Hot deformation behavior and DRX mechanism in a γ-γ/ cobalt-based superalloy

Abstract

γ-γ/cobalt-based superalloys have been the main focus of attention as a new class of high temperature materials. The present research studies the hot deformation, microstructure evolution, and dynamic recrystallization (DRX) mechanisms of a cast Co–Al–W superalloy during the hot compression process. The microstructure of the starting material is constituted of large MC carbide particles within a coarse grain structure. Two hot deformation regimes, i.e., low temperature (950°C–1050 °C) and high temperature (1100°C–1200 °C) were designed and performed. Flow curve and constitutive analysis using a hyperbolic sine equation evidenced two distinct behaviors among the regimes. Microstructural evaluation revealed a large volume fraction of fine γ/particles with radius less than 100 nm, precipitated during heating and isothermal holding, which precluded DRX in the low temperature regime. In the high temperature regime, new grains were formed through a special discontinuous DRX at three different regions in the microstructure: original grain boundaries, vicinity of MC carbides and the interior of the relatively coarse grains; these may be attributed to the mechanisms of SIBM, PSN and sub-grain growth, respectively. A conceptual descriptive model for the especial DRX phenomenon was proposed.