High temperature Strength. Inelastic Constitutive Equations of Ni-Based Superalloy IN738LC under Anisothermal Cyclic Deformation Conditions.

A series of deformation tests was conducted on Ni-based superalloy IN738LC under isothermal and anisothermal conditions between 450°C and 950°C. Under the isothermal conditions, the material showed no rate/time-dependency below 700°C, while there was distinct rate/time-dependency above 800°C. Anomalous inelastic behavior was observed under the anisothermal conditions; with an increase of cycles, stress at higher temperatures became smaller in absolute value, and stress at lower temperatures became larger. Based on the experimental results, the previously proposed viscoplastic constitutive model for IN738LC at 850°C was extended to the anisothermal conditions. In the constitutive model, evolution of formally incorporated variable Y was assumed to be active under the higher temperatures and negligible under the lower temperatures. The extended constitutive model was applied to the anisothermal cyclic loading as well as monotonic tension, stress relaxation, creep and cyclic loading under the isothermal conditions. It was demonstrated that the present constitutive model was successful in describing the inelastic behavior of the material adequately, including the “anomalous inelastic behavior” observed under the anisothermal conditions.