BEHAVIOR OF NICKEL-BASE SUPERALLOY SINGLE-CRYSTALS UNDER THERMAL-MECHANICAL FATIGUE

The thermal-mechanical fatigue behavior of AMI nickel-base superalloy single crystals is studied using a cycle from 600-degrees-C to 1100-de grees-C. It is found to be strongly dependent on crystallographic orie ntation, which leads to different shapes of the stress-strain hysteres is loops. The cyclic stress-strain response is influenced by variation in Young's modulus, flow stress, and cyclic hardening with temperatur e for every crystallographic orientation. The thermal-mechanical fatig ue life is mainly spent in crack growth. Two main crack-initiation mec hanisms occur, depending on the mechanical strain range. Oxidation-ind uced cracking is the dominant damage mechanism in the lifetime of inte rest for turbine blades.