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

Isothermal heat treatment experiments were used to studied the dissolution behavior and kinetics of the gamma ' precipitates within the hot-extruded novel powder metallurgy Ni-based superalloy A1. The characteristics of the gamma ' precipitates were accurately and rapidly extracted by deep learning methods. The JMAK models were established to predict the change of the area fraction of gamma ' 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 gamma ' precipitates are different. The small-sized tertiary gamma ' precipitates (gamma ' t) dissolve first, while the larger-sized primary gamma ' precipitates (gamma ' p) dissolve last. After 15 min at 1120 degrees C, there were only a small amount of gamma ' precipitates with 0.19 +/- 0.03 % area fraction. And there was not significant changed over time. After 1 min at 1150 degrees C, the gamma ' precipitates completely dissolved. During the process of low temperature subsolvus heat treatment (1060 degrees C, 1090 degrees C), the large-sized gamma ' s grown at the expense of consuming the small-sized gamma ' precipitates, and the gamma ' s tend towards directional arrangement due to elastic interaction energy. During the subsolvus heat treatment process, the gamma ' 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.