Formation and repair of oxide dispersion-hardened alloys by alloy melting with oxide injection

Abstract

Process for forming an oxide-hardened alloy, which includes the following: Applying a melting energy (24) to a metal alloy material (23) to create a melt pool (26), wherein the melting energy (24) alternates between a first energy level and a second energy level, the second energy level being less than 50% of the first energy level, and Injecting (33) a metal oxide (34) into the melt bath (26), wherein the metal oxide (34) comprises particles with a higher melting point than the metal alloy material (23), and wherein the injection (33) only takes place when the melting energy has the second energy level; where at least most of the metal oxide (34) is not directly captured by the melting energy at the first energy level and wherein the solidification of the molten bath (26) forms a deposit of the metal alloy material with the metal oxide (34) distributed therein.

Description

Cross-reference to related registrations

[0001] This application claims priority over US patent application no. 14 / 859,816, filed on September 21, 2015, the disclosure of which is incorporated herein in full by reference. Field of invention

[0002] This invention relates generally to the field of metal component manufacturing and repair, and in particular to the formation of oxide dispersion hardened alloys (ODS alloys). Background of the invention

[0003] Oxide dispersion-hardened alloys (ODS alloys) possess superior properties for high-temperature applications, particularly ODS alloys formed from superalloy materials. ODS alloys differ from conventional alloys in the presence of fine-particle dispersoids and an elongated grain shape, which generally develops during recrystallization heat treatment and / or hot and cold forming. This distinctive grain structure enhances the high-temperature deformation characteristics of ODS alloys by suppressing the accumulation of intergranular damage. As a result of these and other properties, components manufactured from ODS alloys exhibit improved high-temperature creep resistance and oxidation resistance compared to conventional alloys.

[0004] The term "superalloy" is used here as it is understood in the field to describe a highly corrosion- and oxidation-resistant alloy that offers both excellent mechanical strength and resistance to creep at high temperatures, as well as good surface stability. Superalloys typically contain a base alloying element of nickel, cobalt, or nickel-iron. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g., IN 700, IN 738, IN 792, IN 939), Rene alloys (e.g., Rene N5, Rene 80, Rene 142), Haynes alloys, Mar M, CM 247, CM 247 LC, C 263, 718, X-750, ECY 768, 282, X45, PWA 1483, and CMSX (e.g., CMSX-4, CMSX-8, CMSX-10) single crystal alloys.

[0005] ODS alloys, especially superalloys, are very difficult to weld and repair using conventional techniques (e.g., tungsten inert gas welding, laser welding, electron beam welding, etc.). Such fusion welding results in a significant loss of strength. Furthermore, these alloys are difficult and uneconomical to process using less traditional methods such as friction welding.

[0006] ODS alloys are manufactured by mechanically alloying mixtures of powders. For example, metal powders such as alloys of iron aluminide, iron-chromium, iron-chromium-aluminum, nickel-chromium, or nickel aluminide, and oxides such as yttrium (Y₂O₃) or aluminum oxide (Al₂O₃) are compressed together in a ball mill. Cutting and smearing the powders creates a fine mixture. A sealed container of the powder is then isostatically hot-pressed and subsequently thermoformed into a desired shape. High-temperature heat treatment then provides stress relief and increases the grain size. Exceptional strength is achievable with ODS materials. However, ODS processing is slow and expensive and offers limited control over component geometry. Additionally, joining and repairing ODS components is very difficult.Conventional arc and energy beam processes cause the fine oxide particles to separate or coalesce, which degrades the result. Nickel-based ODS superalloys are particularly difficult to cold work and recrystallize.

[0007] Additional challenges inherent to ODS alloys include the general design and joining of these materials. Design and joining techniques that preserve the microstructure and intrinsic strength of the ODS alloy are severely limited, often restricting their suitability for incorporation into high-temperature load-bearing structures. For example, excessive heating of ODS alloys can cause the oxide to coalesce, leading to a build-up where the oxide dispersoids are no longer effective in resisting sliding motion at the grain boundaries. Melting ODS alloys also results in slagging of the oxide dispersoids, reducing their strength. Since most ODS alloys derive their strength from an elongated grain structure, such a disruption of the grain structure further reduces strength.

