Process for the formation of dispersion-strengthened alloys

Abstract

Method comprising Melting an alloy material with a heat source to form a melt; introducing solidification particles into the melt so that the solidification particles are dispersed in the melt and form dispersoids; and Cooling and solidifying the melt to form a dispersion-strengthened alloy; characterized in that that the melting of the alloy material with the heat source takes place in the presence of a flux, whereby the flux forms a slag layer on the melt during melting, and that the solidification particles comprise a mixture of different particles with different melting points and / or sizes, wherein the different particles are placed in relatively hotter or cooler parts of the melt with or without direct contact with the heat source depending on the respective melting points and / or the sizes of the particles in order to effect a normalization of the size of the dispersoids.

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 dispersion strengthened alloys. BACKGROUND OF THE INVENTION

[0002] Surface hardening is a process in which the surface of a metal object is hardened while leaving the underlying metal relatively soft. It generally involves the formation of a thin layer of a harder metal on the surface of the metal object. This can be achieved by dispersing strengthening particles such as metal carbides, metal nitrides, metal oxides, or cemented carbides into a metallic matrix to form a dispersion-strengthened alloy that is harder than the base matrix and exhibits improved wear resistance. In some cases, these strengthening particles can be dispersed throughout a substrate or metal object to improve surface hardness and overall strength.

[0003] An example of a dispersion-strengthened alloy is NS-163™, a cobalt-based alloy obtained by heat-treating the base alloy (Co-28Cr-21Fe-9Ni-1.25Ti-1Nb) under a nitrogen atmosphere to form a dispersion of metal nitride particles throughout the resulting alloy. Although the resulting dispersion-strengthened alloy exhibits excellent creep rupture strength at temperatures up to 1204°C, it also suffers from certain drawbacks related to its forming and machinability. For example, the heat-strengthening process is limited to relatively thin substrates, for example, approximately 2.5 mm at most. Also, after fabrication and heat treatment, the alloy cannot be effectively processed by forming or welding, as such heating / melting processes reduce or eliminate the original strengthening effect.This degradation is believed to occur when heat from the subsequent metalworking process reduces, alters, or eliminates the nitride dispersion formed during the original heat treatment process. Thus, the nitride dispersions in that portion of the previously strengthened alloy subjected to subsequent metalworking may be disrupted, rendering the affected portion of the alloy weaker than the rest of the alloy.

[0004] Fig. 1 and Fig. 2 illustrate this problem. Fig. Figure 1 shows a prior art welding process for edge-to-edge joining of two dispersion-strengthened metal substrates, such as NS-163, containing a dispersion of strengthening particles. In a typical, non-limiting example, two dispersion-strengthened metal substrates 2a,b are placed opposite each other such that their respective edges form a joining seam 6 (exemplified in Fig. 1 a single-V groove). A filler 8 containing an alloy material 10 can then be deposited in the groove 6 and subsequently melted by sweeping an energy beam 12 over the surface of the filler 8, whereby a melt (e.g., weld pool) 14 forms within the groove 6. Upon cooling and solidification, the melt 14 forms a weld seam 16 that fuses the two ends of the metal substrates 2a,b together.

[0005] As explained above, the process leads to Fig. 1 introduces weak points into the resulting weld structure by causing a disturbance of the particle dispersions in the previously cured substrate material. Fig. 2 shows a cross-sectional view of the weld structure according to Fig. 1, in which the weld 16 contains a region 22 with reduced and / or demixed dispersions 4. The demixing of nitrides in the melt zone is probably partly due to differences in density between nitride particles (e.g. 5.22 g / cm 3 for TiN and 8.4 g / cm 3 for NbN compared to 7.95 g / cm 3for alloy NS-163). Such nitrides have a higher melting temperature than the general alloy (e.g., 2930°C for TiN and 2573°C for NbN versus 1288 to 1400°C for the substrate NS-163). Thus, after solidification of the nitrides, some nitride particles may segregate at a top surface, and some may sink toward a bottom surface during weld solidification. Furthermore, regions 20 within the heat-affected zone of the original matrix of the dispersion-strengthened substrates 2a,b also lack nitride dispersions or contain nitrides with altered shape and size. The reason for this is likely due to diffusion of nitrogen at elevated temperature, leading to dissolution and agglomeration of nitrides and / or changes in their shape.As a result of segregation and changes of nitrides in the weld 16 and adjacent heat-affected zones, a weak part 24 forms within and in the vicinity of the weld 16.

[0006] In short, welding dispersion-strengthened alloys such as NS-163 is problematic because the heat from welding (e.g., arc, laser, plasma, etc.) can lead to maldistribution of the strengthening particles by dissolving and segregating them and / or changing their size and shape. These combined effects result in a weld zone 24 with inferior properties relative to the original dispersion-strengthened alloy.

