Inducing multiple deformation mechanisms to improve the plasticity of refractory high entropy alloys (RHEAs) is crucial for their engineering applications. In this work, the dendrite structure-induced deformation behavior in a series of novel (TiVCr)100-xWx (x = 5, 7.5, 12.5, 15 at.%) RHEAs was investigated. The formation of dendrite structures was confirmed by both theoretical (CALPHAD) and experimental methods, and the relationship between dendrite structure and mechanical properties was established. The findings indicated that the volume of interdendrite was conducive to enhance the fracture strain while the finer dendrite benefited the increase of yield strength. With the change of dendrite structure, the plastic deformation mode of the RHEAs also changed accordingly. The slip bands tended to concentrate in the interdendrite, and propagate along the softer interdendrite regions while being hindered by the harder dendrite. The dendrite refinement strengthening, as well as the solid solution strengthening contributed to the strength enhancement. Overall, the present (TiVCr)100-xWx RHEAs demonstrated high specific yield strength and good plasticity when compared with the similar W-containing HEAs. The present findings not only give more insight into the deformation behavior in RHEAs, but also provide a potential strategy to tune the mechanical properties of RHEAs with dendrite structures.

In this work, novel WNbMoTaVZrx (x = 0.1, 0.25, 0.5, 0.75, 1.0) refractory high entropy alloys (RHEAs) were developed, and the corresponding phase formation, microstructure and mechanical properties were investigated. As compared with the WNbMoTa and WNbMoTaV derivative alloys, the present WNbMoTaVZrx RHEAs demonstrated significantly improved strength and hardness, especially the specific yield strength. The increase of the strength was attributed to the solid solution strengthening effect, resulting from the severe lattice distortion associated with lager-atomic-sized Zr element. With the increase of Zr content, the microstructure changed from grain morphology to dendritic structures. The formation of the second phase with the increase of Zr content was also observed, and its effects on the strengthening, plastic deformation and fracture behaviors were discussed. The deformation-evolution investigations have shown that under applied loadings, microcracks initiated at interdendritic regions with relatively soft second phase. The phase thermostability analysis suggests that the phase structure of typical WNbMoTaVZrx RHEAs could be stable at elevated temperature.

In this work, the relationship between the accumulation and release of elastic energy during the flow serrations of a bulk metallic glass (BMG) was investigated by use of 10 groups of specimens under varying mixed-mode (I/ II) loading conditions. The findings have shown that both the elastic energy accumulation rates and load drops have significant variations, and the load drop data are more scattered than elastic energy accumulation rates. The large variations of load drops are intrinsic for BMGs, while the variations of elastic energy accumulation rates can be reduced to improve/control the plastic deformation of BMGs. Moreover, smaller elastic energy accumulation rates can result in smaller load drops, resulting from the formation of more shear-band intersections. The present work is of significance for understanding the underlying mechanisms of flow serrations of BMGs. It also suggests that more attention could be paid into the elastic energy accumulation process in order to uncover the plastic deformation mechanisms of BMGs.