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US-12618126-B2 - Chromium-molybdenum-aluminum alloys with oxidation-resistance imparted by thermal pre-treatment

US12618126B2US 12618126 B2US12618126 B2US 12618126B2US-12618126-B2

Abstract

Ternary chromium-molybdenum-aluminum (CrMoAl) alloys that form oxidation-resistant surface films for high-temperature applications are provided. Also provided are methods for thermally pre-treating the alloys to form the oxidation resistant surface films. The surface films have a stratified structure that includes an exterior surface oxide layer comprising chromium oxides and aluminum oxides and an interior aluminum nitride-rich region comprising aluminum nitride precipitates dispersed in a CrMoAl alloy matrix. The interior aluminum nitride precipitates act as oxygen sinks to sequester oxygen diffusing inward into the CrMoAl to prevent further oxidation of the underlying bulk alloy.

Inventors

  • Dan Thoma
  • Michael NIEZGODA

Assignees

  • WISCONSIN ALUMNI RESEARCH FOUNDATION

Dates

Publication Date
20260505
Application Date
20230627

Claims (20)

  1. 1 . An article of manufacture comprising a single-phase ternary chromium-molybdenum-aluminum alloy having the composition Cr (1-x-y) Mo x Al y , where 0.10≤x≤0.20 and 0.10≤y≤0.20.
  2. 2 . The article of manufacture of claim 1 , where 0.14≤x≤0.18 and 0.14≤y≤0.18.
  3. 3 . The article of manufacture of claim 1 , wherein the article of manufacture is an ingot.
  4. 4 . The article of manufacture of claim 1 , wherein the article of manufacture is a coating on a substrate.
  5. 5 . The article of manufacture of claim 1 , wherein the article of manufacture is a component of an aircraft, a missile, a rocket, or a space vehicle.
  6. 6 . The article of manufacture of claim 4 , wherein the substrate is a component of an aircraft, a missile, a rocket, or a space vehicle.
  7. 7 . A method of fabricating an article of manufacture comprising a single-phase ternary chromium-molybdenum-aluminum alloy having the composition Cr (1-x-y) Mo x Al y , where 0.10≤x≤0.20 and 0.10≤y≤0.20, the method comprising forming a melt composed of stoichiometric quantities of Cr, Mo, and Al and cooling the melt to solidify the single-phase ternary chromium-molybdenum-aluminum alloy having the composition Cr (1-x-y) Mo x Al y , where 0.10≤x≤0.20 and 0.10≤y≤0.20, wherein the solidified single-phase ternary chromium-molybdenum-aluminum alloy is formed into an article of manufacture by casting and cooling the melt, by forming a coating of the single-phase ternary chromium-molybdenum-aluminum alloy on a substrate, by laser powder bed fusion (LPBF), or by directed energy deposition (DED).
  8. 8 . The method of claim 7 , wherein the article of manufacture is formed by forming the coating of the single-phase ternary chromium-molybdenum-aluminum alloy on a substrate and the substrate is a component of an aircraft, a missile, a rocket, or a space vehicle.
  9. 9 . The method of claim 7 , wherein the article of manufacture is formed by the laser powder bed fusion (LPBF) or by the directed energy deposition (DED).
  10. 10 . A method of forming an oxidation-resistant chromium-molybdenum-aluminum alloy, the method comprising: forming a single-phase ternary chromium-molybdenum-aluminum alloy having the composition Cr (1-x-y) Mo x Al y , where 0.10≤x≤0.20 and 0.10≤y≤0.20; and exposing the single-phase ternary chromium-molybdenum-aluminum alloy to a heated atmosphere comprising nitrogen gas and oxygen gas at a temperature, T, and for a time sufficient to form a stratified structure comprising: a base layer of a ternary chromium-molybdenum-aluminum alloy; a nitride-rich layer over the base layer, the nitride-rich layer comprising aluminum nitride precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; an oxide-rich layer over the nitride-rich layer, the oxide-rich layer comprising aluminum oxide precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; and a chromia-rich surface oxide layer over the oxide-rich layer, the chromia-rich surface oxide layer comprising chromium oxides and aluminum oxides.
  11. 11 . The method of claim 10 , where 0.14≤x≤0.18 and 0.14≤y≤0.18.
  12. 12 . The method of claim 10 , wherein 1100° C.<T<1500° C.
  13. 13 . The method of claim 10 , wherein 1200° C.<T<1400° C.
  14. 14 . The method of claim 10 , wherein the time is in the range from 6 hours to 36 hours.
  15. 15 . The method of claim 10 , wherein exposing the single-phase ternary chromium-molybdenum-aluminum alloy to the heated atmosphere comprising nitrogen gas and oxygen gas comprises exposing the single-phase ternary chromium-molybdenum-aluminum alloy to a heated ambient air.
  16. 16 . The method of claim 10 , wherein exposing the single-phase ternary chromium-molybdenum-aluminum alloy to the heated atmosphere comprising nitrogen gas and oxygen gas comprises exposing the single-phase ternary chromium-molybdenum-aluminum alloy to a heated oxygen-free atmosphere comprising the nitrogen gas and subsequently exposing the ternary chromium-molybdenum-aluminum alloy to a heated nitrogen-free atmosphere comprising the oxygen gas.
  17. 17 . The method of claim 10 , wherein the atomic ratio of chromium to aluminum in the chromia-rich surface oxide layer is in the range from 3:1 to 6:1.
  18. 18 . The method of claim 17 , wherein the volume fraction of aluminum oxide precipitates in the oxide-rich layer is at least 0.2 and the volume fraction of aluminum nitride precipitates in the nitride-rich layer is at least 0.2.
  19. 19 . The method of claim 10 , further comprising applying the single-phase ternary chromium-molybdenum-aluminum alloy as a coating on a substrate.
  20. 20 . The method of claim 19 , wherein the substrate is a component of an aircraft, a missile, a rocket, or a space vehicle.

