Tensile stress relaxation behaviour of Ni-based superalloy single crystals between 973 and 1273 K

Abstract A series of tensile stress relaxation experiments was conducted on flat specimen of superalloy CMSX-2, oriented with 〈100〉 axis, exploring several temperatures and various initial plastic strains for a fixed temperature. The stress relaxation curves can be described through a hyperbolic type law with a non zero asymptotic stress σ ∞ , which proved to be proportional to the initially applied stress σ 0 for a given temperature. Between 973 K (700°C) and 1173 K (900°C), which is the temperature range where the yield stress of the alloy reaches its maximum, the ratio σ t 8 / σ 0 decreases rapidly from from 0.8 to 0.35, and keeps this value up to 1273 K (1000°C). Several kinds of defects have been observed by Transmission Electron Microscopy in the deformed specimens. Some of these defects are similar to those detectable after creep tests and some others are described here for the first time. The microstructural observations and the numerical results of the relaxation experiments are discussed with reference to previous works on the same kind of alloys and to a recent theoretical model proposed by McLean [ Acta metall . 33 , 545 (1985)].