δ and austenite phases evolution and model in solution treatment of superalloy GH4169

The δ phase evolution and its effect on the austenite grain growth in the solution treatment of superalloy GH4169 were investigated at the solution temperatures of 1233, 1253, 1273 and 1293 K and the holding time of 30, 45 and 60 min. The δ phase is dissolved and transformed from short bars to fine bars or particles gradually with the increasing solution temperature. The holding time affects the morphology and the amount of δ phase slightly. The austenite grain grows with the increasing solution temperature and holding time. It grows slowly at the solution temperatures ranging from 1233 to 1373 K, but sharply from 1273 to 1293 K. The phenomenon suggests that the d phase generates a pinning effect on the austenite grain growth. The kinetic analysis about the austenite grain growth was carried out at the solution temperatures ranging from 1233 to 1373 K. The grain growth exponent n value is calculated to be 1·2 which confirms the pinning effect of δ phase on the austenite grain growth, and activation energy Q value is calculated to be 394·1 kJ mol^-1. Finally, a model with an average difference 9·22% for the austenite grain growth was proposed.