| Summary: | High-temperature deformation around the glass transition temperature T<sub>g</sub> and the dynamic mechanical behavior of La<sub>30</sub>Ce<sub>30</sub>Al<sub>15</sub>Co<sub>25</sub> metallic glass were investigated. According to dynamic mechanical analysis (DMA) results, La<sub>30</sub>Ce<sub>30</sub>Al<sub>15</sub>Co<sub>25</sub> metallic glass exhibits a pronounced slow β relaxation process. In parallel, strain-rate jump experiments around the glass transition temperature were performed in a wide range of strain rate ranges. The apparent viscosity shows a strong dependence on temperature and strain rate, which reflects the transition from non-Newtonian to Newtonian flow. At low strain or high temperature, a transition was observed from a non-Newtonian viscous flow to Newtonian viscous flow. It was found that the activation volume during plastic deformation of La<sub>30</sub>Ce<sub>30</sub>Al<sub>15</sub>Co<sub>25</sub> metallic glass is higher than that of other metallic glasses. Higher values of activation volume in La<sub>30</sub>Ce<sub>30</sub>Al<sub>15</sub>Co<sub>25</sub> metallic glass may be attributed to existence of a pronounced slow β relaxation. It is reasonable to conclude that slow β relaxation in La<sub>30</sub>Ce<sub>30</sub>Al<sub>15</sub>Co<sub>25</sub> metallic glass corresponds to the “soft” regions (structural heterogeneities) in metallic glass.
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