Influence of Al content on martensitic transformation behavior in Zr50Cu50−xAlx

Influence of Al content on martensitic transformation temperature in ZrCu phase was investigated by differential scanning calorimetry for a series of Zr50Cu50−xAlx alloys. The crystallographic structure of the martensite was predominantly a monoclinic Cm, which is a superstructure of B19′. Microstructural observations revealed that a higher Al content above 6 mol% led to a pronounced formation of Zr2Cu and τ5 phases forming complex eutectic microstructures. The electron probe microanalysis indicated that the Al atoms in ZrCu phase substitute the Cu atoms up to 6 mol% and the excess Al atoms exist mainly in the τ5 phase. The increasing Al content from 0 to 6 mol% induced a decrease in the martensitic transformation start temperature, Ms, from 446 K to 311 K, and in the reverse martensitic transformation start temperature, As, from 537 K to 468 K. But Ms remained almost constant when the Al content is over 6 mol%. Thus, the substitution of the Cu atoms by the Al atoms in ZrCu phase led to the decrease in Ms and As.

► Martensite phase was predominantly superstructure with Cm symmetry.
► Ms and As decreased with the increase of the Al addition up to 6 mol%.
► More Al addition induced the formation of Zr2Cu and τ5 phases.
► The substitution of Cu by Al in ZrCu phase leads to a decrease in Ms and As.