Lifetime, Cyclic Deformation and Damage Behaviour of MAR-M247 LC under Thermo-Mechanical Fatigue Loading with 0°, 180°, -90° and +90° Phase Shift between Strain and Temperature

Thermo-mechanical fatigue tests under 0° (in-phase), +180° (out-of-phase), +90° (clockwise diamond) and -90° (counterclockwise diamond) phase shift between mechanical loading and temperature were conducted on nickel-based superalloy Mar-M247 LC. Tests were carried out under total strain control with a temperature range of 100 – 850 °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 Rɛ = -1. Results show, that for the strain amplitudes tested, lifetime varies significantly with strain-temperature phase. In-phase loading gives the shortest lives followed by out-of-phase and the diamond-phase loadings which show comparable lifetimes. Metallographic examination indicates that the dominant damage mechanisms are creep damage at higher temperatures and early cracking of oxide layers at lower temperatures. Both mechanisms occur primarily under tensile stress. Hence, the portion of each mechanism varies with the phase angle.