Thermomechanical processing method for achieving coarse grains in a

Abstract

A method is provided for obtaining a uniform grain size on the order of about ASTM 5 or coarser in at least a portion of an article formed from a .gamma.' precipitation strengthened nickel-base superalloy. The method comprises forming an article by: providing a billet, preheating the billet above 2000.degree. F. for at least 0.5 hours, working at least a portion to near-net shape at working conditions including a first strain rate of less than about 0.01 per second and at a subsolvus temperature at or near the recrystallization temperature, supersolvus heating to form a grain size in the portion of at least 5 ASTM, and cooling to reprecipitate .gamma.' within the article. The method can be utilized to form a .gamma.' precipitation strengthened nickel-base superalloy article whose grain size varies uniformly between portions thereof, so as to yield a desirable microstructure and property gradient in the article in accordance with the in-service temperature and stress-state gradient experienced by the article. The method is particularly useful for the making of relatively large components such as turbine disks used in gas turbine engines, which are subjected to stress and temperature conditions that vary radially from the center of the disk to its outer rim.