Micro-compression studies of face-centered cubic and body-centered cubic high-entropy alloys: Size-dependent strength, strain rate sensitivity, and activation volumes

Abstract

High-entropy alloys (HEAs) are evolving multi-component metallic systems, wherein generally five or more principal elements tend to provide strong solid-solution strengthening. In contrast to typical metals and alloys, the deformation mechanisms in HEAs have not been well understood so far. Here, we employ strain rate jump micro-compression testing to study the deformation mechanisms of two face-centered cubic (fcc) (FeCoNiCuPd and CrMnFeCoNi) and two body-centered cubic (bcc) HEAs (VNbMoTaW and NbMoTaW). The size-dependent strength, strain rate sensitivity, and activation volumes of the HEAs are compared with those of pure fcc and bcc metals. Both the fcc and bcc HEA pillars exhibit relatively low size dependence of strength compared to their corresponding pure metals, which can be attributed to the increased lattice distortion. Both the fcc and bcc HEAs exhibit enhanced strain rate sensitivity (SRS) with reducing pillar sizes. The FeCoNiCuPd HEA exhbits slightly lower size depedence of flow stress and a larger activation volume than those of the CrMnFeCoNi HEA (Cantor alloy), which could be associated with the higher dislocation motion resistance by adding palladium atoms with a markedly larger atomic size. The VNbMoTaW HEA also shows slightly lower size depedence of flow stress than that of the NbMoTaW HEA, which could be due to higher Peierls stress by adding the fifth element vanadium. Although there is no significant difference regarding activation volumes between HEAs and their corresponding pure metals, further studies are still needed to give a fundamental understanding of deformation mechanisms in a broad range of HEAs.