PROCESS FOR THE FORMATION OF OXIDE DISPERSION STRENGTHENED (ODS) ALLOYS

Abstract

Method comprising: Melting an alloy material (24) with an energy beam (28) to form a melt (30); introducing particles (46a,b) comprising a metal oxide (36a,b) into the melt so that the particles are dispersed in the melt; and Cooling and solidification of the melt to form an oxide dispersion strengthened alloy characterized in that that melting of the alloy material (24) with the energy beam (28) takes place in the presence of a flux (26), wherein the flux forms a slag layer (50) on the melt (30) when melted by the energy beam, that the particles (36a,b, 46a,b) comprising the metal oxide are introduced into the melt (30) covered by the slag layer (50), wherein the particles are dispersed in the melt covered by the slag layer, and wherein the size and distribution of the particles (36a,b, 46a,b) are controlled by adjusting the trajectory of the particles that are sprayed or guided into the melt, and that the cooling and solidification of the melt (30) covered by the slag layer (50) takes place in such a way that the oxide dispersion-strengthened alloy (44) which is formed is at least partially covered by the slag layer.

Description

FIELD OF INVENTION

[0001] The present invention relates generally to the field of metal component manufacturing and repair, and more particularly to the formation of oxide dispersion strengthened (ODS) alloys. BACKGROUND OF THE INVENTION

[0002] Oxide dispersion strengthened (ODS) alloys are recognized for their superior properties in high-temperature applications, particularly ODS alloys formed from superalloy materials. ODS alloys differ from conventional alloys by the presence of fine-particle dispersoids and an elongated grain shape that generally develops during recrystallization heat treatment and / or hot and cold working. This particular grain structure improves the high-temperature deformation characteristics of ODS alloys by blocking the accumulation of intergranular damage. As a result of this and other properties, components made from ODS alloys exhibit improved high-temperature creep rupture strength and improved oxidation resistance compared to conventional alloys.

[0003] However, ODS alloys are difficult to weld and repair using conventional techniques (e.g., gas tungsten arc welding, laser welding, electron beam welding, etc.). Such fusion welding causes a significant loss of strength. The alloys are also difficult and uneconomical to process using less conventional processes such as friction welding.

[0004] ODS alloys are typically produced by mechanical alloying (MA) processes, in which various metals, alloys, and oxides are mixed and ball-milled to compress, lubricate, and shear the powders to produce particles composed of all the constituents. The particles are then packaged and extruded or hot isostatically pressed (HIP) to achieve a desired shape. The very fine-grained resulting product, in which small oxide particles are dispersed as dispersoids and which exhibits directional stresses, is then heat-treated to recrystallize and grow large directional grains and / or is processed by additional hot working and cold working. Further improved strength properties can then be obtained by performing a secondary recrystallization heat treatment.The heat treatment consists of annealing at a defined temperature, which depends on the alloy's composition, to increase the grain size within the alloy. A successful secondary recrystallization heat treatment causes abnormal grain growth, producing coarse, anisotropic grains with elongated shapes that resist sliding at the grain boundaries.

[0005] Mechanical alloys suffer from a number of problems. First, the success of heat treatment (secondary recrystallization) for one alloy sample often does not guarantee success for another sample—even for alloys with identical compositions. Thus, yield and predictability are poor. Another problem concerns the difficulty in dispersing certain oxides (e.g., yttrium oxide), which can lead to excessively long milling times or inhomogeneous microstructures. Furthermore, mechanical alloying is often not suitable for mass-produced and / or physically large products containing ODS alloys due to the complicated manufacturing processes and prohibitively high costs. Nickel-based ODS alloys are particularly difficult to cold-work and successfully recrystallize.

[0006] Additional difficulties with ODS alloys include general forming and joining of these materials. Forming and joining techniques that preserve the microstructure and intrinsic strength of ODS alloys are severely limited, often restricting their ability to be incorporated into high-temperature supporting structures. For example, excessive heating of ODS alloys can cause oxide dispersoids to coalesce, resulting in severe agglomeration, so that the dispersoids can no longer effectively resist sliding at grain boundaries. Melting ODS alloys also leads to "slagging" of the oxide dispersoids, reducing their work-strength capability. Since most ODS alloys derive their strength from an elongated grain structure, such disruption of the grain structure ultimately reduces creep rupture strength.

