Glass forming ability of the binary Cu–Hf system studied by thermodynamic calculation and ion beam mixing

Abstract

Based on Miedema's semi-empirical model, a Gibbs free energy diagram is constructed for the Cu–Hf system and shows that the amorphous phase is favored to be formed over 8–94 at.% Hf, which is much broader than the experimentally determined 30–70 at.% Hf. Three Cu–Hf multilayered films were therefore designed with the overall compositions of Cu 93Hf 7, Cu 81Hf 19 and Cu 23Hf 77, respectively, and then an ion beam mixing experiment was conducted using 200 keV xenon ions to see whether the metallic glass forming range of the Cu–Hf system could be extended beyond the previously reported range. Interestingly, ion beam mixing results show that a uniform amorphous phase can be obtained in the Cu 23Hf 77 sample and the amorphous phase is also observed to coexist with crystalline Cu in the Cu 81Hf 19 sample. These results suggest that the metallic glass forming range of the Cu–Hf system could, at least, be extended to 77 at.% Hf, which falls in the range predicted by the Gibbs free energy diagram.