Influence of phase angle on lifetime, cyclic deformation and damage behavior of Mar-M247 LC under thermo-mechanical fatigue

Abstract

This study considers the thermo-mechanical fatigue behavior of Mar-M247 LC under 0° (in-phase), +180° (out-of-phase), +90° (clockwise diamond) and −90° (counterclockwise diamond) phase shift between mechanical loading and temperature. Tests were carried out under total strain control with a temperature range of 100–850°C and a heating and cooling rate of 5K/s. Mechanical strain amplitudes were 0.3% to 0.6% with a strain ratio of Rε=−1. Results show that for the strain amplitudes tested, lifetime depends significantly on the phase angle. For a given strain amplitude, lifetime increases in the sequence: in-phase<out-of-phase<clockwise diamond≈counterclockwise diamond. Metallographic examination indicates that life reducing damage mechanisms are intergranular creep damage under in-phase loading and accelerated crack propagation at high tensile stress under out-of-phase loading. For both diamond phase loadings pure fatigue damage seems to be dominant. Based on the observed damage mechanisms, the lifetime behavior is discussed.