[0007] Various attempts have been made to discover alternative techniques for producing ODS alloys that avoid the disadvantages described above. Park et al. (US 2013 / 0299470), for example, describe a process that Fig. 1, in which a laser beam 6 is used to heat the surface 4 of a metal sheet or tube 2 to form a metallic matrix melt 8. In this process, a nozzle 10 is used to propel a jet of oxide particles 12 contained in an inert carrier gas 14 into the matrix melt 8 to form, upon cooling with a lubricant or coolant, an ODS alloy layer 16 containing oxide dispersoids 18 and bonded to the metal sheet or tube 2.

[0008] Although Park et al.'s process avoids some of the problems associated with mechanical alloying, it is limited to the formation of ODS alloy coatings on metallic objects (i.e., sheets or tubes) whose surfaces can be easily melted with a laser beam. This process also requires the use of a lubricant or coolant to cool the molten ODS alloy matrix and requires the use of an inert gas (i.e., Ar or He) to inhibit oxidation of the ODS alloy during the cooling process.

[0009] Funkhouser et al. (5,449,536) teach the development of an ODS coating on a substrate by spraying the ODS powder into a "hot zone" created by a laser above the substrate. The substrate is not melted, but the partially melted or plasticized powder hits the substrate and adheres. Again, the process is limited to coatings on metal objects and would most likely require an inert process environment.

[0010] A generic process for ODS alloys is known from US2013 / 0299470A1. US2014 / 0220374A1 and US2013 / 0136868 concern superalloys.

[0011] The object of the present invention is to achieve a simplified process for alloying ODS alloys.

[0012] This object is achieved according to the invention by the characterizing features in claim 1. Preferred embodiments are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is explained in the following description with reference to the drawings in which: Fig. 1 illustrates a prior art laser melting process for producing an ODS alloy layer on a surface of a metallic substrate; Fig. 2 shows laser melting processes for producing ODS alloys from a powdered filler in the presence of a flux. DETAILED DESCRIPTION OF THE INVENTION

[0014] It was recognized that there is a need to discover processes for forming ODS alloys that avoid the aforementioned disadvantages. An optimal process would allow for small-scale and large-scale formation of ODS alloys without the need for post-weld heat treatment or strictly air-free conditions. Such a process would also provide an improved ability to control the distribution and characteristics of oxide particles contained in the ODS alloys and produce an optimal grain shape and structure without the need for secondary recrystallization heat treatment.

[0015] Disclosed herein are processes for forming oxide dispersion strengthened (ODS) alloys in which oxide particles are injected into a molten bath of metallic material created with an energy beam, optionally in the presence of a flux. The size and distribution of oxide particles contained in the resulting ODS alloys can be varied by controlling a number of factors, including the melting point, the size and trajectory of the oxide particles, as well as the shape, duration, and intensity of the heat provided by the energy beam. The use of fluxes can obviate the need to conduct these processes under strictly air-free conditions and can unexpectedly provide ODS alloys with desirable elongated grain structures without the need for a secondary recrystallization heat treatment.The grain structure of the resulting alloys can also be formed by directional solidification with refractory materials with different thermal conductivities. Such processes can be applied to the fabrication and repair of ODS alloys in various contexts, and can also be applied to the production of bulk ODS alloys whose mechanical properties can be precisely controlled.

[0016] Fig. Figure 2 shows an exemplary method of the present disclosure applicable to various embodiments. In the present illustration, a filler 22 containing alloy particles 24 is deposited onto a surface of a substrate 20. An energy beam 28 is then passed over the surface of the filler 22 to melt the filler 22 and thus form a melt 30 containing a molten matrix of the alloy (in Fig. 2 as a movement from left to right). As shown in Fig. As shown in Figure 2, the melt 30 includes a heating portion 34 located below the focal point of the energy beam 28 and a non-heating portion 32 located behind the focal point of the energy beam 28. It is understood that a temperature of the melt 30 in the heating portion 34 is generally higher than a temperature of the melt 30 in the non-heating portion 32.

[0017] In the embodiment of Fig. 2, an injection nozzle 42a is used to inject oxide particles 36a contained in a propellant gas 40a into the non-heating portion 32 of the melt 30 such that the oxide particles 36a are not contacted by the energy beam 28. The oxide particles 36a can also be directed into the heating portion 34 of the melt 30 or into both the heating portion 34 and the non-heating portion 32, so that the oxide particles 36 are contacted by the energy beam 28. The outlet of the injection nozzle 42a can be as in Fig. 2, be immersed within the melt 30. In some embodiments, the use of such direct injection improves the uniformity of the molten oxide dispersion, resulting in improved mechanical and / or thermal properties in the resulting ODS alloy layer 44.

