Damage Tolerance of Alloy 718 Turbine Disc Material

Abstract

The influence of a modified heat treatment (MHT) and the standard heat treatment (SHT) on the microstructure and mechanical properties of Alloy 7 18 turbine disc material has been studied over a range of temperatures varying between room temperature and 650C. The influence of these heat treatments has been studied on creep, low cycle fatigue (LCF), and fatigue crack growth rate (FCGR) properties. Test results have shown that the MHT improves the creep rupture life at 650C but results in a loss of LCF crack initiation life at room temperature and 525C. The FCGRs of MHT and SHT materials are very similar at room temperature but the MHT improves the FCGR's of Alloy 718 at 525C and 650C over a wide range of U values. The MHT material is cyclically more stable than the SHT material at all test temperatures. The notch sensitivity of Alloy 718 is also discussed.