Bulk metallic glass formation in the (Ti,Zr)-(Ni,Cu)-S system

Abstract

New bulk glass-forming alloy compositions, exceeding a critical casting thickness of 1 mm, are developed in the (quasi-ternary) (Ti,Zr)–(Ni,Cu)–S system. The ternary eutectic composition Ti65.5Ni22.5Cu12 is stepwise modified through additions of S (0–8 at%) and Zr (0–22.5 at%) at the expense of Ni and Ti, respectively. By increasing the plate thickness of the casted samples from 500 μm to 1.25 mm, the primary precipitating phases are identified which is for the best glass-formers (e.g. Ti58Zr7.5Ni18.5Cu12S4) an icosahedral phase. In calorimetric experiments, several exothermic crystallization events are observed upon heating glassy samples. The first exothermic event, obscuring the glass transition, is attributed to the formation of the icosahedral phase. As the icosahedral phase forms upon heating and cooling for the best glass-formers, the origin of the increased glass-forming ability might be attributed to a pronounced icosahedral short-range order in the liquid state, impeding the formation of the stable crystalline phases.