[0018] Injector nozzles 42a used to inject particles directly into the melt 30 may be in the form of hollow nozzles containing refractory materials such as ceramics (e.g., ZrO2), carbides (e.g., WC), nitrides (e.g., BN), and graphite. In other embodiments, the direct injection nozzle 42a may be in the form of a consumable cored injector. One non-limiting example utilizes a consumable cored injector constructed from a cored wire made of a nickel or nickel alloy sheath surrounding a powdered core material containing at least the oxide particles (e.g., particles 36a). The consumable cored injector is introduced into the melt 30, causing the metallic shell to melt due to its relatively low melting point. The powdered core material is then distributed in the melt 30 to form the dispersed oxide particles 46a, 46b.In some embodiments that utilize a consumable cored injector, the cored injector 42a may be preheated and / or oscillated within the melt, further heating the melt and / or dispersing the oxide particles 36a. In some cases, the powdered core material may contain both the oxide particles 36a and a flux.

[0019] Alternatively, as in Fig. 2, the outlet of an injection nozzle 42b may be positioned above the melt 30 so that a stream 38 of oxide particles 36b contained in a propellant gas 40b is directed into the melt 30 by piercing the surface of the heating and / or non-heating portion 32, 34. If more than one nozzle 42a,b is used, the oxide particles 36a and 36b may be the same or different (in terms of their content and / or sizes), and the propellant gases 40a and 40b may also be the same or different.

[0020] In the presentation of Fig. 2, a flux 26 may be deposited onto the surface of the filler 22 and, upon melting by the energy beam 28, generally forms a resulting slag layer 50 that coats the surface of the ODS alloy layer 44. The flux 26 may be as shown in Fig. 2, or it may be continuously fed onto the filler 22 upstream of the melt 30, or it may be mixed into the filler material 22. The flux 26 may also be introduced into the melt 30 using one or more nozzles 42a,b, where the flux may either be directly injected (as shown with nozzle 42a) or pierced through the surface of the melt 30 (as shown with nozzle 42b). In such cases, the flux material may be introduced into the non-heating and / or heating portion 32, 34 of the melt 30.

[0021] After cooling and solidification of the melt 30, an ODS alloy layer 44 is formed, which contains dispersed oxide particles 46a (and possibly 46b).

[0022] The content, size, and distribution of the oxide particles 46a,b contained in the resulting ODS alloy layer 44 can be controlled by adjusting various parameters, including: (i) the content, size, concentration, and trajectory of the oxide particles 36a,b injected or directed into the melt 30; and (ii) the intensity, duration, and shape of the heating by the energy beam 28. The grain structure of the ODS alloy layer 44 can also be controlled by adjusting various parameters, including: (iii) the metal content of the alloy; (iv) the content, amount, and trajectory of the flux 26; and (v) the arrangement and thermal characteristics of the carrier material 20.

[0023] The oxide particles 36a,b generally consist of at least one metal oxide with a higher melting point than the metallic base alloy of the ODS alloy layer 44. Suitable metal oxides include, among others, oxides of elements such as aluminum, calcium, hafnium, silicon, titanium, thorium, yttrium, and zirconium. Mixtures of oxide particles 36a,b containing different metal oxides and / or having different particle sizes may be used. Preformed ODS alloys may also be used as oxide particles 36a,b. As explained above, the oxide particles 36a,b may be injected directly into the melt 30 (via a refractory nozzle and / or via a consumable nucleated injector, as shown at nozzle 42a), avoiding contact with the atmosphere, or they may be introduced into the melt 30 from above (as shown at nozzle 42b).

[0024] The size of the dispersed oxide particles 46a,b (often referred to as “dispersoids”) embedded in the resulting ODS alloy layer 44 is related to three factors.

[0025] First, the size of the dispersoids 46a,b is directly related to the melting point of the precursor metal oxide 36a,b—such that using an oxide particle 36a,b with a relatively higher melting point produces relatively larger dispersoids 46a,b for a given particle size. As shown, when a mixture of equivalently sized silicon and yttria particles is injected into the non-heating portion 32 of the melt 30, the resulting ODS alloy layer 44 generally contains a mixture of relatively larger yttria dispersoids and relatively smaller alumina dispersoids. This variation in the size of the resulting dispersoids occurs because alumina has a significantly lower melting point (2072°C) compared to yttria (2425°C), allowing a larger proportion of the alumina particles to melt and dissolve into the ODS alloy matrix.This effect allows modulation of the dispersoid size by changing the melting point of a metal oxide contained in the oxide particles 36a,b.

