Fracture behaviors under pure shear loading in bulk metallic glasses.

Cen Chen,Chao Wang,Tzu-Chiang Wang,Wei-Hua Wang,Meng Gao

doi:10.1038/srep39522

Cen Chen, Chao Wang + Show 3 more

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https://doi.org/10.1038/srep39522

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Abstract

Pure shear fracture test, as a special mechanical means, had been carried out extensively to obtain the critical information for traditional metallic crystalline materials and rocks, such as the intrinsic deformation behavior and fracture mechanism. However, for bulk metallic glasses (BMGs), the pure shear fracture behaviors have not been investigated systematically due to the lack of a suitable test method. Here, we specially introduce a unique antisymmetrical four-point bend shear test method to realize a uniform pure shear stress field and study the pure shear fracture behaviors of two kinds of BMGs, Zr-based and La-based BMGs. All kinds of fracture behaviors, the pure shear fracture strength, fracture angle and fracture surface morphology, are systematically analyzed and compared with those of the conventional compressive and tensile fracture. Our results indicate that both the Zr-based and La-based BMGs follow the same fracture mechanism under pure shear loading, which is significantly different from the situation of some previous research results. Our results might offer new enlightenment on the intrinsic deformation and fracture mechanism of BMGs and other amorphous materials.

Highlights

The fracture behaviors of bulk metallic glasses (BMGs) are more complicated than those of crystalline materials due to the unknown atomic structural and metallic bonding[1,2], which is one of the toughest and hottest research directions in the field of material science
Some new fracture criteria have been set up to describe the fracture behaviors of BMGs16,20, a universal scaling law that demonstrated the intrinsic correlation between yielding and glass-liquid transition were reported for the understanding of strength and deformation of BMGs21, and the effect of thermal history on shear band initiation was investigated for the yield behavior in BMGs22
The pure shear strength τ0 of Zr52.5Cu17.9Ni14.6Al10Ti5 BMG satisfy that: sinθT∙cosθT∙σT < τ0 < sinθC∙cosθC∙σC, which is determined by the normal stress effect

Summary

Introduction

The fracture behaviors of BMGs are more complicated than those of crystalline materials due to the unknown atomic structural and metallic bonding[1,2], which is one of the toughest and hottest research directions in the field of material science. Some new fracture criteria have been set up to describe the fracture behaviors of BMGs16,20, a universal scaling law that demonstrated the intrinsic correlation between yielding and glass-liquid transition were reported for the understanding of strength and deformation of BMGs21, and the effect of thermal history on shear band initiation was investigated for the yield behavior in BMGs22 These new theoretical and experimental progresses have greatly promoted the research of mechanical behaviors for BMGs. there still exist some tough problems until now. The STZ theory and free volume model could be used to understand the mechanical behaviors, the normal stress effect is hard to be verified in the existing tensile and compressive fracture experiments[12,13], and the intrinsic deformation and fracture mechanism under the pure shear stress field have not been made clear. All of the methods mentioned above are not suitable for the measurement of shear strength, which is a big challenging bottleneck

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Results

Conclusion