High-temperature fatigue-resistant nickel based superalloy and thermomechanical process

A method of preparing an article from a compact of a powdered nickel base superalloy having a gamma prime strengthening precipitate to increase the resistance to fatigue cracking in the article, comprising:

• forming the compact from the powdered superalloy composition consisting essentially of, by weight percent, about 10 to 12 percent chromium, about 17 to 19 percent cobalt, about 1.5 to 3.5 percent molybdenum, about 4.5 to 6.5 percent tungsten, about 3.25 to 4.25 percent aluminum, about 3.25 to 4.25 percent titanium, about 2.5 to 3.5 percent tantalum, about 0.05 zirconium, about 0.05 carbon, about 0.02 boron, and balance essentially nickel;
• isothermally forging the compact at a rate of straining and within a range of temperatures shown by the hatched area in FIG. 2, to produce a permanent deformation of at least about 20 percent;
• supersolvus annealing the forged compact at a temperature above about 1190.degree. C. but below the incipient melting temperature of the alloy, for a period of time that essentially completely dissolves the gamma prime precipitate;
• and
• slowly cooling the alloy from the supersolvus temperature.

A method for increasing the resistance to fatigue cracking in articles manufactured from a compact of nickel based superalloy powders having a nickel base superalloy matrix and a gamma prime strengthening precipitate, comprising:

• forming the compact from the powdered superalloy composition consisting essentially of, in weight percent, about 10 to 12 percent chromium, about 17 to 19 percent cobalt, about 1.5 to 3.5 percent molybdenum, about 4.5 to 6.5 percent tungsten, about 3.25 to 4.25 percent aluminum, about 3.25 to 4.25 percent titanium, about 2.5 to 3.5 percent tantalum, about 0.05 zirconium, about 0.05 carbon, about 0.02 boron, and balance essentially nickel;
• isothermally forging the compact at a temperature between about 1070.degree. to 1180.degree. C. to produce a permanent deformation of at least about 20 percent, the forging being performed at a strain rate that maintains a fine grain size allowing superplastic forming during forging and introduces sufficient deformation in the grains to cause grain growth to about 50 to 60 microns during a subsequent supersolvus anneal;
• supersolvus annealing the forged superalloy at a temperature above about 1190.degree. C. for a period of time that essentially completely dissolves the gamma prime precipitate;
• and
• slowly cooling the alloy from the supersolvus temperature.