HIGH TEMPERATURE FATIGUE‐CREEP BEHAVIOUR OF SINGLE CRYSTAL SRR99 NICKEL BASE SUPERALLOYS: PART II—FATIGUE‐CREEP LIFE BEHAVIOUR

Abstract—Experimental and theoretical investigations on the influence of temperature, strain dwells and crystal orientation on the high temperature fatigue‐creep life behaviour of single crystal SRR99 nickel base superalloy were performed. For a given temperature and loading condition, the longest fatigue life was observed for tests with [001] orientations, while the [111] orientation yielded the shortest fatigue life. A simple approach, using an orientation function f ( A hkI ), was applied successfully to correlate the influence of orientation. Using this function, the shortest fatigue life was observed for tests with a compressive dwell at 750°C, but at 1050°C tests with a tensile dwell exhibited the shortest life. Compared with continuous cycling tests, tests with tensile dwells showed remarkably longer lives at 750°C, significantly shorter lives at 1050°C, and almost identical lives at 950°C; tests with compressive dwells always exhibited shorter lives than continuous cycling tests at all temperatures. The influence of strain dwells on the life of SRR99 was via the simultaneous effects of mean stress, additional inelastic strain, and time dependent damage. A mean stress modified strain range partitioning method was proposed and used to predict the fatigue‐creep life.