Achieving excellent specific yield strength in non-equiatomic TiNbZrVMo high entropy alloy via metalloid Si doping

In this work, silicide phase was added to the single phase BCC solid solution Ti_1.5NbZrV_0.4Mo_0.6 alloy to improve the mechanical properties. Ti_1.5NbZrV_0.4Mo_0.6Si_x (x = 0-0.9, mole ratio) high entropy alloys (HEAs) was made by vacuum arc melting. The influence of Si on the microstructure, mechanical properties and fracture mechanisms of the alloy were studied. The addition of Si makes lamellar M₅Si₃ silicide phase grow in BCC interdendritic, and the silicides change from lamellar to coarse network. The primary BCC dendrite structure gradually changes to strip and hexagonal silicides. Si element prominently increases the yield strength and decreases the density. When x = 0.9, the alloy has yield strength of 2019.2 MPa, the elongation of 16.5% and the density of 5.91 g·cm^-3, which exhibits a superb specific yield strength (SYS) up to 341.66 MPa·cm³·g^-1. The improvement of mechanical properties is mainly by reason of the silicide phase strengthening. The fracture mechanism changes from quasi cleavage fracture when x = 0.1 to cleavage fracture when x = 0.3-0.7, and then to intergranular fracture when x = 0.9.