 0.7 wt% to 1.1 wt%, and most preferably from 0.8 wt% to 1.0 wt%, based on the total weight of the titanium alloy composition.

[0104] The beta stabilizing elements belonging to the group of isomorphous beta stabilizing elements stabilize the beta phase of titanium without significantly increasing the solidification interval and allow the titanium or titanium alloy to retain a partial beta phase in the final product. One element or a combination thereof selected from the list of V, Mo, Nb, and Ta can be used among the isomorphous beta stabilizing elements. The total amount of the one or more beta stabilizing elements or the combination of two or more beta stabilizing elements that can be present in the titanium alloy composition can be from 1.75 wt% to 5.5 wt%, preferably from 2 wt% to 5 wt%, more preferably from 2.25 wt% to 4 wt%, more preferably from 2.5 wt% to 3.5 wt%, and most preferably from 2.9 wt% to 3.1 wt%, based on the total weight of the titanium alloy composition.

[0105] The titanium alloy composition can include Al as an alpha stabilizer. The total amount of Al that can be present in the titanium alloy composition can be from 3 wt% to 6.75 wt%, preferably from 4 wt% to 6.5 wt%, more preferably from 5 wt% to 6.25 wt%, and most preferably from 5.9 wt% to 6.1 wt%, based on the total weight of the titanium alloy composition.

[0106] In embodiments, it has been found that the addition of Bi to Ti or Ti alloys is effective in suppressing columnar solidification. For example, in embodiments where Bi is added to Ti alloys, columnar solidification is suppressed, transitioning from a predominantly columnar morphology to a predominantly equiaxed morphology. This is shown in Figure 1B and in Figure 2B , Figure 3B and Figure 4B In compositions including Bi in the range of 0.5 wt% - 1.0 wt%, columnar grains are largely eliminated. In some embodiments, the effect of Bi can be more pronounced when Fe is added, as shown in Figure 2C and Figure 3C In some embodiments, the extension of the solidification interval by the addition of Fe can result in further solidification refinement.

[0107] Exemplary titanium alloy compositions can be used in additive manufacturing methods to produce products with the potential for high strength, improved fatigue properties, isotropic material behavior, or a combination thereof due to largely eliminating the presence of coarse columnar solidification structures and reducing the average primary beta grain size by a factor of 10 or more compared to what is achieved in titanium alloys that do not include these alloying additions. Exemplary titanium alloy compositions can be used to make titanium alloy feedstock. The titanium alloy feedstock can be used in any additive manufacturing process that uses titanium alloy feedstock. The titanium alloy feedstock can be in the form of a titanium alloy wire, a titanium alloy ribbon, a titanium alloy rod, a titanium alloy powder, or a combination thereof. A heat source of the additive manufacturing process can be used to melt the feedstock. The heat source can be a plasma arc, a laser beam, an electron beam, or any combination thereof.

[0108] When used in an additive manufacturing process, the exemplary titanium alloy compositions can produce a composition that can exhibit higher strength, improved fatigue properties, and isotropic material behavior due to the largely eliminated presence of coarse columnar solidification structures that are typically produced in additive manufacturing processes. In some embodiments, the average primary β grain size can be reduced by a factor of 10 or more compared to conventional alloy compositions.

[0109] Additional benefits of exemplary embodiments can include a reduced propensity for defects associated with high melt pool surface tension in additive manufacturing. This includes the "balling" phenomenon seen in powder bed selective laser sintering and similar processes. Furthermore, a reduction in melt pool surface tension can be beneficial to bead formation, wetting, and fusion in any additive manufacturing process.

[0110] For some applications, Bi addition can be combined with elements that can increase the solidification interval and solute partitioning. Examples include Fe, Ni, and Cu, alone or in any combination. For example, when Fe is included, the solid phase cannot dissolve as much Fe as the liquid that produces Fe. Thus, Fe will be displaced into the liquid ahead of the solidification front. This Fe enrichment can cause a reduction in the solidification temperature of the liquid adjacent to the solidification front. Thus, this portion of the liquid will not solidify until it cools further. Meanwhile, there is liquid that is not enriched with Fe further away from the solidification front. As the temperature drops, these regions can begin to solidify, causing multiple solidification zones and subsequent refinement of the structure. Addition of Fe alone cannot effectively suppress columnar structure formation unless added in larger amounts of about 2 wt% - 3 wt% and above, which can cause potential composition segregation issues. Thus, it is preferred to combine such additions with the surface nucleation promoting effect of Bi to increase the effectiveness of the smaller solute amounts.

