Effect of Re on Long-Term Creep Behavior of Nickel-Based Single-Crystal Superalloys for Industrial Gas Turbine Applications

Understanding the long-term creep behavior (creep lives longer than 5,000 h) of nickel-based single-crystal (SX) superalloys is of great interest for the service safety of industrial gas turbine (IGT) blades. However, understanding the influence of various factors on long-term creep behavior of nickel-based SX superalloys has always been a challenge. In this study, the creep behavior of nickel-based SX superalloys with or without 2 wt.% Re addition were investigated at 900 degrees C and 200 MPa. Microstructural characterization was systematically conducted to elucidate the microstructural evolution of the experimental alloys after creep rupture tests. The results indicated that the creep lifetime was increased significantly by 2 wt.% Re addition, which dramatically reduced the creep strain rate and caused the lattice misfit of gamma/gamma' phases to inverse from positive to negative, leading to N-type rafting exhibiting a stronger barrier to dislocations during creep. The evolution of lattice misfit of the gamma/gamma' phases was closely associated with the elemental partitioning behavior between the gamma/gamma' phases, which was determined as a consequence of "time accumulation effect" and corresponding elemental diffusion special for prolonged time. This study provides a new insight in the effect of Re on the long-term creep life and microstructure evolution of nickel-based SX superalloys. Such knowledge will be helpful to provide the guideline of superalloys design for large-scale IGT blades.