Development of Inelastic Constitutive Equations for Ni-Based Superalloy IN 738 LC. 1st Report, Inelastic Deformation Behavior at High Temperatures and Applicability of Conventional Unified Constitutive Model.

Abstract

A series of deformation tests was conducted on Ni-based superalloy IN 738 LC at 850°C to clarify inelastic behavior of the material. The inelastic behavior was summarized as follows. The material shows time/rate dependent deformation, no cyclic hardening (or softening) behavior and an eminent shift of stress-strain hysteresis loops with cycle for tensile strain-hold waveforms, which are rarely observed on other materials. The conventional unified constitutive equation (Chaboche model) was applied to the test results to check applicability of the constitutive model for IN 738 LC. It was found that Chaboche model was capable of describing the inelastic behavior well except the condition of tensile strainhold waveforms. For tensile strain-hold waveforms, it showed no shift of hysteresis loops with cycle, and the expression capability of stress-strain response was insufficient. Further, the relationship between the shift of hysteresis loops and kinematic rules of a back stress was discussed.