Dissolution controlled grain growth in Nickel Alloy UDIMET 720Li

Abstract

The present paper examines the mechanisms for simultaneous manipulation of grain size and γ′ dissolution leading to the microstructure that balance creep and fatigue properties in UDIMET 720Li. For sub (near) solvus heat treatments, grain growth and γ′ dissolution occur simultaneously. Grain size following heat treatment is determined largely by the primary γ′ particle dispersion, via Zener-Smith pinning. Remarkably, grain growth occurs only as a result of precipitate dissolution. The resulting grain size is dictated by a combination of initial particle dispersion in the as-received material and heat treatment temperature. It is likely to hold so long as the initial grain size is close to the Zener-Smith limit and where the kinetics of grain growth and dissolution share similar rates.