[0007] A generic process for ODS alloys is known from US2013 / 0299470A1. US2014 / 0220374A1 and US2013 / 0136868 concern superalloys.

[0008] The object of the present invention is to ensure a normalization of the size of dispersoids resulting from the different solidification particles.

[0009] 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

[0010] The invention is explained in the following description with reference to the drawings in which: Fig. Figure 1 is an illustration of a prior art welding process for joining two dispersion strengthened metal substrates; Fig. 2 a cross-sectional view of a welded structure formed by the Fig. 1 shown process is obtained; Fig. 3 shows laser melting processes for producing dispersion strengthened alloys from a powdered filler in the presence of a flux and Fig. 4 is a cross-sectional view of a weld structure obtained by a process of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] It was recognized that there is a need to discover processes for forming dispersion-strengthened alloys that avoid the aforementioned disadvantages. An optimal process would allow dispersion-strengthened alloys to be joined and welded without introducing regions of mechanical weakness caused by disturbance of the original particle dispersions. An optimal process would also allow small- and large-scale formation of dispersion-strengthened alloys with an improved ability to control the distribution and characteristics of the strengthening particles contained in the resulting alloys, as well as the grain shape and structure of the alloy matrix.

[0012] Disclosed herein are processes for forming dispersion-strengthened alloys in which strengthening particles are directed or injected into a molten bath of metallic material generated with a heat source, optionally in the presence of a flux. The size and distribution of strengthening particles contained in the resulting dispersion-strengthened alloys can be varied by controlling a number of factors, including the melting point, density, size, and trajectory of the strengthening particles, as well as the shape, duration, and intensity of the heat provided by the heat source. The use of fluxes can obviate the need to conduct these processes under strictly air-free conditions and can unexpectedly provide dispersion-strengthened alloys with improved mechanical characteristics without the need for additional 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 manufacture and repair of dispersion-strengthened alloys in various contexts, and can also be applied to the mass production of dispersion-strengthened alloys whose mechanical properties can be precisely controlled.

[0013] Fig. Figure 3 shows an exemplary method of the present disclosure applicable to various embodiments. In the present illustration, a filler 8 containing alloy particles 10 is deposited onto a surface of a support material 2. The support material 2 may be a variety of materials, including a dispersion-strengthened alloy such as NS-163. The support property provided by the support material 2 may be applied to various contexts—such as the support property provided by the groove 6 formed by the arrangement of the Fig. 1. Thus, in the context of a metal joining process, the support material 2 may be provided by at least two opposed metal substrates whose adjacent edges influence the shape of a resulting weld. In other contexts applicable to the present disclosure, the support material 2 may be provided by the surface of a single metal substrate (such as in a cladding process) or by the surface of a refractory surface or refractory container (such as in a bulk alloying process).

[0014] A heat source 28 is then passed over the surface of the filler 8 to melt it and thus to form a melt 30 containing a molten matrix of the alloy (in Fig. 3 as moving from left to right). Non-limiting examples of the heat source 28 include an arc, a plasma, an electron beam, and a laser beam. In the non-limiting embodiment of Fig. 3, the heat source 28 is a laser beam. As in Fig. As shown in Figure 3, the melt 30 includes a heating portion 34 located below the focal point of the laser beam 28 and a non-heating portion 32 located behind the focal point of the laser 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.

[0015] In the embodiment of Fig. 3, an injection nozzle 42a is used to inject solidification particles 36a, which are contained in a propellant gas 40a, into the non-heating part 32 of the melt 30 such that the solidification particles 36a are not contacted by the laser beam 28. The solidification particles 36a can also be directed into the heating part 34 of the melt 30 or into both the heating part 34 and the non-heating part 32, so that the solidification particles 36b are contacted by the laser beam 28. The outlet of the injection nozzle 42a can be as in Fig. 3, be immersed within the melt 30. In some embodiments, the use of direct injection improves the uniformity of the molten dispersion, resulting in improved mechanical and / or thermal properties in the resulting dispersion-strengthened alloy 44.

[0016] Injector nozzles 42a used to inject particles directly into the melt 30 may be in the form of hollow nozzles made of 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 wire of a nickel or nickel alloy sheath surrounding a powdered core material containing at least the solidification particles 36a. In such embodiments, the consumable cored injector is introduced into the melt 30, causing the metallic sheath to melt due to its relatively low melting point.The powdered core material is then dispersed into the melt 30 to form the dispersed solidifying particles 46a,b. In some embodiments that utilize a consumable cored injector, the cored injector 42a may be preheated and / or oscillated within the melt 30, further heating the melt 30 and / or dispersing the particles. The consumable cored injector may be introduced into the non-heating portion 32 or the heated portion 34 of the melt 30. In some cases, the powdered core material may contain both the solidifying particles 36a and a flux.

