MULTIAXIAL CREEP OF A NICKEL-BASE DIRECTIONALLY SOLIDIFIED ALLOY - ANISOTROPY AND SIMULATION

Combined tension-torsion creep tests of a nickel-base directionally solidified alloy are performed at 850-degrees-C using thin-walled tubular specimens with [001] oriented in the axial direction. Effects of anisotropy are observed conspicuously on the magnitude of creep rate, but not so markedly on the noncoaxiality between creep rate and stress. To discuss this anisotropic feature, the experimental data of minimum creep rate are compared with the crystal creep analyses of a single crystal element and a 2D directionally solidified plate model. It is shown that the experiments are simulated well if we assume simultaneous operation of the {111}[112] octahedral and {100}[110] cubic slip-systems, and that the plate model is successful if it is based on an admissible stress field.