[0026] Second, the size of the resulting dispersoids 46a,b is directly related to the size of the precursor oxide particles 36a,b. For example, if a mixture of relatively small and large yttrium oxide particles is injected into the non-heating portion 32 of the melt 30, the resulting ODS alloy layer 44 will generally contain a mixture of relatively large yttrium oxide dispersoids (corresponding to the larger oxide particles) and relatively small yttrium oxide dispersoids (corresponding to the smaller oxide particles). This effect allows the size of the dispersoids 46a,b in the ODS alloy layer 44 to be modulated by varying the size of the precursor oxide particles 36a,b.

[0027] Third, the size of the resulting dispersoids 46a,b is directly related to the intensity and duration of heat applied to the oxide particles 36a,b and / or the melt 30 by the energy beam 28. For example, if oxide particles 36a of a particular size and melting point are injected into the non-heating portion 32 of the melt 30, the size of the resulting dispersoids 46a in the ODS alloy layer 44 will generally be larger than the dispersoids 46b that result when the same oxide particles 36b are injected into the heating portion 34 of the melt 30.This size variation may occur because oxide particles 36b introduced into the heating portion 34 of the melt 30 receive more heat in the form of: (i) direct contact with the energy beam 28 as the stream 38 passes through (for example) the energy beam in flight; and / or (ii) relatively higher temperatures encountered in the heating portion 34 of the melt 30 compared to the non-heating portion 32.

[0028] This effect allows the modulation of the dispersoid size by changing the trajectory of the corresponding oxide particles 36a,b (e.g., directing or injecting oxide particles into relatively hotter or cooler parts of the melt 30, with or without direct contact with the energy beam 28). This effect also allows the modification or normalization (e.g., bringing into close agreement) of the size of the dispersoids resulting from different oxide particles by using different trajectories depending on the respective melting points and / or sizes of the oxide particles.For example, an ODS alloy layer 44 containing dispersoids 46a,b of aluminum oxide and yttria of similar sizes can be obtained despite the different melting points of the respective metal oxides by injecting or directing the aluminum oxide-containing particles 36a into the non-heating portion 32 while injecting or directing the yttria-containing particles 36b into the heating portion 34. The angles 48a,b of the nozzles 42a,b represent another factor that can be used to modulate the heating for the oxide particles 36a,b in the melt 30. For example, varying the angle 48a can direct the oxide particles 36a into increasingly hotter regions of the melt 30, as shown in FIG. Fig. 2 shown.

[0029] The size, shape, and distribution of the oxide particles 36a,b can also be altered by modulating the intensity, duration, and shape of the energy beam 28. As mentioned above, applying more heat to the oxide particles 36a,b results in a higher melt fraction, which can reduce the size of the resulting dispersoids 46a,b and potentially affect their shape in the resulting metallic matrix. Excessive heating can also lead to coalescence or slagging of dispersoids 46a,b, which affects the distribution of oxides in the resulting ODS alloy layer 44. Thus, the optimal size, shape, and distribution of the dispersoids 46a,b can be achieved in part by adjusting the heat energy applied by the energy beam (intensity and duration) as well as the size of the heated area (shape).

[0030] The term "energy beam," as used herein, describes, in a general sense, a relatively narrow, propagating stream of particles or energy packets. An energy beam 28, as used in the present disclosure, may include a light beam, a laser beam, a particle beam, a charged particle beam, a molecular beam, etc., which, upon contact with a material, imparts kinetic (heat) energy to the material.

[0031] In some embodiments, the energy beam 28 is a diode laser beam with a generally rectangular cross-sectional shape, although other known types of energy beams may be used, such as an electron beam, a plasma beam, one or more circular laser beams, a scanning laser beam (one-dimensional, two-dimensional, or three-dimensional scanning), an integrated laser beam, a pulsed laser beam (as opposed to a continuous wave laser beam), etc. The rectangular shape may be particularly advantageous for embodiments with a relatively large area to be melted. In some embodiments, the intensity and shape of the energy beam 28 are precisely controlled by using laser scanning (raster) optics to form a melt 30 with a precisely defined size and shape to suit the trajectory of the incoming oxide particles 36a,b.For example, such laser scanning allows a perimeter of the oxide particles 36b introduced into the melt 30 to fit within a perimeter of the melt 30.

[0032] In certain embodiments, the factors described above are adjusted such that only the surfaces of the oxide particles 36a,b are melted. Such surface melting (as opposed to total melting) of the oxide particles 36 generally ensures that the resulting dispersoids 46a,b sufficiently bond to the matrix structure of the ODS alloy layer 44—while simultaneously maintaining the optimal shape and mechanical integrity of the original oxide particles 36a,b to optimize the strength and thermal characteristics of the resulting ODS alloy.