[0017] Alternatively or in addition, as in Fig. 3, the outlet of an injection nozzle 42b can be positioned above the melt so that a stream 38 of solidifying 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 part 32, 34. If more than one nozzle (injector) 42a,b is used, the solidifying particles 36a and 36b can be the same or different (in terms of their content and / or sizes), and the propellant gases 40a and 40b can also be the same or different.

[0018] In the presentation of Fig. 3, a flux 26 may be deposited on the surface of the filler 8 and, upon melting by the laser beam 28, generally forms a resulting slag layer 50 that coats the surface of the dispersion-strengthened alloy 44. The flux 26 may be as shown in Fig. 3, or it may be continuously fed onto the filler 8 upstream of the melt 30, or it may be mixed into the filler material 8. 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 by nozzle 42a) or pierced through the surface of the melt 30 (as shown by nozzle 42b). Alternatively, the flux may be contained in a consumable cored injector, as explained above. In such cases, the flux material may be directed, injected, or guided into the non-heating and / or heating portion 32, 34 of the melt.

[0019] After cooling and solidification of the melt 40, a dispersion-strengthened alloy 44 is formed, which contains dispersed strengthening particles 46a (and possibly 46b).

[0020] The content, size and distribution of the strengthening particles 46a,b contained in the resulting dispersion strengthened alloy 44 can be controlled by adjusting various parameters, including the following: (i) the content, size, concentration and trajectory of the solidification particles 36a,b injected or directed into the melt 30; and (ii) the intensity, duration, and pattern of heating by the heat source 28. The grain structure of the dispersion-strengthened alloy 44 can also be controlled by adjusting various parameters, including, but not limited to, the following: (iii) the metal content of the alloy; (iv) the content, amount, and trajectory of the flux; and (v) the arrangement and thermal characteristics of the substrate 2.

[0021] The strengthening particles 36a,b generally consist of at least one metallic or ceramic particle with a higher melting point than the metallic base alloy of the dispersion-strengthened alloy 44. Suitable strengthening particles include, but are not limited to, metal nitrides, metal carbides, metal oxides, metal cyanides, and cemented carbides. Metal nitrides that can be used as strengthening particles 36a,b include boron nitride, aluminum nitride, silicon nitride, titanium nitride, vanadium nitride, chromium nitride, zirconium nitride, niobium nitride, hafnium nitride, tantalum nitride, and other metal nitrides known in the art. Metal carbides that can be used as strengthening particles 36a,b include boron carbide, aluminum carbide, silicon carbide, calcium carbide, titanium carbide, vanadium carbide, chromium carbide, zirconium carbide, nickel carbide, hafnium carbide, tungsten carbide and other metal carbides known in the relevant art.Suitable metal oxides include oxides of elements such as aluminum, calcium, hafnium, silicon, titanium, thorium, yttrium, and zirconium, as well as other metal oxides known to form oxide dispersion strengthened alloys. Mixtures of different strengthening particles 36a,b and / or particles with different particle sizes may be used. Preformed dispersion strengthened alloys may also be used as strengthening particles 36a,b.

[0022] As explained above, the solidification particles 36a,b may be injected directly into the melt 30 (by means of a refractory nozzle and / or by means of a consumable nucleated injector, as shown in nozzle 42a), avoiding contact with the atmosphere, or they may be introduced into the melt 30 from above (as shown in nozzle 42b).

[0023] The size of the resulting dispersed particles 46a,b (often referred to as “dispersoids”) embedded in the resulting dispersion strengthened alloy 44 is related to three factors.

[0024] First, the size of the dispersoids 46a,b is directly related to the melting point of the strengthening particles 36a,b—such that using a strengthening 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 boron nitride and chromium nitride particles is injected into the warming portion 34 of the melt 30, the resulting dispersion-strengthened alloy 44 generally contains a mixture of relatively larger boron nitride dispersoids and relatively smaller chromium nitride dispersoids. This variation in the size of the resulting dispersoids occurs because chromium nitride has a significantly lower melting point (1770°C) compared to boron nitride (2973°C)—allowing a larger proportion of the chromium nitride particles to melt and dissolve (or decompose) into the matrix of the dispersion-strengthened alloy.This effect allows modulation of the dispersoid size by changing the melting point of a solidifying material contained in the solidifying particles 36a,b.

[0025] Second, the size of the resulting dispersoids 46a,b is directly related to the size of the precursor strengthening particles 36a,b. For example, if a mixture of relatively small and large boron nitride particles is injected into the heated portion 34 of the melt 30, the resulting dispersion-strengthened alloy 44 will generally contain a mixture of relatively large boron nitride dispersoids (corresponding to the larger strengthening particles) and relatively small boron nitride dispersoids (corresponding to the smaller strengthening particles). This effect allows the size of dispersoids 46a,b in the dispersion-strengthened alloy 44 to be modulated by varying the size of the precursor strengthening particles 36a,b.

