Growth and Thermal Stability of γ/γ'-α Eutectic Composite

Abstract

ABSTRACTThe paper summarizes the results of a series of investigations carried out for a γ/γ'-α(Ni-Al-Mo) eutectic. The subjects include a thermal analysis of the composite growth in a high temperature gradient provided by a fluidized bed cooling, a study of defect formation such as the banding structure at unstable thermal conditions, Tem observation and phase identification for micro-phases existed in an as-growth state as well as phases produced after various quench and aging treatments, and an evaluation of the composite thermal stability in terms of the microstructures and the high temperature strength. The fluidized bed placed beneath a melting furnace was proved to establish a temperature gradient equivalent to the liquid metal cooling, and to promote a stable steady growth of the composites without bandings. Quenching the eutectic above a peritectoid temperature diminished the blocky γ'. The subsequent aging treatments induced small Mo platelets above 830°C and blow the temperature a metastable Ni2Mo particle precipitation in the γ phase causing appreciable composite hardening. The creep rupture strength, however, was reduced by the heat treatment due to δ-NiMo phases precipitated during the test in consumption of the Mo fibers.