[0008] Document US 2013 / 299470 A1 discloses a method for the oxide dispersion of a metallic material using a laser. Brief description of the drawings

[0009] The invention is explained in the following description with reference to the drawings, which show the following: Fig. 1A-1D represent a device and steps in a known cold metal transition process. Fig. Figure 2 schematically illustrates aspects of a method and a device for injecting a metal oxide into an alloy melt bath. Fig. 3A-B represent an embodiment of an additional cold metal transition process in which oxide injection alternates with melting energy to avoid trapping the oxide particles with the arc. Fig. 4A-B represents an arc welding configuration in which oxide injection alternates with melting energy. Fig. Figure 5 shows overlapping areas of melting energy and oxide injection at the surface of the melt pool in one embodiment. Fig. Figure 6 shows an oxide pulse driver comprising a rotating oxide carrier cylinder with a gap aligned with a gap in a housing to eject an oxide particle pulse. Detailed description of the invention

[0010] Fig. 1A-1D represent a basic apparatus and steps in a known cold metal transition process 20. In Fig. In step 1A, a melting electrode 22 approaches an electrically conductive substrate 23, forming an arc 24 that melts a molten pool 26 on a surface 28 of the substrate and produces a molten droplet 30 of alloy filler material at the electrode tip. The molten pool solidifies into a deposit 32 on the substrate. Fig. 1B the melting electrode 22 is brought to the melt bath 18. In Fig. At 1C, the molten droplet 30 touches the melt pool, extinguishing the arc. A control unit (not shown) prevents the electric current from spiking during the short circuit. Fig. 1D, the molten droplet 30 adheres to the weld pool and the electrode 22 is withdrawn 19. This draws the droplet 30 from the electrode into the weld pool due to surface tension, thereby adding the droplet to the weld pool as alloy filler material. Compared with other arc welding techniques, this technology minimizes spatter and overheating while providing rapid deposition rates.

[0011] Fig. Figure 2 schematically illustrates an embodiment 20A of a method and apparatus for injecting a metal oxide into a melt pool 26 formed by a cold metal transition. The melt pool has a currently heated section 26A and a currently unheated section 26B. The unheated section 26B can be a trailing section of the melt pool after the electrode 22 has passed, i.e., from the movement of the electrode 22 to the right in the figure relative to the substrate 23. The metal oxide can be formed as a powder and transported by an inert carrier gas. At least most of the oxide 34 can be directed through a nozzle 36 onto or into the unheated section 26B of the melt pool 26, so that at least most of the metal oxide is not directly captured by the arc 24.This prevents the oxide from melting, or allows only surface melting, and avoids or minimizes amalgamation, thereby enabling an essentially uniform distribution of small oxide dispersions 38B in the deposit, thus maximizing their effectiveness in resisting sliding motion at the alloy grain boundaries. The melting electrode 22 may contain a filler metal to construct the metal alloy matrix surrounding the deposit dispersions.

[0012] The substrate 23 can be made of an oxide dispersion-cured alloy (ODS alloy) with dispersoids 38A, and the ODS deposit 32 can be formed from a material matching the substrate for build-up or repair, or the deposit 32 can be formed from a material different from the substrate for substrate surface reinforcement. ODS cladding, layering, or welding can be applied to a substrate that is or is not ODS. In another embodiment, for an additive manufacturing process that builds a component by successive ODS layers, starting with a first layer on the bearing surface, the substrate can be replaced by a volatile or removable bearing surface.

[0013] The metal oxide particles 34 can contain at least one metal oxide that has a higher melting point than the electrode 22 filler alloy. Examples of metal oxides include aluminum, calcium, cerium, chromium, cobalt, hafnium, lanthanum, magnesium, nickel, silicon, titanium, tantalum, thorium, yttrium, and zirconium. Mixtures of oxide particles containing different metal oxides and / or having different particle sizes can be used, or the oxide particles can be changed over time as deposition progresses in space. The oxide particles can be directed into the melt pool 26 from above using the nozzle 36, as shown. Alternatively, they can be injected directly into the melt pool 26 from below its surface using a refractory nozzle to avoid contact with the atmosphere.

[0014] Excessive heating of the oxide can lead to the amalgamation and slagging of the dispersoids 30B, which adversely affects the oxide distribution in the ODS deposit. The optimal size, shape, and distribution of the dispersoids 30B can be achieved, in part, by adjusting the alloy melting energy through the arc intensity and the arc on / off dwell times. The arc power and dwell times can be controlled so that the melt pool reaches or exceeds the melting point of the electrode 22 filler alloy and the substrate, but does not reach the melting point of the oxide particles. This prevents oxide amalgamation and slagging.

