Substructural evolution in a directionally solidified nickel-base superalloy during relaxation fatigue tests at 850 °C

This paper reports new dislocation configurations responsible for cyclic hardening/softening behaviour of a directionally solidified nickel base superalloy after relaxation fatigue tests at 850 °C with hold durations of 1 and 5 min. Dislocation interactions in the gamma (γ)-matrix and the formation of new dislocation configurations during relaxation fatigue (RF) test with 1 min hold duration is responsible for the cyclic hardening behaviour, whereas, the coarsening of gamma prime (γ′)-precipitates are attributed to the cyclic softening behaviour during 5 min hold testing.