The influence of aluminum content on the microstructure and mechanical properties of TiZrHfNbAlx refractory high entropy alloys

Abstract

The global scientific and engineering communities have continuously pursued novel high-temperature alloys capable of performing under increasingly severe thermal conditions. Refractory high entropy alloys (RHEAs), which consist of elements with high melting points, exhibit outstanding mechanical properties at both ambient and elevated temperatures, making them promising candidates for aerospace applications requiring high-temperature resistance. However, their practical engineering applications are hindered by several limitations, such as relatively high density and limited room-temperature ductility. This study incorporated aluminum into a TiZrHfNb refractory high entropy alloy matrix, fabricating TiZrHfNbAl_x (x = 5, 10, 15, 20 at.%) refractory high entropy alloys via vacuum arc melting. The research systematically examined the microstructural characteristics, mechanical properties at both room and elevated temperatures, and tribological behavior under ambient conditions. Experimental results demonstrate that all the alloys possess a BCC solid solution phase. However, in the Al-20 alloy, an ordered BCC phase (B2) forms due to the limited solubility of aluminum. With increasing Al content, the hardness and room-temperature compressive yield strength of the alloys are enhanced, although the compressive ductility of the Al-20 alloy is somewhat reduced. At 1000 °C, the high-temperature compressive yield strength of the alloys first decreases and subsequently increases with further addition of Al. Under room-temperature friction conditions, all tested alloys undergo both abrasive and oxidative wear, with higher Al content contributing to improved wear resistance.