A new interpretation of flow-stress measurements of high-purity NaAl below room temperature

Abstract

Abstract The temperature and strain-rate dependence of the critical resolved shear stress CRSS) of high-purity NiAl single crystals in soft orientation (tensile axis near 〈111〉) was measured in tensile tests with constant strain rate, e.p = 10−4 s−1, between 77 and 325 K. After pre-straining at room temperature, the crystals were plastically deformed by strain increments of Δϵp a 0.005 at successively decreasing temperatures. Below 325 C the CRSS on the {011} slip system slowly increases with decreasing temperature, followed by a steeper increase below about 200 K. The strain-rate sensitivity of the CRSS measured by stress-relaxation experiments exhibits comparable behaviour. The parameters for thermally activated dislocation motion, activation volume and activation energy, suggest that different mechanisms control the dislocation motion above and below 200 K. For low stresses, at temperatures above 200 K, an interpretation of the results within the framework of solid solution hardening theory is su...