Creep Crack Growth Behavior of Alloy 718 During High Temperature Exposure

摘要

Alloy 718 is a precipitation strengthened nickel-based superalloy based on the precipitation of gamma"-Ni_3Nb (DO_(22) structure) and gamma'-Ni_3(Al,Ti) (Ll_2 structure) phases. Creep crack growth rate (CCGR) was investigated after high temperature exposure at 593, 650 and 677 deg C for 2000h in Alloy 718. In addition to the coalescence of gamma' gamma'" and the amount increasing of 8 phase, the existence of a bcc chromium enriched alpha-Cr phase was observed by SEM, and the weight fraction of alpha-Cr and other phases were determined by chemical phase analysis methods. The CCGR behavior and regulation have been analyzed by means of strength and structure analysis approaches. The experimental results show higher the exposure temperature and longer the exposure time, lower the CCGR. This is probably attributed, to the interaction of material softening and briitling due to complex structure changes during high temperature exposure. Therefore, despite alpha-Cr phase formation and amount enhancement were run in this test range. It seems to us a small amount of alpha-Cr will be not harmfid for creep crack propagation resistance, which is critical for disk application in aircraft and land-based gas turbine.