[0111] Other materials can be included in the titanium alloy compositions provided herein. The titanium alloy compositions provided herein can include one or more inoculants. Inoculants can provide nucleation sites for grain development. Examples of inoculants that can be included are TiB or TiB2, typically in amounts of 0.05 wt% to 0.5 wt%, and / or Y2O3, typically in amounts of 0.02 wt% to 0.2 wt%, based on the total mass of the alloy composition. It is believed that, under most conditions, TiB2 can dissolve in the titanium alloy melt pool and not act as an inoculant, but rather act through its effect on solute partitioning and solidification interval (similar to Fe, Ni, and Cu).

[0112] Exemplary titanium alloy compositions can contain oxygen in an amount ranging from about 0.01 wt% to about 0.3 wt% based on the total weight of the titanium alloy composition. The titanium alloy composition can contain oxygen in an amount ranging from about 0.05 wt% to about 0.3 wt% based on the total weight of the titanium alloy composition.

[0113] Exemplary titanium alloy compositions can be provided as weldable welding wire made by any conventional titanium alloy welding wire production process, including melting and ingot casting, followed by a series of forming steps including, for example, billet forging, rolling, and wire drawing.

[0114] C. Additive manufacturing method

[0115] Additive manufacturing methods using the titanium alloy compositions according to the first aspect of the application as feedstock are also provided. Additive manufacturing methods are known in the art. See, for example, U.S. Patent Nos. 5,745,834 (Bampton et al., 1998); 6,143,378 (Harwell et al., 2000); 7,326,377 (Adams, 2008); 8,994,592 (Scott et al., 2015); 9,064,671 (Ljungblad et al., 2015); 9,174,300 (Stecker et al., 2015); 9,175,568 (Ryan et al., 2015); 9,352,421 (Illston, 2016); 9,399,264 (Stecker, 2016); 9,481,931 (Stempfer, 2016); 9,522,426 (Das et al., 2016); 9,713,844 (Ackelid, 2017); 9,776,282 (Subramanian et al., 2017); and U.S. Patent Application Publication US2016 / 0318130 (Stempfer et al.).

[0116] Exemplary embodiments provide a method of manufacturing an additively manufactured metal component, which can include: (a) providing a metal feedstock comprising the above-described titanium alloy composition of the first aspect of the present invention; (b) exposing at least a portion of the metal feedstock to an energy source for melting at least a portion of the metal feedstock to form a molten metal; (c) depositing the molten metal on a substrate from a first start position to a first stop position to form a molten layer corresponding to a first virtually vectorized layered model of the part; (d) at least partially solidifying the molten layer, thereby producing a first metal layer of the additively manufactured metal component; (e) repositioning the substrate or the energy source or both to a start position of a next layer of the virtually vectorized layered model of the part; and repeating steps (b) through (e) a plurality of times to produce a plurality of solid layers by sequentially solidifying the plurality of molten layers in an additive manufacturing build direction. In any of the additive manufacturing techniques used, post-production processes such as heat treatment, optical machining, surface finishing or other finishing operations can be performed. In embodiments, one or more additively manufactured parts can be joined together to produce a final component.

[0117] Typical process conditions for additive manufacturing generally result in directional solidification and growth of columnar crystals due to the presence of steep thermal gradients, but this can depend on the alloy utilized. For example, for Ti-6Al-4V alloys, solidification is directional and epitaxial, with the spatial and crystallographic orientation of the beta grains determined by process characteristics including steep thermal gradients from the heat source / melt pool to the workpiece. The crystallography and morphology of the alpha-beta microstructure in Ti-6Al-4V alloys at the allotropic transformation is directly influenced by the primary beta grain structure, which is produced by the alignment of the orientation relationship, grain boundary nucleation, and differences in interfacial energy, diffusion rates, and thermal conductivity between different crystallographic directions in the lattice. This macro-micro interaction can result in long-range constraints on the crystallographic and morphological diversity within the primary beta grains, and thus significant differences in strain response between the beta grain boundaries.

[0118] In the methods provided herein, the titanium alloy composition comprising the alloying elements can be used as a metal material or metal feedstock for building a component. The metal composition can result in a workpiece with reduced columnar grains. The metal composition can produce a workpiece that can comprise a substantially equiaxed grain structure. The metal composition can result in a workpiece that exhibits a fine solidification structure. The presence of Bi, and particularly Bi in combination with Fe or other beta eutectoid elements, can result in increased crystallographic diversity in the workpiece.

