Improvement in the microstructure and tensile properties of inconel 718 superalloy by HIP treatment

Abstract

Hot Isostatic Pressing (HIP) is a process that uniquely combines higher pressure and temperature to produce materials and parts with substantially better properties than those by other methods. The aim of this paper is to discuss the methods and to find a suitable process of HIP for Inconel 718 superalloy. In this study, the HIP process parameters considered were; temperatures: 1423, 1448, 1453 and 1478 K, pressures: 100, 150, 175 and 200 MPa, and soaking times of 2, 3 and 4 hours. The Inconel 718 superalloy is used throughout this study. To evaluate the effects of microstructure and tensile properties of 718 alloy by HIP process, tensile test at two different strain rates at room and high temperature were evaluated. The microstructure, TEM and XRD inspections were performed. The experiment results show that at 1453 K, 175 MPa, 4 hours of HIP treatment for Inconel 718 superalloy was optimal. It can improve the microstructure and tensile properties of 718 castings. Through the optimal HIP treatment, the grain sizes are uniform and the segregated structure is improved. At fast strain rate (0.001 s-1), it increased the tensile strength by 31% at 298 K, 27% at 813 K, and 24% at 923 K. The 0.2% yield strength increased 40% at 298 K, 31% at 813 K, and 28% at 923 K. Meanwhile the elongation increased 100% at 298 K, 130% at 813 K, and 60% at 923 K after tension tests. When the strain rate was very slowly (0.0001 s-1), it also increased the tensile strength by 24% at 298 K and 20% at 813 K. The 0.2% yield strength increased 29% at 298 K and 27% at 813 K. The elongation increased 54% at 298 K and 282% at 813 K. ©2006 The Japan Institute of Metals.