Plastic Flow and Microstructure Evolution During Thermomechanical Processing of a PM Nickel-Base Superalloy (Preprint).

摘要

Plastic flow and microstructure evolution during sub- and super- solvus forging and subsequent supersolvus heat treatment of the powder- metallurgy superalloy LSHR (low-solvus, high-refractory) were investigated to develop an understanding of methods that can be used to obtain a moderately- coarse gamma grain size under well-controlled conditions. To this end, isothermal, hot compression tests were conducted over broad ranges of temperature (1144 - 1450K, or 871 - 1177 degrees C) and constant true strain rate (0.0005 - 10 s-1). At low temperatures, deformation was generally characterized by flow-softening and dynamic recrystallization that led to a decrease in grain size. At high subsolvus temperatures and low strain rates, steady-state flow or flow hardening were observed. These latter behaviors were ascribed to superplastic deformation and microstructure evolution characterized by a constant grain size or concomitant dynamic grain growth, respectively. During supersolvus heat treatment following subsolvus deformation, increases in grain size whose magnitude was a function of the prior deformation conditions were noted.