Glass-forming ability of Pr-(Cu,Ni)-Al alloys in eutectic system

A eutectic point in Pr-rich Pr-(Cu,Ni)-Al alloys was experimentally determined by measuring the solidus temperature (T_m) and liquidus temperature (T_l). It was found that Pr₆₈(Cu_0.5Ni_0.5)₂₅Al₇ (at.%) is at the eutectic composition in the pseudoternary Pr-(Cu_0.5Ni_0.5)-Al alloys. The alloy Pr₆₈(Cu_0.5Ni_0.5)₂₅Al₇ exhibits better glass-forming ability (GFA) than the ternary eutectic alloy Pr₆₈Cu₂₅Al₇. However, the best GFA was obtained at an off-eutectic composition (Pr₅₄[Cu_0.5Ni_0.5]₃₀Al₆) in the Pr-(Cu_0.5Ni_0.5)-Al alloys, which can be formed in fully amorphous rods with diameter of 1.5 mm by copper mold casting. Moreover, the glass-transition temperature T_g increases quickly (from 367 to 522 K) with the increasing of the Al content (from 3 to 27 at.%). The deviation of the best GFA composition from the eutectic point [Pr₆₈(Cu_0.5Ni_0.5)₂₅Al₇] was explained in terms of the asymmetric coupled eutectic zone, the competition between growth of crystalline phase and formation of amorphous, and the higher glass-transition temperature T_g on the hypereutectic side.