Description

BACKGROUND At extreme speeds, sharp aerodynamic bodies such as leading edges, nose cones, and control surfaces are subject to aerodynamic heating. These intense thermal environments can cause degradation of flight surfaces or malfunction of components, resulting in extended maintenance schedules, high costs, and low mission readiness. Therefore, it has been proposed to place thermally resistant metals, metal alloys, such as nickel-based alloys, and ceramic matrix composites (CMCs) in areas of high thermal impingement. Refractory metal alloys have seen a resurgence in interest for these types of high temperature aerospace applications in recent years. Molybdenum alloys have much higher melting points compared to nickel-based alloys, and improved strength at high temperature, better manufacturability and inherent toughness over ceramics and CMCs. However, the use of molybdenum alloys has been limited by their tendency to degrade in oxidizing environments. SUMMARY Articles of manufacture formed from ternary chromium-molybdenum-aluminum alloys that form oxidation-resistant surface films for high-temperature applications upon thermal pre-treatment are provided. Also provided are methods for thermally pre-treating the alloys to form the oxidation resistant surface films. Some embodiments of the ternary chromium-molybdenum-aluminum alloys from which articles for use in extreme high-temperature environments can be made have the composition Cr(1-x-y)MoxAly, where 0.10≤x≤0.20 and 0.10≤y≤0.20. One embodiment of a thermally pre-treated oxidation-resistant chromium-molybdenum-aluminum alloy includes: a base layer of the ternary chromium-molybdenum-aluminum alloy; a nitride-rich layer over the base layer, the nitride-rich layer comprising aluminum nitride precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; an oxide-rich layer over the nitride-rich layer, the oxide-rich layer comprising aluminum oxide precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; and a chromia-rich surface oxide layer over the oxide-rich layer, the chromia-rich surface oxide layer comprising chromium oxides and aluminum oxides. One embodiment of a method of forming an oxidation-resistant chromium-molybdenum-aluminum alloy of a type described herein includes the steps of: forming a single-phase ternary chromium-molybdenum-aluminum alloy having the composition Cr(1-x-y)MoxAly, where 0.10≤x≤0.20 and 0.10≤y≤0.20; and exposing the single-phase ternary chromium-molybdenum-aluminum alloy to a heated atmosphere comprising nitrogen gas and oxygen gas at a temperature, T, and for a time sufficient to form a stratified structure comprising: a base layer of a ternary chromium-molybdenum-aluminum alloy; a nitride-rich layer over the base layer, the nitride-rich layer comprising aluminum nitride precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; an oxide-rich layer over the nitride-rich layer, the oxide-rich layer comprising aluminum oxide precipitates dispersed in a chromium-molybdenum-aluminum alloy matrix; and a chromia-rich surface oxide layer over the oxide-rich layer, the chromia-rich surface oxide layer comprising chromium oxides and aluminum oxides. Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements. FIG. 1A-1E is a schematic diagram of a mechanism for the formation of an oxidation resistant film on the surface of a CrMoAl alloy. FIG. 1E is an Energy Dispersive X-ray Spectroscopy (EDS) image showing the microstructure of an oxidation resistant film formed on a CrMoAl alloy. FIGS. 2A-2F show images showing the microstructural evolution of the MoCrAl-1 alloy of the Example at different temperature exposures: 1000° C. (FIG. 2A); 1100° C. (FIG. 2B); 1200° C. (FIG. 2C); 1300° C. (FIG. 2D); 1400° C. (FIG. 2E); and 1500° C. (FIG. 2F). FIG. 3 shows the atomic composition (Table left) of the stratified structure formed in the surface of MoCrAl-1 alloy (EDS image, right) of the Example. FIG. 4 is a ternary Cr—Mo—Al phase diagram at 727° C. FIGS. 5A-5B show thermogravimetric analysis curves for Samples 1, 6, and 7 of the Example at 1100° C. FIGS. 6A-6B show thermogravimetric analysis curves for Samples 1, 6, and 7 of the Example at 1300° C. DETAILED DESCRIPTION Ternary chromium-molybdenum-aluminum (CrMoAl) alloys that form oxidation-resistant surface films for high-temperature applications are provided. Also provided are methods for thermally pre-treating the alloys to form the oxidation resistant surface films. The CrMoAl alloys are useful for the fabrication of articles of manufacture that are exposed to high-temperature oxidizing environments during use. As used herein, the p