Combined tensile and bending fatigue behavior and failure mechanism of a blade-like specimen at elevated temperature

Abstract

Combined tensile and bending fatigue (CTBF) behavior and failure mechanism of a blade-like specimen, made of a Ni-based alloy DZ125, are experimentally investigated. In order to reveal the geometrical feature and the stress state of the fillet between turbine blade bottom and platform, a blade-like specimen was designed. A novel high temperature experimental methodology was developed to apply the cyclic tensions and high frequency transverse vibration, to the blade-like specimen. CTBF, dwell fatigue (DF) and high stress ratio bending fatigue (BF) tests were performed at 850 °C. Experiment results show that the introduction of high frequency vibration significantly reduced the cyclic life in comparison with DF, while the cyclic tension related dynamic strain aging (DSA) has a positive effect on high cycle fatigue (HCF) life. LCF-related and HCF-related multi-cracks are initiated at the surface due to the effect of bending stress gradient. During CTBF at elevated temperature, LCF, HCF, creep, oxidation, and their interactions contribute to the crack initiation, and linked creep voids, oxidation, and carbide precipitates accelerate the crack growth.