The dependence of stress and strain rate on the deformation behavior of a Ni‐based single crystal superalloy at 1050°C

Abstract

AbstractNi‐based single crystal (SX) superalloys are important high‐temperature materials used for manufacturing turbine blades in aero‐engines. During service under combinational impacts of temperature and stress, the SX superalloy may reach its life due to plastic deformation, which normally accompanies time‐dependent microstructural degradation. To reveal this dynamically mechanical response, tensile tests at 1050°C are carried out to record stress‐strain curves at five stain rates as well as creep curves at four applied stresses. Deformed microstructures and defects have been analyzed to understand mechanical behaviors and the underlying mechanism by using advanced scanning electron and scanning transmission electron microscopes. Results show that the deformation mode of the alloy strongly depends on the strain rates/applied stresses under mechanical loading. The dislocation density inside the γ phase is extremely low at all tests, indicating that the γ phase is relatively weak and ready to flow at this temperature even at a very fast strain rate. The deformation behavior of the γ′ phase is much complicated. At fast strain rates or high applied stresses, the dislocation density in the γ′ phase is very high, contributing to high‐stress requirements to deform the material. At slow strain rates or low applied stresses, rafting microstructures develop and the deformation mode becomes directional coarsening/diffusion‐dominated. Our results demonstrate a comprehensive understanding of the deformation mechanism of Ni‐based SX superalloys, which may provide lifetime prediction of the mechanical failure, as well as the database for superalloy applications in mechanical systems.