Temperature dependence of the plastic flow of high-purity tungsten single crystals

Abstract

AbstractThe influence of temperature on the plastic deformation of high-purity tungsten single crystals with an orientation favouring single slip on the (110) or (112) planes, has been studied using tensile tests in the temperature range 26 K to 800 K with emphasis on temperatures below 400 K. The crystals were deformed with an initial applied plastic strain rate of γa= 8.5 · 10−4s−1either isothermally until fracture or necking terminated the experiment (called isothermal straining tests) or in small straining intervals at different decreasing temperatures (called isothermal-straining – temperature- lowering tests). After initial plastic deformation at high enough temperatures (T ≥ 650 K; γ ≍ 0.08) tests at lower temperatures (T ≤ 400 K) reveal that the workhardening behaviour changes completely if compared with work-hardening behaviour of tests at the lower temperatures. A combination of tests suggests that work hardening of tungsten cannot be interpreted solely in terms of an increase in the athermal component of the flow stress or an exhaustion of non-screw dislocations. Rather, the results suggest that the different mobilities of screw and non-screw dislocations and their dependence on temperature and strain rate contribute essentially to work hardening at the beginning of plastic flow. Additionally, this is strongly influenced by changes of the slip systems towards the low-temperature regime below about 230 K. Consequences of these features for work hardening and its dependence on temperature, flow stress, critical resolved shear stress are analysed and discussed.