High Temperature Fatigue Life Analysis of Single Crystal Ni-Base Superalloys Considering γ/γ' Microstructure

Abstract

Strain controlled thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) tests were conducted in a single crystal Ni-based superalloy, CMSX-4, under various test conditions. At first, it was shown ex-perimentally that the superalloy revealed the TMF and LCF lives associated with some unique charac-teristics, which were not always interpreted well, so far as the traditional stress-based and/or strain-based criteria were employed : e.g., Manson-Coffin law and Ostergren method. New micromechanics model is proposed to estimate the TMF and LCF lives taking account of the unique microstructure of superalloys. The proposed method enabled us to estimate some unique characteristics in the TMF and LCF failures of superalloys, although some quantitative hurdles should be overcome further.