Characteristics of stress relaxation kinetics of La60Ni15Al25 bulk metallic glass

Fig. 1 shows temperature dependence of the normalized loss modulus of La60Ni15Al25 bulk metallic glass (heating rate: 3K/min and driving frequency: 3K/min): (1) As-cast, (2) annealed one (annealing temperature: 448K and annealing time: 16h). A pronounced β relaxation process was observed at lower temperature (∼360K). In addition, the α relaxation was detected at a higher temperature (∼500K). [Display omitted] The β relaxation typically plays an important role in the plastic deformation of glassy materials. Compared with amorphous polymers, most of the metallic glasses do not show evident β relaxation based on mechanical spectroscopy. However, La60Ni15Al25 bulk metallic glass (BMG) exhibits a prominent β relaxation process, which could be an ideal model alloy to investigate the correlation between the β relaxation and mechanical behavior of metallic glasses. In this work, compressive properties and stress relaxation at high temperature (below glass transition temperature Tg) were studied. Stress relaxation of La60Ni15Al25 BMG was measured by uniaxial compressive tests and mechanical spectroscopy around both α and β relaxation temperature domain. At higher temperatures and sufficiently low strain rate, the flow behavior of the La60Ni15Al25 BMG could be simulated by a master curve, showing that the behavior is independent of temperature, especially on the proximity of the β relaxation process. Because the existence of the β relaxation, a high value of the activation volume for the plastic deformation could be ascribed to the existence of a specific atomic arrangement in the La60Ni15Al25 BMG. It is found that compressive stress relaxation kinetics parameter remains temperature independent below Tg.