Corrosion resistant article and methods of making

Abstract

An article and method of forming the article are disclosed. The article has a surface comprising a duplex 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 includes both a ferrite phase and an austenite phase. Further, a concentration of a chi phase or a sigma phase in the duplex 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 duplex nanostructured ferritic alloy at the surface.

1 . An article, comprising:
 a surface comprising a duplex nanostructured ferritic alloy, the 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;   the iron-bearing alloy matrix comprising both a ferrite phase and an austenite phase, wherein
 a concentration of a chi phase or a sigma phase in the duplex nanostructured ferritic alloy is less than about 5 volume percent. 
   
     
     
         2 . The article of  claim 1 , wherein the ferrite phase in the iron-bearing alloy matrix is in a range from about 10 volume percent to about 50 volume percent of the matrix. 
     
     
         3 . The article of  claim 1 , wherein the austenite phase in the iron-bearing alloy matrix is in a range from about 50 volume percent to about 90 volume percent of the matrix. 
     
     
         4 . The article of  claim 1 , wherein a total concentration of the chi phase and the sigma phase is less than about 5 volume percent. 
     
     
         5 . The article of  claim 1 , wherein a concentration of titanium in the duplex nanostructured ferritic alloy surface is in a range from about 0.15 wt % to about 2 wt %. 
     
     
         6 . The article of  claim 1 , wherein the matrix phase comprises chromium in an amount from about 20 weight percent to about 27 weight percent. 
     
     
         7 . The article of  claim 1 , wherein the matrix phase comprises nickel in an amount from about 5 weight percent to about 8 weight percent. 
     
     
         8 . The article of  claim 1 , wherein the matrix phase comprises molybdenum in an amount from about 1 weight percent to about 5 weight percent. 
     
     
         9 . The article of  claim 1 , wherein the matrix phase comprises nitrogen in an amount from about 0.2 weight percent to about 0.3 weight percent. 
     
     
         10 . The article of  claim 1 , wherein the matrix phase comprises tungsten in an amount less than about 1 weight percent. 
     
     
         11 . The article of  claim 1 , wherein the surface is substantially free of chi phase. 
     
     
         12 . The article of  claim 1 , wherein the surface is substantially free of sigma phase. 
     
     
         13 . The article of  claim 1 , wherein the nanofeatures have an average size in a range of from about 1 nanometer to about 50 nanometers. 
     
     
         14 . The article of  claim 1 , wherein the nanofeatures have a number density in a range from about 10 21  to 10 24  per cubic meter of the duplex nano structured ferritic alloy. 
     
     
         15 . The article of  claim 1 , wherein a grain size of the matrix is in a range from about 0.2 micron to about 1 micron. 
     
     
         16 . 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;   cooling the annealed component to form a processed component,   
       wherein the processed component comprises a surface comprising a duplex nanostructured ferritic alloy, the duplex 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; and
 the matrix comprises both a ferrite phase and an austenite phase, 
 
 wherein a concentration of a chi phase or a sigma phase in the duplex 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. 
 
     
     
         17 . The method of  claim 16 , wherein the step of thermomechanically consolidating comprises hot isostatic pressing, extruding, hot forging, cold forging, compacting, or a combination of any of these. 
     
     
         18 . The method of  claim 16 , wherein a concentration of chromium is in a range from about 20 weight percent to about 27 weight percent, a concentration of nickel is in a range from about 5 weight percent to about 8 weight percent, a concentration of molybdenum is in a range from about 1 weight percent to 5 weight percent, a concentration of nitrogen is in a range from about 0.2 weight percent to 0.3 weight percent, a concentration of tungsten is less than 1 weight percent. 
     
     
         19 . The method of  claim 16 , wherein the surface is substantially free of chi phase. 
     
     
         20 . The method of  claim 16 , wherein the surface is substantially free of sigma phase.