High copper content bulk glass formation in bimetallic Cu-Hf system

Abstract

We report in this article that strip-shaped amorphous samples with thicknesses from 0.5 to 2 mm were successfully synthesized for binary Cu-Hf alloys containing 60 to 68 at. pct Cu by the traditional copper mold casting method. The best glass former Cu₆₆Hf₃₄ with casting thickness up to 2 mm has an undercooled liquid region (ΔT=T_x –T_g , where T_g is the glass transition temperature and T_x is the onset temperature of the first crystallization event) of 51 K, which is somewhat narrow compared with other neighboring alloys in the same system. The bulk glassy Cu₆₆Hf₃₄ alloy exhibits Vicker’s Hardness (H_v ) ∼779 kg/mm², Young’s modulus ∼108 GPa, fracture strength ∼2.1 GPa, and an almost constant elastic elongation ∼1.8 pct upon compression. The discovery of Cu₆₆Hf₃₄ as a bulk glass confirms the existence of rather simple bulk-glass-forming metallic systems. Moreover, the present Cu-Hf alloys may be the highest copper content bulk metallic glasses reported to date, to the best of our knowledge.