[0119] In the methods provided herein, the component can be manufactured by melting a titanium alloy feedstock containing the described alloying elements into a layer of metallic material deposited onto a base material and fusing successive deposits of metallic material together. The method can include using a heating device to heat and melt a portion of the consumable welding wire containing Bi such that molten metallic material is formed and deposited onto a target area of the base material. The titanium alloy feedstock can be provided in the form of a consumable welding wire or powder or a combination thereof. In some methods, two heating devices can be used. A first heating device can be used to pre-heat at least a portion of the surface of the base material, for example, at the location where the metallic material is to be deposited. A second heating device can be used to heat and melt the consumable welding wire containing Bi such that molten metallic material from the melted consumable welding wire is deposited onto the pre-heated area of the base material. Each heating device can be controlled individually. Each heating device can be adjusted to produce an individual temperature effect.

[0120] The heating device can include any device capable of providing sufficient energy to the consumable welding wire to melt the consumable welding wire into molten metallic material. In the methods provided herein, the heating device or heating devices can include a welding gun (PAW, PTA, GMAW, or MIG type), an electron beam device, a laser device, or any combination thereof. In methods using two heating devices, the heating devices can be the same, or they can be different from one another. For example, a first welding gun can be used to pre-heat a target deposition area on the base material to form a pre-heated area. A second welding gun can be used to heat and melt the consumable welding wire. This can result in molten metal dropping into the pre-heated area of the target deposition area. Alternatively, a laser device can be used to pre-heat a target deposition area on the base material to form a pre-heated area, and a welding gun can be used to heat and melt the consumable electrode, resulting in molten metal dropping into the pre-heated area of the target deposition area. In some methods, a welding gun can be used to pre-heat a target deposition area on the base material to form a pre-heated area, and a laser device can be used to heat and melt the consumable welding wire, resulting in molten metal dropping into the pre-heated area of the target deposition area. In some methods, the first heating device can be a laser, and the second heating device can be an electron beam. In some methods, the first heating device can be an electron beam device, and the second heating device can be a laser. In some methods, the first heating device can be a welding gun, and the second heating device can be an electron beam. In some methods, the first heating device can be an electron beam device, and the second heating device can be a welding gun.

[0121] In embodiments, the methods provided herein can allow for refinement of the solidification structure in titanium alloy workpieces made by additive manufacturing processes. The methods can eliminate or significantly reduce the coarse columnar structures typically produced by conventional additive manufacturing methods and materials. Eliminating these coarse columnar structures can result in manufactured products that can exhibit higher strength, ductility, fatigue resistance, or combinations thereof than achieved in conventional additive manufacturing processes.

[0122] D. Examples

[0123] The following examples are included for illustrative purposes only and are not intended to limit the scope of the embodiments provided herein.

[0124] Example 1

[0125] Cylindrical bolts having a diameter of 25 mm, a total mass per bolt of 600 g, and a variety of chemical compositions were prepared by mixing comminuted titanium sponge having a particle size distribution up to 0.5 mm. The comminuted sponge bodies were passed through a 500 micron sieve and mixed with 5.5 wt% Al, 0.26 wt% V, 3.18 wt% Mo, and 0.58 wt% Bi, each having an average particle size from 50 to 250 pm. The mixture was blended in a mixer until a substantially uniform composition was obtained. A typical mixing time was approximately two hours.

[0126] The bolts were then manufactured by pressing an amount of powder (about 600 g per bolt) and subjecting the powder to gradually increasing pressure. This resulted in a density of the bolts in the range of 92% to 96% of the maximum theoretical density.

[0127] The bolts were sintered at 1250 °C for 8 hours in an inert atmosphere. The compacted and sintered bolts having a diameter of about 25 mm were subjected to several rolling steps to form rods having a diameter of 14 mm. Each rolling step was performed by heating the extruded rod to a temperature of 600 °C and holding for 15 min to eliminate stresses, followed by a rolling step that reduced the diameter by a certain percentage. This was repeated until the desired diameter was reached. To test different chemical compositions and their effect on grain refinement, the rods were turned to a diameter of 12 mm to remove surface oxides and then used directly as feedstock in plasma and wire-based additive manufacturing systems. Production of the wire can be achieved by further reduction and wire drawing steps.

