Precipitation behaviour of β and γ ′ in high Al low thermal expansion superalloy

Abstract

The precipitation behaviour of β and γ′ in a low thermal expansion superalloy IN783 was investigated. It was demonstrated that coarse γ′ precipitates do form during β aging at 845°C. During aging at lower temperatures, not only fine γ′ particles are formed, the coarse γ′ particles also change from spherical to cuboidal. Therefore, a bimodal distribution of γ′ is formed in the matrix after standard aging treatment. The formation of β consumes Al atoms, which constrains the formation of coarse γ′ in the zone around β during aging at 845°C. During γ′ aging, a fine γ′ precipitating zone is formed around β. Prolonging the β aging duration markedly promotes the formation of β at grain boundaries and in the matrix, significantly enlarges the fine γ′ precipitating zone and influences the precipitation of coarse γ′.