Microstructural Development and Coarsening Behavior of γ′ Precipitates in Co–Ni–Al–W-Base ODS Alloys

Abstract

Co–Ni–Al–W-base alloy, strengthened by nanosized oxide and γ′ precipitate is a novel type of high-temperature structural material. The microstructural evolution of the alloys during heat treatment was investigated, and the γ–γ′ misfit and the coarsening kinetics of γ′ precipitate were discussed. The alloys consisted of γ/γ′ two-phase region, discontinuously formed area and several secondary phases (Al_xCo, Co₃W and Co₇W₆). An increase in the solution temperature and Ni contents favored the precipitation of γ′ phase due to the enhanced solid solubility of Al and W in cobalt matrix. The ordered arrangement of near cuboidal γ′ precipitates was observed, and the γ–γ′ misfit was calculated to be 0.57%. The coarsening kinetics of γ′ precipitates conformed to the L-S-W model. The Arrhenius analysis yielded the activation energy of 188 KJ·mol⁻¹.