Effects of Si additions on microstructures and mechanical properties of VNbTiTaSi_x refractory high-entropy alloys

(VNbTiTa)_100-xSi_x (x = 0, 2.5, 5, 10) refractory high-entropy alloys (RHEAs) are investigated in this paper. The equal molar VNbTiTa RHEA exhibits a room-temperature yield strength of 704 MPa and good compressive ductility (fracture strain> 50%). Si additions can introduce BCC+M₅Si₃ eutectic formed at inter-dendrite areas, and when the Si content reaches 10% in mole, extra bulk M₃Si phase was observed. The precipitated silicides greatly improve the yield strength up to 1671 MPa. As the temperature increases, the strengthening effect of silicide becomes weaker, and almost disappeared at 1200 ℃. Nanoscale silicides can precipitate during high-temperature deformations. (VNbTiTa)_97.5Si_2.5 RHEA possesses an excellent combination of room-temperature ductility 34% and yield strength 505 MPa at 1000 ℃.