In-situ thermographic observation of mechanical damage in bulk-metallic glasses during fatigue and tensile experiments

One of the major limitations on bulk-metallic glasses (BMGs) as potential structural materials are their poor reliabilities under tension-loading conditions. It is essential to investigate the mechanical-damage processes of BMGs in order to improve their reliability. Up to now, however, the mechanical-damage mechanism of BMGs has not been fully understood, especially during fatigue processes. In the current research, the mechanical-damage processes of Zr-based BMGs during both fatigue and tensile tests were investigated in-situ by thermography technologies. Except for the final fracture moment, the mechanical behaviors of BMGs have been observed to be dominated by elastic deformations. In the present study, the thermoelastic effect was used to predict the stress concentration at the center-notch region of the BMG specimens. An obvious thermoelastic degradation phenomenon was observed at the center-notch region of the specimen, which could result from the free-volume-accumulation process during fatigue, and can be used to predict the fatigue-damage-evolution process and the final failure. Multiple shear bands were observed in-situ and analyzed on BMGs before failures during tensile tests by thermography, while no shear bands were observed during fatigue tests, which indicated that the failure mechanism during fatigue could be different from that during the tensile test. Furthermore, instant melting and liquid splitting of BMGs at the fracture moment was captured in-situ by thermography. As a new nondestructive-evaluation method, thermography could open up wide applications in detecting in-situ mechanical-damages of materials and structural components.