[0033] The distribution of dispersoids 46a,b in the ODS alloy layer 44 can also be controlled by varying both the velocity and concentration of oxide particles 36a,b injected and / or introduced into the melt 30 and by scanning the energy beam 28 to create streams of molten material in the melt 30. Increasing either the velocity or the concentration of oxide particles 36a,b shot into the melt 30 generally increases the proportion of dispersoids 46a,b contained in the resulting ODS alloy layer 44. Increasing the velocity can also provide a more uniform distribution when the melt 30 is particularly viscous.In some embodiments, laser scanning is also used to create flows of molten material within the melt 30 (e.g., the Marangoni effect), which can further distribute the oxide particles 36a,b throughout the melt.

[0034] As explained above, the grain structure of the ODS alloy layer 44 can be varied by adjusting various parameters, including the metal content of the alloy. The filler 22 is often used in powder form and contains alloy particles 24 that at least partially define the composition of the resulting ODS alloy layer 44. The ODS alloy layer 44 can be composed of a high-temperature metal matrix, such as iron aluminide, iron-chromium, iron-chromium-aluminum, nickel-chromium, and nickel aluminide, among others. In certain applications, the ODS alloy layer 44 contains a superalloy metal matrix with a base alloying element of nickel, cobalt, or nickel-iron, as well as other superalloy materials.

[0035] The term "superalloy" is used herein as it is generally understood in the art, meaning a highly corrosion- and oxidation-resistant alloy that exhibits excellent mechanical strength and resistance to creep at elevated temperatures. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g., IN 738, IN 792, IN 939), Rene alloys (e.g., Rene N5, Rene 80, Rene 142), Haynes alloys (e.g., NS-163), Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, X45, PWA 1483, and CMSX (e.g., CMSX-4) single-crystal alloys.

[0036] Although embodiments of the present disclosure allow the formation of ODS superalloys (e.g., MA 956, MA 957, MA 754, MA 758, MA 760, MA 6000, PM 1000, PM 2000, PM 3030, ODM 751), the present method is not limited to such materials and can be applied to other alloys as well, such as thoriated tungsten, thoriated nickel, aluminum-based alloys, lithium-based alloys, aluminum-titanium, AlMgLi, AlSiC, NiTiC, FeNdB, 9Cr ferritic / martensitic steel, 18Cr ferritic steel, CuAl2O3, CuWC and CuZrO2.

[0037] In some embodiments, the metallic composition of the ODS alloy layer 44 is provided by both the alloy particles 24 and additional metallic components that are either separately contained in the filler 22 or separately introduced or directed into the melt 30. For example, additional metallic components may be directly injected (e.g., via nozzle 42a) and / or flowed (e.g., via nozzle 42b) into the melt to supplement the metallic composition of the filler 22. In other cases, the metallic composition may be supplemented by metals contained in the oxide particles 36a,b (e.g., via melting low-melting-point oxides). In other examples, the metallic composition may be supplemented by metals contained in at least one flux.In still other embodiments, the metallic composition may be supplemented by metal contained in a consumable cored injection (for example, in a metallic shell).

[0038] In some embodiments, the composition of an ODS alloy layer 44 may be configured to function as a bond coat or as a thermal barrier coating. The terms "bond coat" and "thermal barrier coating" are used herein as they are commonly used in the art. For example, the filler 22 and the oxide particles 36a,b may be selected such that the resulting ODS alloy layer 44 contains an MCrAlY alloy (where M is selected from Ni, Co, Fe, and mixtures thereof, and Y is selected from Y, La, and Hf) suitable for use as a bond coat. Alternatively, the filler 22 and the oxide particles 36a,b may be selected such that the resulting ODS alloy layer 44 contains ceramic materials, such as zirconium oxide and yttrium oxide, and is suitable for use as a thermal barrier coating.

[0039] The flux 26 and the resulting slag layer 50 provide a number of functions that are beneficial for ODS alloys of the present disclosure.

[0040] First, they function as a shield of both the melt 30 and the solidified (and still hot) ODS alloy layer 44 from the atmosphere. The flux 26, in some embodiments, may be formulated to create a shielding gas, thereby avoiding or minimizing the use of vacuum conditions or expensive inert gas. The shielding gas may be a reducing gas, such as hydrogen, which reduces oxidation of the molten or cooling metal. The slag 50 floats to the surface of the melt 30 to further separate the molten or hot metal from the atmosphere. Due to the shielding effects of the flux 26 and the resulting slag 50, in certain embodiments, the process may be conducted under an oxygen-containing atmosphere—as opposed to using inert gas and / or vacuum conditions.In this regard, the propellant gas 40a,b may be selected from inert gases such as nitrogen, argon, and helium, or from oxygen-containing gases, including air and gaseous mixtures (e.g., lower-grade inert gases) containing significant amounts (e.g., more than 5% by volume) of oxygen. In some embodiments, the propellant gas 40a,b is an inert gas (e.g., argon, helium, nitrogen), but the melting / solidification process may be performed under an oxygen-containing atmosphere.