[0015] Fig. 3A-B represent an embodiment 20B of an additional cold metal transition process in which the oxide injection 33 alternates with the arc 24. In Fig. In 3A, arc 24 is present and the oxide injection is stopped by a control unit 44. The oxide can flow continuously in a return channel 40 in one direction perpendicular to the side in order to maintain the suspension of the particles in a carrier gas. Fig. 3B, the arc is extinguished when the molten droplet 30 touches the melt pool 26, as in a cold metal transition process. At this time, the oxide is injected 33 by an oxide particle pulse driver 42, for example, an acoustic driver, an electrostatic particle deflector, or a solenoid. This separation in the timing of the injection 33 and the arc 24 prevents the oxide from being captured by the arc and prevents the oxide from melting with the arc. The timing of the injection can be coordinated by alternately switching the pulse driver and the arc power. Such switching can optionally be triggered by a short-circuit detector in the control unit 44. The electrode 22 can be automatically moved towards and away from the melt pool 18 several times per second—for example, at least 10 times per second in some embodiments and up to 130 times per second in some embodiments.This process generates turbulence and forced convection in the melt bath, which thoroughly mix the oxide particles within it before solidification. At least some of the particles 33 can be injected to capture the melt droplet 30, so that they are carried into the melt bath 26 along with the material of the melt droplet 30.

[0016] Fig. 4A-B represents a further embodiment 20C in which the oxide injection 33 alternates with an arc 24. In this example, a non-consumable electrode 45 produces an oxide dispersion-cured autogenous weld or layer 47 on a non-ODS substrate 49. Alternatively, an energy beam, such as a laser or an electron beam, or a consumable electrode as in Fig. 3A-B can be used. In addition to a non-consumable electrode or energy source, an additional filler metal can be added. The process of Fig. 4A-B contains no filler material, but it serves to form a layer 47 containing dispersoids 38B. In Fig. 4B, the arc 24 is switched off and the oxide material 34 is injected by an oxide particle pulse driver 42 33. Here, the oxide injection spatially overlaps with the arc, but they are mutually exclusive in time, so that the oxide is not directly captured by the arc. The spatial overlap allows the particles to be injected into the most active part of the melt pool to simplify mixing before solidification.

[0017] Fig. Figure 5 shows an overlap between the melting energy 24 and the oxide injection 33 at the surface of the melt bath 26. For example, the area of ​​the melting energy at the surface of the melt bath can overlap with the area of ​​the oxide injection at the surface of the melt bath by at least 40% or 60%, or the area of ​​the oxide injection at the surface of the melt bath can overlap with the area of ​​the melting energy at the surface of the melt bath by at least 40% to 60%.

[0018] The distribution of the dispersoids 38B in the ODS alloy deposit 32 can be controlled by changing the velocity and concentration of particles of the oxide material 34 injected into the melt bath 26. Increasing the velocity or concentration of the oxide particles injected into the melt bath increases the proportion of dispersoids in the resulting deposit 32. Increasing the velocity can also provide a more uniform distribution if the melt bath is particularly viscous.

[0019] Fig.Figure 6 shows an oxide pulse driver 46 comprising a rotating oxide carrier cylinder 48 or a wheel with a gap 50 aligned with a gap 52 in a housing 54 to generate a pulse 56 of oxides 34. The rotational speed of the carrier cylinder can be synchronized with the cyclic displacement of the electrode tip in a cold metal transition process or with the alloy melting energy in any process, so that the oxide pulse does not overlap in time with the melting energy. The carrier cylinder 48 can be part of a feedback circuit as described previously.

[0020] Cold metal transition welding and pulsed arc welding are shown here as examples. Alternative technologies that can provide alloy melting energy include pulsed gas metal arc welding (GMAW), pulsed gas tungsten arc welding (GHW), pulsed tip TIG welding, and pulsed energy beams, for example, including a laser beam, particle beam, charged particle beam, molecular beam, etc. The cold metal transition process is advantageous due to its mechanical mixing of the molten pool through repeated rapid immersion of the electrode tip, its high degree of deposit control, and its relatively low heat generation. In addition to welding and cladding, it can form a wide variety of additional deposit shapes and wall growth directions.Tip-type tungsten inert gas welding can also be advantageous due to its superimposed mechanical oscillation of the feed wire, which helps to agitate the molten weld pool and promote oxide distribution within it. The on / off switching of the alloy melting energy described here, in some embodiments, involves switching between a first energy level (On) and a second energy level (Off) that is less than 50% of the first energy level.

