Influence of Element Re on Creep Behavior of Single Crystal Nickel-Based Superalloys at Intermediate Temperature

Abstract

AbstractBy means of creep curves measurement and microstructure observation, an investigation has been made into the influence of the element Re on creep behaviors of single crystal nickel-base superalloy at intermediate temperature. Results show that, after fully heat treated, microstructure of the alloy consists of the cubic γ′ phase embedded coherent in the γ matrix. Comparing with Re-free superalloy, 4.5% Re alloy displays a better creep resistance and longer creep rupture life in the ranges of the applied stresses and temperatures. After crept for 425 h up to fracture at 760 °C/800 MPa, the γ′ phase in the alloy keeps still the regular cubical configuration, which is attributed to the effect of the element Re decreasing the diffusing rate of other elements during creep. The deformation features of the alloy during creep are that the dislocations move in the γ matrix channels and shear into the γ′ phase, the 〈110〉 super-dislocation shearing into the γ′ phase may be decomposed to form the configuration of (1/3)〈112〉 super-Shockleys partials plus the stacking fault, which may hinder dislocations movement and restrain the cross-slipping of dislocations. This is thought to be the main reason of the alloy having a better creep resistance. In the latter stage of creep, the crack is firstly initiated in the interface of γ′/γ phases and propagated along the interface vertical to the stress axis up to the occurrence of the creep fracture, which is thought to be the fracture mechanism of the alloy during creep.