Dissolution behavior and kinetics of the γ′ precipitates within a novel powder metallurgy Ni-based superalloy

Abstract

Isothermal heat treatment experiments were used to studied the dissolution behavior and kinetics of the γ′ precipitates within the hot-extruded novel powder metallurgy Ni-based superalloy A1. The characteristics of the γ′ precipitates were accurately and rapidly extracted by deep learning methods. The JMAK models were established to predict the change of the area fraction of γ′ precipitates during heat treatment. The determination coefficient R2 of model is 0.99. The results indicate that the dissolution sequence, morphological evolution, and dissolution mechanisms of the three types of γ′ precipitates are different. The small-sized tertiary γ′ precipitates (γ′t) dissolve first, while the larger-sized primary γ′ precipitates (γ′p) dissolve last. After 15 min at 1120 °C, there were only a small amount of γ′ precipitates with 0.19 ± 0.03 % area fraction. And there was not significant changed over time. After 1 min at 1150 °C, the γ′ precipitates completely dissolved. During the process of low temperature subsolvus heat treatment (1060 °C, 1090 °C), the large-sized γ′s grown at the expense of consuming the small-sized γ′ precipitates, and the γ′s tend towards directional arrangement due to elastic interaction energy. During the subsolvus heat treatment process, the γ′p spilt due to elastic strain energy and the uneven diffusion of alloying elements, while neck-connected coalescence coarsening occurs due to the overlapping diffusion fields.