WEB Understanding the plasticity of refractory high entropy alloys using nanoindentation
Refractory high-entropy alloys (HEA) with single-phase body-centered cubic (bcc) structure, such as the NbMoCrTiAl system and TaNbHfZrTi, are promising candidates for high-temperature applications. NbMoCrTiAl, like other refractory HEAs, are typically brittle at ambient temperature and fail in a catastrophic manner during conventional mechanical testing. However, TaNbHfZrTi shows ductility up to 40% strain. There is limited research to understand the difference in these deformation behaviors and mechanisms. In this study, to understand the mechanical behavior of the bcc refractory HEAs in terms of dislocation nucleation and motion, different nanoindentation methods were used.
The comparison of dislocation nucleation of the different alloys was made based on a statistical analysis of the pop-in phenomena, which yielded the activation volume for dislocation nucleation. Considering the bcc structure of the alloys, the nucleation is expected to be heterogeneous and may be aided by atom-vacancy exchange. The activation volume for dislocation motion was determined from the indentation strain rate jump test. There are clear differences in the behaviors of the two alloys studied, which will be discussed with regard to our current understanding of bcc metals and alloys.
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