Phases, microstructure and mechanical properties of (Ti35Zr40Nb25)100-xAlx (x= 0, 5, 10, 15, 20) high entropy alloys

The refractory high entropy alloys (HEAs) based on refractory elements are developed for potential applications in high temperature areas, since these alloys always have melting temperature higher than 1800 ℃, high temperature structural stability and high resistance to heat softening. However, large density induced lower specific strength and room temperature brittleness hinder their application.In this study, the light-weight non-equimolar (Ti35Zr40Nb25)100-xAlx (x=0, 5, 10, 15, 20) HEAs were designed and fabricated, then the effect of Al content on the phases, microstructure and mechanical properties were investigated. X-ray diffraction results indicate that the phase changes from the disorder BCC to ordered B2 of other alloys with the increase of Al content. Five alloys have similar phase morphology. Lots of long and slender dendrites grow along the cooling direction at the edge of the ingots, while equiaxed dendrites form at the center of the samples. Energy dispersive X-ray analysis imply the enrichment of Nb in dendritic regions, while Al and Zr segregate in the interdendritic regions.This can be attributed to the highest melting temperature of Nb and stronger bonding between Al and Zr. Room temperature tests reveal that the increase of Al content leads to the increase of both the yield stress and compression stress, but has less influence on the room temperature ductility, the fracture strain of all alloys exceeds 50%.