Effect of Al addition on mechanical properties and microstructure of refractory AlxHfNbTaTiZr alloys

• The study developed a series of refractory AlxHfNbTaTiZr HEAs.
• The aim to improve strength, and reduce density of the very ductile base alloy.
• These HEAs mainly consist of a simple BCC solid solution.
• The addition of Al significantly improved the strength characteristics.
• Solution hardening led to a decrease in ductility.

This study developed a series of refractory AlxHfNbTaTiZr high-entropy alloys (HEAs) with an aim to improve strength, and reduce density of the very ductile base alloy HfNbTaTiZr. Despite the diversity of crystal structures among the constituent elements, all the HEAs are single solid solution phase with body-centered cubic (BCC) structure. The addition of Al significantly improves the strength but reduces the ductility due to large solution hardening. The linear relation between yield strength and atomic percentage of Al suggests that the strengthening effect of a certain element in a single-phase HEA alloy can be explained based on quasi-binary alloy concept. Crack formations in deformed AlHfNbTaTiZr alloy with the lowest fracture strain are mainly along the boundaries between dendrite and interdendrite. This agrees with its large deviation of Al content and thus strength between dendrite and interdendrite.