INFLUENCE OF TEMPERATURE AND ENVIRONMENT ON CREEP CRACK-GROWTH BEHAVIOR OF ALLOY-800

Creep crack growth (CCG) experiments were performed to ascertain the i nfluence of temperature (973 and 1123 K) and environment (air and vacu um) on CCG behaviour of Alloy 800. The tests were conducted under domi nantly steady state creep conditions. The results indicate that the no nlinear crack tip parameter, energy rate integral C is an appropriate descriptive parameter for the steady state creep crack growth of Allo y 800. Further, the creep crack growth rate (da/dt) vs. C data spanni ng two temperatures and three orders of magnitude of CCG rates in air and vacuum were consolidated within a scatter band, thereby indicating only weak temperature and environment dependence. Stress assisted nit ridation was observed ahead of creep crack in air environment presumab ly due to dynamic rupture of oxide scales. The nitridation in air did not influence the da/dt - C relationship. Further, the crack growth m echanism remained dominantly intergranular in all test conditions inve stigated.