Dependence of room-temperature nanoindentation creep behavior and shear transformation zone on the glass transition temperature in bulk metallic glasses

• Creep resistance of metallic glasses depends on glass transition temperature.
• Shear transformation zone (STZ) was studied by analyzing the first pop-in events.
• Activation energy of STZ determines creep resistance in metallic glasses.

Room-temperature nanoindentation creep behavior of bulk metallic glasses (BMGs) with various glass transition temperature (Tg) was investigated through using spherical indenter. The activation information of shear transformation zone (STZs) was studied by analyzing statistical distributions of the first pop-in events during nanoindentation. It was revealed that the higher Tg the BMG possessed, the more difficult the creep deformation became, being linked with lower ε̇s/Pmax (apparent steady creep strain rate normalized by applied maximum load), which was discovered to be a good indicator of room-temperature nanoindentation creep resistance. We demonstrated that it was the smaller nucleation site density, m, and higher activation energy upon yielding, WSTZ, that hindered the activation and cooperative shearing of STZs, causing better creep resistance in harder BMGs with higher Tg. However, no dependence of creep resistance on structural heterogeneity in each BMG was observed. Intrinsically, in local harder region as compared to local softer region, the lower WSTZ promotes activation of STZs and reduce creep resistance, while the smaller m denotes less potential nucleation site prone to be activated and helps to enhance creep resistance. It is this kind of competition that gives rise to the independence of creep resistance on structural heterogeneity in each BMG.

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