HIGH TEMPERATURE FATIGUE‐CREEP BEHAVIOUR OF SINGLE CRYSTAL SRR90 NICKEL BASE SUPERALLOYS: PART 1—CYCLIC MECHANICAL RESPONSE

Abstract—High temperature low cycle fatigue tests, with and without strain dwells, were conducted at 750°C, 950°C and 1050°C, on single crystal SRR99 nickel base superalloy, with different crystal orientations. At 750°C, SSR99 exhibited cyclic stability regardless of cycle type. The presence of strain dwells caused cyclic softening at 950°C compared with continuous cycling tests. At 1050°C, cyclic softening was observed for all the tests. The introduction of strain dwells produced significant stress relaxation at 950°C and 1050°C, but not at 750°C for the strain ranges in this study. Significant mean stress was observed at the three temperatures for tests with tensile or compressive strain dwells. The crystal orientation was found to have a dominating influence on the cyclic stress strain relationship and stress relaxation response. A simple approach is developed to correlate the effect of orientation on the cyclic mechanical response.