[0021] Embodiments of the present disclosure enable the formation and repair of ODS superalloy components. However, the invention is not limited to such materials and can also be applied to other ODS materials.

[0022] Although various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided only as examples. Numerous variations, modifications, and substitutions can be made without departing from the invention presented here. Accordingly, it is determined that the invention is limited only by the spirit and scope of the appended claims.

Claims

[1] Process for forming an oxide-hardened alloy, comprising the following: Applying a melting energy (24) to a metal alloy material (23) to create a melt pool (26), wherein the melting energy (24) alternates between a first energy level and a second energy level, the second energy level being less than 50% of the first energy level, and Injecting (33) a metal oxide (34) into the melt bath (26), wherein the metal oxide (34) comprises particles with a higher melting point than the metal alloy material (23), and wherein the injection (33) only takes place when the melting energy has the second energy level; where at least most of the metal oxide (34) is not directly captured by the melting energy at the first energy level and wherein the solidification of the molten bath (26) forms a deposit of the metal alloy material with the metal oxide (34) distributed therein. [2] Process according to claim 1, wherein the injection of the metal oxide (34) into the melt bath (26) is separated from the application of the melting energy (24) at first energy level by a space sufficient to prevent the complete melting of at least most of the metal oxide (34). [3] Process according to any of the preceding claims, wherein the application of the melting energy at first energy level and the injection (33) of the metal oxide (34) overlap spatially at mutually exclusive times, so that the metal oxide (34) is not directly trapped by the melting energy at first energy level. [4] Process according to any of the preceding claims, wherein an area of ​​application of the melting energy (24) with first energy level on a surface of the melt bath (26) overlaps at least 40% with an area of ​​oxide injection (33) on the surface of the melt bath (26) or the area of ​​oxide injection (33) on the surface of the melt bath (26) overlaps at least 40% with the area of ​​application of the melting energy (24) with first energy level on the surface of the melt bath (26). [5] Process according to any one of the preceding claims, further comprising: alternating the injection of the metal oxide (34), such that the injection of the oxide (34) into the melt bath (26) is carried out when the melting energy has the second energy level, wherein the second energy level is between an energy level corresponding to a switched-off melting energy and an energy level of 50% of the first energy level. [6] Process according to any of the preceding claims, further comprising: Moving an electrode (22) towards and away from the melt bath (26) to alternately create and close a gap between the electrode (22) and the surface of the melt bath (26) many times per second; Alternating switching on the electrode (22) to a first energy level to generate an arc (24) in the gap, and switching off the power or reducing it to a second energy level that is less than 50% of the first energy level when the gap is closed, and Activating a particle injection pulse driver (46) which only supplies pulses of metal oxide particles (34) into the melt bath (26) when the melting energy of the arc (24) has the second energy level. [7] Process according to claim 6, wherein the pulse driver comprises a rotating oxide particle containment cylinder (48) or a wheel comprising a gap (50) which aligns at intervals with a gap (52) in a housing (54), thereby measuring and ejecting the oxide particles (34), wherein a rotational speed of the cylinder or wheel is synchronized with the switching on of the electrode, so that the oxide injection pulses do not overlap in time with the first energy level. [8] Device for forming an oxide dispersion-hardened alloy deposit, comprising: a first device (22) that supplies localized melting energy to a metal alloy material to form a melt pool (26); a second device (42) suitable for delivering pulses of a metal oxide (34) to the melt bath (26), and a control unit (44) that controls the first and second devices to alternately switch on the localized melting energy (24) and the pulses of the metal oxide (34) so ​​that the localized melting energy and the pulses of the metal oxide (34) do not overlap in time. [9] Device according to claim 8, wherein the second device (42) comprises a pulse driver which emits particles of the metal oxide (34) perpendicular to a flow of particles in a carrier gas in a return channel (40). [10] Device according to claim 8, wherein the second device (42) comprises a rotating oxide particle containment cylinder (48) or a wheel comprising a slot which aligns at intervals with a slot in a housing to measure and eject the oxide particles (34), wherein a rotational speed of the cylinder or wheel is synchronized with the localized melting energy so that the metal oxide pulses (34) do not overlap in time with the localized melting energy.

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