[0026] Third, the size of the resulting dispersoids 46a,b is directly related to the intensity and duration of heat applied to the strengthening particles 36a,b and / or the melt 30 by the heat source 28. For example, if strengthening 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 dispersion-strengthened alloy 44 will generally be larger than the dispersoids 46b that result when the same strengthening particles 36b are injected into the heating portion 34 of the melt 30.This size variation may occur because solidification particles 36b introduced into the heating portion 34 of the melt 30 receive more heat in the form of: (i) direct contact with the heat source 28 when the stream 38 passes through (for example) a laser 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.

[0027] This effect allows the modulation of the dispersoid size by changing the trajectory of the corresponding solidifying particles 36a,b (e.g., directing or injecting solidifying particles into relatively hotter or cooler parts of the melt 30) with or without direct contact with the heat source 28). This effect also allows the modification or normalization (e.g., bringing into close agreement) of the size of the dispersoids resulting from different solidifying particles by using different trajectories depending on the respective melting points and / or sizes of the solidifying particles.For example, a dispersion-strengthened alloy 44 containing dispersoids 46a,b of boron nitride and chromium nitride of similar sizes can be obtained despite the different melting points of the corresponding particles by injecting or directing the CrN-containing particles 36a into the non-heating portion 32 while injecting or directing the BN-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 strengthening particles 36a,b in the melt 30. For example, varying the angle 48a can direct the strengthening particles 36a into increasingly hotter regions of the melt 30, as shown in FIG. Fig. 3 shown.

[0028] The size, shape, and distribution of the strengthening particles 36a,b can also be altered by modulating the intensity, duration, and shape of the heat source 28. As mentioned above, applying more heat to the strengthening 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, affecting the distribution of strengthening particles in the resulting dispersion-strengthened alloy 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 heat source (intensity and duration) as well as the size of the heated region (shape).

[0029] The term "heat source," as used herein, generally describes a photon beam, an electron beam, an ion beam, and a plasma beam. The term "energy beam," as used herein, generally describes a relatively narrow, propagating stream of particles or energy packets. Embodiments employing an energy beam as the heat source 28 may include the use of 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.

[0030] In some embodiments, the heat source 28 is an energy beam in the form of 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 using laser scanning (raster) optics to form a melt 30 with a precisely defined size and shape to suit the trajectory of the incoming solidification particles 36a,b.For example, such laser scanning allows a perimeter of the solidification particles 36b introduced into the melt 30 to fit within a perimeter of the melt 30.

[0031] In certain embodiments, the factors described above are adjusted such that only the surfaces of the strengthening particles 36a,b are melted. Such surface melting (as opposed to total melting) of the strengthening particles generally ensures that the resulting dispersoids 46a,b sufficiently bond with the matrix structure of the dispersion-strengthened alloy 44—while simultaneously maintaining the optimal shape and mechanical integrity of the original strengthening particles 36a,b to optimize the strength and thermal characteristics of the resulting dispersion-strengthened alloy.

[0032] The distribution of dispersoids 46a,b in the dispersion-strengthened alloy 44 can also be controlled by varying both the velocity and concentration of strengthening particles 36a,b injected and / or introduced into the melt 30, and by scanning the energy beam 28 to create streams of molten material and effective mixing within the melt 30. Increasing either the velocity or the concentration of the strengthening particles 36a,b shot into the melt 30 generally increases the proportion of dispersoids 46a,b contained in the resulting dispersion-strengthened alloy 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 (for example, by inducing the Marangoni effect), which can further distribute the solidification particles 36a,b throughout the melt.

[0033] As explained above, the grain structure of the dispersion-strengthened alloy 44 can be varied by adjusting various parameters, including the metal content of the alloy. The filler 8 is often used in powder form and contains alloy particles 10 that at least partially define the composition of the resulting dispersion-strengthened alloy 44. The dispersion-strengthened alloy 44 may contain a high-temperature metal matrix, such as iron aluminide, iron-chromium, iron-chromium-aluminum, nickel-chromium, and nickel aluminide, as well as other alloy systems based on iron, vanadium, and niobium, including stainless steels. In certain applications, the dispersion-strengthened alloy 44 contains a superalloy metal matrix with a base alloying element of nickel, cobalt, or nickel-iron, as well as other superalloy materials.

[0034] 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.

