Lifetime, cyclic deformation and damage behaviour of MAR-M-247 CC Under in-Phase, out-of-Phase and phase-Shift TMF-Loadings

Abstract

Abstract In-Phase-, Out-of-Phase- and Phase-shift-TMF tests were carried out on MAR-M-247 CC. A minimum temperature of 400°C, maximum temperatures from 800°C up to 1050°C, total mechanical strain amplitudes between 70% and 100% of the thermal strain amplitude and dwell times at maximum temperature from 0s up to 1800s were applied. Out-of-Phase-TMF leads to higher tensile mean stresses than Phase-Shift-TMF. In-Phase-TMF loadings induce compressive mean stresses. The amounts of the mean stress, the stress amplitude and the plastic strain amplitude generally increase with increasing maximum temperature and dwell time. Out-of-Phase- and Phase-Shift-TMF lead to higher numbers of cycles to failure than In-Phase-TMF. Under Out-of-Phase-TMF a transgranular fracture path is observed even at high maximum temperatures and dwell times. This loading condition leads to compressive stresses at high temperatures and tensile stresses at lower temperatures. Due to that, intergranular creep damage is suppressed. Under In-Phase-TMF the tensile stresses occurring at high temperatures lead to creep induced intergranular crack propagation even at loadings with a dwell time of zero and relatively low maximum temperatures. Under Phase-Shift-TMF loadings transgranular crack propagation occurs at low maximum temperatures, whereas higher maximum temperatures and dwell times lead to intergranular damage. Because the damage mechanisms depend on the phase relationship and the dwell time, the damage parameter POST which accounts for the plastic strain amplitude and the maximum stress as damage relevant quantities is not able to give a common description of the lifetime behaviour for all considered TMF cycle types.