Peculiarities of work hardening of high-purity tungsten single crystals below 800 K

摘要

The work-hardening behaviour of high-purity tungsten single crystals was studied below and above a transition temperature T_t, which is about 0.1-0.2 of the melting temperature and is known to subdivide temperature regimes with different work-hardening behaviour. Tensile tests were performed below 800 K with specimens oriented for single slip applying the following procedures of incremental straining tests: (ⅰ) pre-straining below, re-straining above and below T_t, (ⅱ) pre-straining above and re-straining below T_t, and (ⅲ) pre-straining above T_t and re-straining below, above, and below T_t. The results show that a flow-stress increase due to work hardening induced either below or above T_t is not preserved if subsequent straining takes place at higher ( > T_t) or lower ( < T_t) temperatures, respectively. These phenomena clearly indicate that work hardening below and above T_t must originate from different work-hardening modes and are interpreted in terms of the low mobility of screw dislocations below T_t and nearly equal mobilities of screw and edge dislocations above T_t in body-centred cubic metals.