[0041] Second, the slag layer 50 acts as a blanket, allowing the solidified ODS alloy layer to cool slowly and uniformly—thereby reducing residual stresses that can contribute to post-weld reheat cracking and strain age cracking. The blanket effect also improves the mechanical properties of the resulting ODS alloy by allowing more time for cooling of the ODS alloy layer 44, thereby unexpectedly forming elongated grains. The use of fluxes leading to the slag layer 50, in some embodiments, can also unexpectedly increase the mechanical strength of the ODS alloy layer 44 without the need for a secondary recrystallization heat treatment—likely due to the insulating effect of the slag layer 50.

[0042] In some embodiments, the grain structure of the resulting ODS alloy layer 44 can be adjusted by controlling the content, shape, and amount of the flux 26.

[0043] Selecting fluxes that result in a slag layer 50 with relatively lower thermal conductivity reduces the cooling rate of the ODS alloy layer 44, providing additional time for secondary recrystallization to produce anisotropic grains with elongated shapes that ultimately resist sliding at grain boundaries (thereby improving high-temperature creep rupture strength). Suitable fluxes include commercially available fluxes used in laser welding applications. Fluxes containing higher proportions of refractory substances, such as zirconium oxide, for example, can result in a slag layer 50 with lower thermal conductivity, which enhances the increased creep rupture strength of the resulting ODS alloys.

[0044] The shape of the flux can also be controlled, for example, by grinding the flux into smaller particle sizes to increase the density of the resulting flux powder. In some embodiments, it is advantageous to grind the fluxes into powders with average particle sizes in the range of 0.02 mm to 0.08 mm (22-88 µm).

[0045] The amount of flux applied to the filler 22 and / or the melt 30 also influences the grain structure. Increasing the amount of flux 26 increases the thickness of the resulting slag layer 50. In some embodiments in which a powdered flux 26 is deposited on the surface of the filler 22, a thickness of the powdered flux 26 is in the range of 3 mm to 20 mm. In other embodiments, the thickness is in the range of 5 mm to 13 mm. The amount of flux 26 can also be modulated based on the thickness of the resulting slag layer 50. For example, in some cases, the amount of flux 26 is adjusted such that a thickness of the resulting slag layer 50 is in the range of 1 mm to 10 mm. In other embodiments, the thickness of the slag layer 50 is set to a range of 2 mm to 5 mm.

[0046] Third, the slag layer 50 helps shape the melt 30 to keep it close to a desired height-to-width ratio. In some cases, the desired height-to-width ratio is in the range of 1:2 to 1:4. In other embodiments, the desired height-to-width ratio is approximately 1:3.

[0047] Fourth, the flux 26 provides a cleaning effect to remove traces of impurities such as sulfur and phosphorus, which contribute to weld cracking. Such cleaning includes deoxidation of the alloy particles 24 in the filler 22 as well as deoxidation of metallic components of the melt 30.

[0048] Fifth, the flux 26 can provide an energy absorption and capture function to more effectively convert the energy beam 28 into heat energy, thereby facilitating more precise control of heat input and resulting fine control of temperatures in both the non-heating and heating portions 32, 34 of the melt 30.

[0049] Finally, the flux 26 may be formulated to compensate for loss of volatilized elements (e.g., Ti evaporating as TiO2) during processing, or to actively contribute elements to the melt 30 not otherwise contained in the filler 22.

[0050] After cooling and solidification of the melt 30, the resulting slag layer 50 can be removed by physical and / or chemical methods known in the relevant field.

[0051] The procedure described in Fig. 2, can be configured to perform a variety of processes involving the formation of ODS alloy materials. These include the formation and repair of ODS alloy coatings on metallic substrates and the production of bulk ODS alloys (not attached to a metallic substrate) that can be processed into various forms, such as sheets, ingots, and powders.

