Microstructure and mechanical properties of Si micro-alloyed (Ti28Zr40Al20Nb12)100-xSix (x=0, 0.1, 0.2, 0.5) high entropy alloys

The effect of Si micro-alloying on the microstructure and mechanical properties of (Ti28Zr40Al20Nb12)100-xSix (x = 0, 0.1, 0.2, 0.5) high entropy alloys are studied. Coarse grains mainly composed of two ordered B2 phases are obtained during solidification, while the hcp-Zr5Al3 type precipitate formed after annealing at 1200 degrees C for 24h. As the Si content increases, the phase morphology at the grain boundaries gradually changes from a completely continuous structure to a partially continuous structure, and finally transfers to a necklace-type structure. The phase morphology inside the grains simultaneously transforms into merely randomly distributed particles. The changes in phase morphology are attributed to the stronger chemical affinity between Zr and Si. Owing to the severe inhomogeneity caused by the Si addition, a dramatic decrease of the fracture strain is observed in compression tests for as-cast samples. For Si micro-alloyed alloys, the annealed samples show an improvement of both compression strength and fracture strain. The obtained results suggest that Si micro-alloying has less impact on phase composition, but significantly affects elemental segregation, phase morphology and thus the me-chanical properties.