Phase stability and compressive properties of low-density (Zr50Ti35Nb15)100-xAlx high entropy alloys

Abstract

In the present study, phase stability and compressive mechanical properties of the (Zr50Ti35Nb15)100-xAlx (x = 0 to 30 at.%) high-entropy alloys were investigated. It was found that the crystalline structure of cast alloys changed from the initial disordered body-centered cubic (BCC) structure to an ordered body-centered cubic (B2) structure as the Al concentration was increased. Their microstructure and phase evolution after long-term annealing up to 1000 h at temperature ranging from 900 °C to 1100 °C were analyzed. Annealing has no obvious influence on the matrix phase of Zr50Ti35Nb15, which keeps BCC structure during all the annealing processes. For the alloys (Zr50Ti35Nb15)80Al20 and (Zr50Ti35Nb15)70Al30 with higher Al content, secondary phase (Al3Zr5) precipitates after annealing at 900 °C. With the increasing annealing temperature to 1000 °C or 1100 °C，there is a tendency that the amount of the Al3Zr5 phase decreases slightly, indicating that Al3Zr5 phase is unstable at high temperature. Accompanied by the phase change, there were also corresponding variations in compressive properties. The secondary phase precipitated in the (Zr50Ti35Nb15)80Al20 and (Zr50Ti35Nb15)70Al30 decreases the compressive plasticity, but has little influence on the yield strength. Meanwhile, the compressive properties of as-cast (Zr50Ti35Nb15)90Al10 and (Zr50Ti35Nb15)85Al15 were also tested to investigate the effect of Al content on the yield strength. Our findings provide a new insight in developing low-density high entropy alloys containing Al.