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

An oxidation-resistant chromium-molybdenum-aluminum alloy 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.

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)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.