EFFECTS OF STRAIN RATIO ON THERMAL-MECHANICAL CYCLIC STRESS-STRAIN RESPONSE AND FATIGUE LIFE IN DS SUPERALLOY DZ125

The effects of strain ratio on thermal-mechanical cyclic stress-strain response and fatigue life in DS superalloy DZ125 have been studied by performing tests at various strain ratio experiments, under strain-controlled and temperature cycling from 550to 1000 C. It is shown that thermal-mechanical cyclic stress-strain response behavior not only depend on magnitude of strain, and temperature-loading phase angle, but also strain ratio. Fatigue life at strain ratio Re=-0.3 is longer than that of strain ratio Rε=-1. 0, under in-phase thermal-mechanical loading. However, Fatigue life at strain ratio Rε=-0. 3 is shorter than that of strain ratio Rε=-1.0, under out-of-phase thermal-mechanical loading. The thermal-mechanical fatigue (TMF) damage model was discussed. Results of fractography show that fatigue, creep and oxidation damage always occur during TMF. The main damage mode depends on loading wave, strain ratio and magnitude of strain.