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

This study considers the thermo-mechanical fatigue behavior of Mar-M247 LC under 0 degrees (in-phase), +180 degrees (out-of-phase), +90 degrees (clockwise diamond) and -90 degrees (counterclockwise diamond) phase shift between mechanical loading and temperature. Tests were carried out under total strain control with a temperature range of 100-850 degrees C and a heating and cooling rate of 5 K/s. Mechanical strain amplitudes were 0.3% to 0.6% with a strain ratio of R-epsilon = -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 approximate to 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. (C) 2015 Elsevier B.V. All rights reserved.