Constitutive Relation of Nickel-Base Single Crystal and Directionally Solidified Superalloys under Multiaxial Cyclic Loading

This paper studies yield surface and stress amplitude ellipse for Nickel-base single crystal (SC) superalloy CMSX-2 and directionally solidified (DS) superalloy Mar-M247LC under multiaxial cyclic loadings. Mises' strain controlled tension/torsion cyclic loading tests were carried out at 1173K in air and the stress-strain relations were obtained experimentally. The inelastic constitutive equation based on slip theory, taking account of {111} ‹110› octahedral and {100} ‹110› cube slip systems, was developed. The yield surface and stress amplitude ellipse obtained from the slip theory were compared with the experimental results. The theory well explained the plastic deformation behavior for SC and DS superalloys, where somewhat different plastic deformation behavior was found between the two superalloys, caused by the different contribution of the two slip systems. Coaxiality between the Mises' stress and strain was extensively discussed based on the slip theory.