Microstructure and mechanical properties of refractory HfMo_0.5NbTiV_0.5Si_xhigh-entropy composites

HfMo_0.5NbTiV_0.5Si_x(x = 0, 0.3, 0.5, 0.7) high-entropy alloys are synthesized by induction levitation melting with the aim of achieving a balanced combination of excellent strength at elevated temperature and reasonable ductility at room temperature (RT). The microstructure, phase evolution and compression mechanical properties of the alloys from 20 °C to 1200 °C are reported in this paper. It is found that the HfMo_0.5NbTiV_0.5matrix forms a simple disordered body-centered cubic (BCC) phase. After adding the Si element, multi-component silicide (Hf, Nb, Ti)₅Si₃is generated inside the alloys and exhibits a transition from hypoeutectic structure to eutectic structure and then to hypereutectic structure as the Si content increases. The addition of Si significantly improves the hardness and strength but reduces the ductility. At room temperature, The HfMo_0.5NbTiV_0.5and HfMo_0.5NbTiV_0·5Si_0.7alloys show yield strengths of 1260 MPa and 2134 MPa, respectively, and the compressive mechanism transitions from ductile deformation to brittle fracture from x = 0 to x = 0.7. Strain softening and silicide segmentation are found to be typical during compression deformation of these alloys at elevated temperatures. In these conditions, the alloys survive at least 35% of engineering compression strain without fracture. During deformation at 1200 °C, the yield strengths of HfMo_0.5NbTiV_0.5and HfMo_0.5NbTiV_0·5Si_0.7alloys are 60 MPa and 235 MPa, respectively. The attractive strength of the Si-containing alloys at elevated temperatures is strongly dependent on the strengthening effect caused by the silicides.