[0128] The rolled bar was used in an additive manufacturing process using a plasma arc welding torch, with the bar being fed incrementally to melt and deposit droplets in layers. This produced columnar deposits with a diameter of approximately 15 mm and a height of up to 30 mm. Six to ten layers were deposited, with a one-minute waiting time between each layer to simulate typical process conditions for additive manufacturing. The previous layer was partially remelted by the arc before the next layer was deposited. The welding current used on the transferred plasma arc was 150 A.

[0129] Slices of solid shape test objects are used for metallographic examination. Figure 2A The diagram shows a macroscopic view. Figure 3A An overview image composed of stitched micrographs showing the delineated grains is displayed. It can be seen that the Bi-containing composition yields a solid-state test object with minimized columnar grains. The presence of Bi inhibits columnar solidification. The grain structure in the test object is approximately equiaxed and exhibits a refined structure. Figure 3A The average particle size was measured to be 0.60 mm².

[0130] Comparative Example 1

[0131] To confirm that the minimization or elimination of columnar solidification could be attributed to the addition of Bi, a Bi-free comparative alloy rod was prepared. The rod was prepared as described in Example 1 above by mixing pulverized titanium sponge with a particle size distribution of up to 0.5 mm with 5.41 wt% Al, 0.25 wt% V, and 3.01 wt% Mo (each having an average particle size fraction of 50 to 250 µm).

[0132] Slices of solid shape test objects are used for metallographic examination. Figure 2B The diagram shows a macroscopic view. Figure 3B An overview image composed of stitched micrographs showing the outlined grains is displayed. It can be seen that the composition without Bi produces a solid-state test object with prominent columnar grains. Columnar grain growth is visible across several deposition layers, and the grain structure is coarse. Figure 3B The average particle size was measured to be 8.76 mm². This is approximately 15 times that of the equivalent composition with added Bi.

[0133] Example 2

[0134] The effects of adding Bi and a small amount of Fe to increase the solidification range were also tested. Bi-containing alloy rods were prepared according to the steps outlined in Example 1, but the rods in this example also contained Fe in addition to Bi. The composition was 89.44 wt% Ti, 6.00 wt% Al, 0.24 wt% V, 3.03 wt% Mo, 0.73 wt% Fe, and 0.57 wt% Bi.Figure 2C The diagram shows a macroscopic view. Figure 3C An overview image is shown, composed of stitched micrographs of the delineated grains. It is evident that the composition results in a solid-state test object in which columnar grains are largely eliminated, and the solid exhibits a refined solidification structure. This grain structure is approximately equiaxed. Fe has an increased solidification range, which may induce compositional supercooling and contribute to refinement in the presence of Bi. Figure 3C The average particle size was measured to be 0.10 mm².

[0135] Example 3

[0136] To test the effect of Bi addition on the basic alloy composition of Ti-6Al-4V, according to the actual... Applied The steps outlined in Example 1 are used to prepare the alloyed rod, but with the following composition: 89.25 wt% Ti, 6.04 wt% Al, 4.03 wt% V, and 0.67 wt% Bi. Figure 4A The macroscopic diagram is shown. It is evident that adding approximately equal amounts of Bi (in wt% but in atomic%) to the Ti-6Al-4V alloy helps to largely eliminate the columnar solidification structure. Figure 4A The average grain size was measured to be 0.91 mm². Comparing the results with the base alloy from Example 1, which has Mo but not V, it appears that Bi addition is a more effective grain refiner in the presence of Mo.

[0137] Comparative Example 3

[0138] To confirm the relative effect of Fe addition compared to Bi addition in minimizing or eliminating columnar solidification, and to test the effect of Fe addition alone on the basic alloy composition of Ti-6Al-4V, based on actual... Applied The alloy rod is prepared using the steps outlined in Example 1, but with the following composition: 89.40 wt% Ti, 6.02 wt% Al, 4.01 wt% V, and 0.57 wt% Fe. This constitutes a larger Fe addition than that present in conventional Ti-6Al-4V, which may have up to 0.25 wt% Fe. Figure 4B The macroscopic diagram is shown. It can be seen that adding Fe alone to the Ti-6Al-4V alloy does not effectively suppress the columnar solidification structure. The average grain size is... Figure 4B The measured value is 2.49 mm².

[0139] Example 4

[0140] Figure 5The bar chart shows the average grain size (area) of objects constructed using different titanium alloys from a series of ten comparative tests. All objects were fabricated according to the steps outlined in Example 1, but the number of layers deposited on all samples was limited to 5 or 6.

[0141] The ten titanium alloy samples have the elemental compositions given in Table 1.

