Abstract:The influence of Hf element on enthalpy and hardness relaxation behavior of Zr70Al7.5Ni8Cu14.5 (70Zr), Zr55Al10Ni5Cu30 (55Zr) and (Zr0.75Hf0.25)65Al7.5Ni10Cu17.5 (65Zr0.75Hf0.25) bulk glass-type alloys with large diameters of centimeter-level was examined by measuring the temperature dependence of apparent specific heats in as-spun and annealed states. Results show that the structural relaxation of 70Zr and 55Zr alloys occurs through a single-stage mode where the relaxation peak is observed at the annealing temperature (Ta) near glass transition temperature (Tg), while 65Zr0.75Hf0.25 alloy shows a double-stage reaction with enthalpy relaxation peaks appearing at 523 and 648 K near Tg. The single-stage relaxation mode for 70Zr and 55Zr alloys indicates that these alloys have high resistance to annealing-induced relaxation over the whole temperature range up to Tg, because the distinct relaxation occurs only around the temperature of Tg. 65Zr0.75Hf0.25 glassy alloy shows a relaxation sub-peak around 523 K presumably due to the weaker bonding nature of Zr-Hf atomic pair with nearly zero in heat of mixing, and the distinct main relaxation occurs near Tg. The Vickers hardness also shows the similar double-stage peak behavior as a function of Ta for 65Zr0.75Hf0.25 as well as (Zr0.5Hf0.5)65-Al7.5Ni10Cu17.5 (65Zr0.5Hf0.5) alloys, so the Ta for the first-stage hardness peak agrees with that for the enthalpy relaxation. These results imply that icosahedral-like medium range ordered structure consisting of Zr, Al, Ni and Cu elements with the three components rule for stabilization of supercooled liquid remains stable during the low Ta relaxation. The double-stage enthalpy and hardness relaxation only appear in 65Zr0.75Hf0.25 and 65Zr0.5Hf0.5 glassy alloys which deviate from the three components rule, implying that the unnecessary multiplication for the formation of bulk glassy alloys leads to an increase in structural instability during low-temperature annealing.