Effect of different heat treatment processes on microstructure and mechanical properties of K4169 superalloy

Abstract

The microstructure and mechanical properties of different heat-treated K4169 alloys after standard heat treatment (SHT), hot isostatic pressing + standard heat treatment (HIP + SHT) and hot isostatic pressing + heat treatment without homogenization (HIP + HTWH) were compared. The feasibility of heat treatment without homogenization of K4169 alloy after HIP was analyzed. A suitable heat treatment system for casting K4169 alloy was proposed. The results on microstructure show that the hot isostatic pressing (1170 °C/140 MP/4 h) can basically eliminate the Laves phase and δ phase of the alloy. Compared with the alloys after HIP + SHT, discontinuous short rod-like δ phase is existed at some grain boundaries of the sample without homogenization heat treatment (HIP + HTWH), which has no substantial influence on the uniformity of microstructure. The results on mechanical properties show that compared with the alloys after SHT, the yield strength at room temperature of alloys after HIP + SHT and HIP + HTWH is increased by 73 MPa and 91 MPa, and the stress-rupture life (704 °C / 448 MPa) is increased by 35% and 32% respectively. Although the dispersion of stress-rupture life and plasticity for alloys after HIP + HTWH are higher than that of HIP + SHT, the mechanical properties meet the requirements of AMS5383 for K4169 alloy. The HIP+HTWH heat treatment process has the practical application potential for K4169 alloy structure by comprehensive analysis of various factors such as reduction of process cost, the increase of production efficiency and the improvement of mechanical properties.