[0035] In some embodiments, the metallic composition of the dispersion-strengthened alloy 44 is provided by both the alloy particles 10 and by additional metallic components that are either separately contained in the filler 8 or separately introduced or directed into the melt 30. For example, additional metallic components may be injected (e.g., via nozzle 42a) and / or flowed (e.g., via nozzle 42b) directly into the melt to supplement the metallic composition of the filler 8. In other cases, the metallic composition may be supplemented by metals contained in the strengthening 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 sheath).

[0036] In some embodiments, the composition of a dispersion-strengthened 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 8 and the strengthening particles 36a,b may be selected such that the resulting dispersion-strengthened 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 8 and the strengthening particles 36a,b may be selected such that the resulting dispersion-strengthened alloy layer 44 contains ceramic materials, such as zirconium oxide and yttrium oxide, and is suitable for use as a thermal barrier coating.

[0037] The flux 26 and the resulting slag layer 50 provide a number of functions that are beneficial for dispersion strengthened alloys of the present disclosure.

[0038] First, they function to shield both the melt 30 and the solidified (and still hot) dispersion-strengthened alloy 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 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.

[0039] Second, the slag layer 50 acts as a blanket, allowing the solidified dispersion-strengthened alloy 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 dispersion-strengthened alloy by allowing more cooling time, which leads to the formation of grains of specific sizes and shapes. The use of fluxes leading to the slag layer 50 can, in some embodiments, also unexpectedly increase the mechanical strength of the dispersion-strengthened alloy 44 without the need for subsequent heat treatment—likely due to the insulating effect of the slag layer 50.

[0040] In some embodiments, the grain structure of the resulting dispersion-strengthened alloy 44 can be adjusted by controlling the content, shape, and amount of flux 26. Selecting fluxes that result in a slag layer 50 with relatively lower thermal conductivity reduces the cooling rate of the dispersion-strengthened alloy 44, providing additional time for grain formation, resulting in increased strength. Fluxes containing, for example, higher proportions of refractory substances, such as zirconium oxide, can result in a slag layer 50 with lower thermal conductivity, enhancing the increased strength of the resulting dispersion-strengthened alloys.

[0041] 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.

[0042] 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 10 in the filler 8 as well as deoxidation of metallic components of the melt 30.

[0043] Fifth, the flux 26 can provide an energy absorption and capture function to more effectively convert an 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.

[0044] 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 8.

[0045] Fluxes can be selected to provide any number of the functions described above, as well as other functions described below. Suitable fluxes include individual organic or inorganic compounds, as well as mixtures of compounds. Such mixtures include commercially available fluxes, sometimes adapted to the heat source 28 used (for example, commercially available fluxes used in laser welding applications).

[0046] Examples of commercially available fluxes that can perform at least one of the functions described above include Lincolnweld P2007, Bohler Soudokay NiCrW-412, ESAB OK 10.16 or 10.90, Special Metals NT100, Oerlikon OP76, Sandvik 50SW or SAS1.

[0047] Examples of organic fluxes include high molecular weight hydrocarbons (e.g. beeswax, paraffin), carbohydrates (e.g. cellulose), natural and synthetic oils (e.g. palm oil), organic reducing agents (e.g. coal, coke), carboxylic acids and dicarboxylic acids (e.g. abietic acid, isopimaric acid, neoabietic acid, dehydroabietic acid, rosin), carboxylic acid salts (e.g. rosin salts), carboxylic acid derivatives (e.g. dehydroabietylamine), amines (e.g. triethanolamine), alcohols (e.g. high polyglycols, glycerols), natural and synthetic resins (e.g. polyol esters of fatty acids), mixtures of such compounds and other organic compounds that fulfill at least one function described above.

[0048] Examples of inorganic fluxes include reactive metals (e.g. iron ore), metal oxides (e.g. magnesium oxide, manganese oxide, aluminum oxide, silicon oxide, calcium oxide, titanium oxide, yttrium oxide, zirconium oxide, hafnium oxide, copper oxide, cerium oxide), metal halides (e.g. lithium chloride, zinc chloride, barium chloride, magnesium chloride, tin chloride, calcium fluoride), halide salts (e.g. ammonium chloride), borates (e.g. borax), metal fluoroborates (e.g. potassium fluoroborate), metal sulfides (e.g. lead sulfide), metal carbonates (e.g. calcium carbonate, sodium carbonate), metal aluminates (e.g. cryolite), mineral acids (e.g. hydrochloric acid, hydrobromic acid, phosphoric acid), metal silicates (e.g. sodium silicate), mixtures of such compounds and other inorganic compounds capable of performing at least one function described above.

[0049] 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).

[0050] The amount of flux applied to the filler 8 and / or the melt 30 also influences the grain structure. Increasing the amount of flux 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 8, a thickness of the powdered flux 26 is in the range of 1 mm to 7 mm. In other embodiments, the thickness is in the range of 5 mm to 13 mm. The amount of flux can also be modulated based on the thickness of the resulting slag layer 50. For example, in some cases, the amount of flux 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.

