Ultra-high-temperature creep behavior of a single-crystal nickel-based superalloy containing 6% Re/5% Ru

Abstract

The creep behavior and influence factors of a nickel-based single-crystal superalloy containing 6% Re/5% Ru (mass fraction) at ultra-high-temperatures were studied through microstructural observations and ultra-high-temperature creep property measurements. The results indicated that the alloy's creep life at 1170 °C/110 MPa was 193 h. During steady-state creep, the alloy's deformation mechanism involved a large number of dislocations sliding in the γ matrix and climbing over the rafted γ' phases. With the increase in the content of refractory elements, the resistance of dislocation movement in the γ matrix increased. In the later stage of ultra-high-temperature creep, the dislocations shearing into the γ' phase could cross-slide from the {111} plane to the {100} plane to generate the Kear–Wilsdorf (K-W) dislocation locks. A greater number of K-W dislocation locks could inhibit the sliding and cross-sliding of dislocations to enhance the alloy resistance, which was one of the reasons for the smaller strain rate and better creep resistance. The larger effective stress in the necking area could initiate the dual-orientation slip of the dislocations, causing the rafted phase to twist. Crack initiation occurred in the kinking area. The initiated crack propagated along the direction perpendicular to the stress axis and expanded until fracture. This process was considered to be the alloy's deformation and damage mechanism during ultra-high-temperature creep. The Ru dissolved in γ' phase could replace Al atoms. The interactions of Ru with Re and W atoms in the high-concentration Re/Ru alloy caused more Re and W atoms to dissolve in the γ' phase, delaying elemental diffusion and depressing dislocation movement. This was the main reason for the retention of more K-W dislocation locks and the good resistance during creep at ultra-high temperatures.