Influence of hot isostatic pressing on the fracture transitions in the fine grain MAR-M247 superalloys

The application of hot isostatic pressing (HIP) on the fine grain MAR-M247 superalloys was investigated for obtaining superior mechanical behaviors. The as-cast samples with grain sizes ranging from 70 to 90 mum were prepared using the fine grain process by varying overheating casting temperatures. Part of test bars was preceded with HIP for comparison. The tensile tests were carried out at elevated temperatures and the fracture morphologies were observed using scanning electron microscopy. The experimental results show that the tensile strengths and elongations of the as-cast fine grain MAR-M247 superalloys are deteriorated due to the presence of microporosity resulting from the liquid metal solidification and contraction. The microporosity can be eliminated by HIP and the tensile strengths and elongations are significantly improved. Nevertheless, the yield strengths of the fine grain MAR-M247 superalloys after HIP decreases because of the formation of coarsened gamma' phase at high temperature and high pressure during HIP. On the other hand, the mechanical behaviors at elevated temperatures are degraded due to the growth of gamma' precipitates around 760degreesC. (C) 2003 Elsevier B.V. All rights reserved.