[0051] After cooling and solidification of the melt 30, the resulting slag layer 50 can be removed by means of physical and / or chemical methods known in the relevant field.

[0052] Methods of the present disclosure also benefit from the ability to control the outcome of the melting / solidification process based on the melting point and density of the solidifying particles and / or flux. The following table shows data for an exemplary set of possible melt constituents. Bestandteil MP (°C) Dichte (g / cm 3 ) Bestandteil MP (°C) Dichte (g / cm 3 ) NS-163 1288 - 1400 7,9 Metallnitride BN 2973 2,1-3,5 CrN 1770 5,9 TiN 2930 5,2 ZrN 2952 7,1 NbN 2573 8,5 VN 2050 6,1 AlN 2200 3,3 HfN 3305 13,8 SiN 1900 3,2 TaN 3090 14,3 Metallcarbide BC 2763 2,5 CrC 1895 6,7 AlC 2200 2,4 ZrC 3532-3540 6,7 SiC 2730 3,2 NiC 3490 7,8 CaC 2160 2,2 HfC 3900 12,2 TiC 3140 4,9 WC 2785-2830 15,6 VC 2810 5,8 Flussmittel Al2O3 2072 3,9-4,1 CaF2 1418 3,2 SiO2 1600-1725 2,6 CaCO3 1339 2,7

[0053] Particle size and shape can be controlled to some extent by adjusting the melting point of the strengthening particles relative to that of the base metal alloy. As shown in the table above, the melting point for the base alloy NS-163 ranges from 1288°C to 1400°C. The most common metal nitrides and metal carbides have melting points that exceed the melting points of the base alloy NS-163, which is partly responsible for the strengthening ability of dispersions containing these materials. However, as melt temperatures approach or exceed the melting points of certain agents with lower melting points (e.g., CrN, SiN, CrC, CaC, AlC), a higher proportion of the strengthening particles melt and dissolve into the alloy matrix. Such enhanced partial melting reduces the size of the resulting dispersoids 46a,b and can also change their shape.Thus, the particle size and shape can be changed by selecting solidifying particles with relatively lower melting points or by increasing the heating of the melt and / or by bringing the solidifying particles into direct contact with the heat source.

[0054] Particle dispersion can also be controlled to some extent by adjusting the density of the strengthening particles relative to that of the base metal alloy. As shown in the table above, the density of the base alloy of NS-163 is approximately 7.9 g / cm 3. Optimal mixing of the strengthening particles in the melt can be facilitated by selecting strengthening materials (e.g., NbN, ZrN, NbN, NiC) with a similar density to that of the base alloy. Conversely, if a higher concentration of strengthening dispersions is desired in the upper part of the resulting dispersion-strengthened alloy, such a particle concentration gradient can be promoted by selecting strengthening materials (e.g., BN, TiN, AlN, SiN, Bc, AlC, SiC, CaC) with a lower density than that of the base alloy. A higher concentration of strengthening dispersions can also be promoted in the lower part of the resulting dispersion-strengthened alloy by selecting strengthening materials (e.g., HfN, TaN, HfC, WC) with a higher density than that of the base alloy.

[0055] The protective and thermal functions of the slag layer 50 can also be controlled to some extent by adjusting the melting point and density of the flux relative to those of the base metal alloy. It is often most advantageous to select a flux with a lower melting temperature than that of the strengthening particles. However, in some embodiments, the melting temperature of the flux may exceed that of the strengthening particles. A relatively lower melting temperature of the flux (e.g., CaF2, CaCO3) may promote faster melting and formation of the protective slag layer 50—thus allowing some processes of the present disclosure to be performed under an oxygen-containing atmosphere. Rapid formation of the slag layer 50 can also be promoted by selecting fluxes with a lower density (e.g., SiO2, CaCO3) relative to that of the base alloy.

[0056] The procedure described in Fig. 3, can be designed to perform a variety of processes involving the formation of dispersion-strengthened alloy materials. These include the formation and repair of dispersion-strengthened alloy coatings on metallic substrates, the joining of dispersion-strengthened (and non-dispersion-strengthened) alloy materials, as shown in Fig. 1) and the small-scale and large-scale production of dispersion-strengthened alloys (not attached to a metallic substrate) that can be processed into various forms such as sheets, ingots, and powders.

[0057] Repair processes may include joining structures containing dispersion-strengthened alloys or repairing damaged or worn dispersion-strengthened alloys. Such processes may also be applied to non-dispersion-strengthened alloys—so that the resulting layer or weld is a dispersion-strengthened alloy. In such repairs, the surface of the substrate 2 (or workpiece) may be abraded to remove defects and then cleaned using techniques known in the art before depositing the dispersion-strengthened alloy 44 according to the present disclosure.

