Enhancing the Energy State and Plasticity of Relaxed Cu₄₉Hf₄₂Al₉ Bulk Metallic Glass by Rejuvenation

Rejuvenation has been considered to be an effective method for enhancing the mechanical properties of metallic glass. Herein, the effect of two rejuvenation methods, by enthalpy relaxation and through cryogenic thermal cycling (CTC) treatment, on the mechanical properties and energy state of a relaxed Cu₄₉Hf₄₂Al₉ bulk metallic glass (BMG) is investigated. It is revealed that the method of rejuvenation by enthalpy relaxation is applicable to the present relaxed metallic glass system, where the energy state is lifted to a higher one from the relaxed state and the compressive plasticity surpasses that of the as-cast MG after rejuvenation. The CTC treatment can also recover the compressive plasticity of the relaxed MG even though only with a slight increase in the energy state. The combination of the above two methods, however, shows an unexpectedly stronger rejuvenation effect in the relaxed Cu₄₉Hf₄₂Al₉ BMG, where the energy state of the optimally rejuvenated sample is comparable to that of the as-cast sample and the compressive plasticity of the optimally rejuvenated sample is more than twice and six times that of the as-cast sample and the relaxed sample, respectively. Our results show that a significant rejuvenation effect can be achieved by combining two or more rejuvenation methods, which opens a new route to tailor the properties of MGs.