Thermal-mechanical fatigue behaviour of a new single crystal superalloy: Effects of Si and Re alloying

The thermal-mechanical fatigue (TMF) behaviour of a new single crystal superalloy suitable for power generation applications is considered. Effects of alloying with either Si or Re are elucidated. Out-of-phase TMF is emphasised, although to clarify the effects arising some static creep deformation tests are also carried out. A significant Si-effect is found: a modest addition of 0.25 wt.% Si increases the TMF life by a factor of 2. A greater lower temperature yield stress and thinner slip bands traversing the γ′-phase - with a concomitant greater resistance to recrystallisation and cracking along them - contribute to the enhanced TMF performance promoted by Si alloying. Alloying with Re, whilst improving the creep behaviour more markedly than Si, does not have such a strong effect on TMF life. The results provide insights into the composition/performance relationships relevant to the TMF performance of single crystal superalloys.