Method for minimizing nonuniform nucleation and supersolvus grain growth in a nickel-base superalloy

摘要

A method is provided for obtaining uniform grain growth within &ggr; ' precipitation strengthened nickel-base superalloys. The method includes forming a billet having a very fine grain size in order to achieve optimum superplasticity of the superalloy during forging. The article is then heated to a pre-working hold temperature in a manner which prevents coarsening of the microstructure and a loss of superplasticity. The article is then worked, such as by forging, at a temperature below the . gamma.' solvus temperature of the alloy, so as to maintain local strain rates within the article below a critical strain rate for random grain growth, and so as to maintain the strain rate gradient throughout the article below a critical upper limit. After working, the article is subjected to annealing at a temperature which is less than the &ggr;' solvus temperature of the alloy, and for a duration which is sufficient to remove accumulated metallurgical strain in the article. A supersolvus heat treatment is then performed by further heating the article to a temperature above the &Ggr;' solvus temperature of the superalloy for a duration sufficient to uniformly coarsen the grains of the article.