Morphology and kinetics evolution of γ′ and γ phases in Ni-xAl-(20‒x)Cr at% alloys

Abstract

The morphology and kinetics evolution of γ′ and γ phases in Ni-xAl-(20‒x)Cr at% (x = 7.5–13.7) alloys aged at 700 °C were studied by utilizing the phase-field simulation. The separated γ′ phases from γ matrix in low Al content (x < 13) alloys transferred to the interconnected morphology with separated γ phases in high Al content (x > 13) alloys, and long-time aging produced near cubic γ′ phase. The coarsening rate of γ′ phase declined firstly when the Al content x = 7.5–9.0, then increased sharply as x ranges from 9 to 12, while the coarsening rate of γ phase declined directly. Additionally, the average edge-to-edge distance of neighboring γ′ phases showed a three-stage variation when Al content x < 9, it decreased to minimum value and increased slowly then decreased again with aging time. In contrast, when 9 ≤ x < 13, the average particle distance of γ′ phase decreased to a nearly constant value. With the coarsening of γ phase, their average particle distance increased. The kinetics evolution was clarified with the combined variations of the particle number density, average particle radius and volume fractions in the continuous composition Ni-xAl-(20‒x)Cr at% alloys.