High-temperature creep behaviour and deformation mechanism of a high-concentration Re/Ru single-crystal nickel-based alloy

Abstract

In this study, the deformation and damage mechanisms of a high-concentration Re/Ru single-crystal nickel-based alloy at ultrahigh temperatures are studied via creep performance tests, microstructural observations and dislocation configuration diffraction contrast analyses at 1170 °C. The results show that the alloy has good mechanical properties. In addition, the creep life is 155 h at 1170 °C and 120 MPa. During creep, dislocations moving in the γ matrix can react with each other to form a dense and complete dislocation network. This dense and complete dislocation network can effectively prevent dislocations from shearing into the γ′ phase and reduce the creep rate during the steady-state creep period. In the late stage of ultrahigh-temperature creep, stacking faults are found in the γ′ phase, indicating that the alloy has a low stacking fault energy and that the stacking faults that form in this alloy can serve as obstacles for dislocation movement. In addition, the dislocations that cut into the γ′ phase in the late stage of ultrahigh temperature creep can cross-slip from the {111} plane to the {100} plane, forming a KW lock, which can inhibit the slip and cross-slip dislocation movement modes. Therefore, the presence of dislocation networks, stacking faults and KW locks in alloys is the main reason for the relatively low strain rate and good creep resistance of these alloys under ultrahigh-temperature creep conditions. In the late stage of creep, the initiated dislocations slip in two orientations, resulting in kinking of the rafted γ′ phase and crack initiation at the top interface of the twisted rafted γ/γ′ two phases. Under the action of shear stress, the crack generates tensile stress perpendicular to the stress axis, and it expands in this direction. This crack is the damage mechanism of the alloy during ultrahigh-temperature creep.

Keywords

• Single-crystal nickel-based alloy
• High-temperature creep
• Stacking fault
• Dislocation network
• Deformation and damage characteristics