[0058] By applying methods of the present disclosure (such as in Fig. 3) to achieve edge-to-edge joining of at least two dispersion strengthened metal substrates (as shown in Fig. 1), one can advantageously obtain a welded object that is free from the Fig. 2 defects shown. Fig. 4 shows a cross-sectional view of a weld structure used in the Fig. 1 shown type, but a method as in Fig. 3. In this method, a laser beam 28 is used to melt a filler 8 covered by a layer of flux 26 to form a melt 30 in which metal nitride particles 36a are injected into the unheated part 32 of the melt 30. After cooling and solidification of the melt 30, a weld 16 is formed with those of Fig. 2 superior properties. In contrast to the welded object of Fig. 2 contains the resulting weld 16 in Fig. 4 a normal dispersion 80 of the nitride particles 4, and the adjacent parts of the dispersion strengthened metal substrates 2a,b also contain normal dispersions 82. Thus, the resulting weld structure of Fig. 4 not the weak points 24 that are present in the welded structure of Fig. 2 were observed.

[0059] The same advantage accompanies other embodiments of the present disclosure in which dispersion-strengthened alloys are formed. Thus, in processes in which cladding layers or bulk dispersion-strengthened alloys are formed, the present disclosure provides an improved ability to control the size and distribution of the resulting dispersoids 46a,b, resulting in consistently improved mechanical properties.

[0060] In some embodiments, the carrier material 2 is a metallic substrate, such that the resulting dispersion-strengthened alloy layer 44 is deposited onto the surface of the metallic substrate to form a dispersion-strengthened cladding layer. Suitable metallic substrates include any metallic materials known in the art to be compatible with dispersion-strengthened alloys, including alloys in which the matrix is ​​generally based on iron, vanadium, niobium, nickel, cobalt, chromium, platinum, or rhodium, as well as stainless steels. In some cases, the carrier material 2 and / or the dispersion-strengthened alloy layer 44 may contain a nickel-, cobalt-, or nickel-iron-based superalloy material.The surface of the substrate 2 (to which the resulting dispersion-strengthened alloy layer 44 is applied) can also be in the form of a pre-existing dispersion-strengthened alloy layer, forming multilayer ODS alloy materials. In such cases, at least a portion of the pre-existing dispersion-strengthened alloy layer is melted, so that the resulting dispersion-strengthened alloy layer 44 is bonded to the pre-existing dispersion-strengthened alloy layer.

[0061] Bulk dispersion strengthened alloys can also be prepared by the present processes (such as the one described in Fig. 3) using a fugitive carrier as the support material 2. The term "fugitive" means removable after formation of the dispersion-strengthened alloy layer 44. Such removal may take place, for example, by means of direct (physical) removal, mechanical processes, fluid washing, chemical leaching, and / or by means of any other known process by which applicable volatile support materials can be removed. The fugitive support material 2 may contain a refractory material such that the resulting dispersion-strengthened alloy layer 44 can be easily removed from the support material after solidification and cooling. A non-limiting example of a suitable refractory support material 2 is a crucible, and as shown, a crucible made of zirconium.

[0062] In these embodiments, the filler 8 is deposited or supplied onto the surface of the fugitive support material 2, and then a metal deposition process of the present disclosure is performed, optionally in the presence of a flux, to produce a dispersion-strengthened alloy layer 44 located on the fugitive support material 2. After deposition of one or more layers 44, the fugitive support material 2 may be removed, revealing an object containing the dispersion-strengthened alloy whose shape and grain structure are determined in part by the shape and composition of the fugitive support material 2.

[0063] Many forms of the volatile carrier material 2 can be used, as long as the material can support the filler 8, the melt 30, as well as the dispersion-strengthened alloy layer 44, and can then be removed from the dispersion-strengthened alloy layer 44. In some embodiments, the volatile carrier 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 carrier material 2 are smaller than particle sizes in the filler 8. Such an arrangement can reduce or minimize the ingress of the melt 30 into the bed of the volatile carrier material 2. In other cases, the volatile carrier material 2 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 dispersion-strengthened alloy 44.

[0064] Bulk dispersion strengthened alloys produced by methods of the present disclosure benefit from an ability to precisely control the content, size, shape, and distribution of the strengthening dispersoids 46a,b, as explained above. Furthermore, the use of at least one flux allows the production of some bulk dispersion strengthened alloys without requiring vacuum conditions or using inert atmospheric conditions. In some embodiments, bulk dispersion strengthened alloys can be produced in the presence of significant amounts of atmospheric oxygen. In some cases, bulk dispersion strengthened 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 in the melt 30 (and the resulting slag layer 50) can produce bulk dispersion strengthened alloys with optimal (strengthening) grain structure without the need for subsequent heat treatment of the bulk dispersion strengthened alloy. Additional heat treatment may optionally be performed to further improve the mechanical properties of bulk dispersion strengthened alloys produced by methods of the present disclosure.