[0052] In some embodiments, the carrier material 20 is a metallic substrate, such that the resulting ODS alloy layer 44 is deposited onto the surface of the metallic substrate to form an ODS cladding layer. Suitable metallic substrates include any metallic materials known in the art to be compatible with ODS alloys, including alloys where the matrix is ​​generally based on nickel, cobalt, chromium, platinum, rhodium, or iron. In some cases, the carrier material 20 and / or the ODS alloy layer 44 may contain a nickel, cobalt, or nickel-iron-based superalloy material. The surface of the carrier material 20 (to which the resulting ODS alloy layer 44 is applied) may also be in the form of a pre-existing ODS alloy layer to form multilayer ODS alloy materials.In such cases, at least a portion of the pre-existing ODS alloy layer is melted so that the resulting ODS alloy layer 44 is bonded to the pre-existing ODS alloy layer.

[0053] Repair processes may include joining structures containing ODS alloys or repairing damaged or worn ODS alloys. In such repairs, the surface of the substrate 20 (e.g., a superalloy object) may be abraded to remove defects and then cleaned using techniques known in the art before laser deposition of the ODS alloy layer 44 is performed in accordance with the present disclosure.

[0054] Bulk ODS alloys can also be produced using the present processes (such as the one described in Fig. 2) using a fugitive carrier as the support material 20. The term "fugitive" means removable after formation of the ODS alloy layer 44. Such removal may take place, for example, by direct (physical) removal, mechanical processes, fluid washing, chemical leaching, and / or by any other known process capable of removing applicable fugitive support materials. The fugitive support material 20 may include a refractory material such that the resulting ODS alloy layer 44 may be readily removed from the support material after solidification and cooling. A non-limiting example of a suitable refractory support material 20 is a crucible, and for example, a crucible made of zirconium oxide.

[0055] In these embodiments, the filler 22 is deposited or delivered onto the surface of the fugitive support material 20, and then a laser cladding process of the present disclosure is performed, optionally in the presence of a flux 26, to produce an ODS alloy layer 44 located on the fugitive support material 20. After deposition of one or more layers 44, the fugitive support material 26 may be removed, revealing an object containing the ODS alloy whose shape and grain structure is determined in part by the shape and composition of the fugitive support material 26.

[0056] Many forms of the volatile support material 26 may be used, as long as the material can support the filler 22, the melt 30, as well as the ODS alloy layer 44 and can then be removed from the ODS alloy layer 44. In some embodiments, the volatile support material is in the form of a bed of an oxide-containing material (e.g., zirconium oxide) or in the form of a flux. In some cases, it is advantageous to use a bed of a powdered oxide-containing material or a powdered flux such that particle sizes in the volatile support material 26 are smaller than particle sizes in the filler 22. Such an arrangement can reduce or minimize the ingress of the melt 30 into the bed of the volatile support material 26. In other cases, the volatile support material 20 is in the form of a refractory container (e.g.,a crucible or mold) designed to control the shape and, if appropriate, the grain structure of the resulting ODS alloy 44.

[0057] Bulk ODS alloys produced by methods of the present disclosure benefit from an ability to precisely control the content, size, shape, and distribution of the oxide dispersoids 46a,b, as explained above. Furthermore, the use of at least one flux 26 allows the production of some bulk ODS alloys without requiring vacuum conditions or using inert atmospheric conditions. In some embodiments, bulk ODS alloys can be produced in the presence of significant amounts of atmospheric oxygen. In some cases, bulk ODS alloys can be produced such that at least one of the propellant gases 40a,b contains some amount of oxygen or is air.Surprisingly, the presence of a flux 26 in the melt 30 (and the resulting slag layer 50) can produce bulk ODS alloys with optimal (elongated) grain structure without the need for secondary recrystallization heat treatment. Additional heat treatment may optionally be performed to further improve the mechanical properties of bulk ODS alloys produced by methods of the present disclosure.

[0058] Bulk ODS alloys produced by methods of the present disclosure also benefit from an ability to control the grain structure of the resulting ODS alloy layer 44 through directional solidification. Fig. 2 also shows the optional use of a solidification mold 52 (left part in the illustration) which includes a mold bottom part 54 and a mold side part 56.

[0059] Selecting refractory materials with relatively low or high thermal conductivity allows for directed control of heat transfer during cooling of the formed ODS alloy layer—so that the resulting ODS alloy layer 44 can contain either uniaxial (columnar) or equiaxial grain structures. For example, in the non-limiting illustration of Fig. 2, the mold bottom portion 54 may be made of a material with high thermal conductivity (e.g., graphite), and the mold side portion 56 may be made of a material with low thermal conductivity (e.g., zirconium oxide), causing directional solidification to produce uniaxial (columnar) grains 58 oriented perpendicular to the plane of the mold bottom portion 54. By controlling the thermal conductivity of the bottom and side portions 54, 56 of the refractory solidification mold 52, the grain structure of the resulting ODS alloy layer 44 can be adjusted and varied. Directional solidification may also be achieved by using at least one cooling plate (in Fig. 2 not shown), which is arranged such that it is in contact with the mold bottom part 54 and / or the mold side part 56.