[0142] Grain size measurement is performed in a computer application by manually drawing lines at the primary β grain boundaries on a macroscopic image to form polygons representing each individual grain. The software can then calculate the average grain area based on the image magnification and the size of the polygons drawn on the image.

[0143] Table 1. Elemental composition of the Ti alloys used in the comparative tests.

[0144] It will be apparent to those skilled in the art that various modifications and variations can be made to the invention without departing from its spirit or scope. Therefore, the invention is intended to cover such modifications and variations if they fall within the scope of the appended claims and their equivalents.

Claims

1. A titanium alloy, wherein the titanium alloy is any one of the following: The first alloy composition, characterized in that Include: -Al from 2 wt% to 7 wt%, -Mo from 1.5 wt% to 6 wt%, -Bi from 0.25 wt% to 1.5 wt%, -Optionally from 0 to 1 wt% V, and - The balance is wt% Ti, such that the total content of the components in the titanium alloy composition is 100 wt%. The weight percentages are based on the total mass of the titanium alloy composition. or: The second alloy composition is characterized by comprising: -Al from 2 wt% to 7 wt%, - One or more of Mo and V in total amounts ranging from 1.5 wt% to 6 wt%, -Bi from 0.25 wt% to 1.5 wt%, - One or more elements selected from the group consisting of β-eutectoid stabilizers, in total amounts from 0.3 wt% to 1.5 wt%; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si, and - The balance is wt% Ti, such that the total content of the components in the titanium alloy composition is 100 wt%. The weight percentages are based on the total mass of the titanium alloy composition. or: The third alloy composition is characterized by comprising: -Al from 2 wt% to 7 wt%, -V from 1.5 wt% to 6 wt%, -Bi from 0.25 to 1.5 wt%, - One or more elements selected from the group consisting of β-eutectoid stabilizers, in total amounts from 0.3 wt% to 1.5 wt%; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si, and - The balance is wt% Ti, such that the total content of the components in the titanium alloy composition is 100 wt%. The weight percentage is based on the total mass of the titanium alloy composition.

2. The titanium alloy according to claim 1, wherein... The first alloy composition comprises the following: -Al from 2 wt% to 7 wt%, -Mo from 1.5 wt% to 6 wt%, -Bi from 0.25 wt% to 1.5 wt%, -Optionally from 0 to 1 wt% V, and - The margin is Ti and unavoidable impurities. The weight percentages are based on the total mass of the titanium alloy composition. or: The second alloy composition comprises the following: -Al from 2 wt% to 7 wt%, - One or more of Mo and V in total amounts ranging from 1.5 wt% to 6 wt%, -Bi from 0.25 wt% to 1.5 wt%, - One or more elements selected from the group consisting of β-eutectoid stabilizers, in total amounts from 0.3 wt% to 1.5 wt%; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si, and - The margin is Ti and unavoidable impurities. The weight percentages are based on the total mass of the titanium alloy composition. or: The third alloy composition comprises the following: -Al from 2 wt% to 7 wt%, -V from 1.5 wt% to 6 wt%, -Bi from 0.25 wt% to 1.5 wt%, - One or more elements selected from the group consisting of β-eutectoid stabilizers, in total amounts from 0.3 wt% to 1.5 wt%; Fe, Cr, Co, Cu, Ni, Mn, W, B, and Si, and - The margin is Ti and unavoidable impurities. The weight percentage is based on the total mass of the titanium alloy composition.

3. The titanium alloy according to claim 1 or 2, wherein the total content of one or more elements selected from the group consisting of β-eutectoid stabilizers in the second alloy composition or the third alloy composition; Fe, Cr, Co, Cu, Ni, Mn, W, B and Si is in an amount from 0.4 wt% to 1.4 wt%, preferably from 0.5 wt% to 1.3 wt%, more preferably from 0.6 wt% to 1.2 wt%, more preferably from 0.7 wt% to 1.1 wt%, and most preferably from 0.8 wt% to 1.0 wt%, and wherein the weight percentage is based on the total mass of the titanium alloy composition.

4. The titanium alloy according to any one of the preceding claims, wherein the aluminum content in the first alloy composition, the second alloy composition, or the third alloy composition is in the range of 3 wt% to 6.75 wt%, preferably from 4 wt% to 6.5 wt%, more preferably from 5 wt% to 6.25 wt%, and most preferably from 5.9 wt% to 6.1 wt%, and wherein the weight percentage is based on the total mass of the titanium alloy composition.

