Unveiling microstructure evolution and mechanical properties of silicide-strengthened (TiZrHfNb)100-xSix (x = 0, 1, 5, 7, 10 and 15) refractory high-entropy alloys

The ductile TiZrHfNb refractory high-entropy alloy is selected to form silicide-strengthened (TiZrHfNb)_100-xSi_x (x = 0, 1, 5, 7, 10 and 15, in at. %) alloys, and the influence of Si content on the microstructure and mechanical properties was systematically investigated. The solidification microstructure and the type of silicide show strong dependence on Si content from 1 % to 15 %, with the former changing from hypoeutectic to hypereutectic structure, and the latter evolving from M₃Si-type to tetragonal-M₅Si₃-type silicide, and finally to the co-existence of both tetragonal- and hexagonal- M₅Si₃-type silicide. The formation of silicide phase enhances the strength both at the ambient and elevated temperatures, and a significant improvement of peak compressive strength from 221.3 MPa to 511.59 MPa at 800℃ was obtained after alloying 15 % Si to the prototype TiZrHfNb alloy. It was found that heterodeformation-induced strengthening, resulting from dislocation pile-ups at phase boundaries, was responsible for the enhancement in the strength. During hot deformation, the flow stress begins to decrease after reaching the peak value due to the presence of the dynamic recovery and dynamic recrystallization, which becomes more pronounced at higher Si content.