A Unified Anisotropic Constitutive Model for a Ni Base Directionally Solidified Superalloy

Abstract

Macroscopic deformation behavior of a Ni base directionally solidified (DS) superalloy was experimentally investigated and an anisotropic constitutive model for the material was developed. Monotonic and creep tests were performed on uniaxial test specimens machined from DS plates so that the angles between loading direction and the solidified grain direction varied between 0 to 90 degrees. Tension-torsion creep tests were also conducted to examine the anisotropic behavior under multiaxial stress conditions. The material exhibited remarkable anisotropy under elastic and viscous deformation conditions, while it showed isotropy under plastic deformation conditions of high strain rates. Then crystal plasticity analyses were carried out to identify slip systems under creep loading conditions and presume the anisotropic creep behavior of the DS material analytically. A unified constitutive model was proposed to express both the anisotropic elasticity-viscosity and the isotropic plasticity. The elastic constants were determined applying a self-consistent approach to the material, and viscous parameters were modeled on the basis of the crystal plasticity analyses. Calculation results obtained using the constitutive model were compared to the experimental data to evaluate validity of the model. It was demonstrated that the constitutive model could adequately describe the anisotropic behavior under uniaxial and multiaxial stress conditions with a set of material parameters.