Glass Transition Behavior of an Amorphous Pd₄₈Ni₃₂P₂₀ Alloy Produced by Mechanical Alloying

Abstract

An amorphous Pd₄₈Ni₃₂P₂₀ alloy was formed by mechanical alloying (MA) of the pre-alloyed ingot for the periods longer than about 72 ks (20 h). The amorphous alloy prepared by MA for 1.08 Ms (300 h) translated into a supercooled liquid accompanied by a distinct glass transition (T_g) at 581 K, followed by crystallization at 621 K. In addition, the difference in specific heat between amorphous solid and supercooled liquid and the heat of crystallization (ΔH_x) are 10.5 J/mol·K and 3.90 kJ/mol, respectively. Compared with the data on an amorphous Pd₄₈Ni₃₂P₂₀ prepared by liquid quenching, the onset temperature of structural relaxation decreases accompanied by an increase of the heat of structural relaxation in the low temperature range below 450 K. Furthermore, an endothermic peak combined with an increased temperature dependence of specific heat appears near T_g while there is no distinct difference in T_g and ΔH_x. It is therefore interpreted that the MA-induced amorphous phase has a disordered structure with a more developed short-range ordering and contains a larger milling-induced stored energy as compared with the melt-spun amorphous alloy.