[0065] Bulk dispersion strengthened alloys produced by methods of the present disclosure also benefit from an ability to control the grain structure of the resulting dispersion strengthened alloy layer 44 through directional solidification. Fig. 3 also shows the optional use of a solidification mold 52 (left part in the illustration) containing a mold bottom portion 54 and a mold side portion 56. Selecting refractory materials with relatively low or high thermal conductivity allows for directed control of heat transfer during cooling of the formed dispersion-strengthened alloy layer—so that the resulting dispersion-strengthened alloy layer 44 can contain either uniaxial (columnar) or equiaxial grain structures. For example, in the non-limiting illustration of Fig. 3, 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), which causes 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 dispersion-strengthened alloy layer 44 can be adjusted and varied. Directional solidification may also be achieved by using at least one cooling plate (in Fig. 3 not shown) arranged to be in contact with the mold bottom part 54 and / or a heating plate arranged to be in contact with the mold side part 56.

[0066] In some embodiments of the present disclosure, the use of filler is excluded, and instead, a heat source is used to directly melt the surface of a metallic substrate to form the melt. In some embodiments, the melt may be formed in the presence of a flux that is either deposited on the surface of the metallic substrate or introduced into the melt via at least one nozzle. In such cases, a resulting slag layer provides the same advantages described above. The resulting dispersion-strengthened alloy layer is thus bonded to the metallic substrate.

[0067] While various embodiments of the present invention have been shown and described, 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 with a heat source to form a melt; introducing solidification particles into the melt so that the solidification particles are dispersed in the melt and form dispersoids; and Cooling and solidifying the melt to form a dispersion-strengthened alloy; characterized by , that that the melting of the alloy material with the heat source takes place in the presence of a flux, whereby the flux forms a slag layer on the melt during melting, and that the solidification particles comprise a mixture of different particles with different melting points and / or sizes, wherein the different particles are placed in relatively hotter or cooler parts of the melt with or without direct contact with the heat source depending on the respective melting points and / or the sizes of the particles in order to effect a normalization of the size of the dispersoids. [2] The method of claim 1, further comprising depositing a powdered filler comprising the alloy material onto adjacent surfaces of at least two opposed metal substrates such that the dispersion strengthened alloy forms a dispersion strengthened weld that fuses the at least two opposed metal substrates together, or further comprising depositing a powdered filler comprising the alloy material onto a surface of a metallic substrate such that upon cooling of the melt, the dispersion strengthened alloy is bonded to the surface of the metallic substrate. [3] The method of claim 1, further comprising: Depositing a powdered filler comprising the alloy material onto a volatile carrier material so that upon cooling of the melt, the dispersion-strengthened alloy solidifies on the volatile carrier material; and Removing the volatile support material while obtaining an object comprising the dispersion strengthened alloy. [4] A method according to any one of claims 1 to 3, comprising melting a surface of a metallic substrate comprising the alloy material with the heat source to form the melt, such that upon cooling of the melt the dispersion-strengthened alloy is bonded to the metallic substrate. [5] A method according to any one of claims 1 to 4, wherein the strengthening particles comprise a metal nitride, a metal carbide, or both, or the strengthening particles comprise at least one selected from the group consisting of boron nitride, aluminum nitride, silicon nitride, titanium nitride, vanadium nitride, chromium nitride, zirconium nitride, niobium nitride, hafnium nitride, tantalum nitride, boron carbide, aluminum carbide, silicon carbide, calcium carbide, titanium carbide, vanadium carbide, chromium carbide, zirconium carbide, nickel carbide, hafnium carbide, and tungsten carbide. [6] A method according to any one of claims 1 to 5, wherein the heat source is selected from the group consisting of a photon beam, an electron beam and a plasma beam. [7] A process according to any one of claims 1 to 6, wherein the solidifying particles are introduced into the melt through a refractory injection nozzle passing through the slag layer or through a consumable nucleated injector passing through the slag layer. [8] Method according to one of claims 1 to 7, wherein at least one of the following is fulfilled: the solidification particles are introduced into the melt with at least one propellant gas selected from the group consisting of air, argon, nitrogen and helium and Melting of the alloy material and formation of the dispersion-strengthened alloy take place under an oxygen-containing atmosphere. [9] A method according to any one of claims 1 to 8, wherein the melting takes place by scanning a laser beam over a surface of a powdered filler comprising the alloy material so that at least one of the following is satisfied: a perimeter of the solidification particles introduced into the melt fits into a perimeter of the melt; and Scanning the laser beam creates streams of molten material within the melt, which disperses the solidifying particles in the melt.

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