Coupled size and temperature effects on intermittent plasticity of BCC micro-crystals

The intermittent plasticity of pure Mo microcrystals with diameters from 500 to 3500 nm was studied using micro-pillar compression methodology at temperatures ranging from 25 degrees C to 200 degrees C, in order to explore its dependence on external size and temperature. The technological background is the potential value of BCC metals in the manufacture of high-temperature components in modern fields requiring miniaturization, such as microelectronics. We analyzed plastic fluctuations in terms of wildness, avalanche size distribution, and burst peak velocity. This reveals coupled size and temperature effects on a mild-to-wild transition: the transition temperature decreases with decreasing sample diameter, while the transition diameter increases with rising temperature. In addition, strain-rate sensitivity tests were conducted, implying that mild plasticity is associated to screw dislocation motions controlled by thermally activated nucleation of kink-pairs, whereas wild plasticity is nearly athermal. This experimental observation is interpreted by a damping effect of the thermally activated motion of screw dislocations on the propagation of avalanches. From this, we propose a controlling parameter based on a simple dislocation source model, which unifies the coupled sample size and temperature effects on the mild-to-wild transition, and which could be of practical significance for microscale applications.

Automated summary

The intermittent plasticity of pure Mo microcrystals was studied to explore its dependence on external size and temperature. The study found that there is a coupled size and temperature effect on the mild-to-wild transition in plastic fluctuations. Strain-rate sensitivity tests were conducted, indicating that mild plasticity is associated with screw dislocation motions controlled by thermally activated nucleation of kink-pairs, while wild plasticity is nearly athermal. A controlling parameter based on a simple dislocation source model was proposed to unify the coupled sample size and temperature effects on the mild-to-wild transition, which could have practical significance for microscale applications.