Corrosion resistant article and methods of making
An article and method of forming the article are disclosed. The article has a surface comprising a nanostructured ferritic alloy. The surface includes a plurality of nanofeatures that include complex oxides of yttrium and titanium disposed in an iron-bearing alloy matrix. The iron-bearing alloy matrix at the surface includes about 5 weight percent to about 30 weight percent of chromium, and about 0.1 weight percent to about 10 weight percent of molybdenum. Further, a concentration of a chi phase or a sigma phase in the nanostructured ferritic alloy at the surface is less than about 5 volume percent. The method generally includes the steps of milling, thermo-mechanically consolidating, annealing, and then cooling at a rate that hinders the formation of chi and sigma phases in the nanostructured ferritic alloy at the surface.
1. A method, comprising:
milling an iron-bearing alloy powder in the presence of yttrium oxide until the oxide is substantially dissolved into the alloy;
thermo-mechanically consolidating the powder to form a consolidated component;
annealing the consolidated component to form an annealed component; and
cooling the annealed component at a rapid rate to form a processed component,
wherein the processed component comprises a surface comprising a nanostructured ferritic alloy, the nanostructured ferritic alloy comprising a plurality of nanofeatures disposed in an iron-bearing alloy matrix, the plurality of nanofeatures comprising complex oxide particles, wherein the complex oxide particles comprise yttrium and titanium;
wherein the matrix at the surface comprises about 5 weight percent to about 30 weight percent chromium, and about 0.1 weight percent to about 10 weight percent molybdenum;
wherein a concentration of a chi phase or a sigma phase in the nanostructured ferritic alloy at the surface is less than about 5 volume percent; and
wherein the annealing step is performed at a temperature above the solvus temperature of the chi phase and the sigma phase.
2. The method of claim 1 , wherein the step of thermomechanically consolidating comprises hot isostatic pressing, extruding, forging, compacting, or a combination of any of these.
3. The method of claim 1 , wherein the surface is substantially free of chi phase.
4. The method of claim 1 , wherein the surface is substantially free of sigma phase.
5. The method of claim 1 , wherein cooling the annealed component at a rapid rate comprises cooling at a rate rapid enough to inhibit precipitation of chromium or molybdenum-enriched secondary phases.
6. The method of claim 1 , wherein cooling the annealed component at a rapid rate comprises water quenching the annealed component.
7. The method of claim 1 , wherein the matrix comprises molybdenum in an amount from about 3 weight percent to about 10 weight percent.
8. The method of claim 7 , wherein the matrix comprises molybdenum in an amount from about 6 weight percent to about 10 weight percent.
9. The method of claim 1 , wherein the consolidated component comprises sigma phase.