Multiaxial creep damage constitutive relationship for nickel-base single crystal superalloys based on the microstructural assessment and application

Full text: A multiaxial creep damage constitutive relationship has been presented for nickel-base single crystal superalloys, which takes the microstructural assessment into consideration. It consists of three parts. In the first part, based on the relief of interfacial energy density by dislocation generation at the gamma prime γ' interfaces, a rafting prediction criterion has been developed for nickel-base single crystals under multiaxial stresses. The diagrams of rafting have been presented, and confirmed by experimental results. The rafting processes have been analyzed quantitatively by the relief of interfacial energy. The criterion has been related to study the creep life behavior. The example of creep life analysis shows that the criterion can be correlated satisfactorily to the crystallographic orientation dependence of creep behavior. In the second part, based on the microstructural assessment, a two-state-variable crystallographic creep damage constitutive equation has been presented. The constitutive equation takes into consideration of the rafting-derafting and the damage of the voids simultaneously. With the uniaxial creep experimental data, the constitutive equation can model the creep damage of nickel-base single crystal superalloys, especially the dependence of the creep behavior on the crystallographic orientation. The third part is applications of the constitutive equation. The constitutive equation has been implemented as a user subroutine umat into ABAQUS. The creep experiments of double shear specimens have been carried out to validate the constitutive equation. There is a good agreement between the finite element analytical results and experiment results. The distributions of damage in the double shear creep specimens are given out. (author)