5. The titanium alloy according to any one of the preceding claims, wherein... The molybdenum content in the first alloy composition is in the range of 1.75 wt% to 5.5 wt%, preferably 2 wt% to 5 wt%, more preferably 2.25 wt% to 4 wt%, more preferably 2.5 wt% to 3.5 wt%, and most preferably 2.9 wt% to 3.1 wt%, and / or The total content of molybdenum and vanadium in the second alloy composition is in the range of 2 wt% to 5.5 wt%, preferably 2.5 wt% to 5 wt%, more preferably 3 wt% to 4.5 wt%, more preferably 3.25 wt% to 4.0 wt%, and most preferably 3.4 wt% to 3.6 wt%, wherein the weight percentage is based on the total mass of the titanium alloy composition.

6. The titanium alloy according to any one of the preceding claims, wherein the bismuth content in the first alloy composition, the second alloy composition, or the third alloy composition is from 0.3 wt% to 1.4 wt%, preferably from 0.35 wt% to 1.3 wt%, more preferably from 0.4 wt% to 1.2 wt%, more preferably from 0.45 wt% to 1.1 wt%, more preferably from 0.5 wt% to 1 wt%, more preferably from 0.6 wt% to 0.9 wt%, and most preferably from 0.7 wt% to 0.8 wt%, and wherein the weight percentage is based on the total mass of the titanium alloy composition.

7. The titanium alloy according to any one of claims 1 to 6, wherein, based on the total mass of the alloy composition, the first alloy composition, the second alloy composition, or the third alloy composition further comprises less than 0.5 wt% O, preferably less than 0.4 wt% O, more preferably less than 0.3 wt% O, more preferably less than 0.2 wt% O, and most preferably between 0.06 wt% and 0.18 wt% O.

8. The titanium alloy composition according to any one of claims 1 to 7, wherein, based on the total mass of the alloy composition, the first alloy composition, the second alloy composition, or the third alloy composition further comprises 0.05 wt% to 0.5 wt% of TiB or TiB2, and / or 0.02 wt% to 0.2 wt% of Y2O3.

9. The titanium alloy composition according to any one of claims 1 to 8, wherein, based on the total mass of the titanium alloy composition, the first alloy composition, the second alloy composition, or the third alloy composition further comprises a total amount of 0.1 wt% to 5.0 wt% Sn and / or 0.1 wt% to 6.0 wt% Zr.

10. A welding wire, characterized in that, It is made of a titanium alloy composition according to any one of claims 1 to 9.

11. The welding wire of claim 10, wherein the welding wire has a nominal diameter in the range of 0.5 to 10.0 mm, preferably from 0.7 to 5.0 mm, more preferably from 0.8 to 2.5 mm, more preferably from 0.9 to 2.0 mm, more preferably from 1.0 to 1.8 mm, and most preferably from 1.2 to 1.6 mm.

12. A metal powder, characterized in that, It is made of a titanium alloy composition according to any one of claims 1 to 9.

13. The metal powder according to claim 12, wherein, The metal powder has a nominal diameter in the range of 15 to 200 µm, as determined by laser diffraction analysis according to standard ISO 13320:2020.

14. A method for manufacturing a three-dimensional part made of titanium alloy, characterized in that, The method includes forming the three-dimensional component by applying a titanium alloy according to any one of claims 1 to 9 through an additive manufacturing process.

15. The method according to claim 14, wherein, The additive manufacturing includes: - The three-dimensional component is constructed by fusing together continuous deposits of the titanium alloy on a substrate material, through: - A melting tool is used to heat and melt the titanium alloy raw material, and the molten raw material is deposited onto the deposition area of ​​the substrate material, and a) The substrate material is moved relative to the first melting tool along a predetermined path, causing the continuously deposited molten material to solidify and form the three-dimensional component. or: b) Move the first melting tool relative to the substrate material along a predetermined path, so that the continuously deposited molten material solidifies and forms the three-dimensional component.

16. The method according to claim 14 or 15, wherein, The method further includes applying the raw material of the titanium alloy shaped into a welding wire according to claim 10 or 11.

17. The method of claim 16, wherein the method further comprises applying: - A first plasma-transfer arc welding torch (PTA), electrically connected to a first DC power supply, such that the electrode of the first plasma-transfer arc welding torch becomes the cathode and the substrate material becomes the anode, and - A second plasma transfer arc welding gun (PTA) is electrically connected to a second DC power supply, such that the electrode of the second plasma transfer arc welding gun becomes the cathode and the welding wire becomes the anode.

18. Use of the titanium alloy according to any one of claims 1 to 9 in an additive manufacturing process.

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