[0060] In some embodiments of the present disclosure, the use of filler is excluded, and instead an energy beam 6 is used to directly melt the surface of a metallic substrate 2 to form the melt 8, as in Fig. 1. In some embodiments, the melt 8 can be formed in the presence of a flux 26, which is either deposited on the surface 4 of the metallic substrate 2 or introduced into the melt 8 via a nozzle 42a,b. In such cases, a resulting slag layer 50 provides the same advantages described above. The resulting ODS alloy layer 16 is thus bonded to the metallic substrate 2.

[0061] While various embodiments of the present invention have been shown and described herein, it is to be understood that such embodiments have been provided merely by way of example. Various variations, changes, and substitutions may be made without departing from the present invention.

Claims

[1] Method comprising: Melting an alloy material (24) with an energy beam (28) to form a melt (30); introducing particles (46a,b) comprising a metal oxide (36a,b) into the melt so that the particles are dispersed in the melt; and Cooling and solidification of the melt to form an oxide dispersion strengthened alloy characterized by , that that melting of the alloy material (24) with the energy beam (28) takes place in the presence of a flux (26), wherein the flux forms a slag layer (50) on the melt (30) when melted by the energy beam, that the particles (36a,b, 46a,b) comprising the metal oxide are introduced into the melt (30) covered by the slag layer (50), wherein the particles are dispersed in the melt covered by the slag layer, and wherein the size and distribution of the particles (36a,b, 46a,b) are controlled by adjusting the trajectory of the particles that are sprayed or guided into the melt, and that the cooling and solidification of the melt (30) covered by the slag layer (50) takes place in such a way that the oxide dispersion-strengthened alloy (44) which is formed is at least partially covered by the slag layer. [2] The method of claim 1, further comprising depositing a powdered filler (22) comprising the alloy material (24) onto a surface of a metallic substrate (20) such that upon cooling of the melt, the oxide dispersion strengthened alloy (44) bonds to the surface of the metallic substrate. [3] The method of claim 1, further comprising: Depositing a powdered filler (22) comprising the alloy material (24) onto a volatile carrier material (20) so that upon cooling of the melt, the oxide dispersion-strengthened alloy solidifies on the volatile carrier material; and Removing the volatile support material while obtaining an object comprising the oxide dispersion strengthened alloy. [4] The method of claim 3, wherein the volatile carrier material (20) comprises a refractory container having a bottom portion (54) comprising a first refractory material and a side portion (56) comprising a second refractory material, wherein a thermal conductivity of the first refractory material differs from a thermal conductivity of the second refractory material to influence directional cooling of the melt such that the oxide dispersion strengthened alloy comprises uniaxial grains. [5] The method of claim 1, comprising melting a surface of a metallic substrate (20) comprising the alloy material (44) with the energy beam to form the melt, such that upon cooling of the melt, the oxide dispersion strengthened alloy is bonded to the metallic substrate. [6] A method according to claim 1, wherein the particles are directed into a non-heating portion I (34) of melt (30) so that the particles are not contacted by the energy beam. [7] A method according to claim 6, comprising: Injecting the particles into the non-heating part (34) of the melt (30) through an injection nozzle passing through the slag layer, wherein the injection nozzle comprises at least one refractory material selected from the group consisting of a metal oxide, a metal carbide, a metal nitride and a graphite; or Directing the particles into the non-heating portion (34) of the melt (30) through a consumable cored injector passing through the slag layer, the consumable cored injector comprising a nickel-containing shell surrounding a powdered core material comprising the particles. [8] A method according to claim 1, comprising: Injecting particles comprising a first metal oxide into a non-heating portion (34) of the melt through a refractory injection nozzle or a consumable cored injector passing through the slag layer (50); and Passing particles comprising a second metal oxide into a heating part (32) of the melt (30) through a nozzle located above the melt so that the particles comprising the second metal oxide are contacted by the energy beam. [9] A method according to any one of claims 1 to 8, wherein the metal oxide is an oxide of at least one element selected from the group consisting of aluminum, calcium, hafnium, silicon, titanium, thorium, yttrium and zirconium. [10] A method according to any one of claims 1 to 9, wherein the alloy material is a superalloy material.

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