Theoretical prediction and experimental evaluation of glass forming ability, density and equilibrium point of Ta based bulk metallic glass alloys

Abstract

The present investigation aims at evaluating the Glass Forming Ability (GFA), density (ρ) and equilibrium melting point (T0) of Ta(W/Hf)-Ni-B based bulk metallic glass (BMG) alloy system. Initially, the theoretical GFA, based on thermodynamic parameters PHSS, ρth, based on rule of mixture of volume and T0th, using Thermo-cal software for all alloy systems have been calculated and then mapped in Ta-Ni-B, Ta(W)-Ni-B and Ta(Hf)-Ni-B diagrams respectively. Maps for individual alloy system were then superimposed based on high GFA (< −5 kJ/mol), high density (>13 g/cc) and low melting point (<1400 °C). A series of compositions of ternary TaxNiyBz, (where x = 46, 47, y = 44, 45 and z = 8, 9, 10 at.%) and quaternary Ta50Ni(49.5-u)WuB0.5, (where u = 1, 2, 3, 5 at.%) and Ta(50-v)Ni(50-w)Hf(v+w-0.5)B0.5 (where v = 7, 9 and w = 8,10 at.%) alloys have been selected based on the intersections of overlapped PHSS, ρth and T0th regions in respective superimposed diagrams and subsequently considered for conducting experiments for validation. All these alloys of selected compositions were first cast from elemental mixture, followed by processing through rapid solidification route to produce ribbons and characterizing for structural and thermal analyses. It reveals that crystalline phases exist along with amorphous phase in TaxNiyBz alloys, whereas completely amorphous phase can be observed in quaternary Ta50Ni(49.5-u)WuB0.5, and Ta(50-v)Ni(50-w)Hf(v+w-0.5)B0.5 alloy systems. B has detrimental effect for the formation of glassy phase, whereas W bearing Ta-Ni-B alloys have higher GFA as compared to that of Hf bearing Ta-Ni-B alloys. The experimental results are also corroborated with the theoretical prediction.