Abstract
Body-centered cubic metals like molybdenum and tungsten are interesting structural materials for high-temperature applications. These metals, are however, brittle at low homologous temperature, caused by the limited mobility of screw dislocations. In this study, the thermally activated deformation mechanisms in bcc Mo have been investigated using strain rate jump nanoindentation and compression tests as well as Charpy V-notch impact testing. The material shows a significant softening with increasing temperature and a maximum in strain rate sensitivity is found at the critical temperature, before decreasing again in the ductile regime. The activation volume, however, showed a distinct increase from about 5 b3 at the onset of the brittle to ductile transition temperature. Here we propose to use temperature-dependent nanoindentation strain rate jump testing and the activation volume as a complementary approach to provide some indication of the brittle to ductile transition temperature of bcc metals.Graphic
Highlights
Body-centered cubic, refractory metals like molybdenum or tungsten are interesting candidates for structural applications due to their high strength at elevated temperatures
This well-studied behavior is caused by the crystal lattice and the activated slip systems: In the low-temperature regime, the plastic deformation of bcc metals is mainly governed by the slip of a 2 screw dislocations on {110} planes, whereas at high temperatures, additional {112} and {123} slip planes are activated [1,2,3,4]
The active deformation mechanisms in bcc Mo have been investigated using different mechanical testing approaches and following conclusions could be drawn: 1. The absolute value of strain rate sensitivity parameter (m) for bcc metals is dependent on the net flow stress
Summary
Body-centered cubic (bcc), refractory metals like molybdenum or tungsten are interesting candidates for structural applications due to their high strength at elevated temperatures. The temperature at which the brittle to ductile transition (BDT) takes places is referred as the brittle to ductile transition temperature (BDTT) This well-studied behavior is caused by the crystal lattice and the activated slip systems: In the low-temperature regime, the plastic deformation of bcc metals is mainly governed by the slip of a 2 screw dislocations on {110} planes, whereas at high temperatures, additional {112} and {123} slip planes are activated [1,2,3,4]. The Peierls potential or the Peierls–Nabarro barrier will increase, resulting in a higher resistance of motion of the screw dislocations The strength of this barrier is reduced by thermal activation and the formation of kinks in the dislocation line. Extrinsic effects like impurity atoms can constrain the kink mobility [3]
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