Composition distribution and kinetics evolution of γ′ phase in Ni-(17−x) Al-x Mo (at.%) alloys

Abstract

Molybdenum plays a role in solid solution strengthening in Ni-based superalloys by sitting in the sublattice of L12 structure γ′-Ni3(Al,Mo) precipitates and dissolving in γ matrix. By coupling the sublattice free energy with a phase-field model, the precipitation kinetics and composition distribution of the γ′ phase in the Ni-x Al-(17−x) Mo (at.%) alloys were investigated, and the influences of Mo on the precipitation and growth of the γ′ phases was revealed by the element diffusion potential. Mo gathers firstly inside of γ′ phase at nucleation and growth stage, then Mo diffuses into the γ matrix and accumulates around the γ′ phase, for the slower diffusion of Mo than that of Al. This inequality diffusion supports Mo to hinder the element diffusion between the γ/γ′ phases and reduces the interconnection and the coarsening rate of γ′ phase. As the Mo content increases from 2 at.% to 4 at.%, the diffusion potential of Al and Mo in γ′ phases raises and the coarsening rate of γ′ phase decreases.

Keywords

• Ni–Al–Mo
• Composition distribution
• Precipitation
• Diffusion potential