Energy-state-dependent mechanical and structural heterogeneity in metallic glasses probed by nanoindentation

S.Q. Fu^a, Y.J. Duan^b, K. Tao^c, K.K. Song^d, Y.J. Wang^e, E. Pineda^f, Q.F. He^g, Z.Q. Zhang^h, Y. Yang^b,e,*, J.C. Qiao^a,i,*

^aDepartment of Mechanical Engineering, College of Engineering, City University of Hong Kong, Tat Chee ^bAvenue, Kowloon Tong, Kowloon, Hong Kong SAR, China
^cSchool of Mechanical Engineering, Jiangsu Ocean University, Lianyungang, 222005, China
^dSchool of Mechanical, Electrical & Information Engineering, Shandong University, Weihai 264209, China
^eDepartment of Materials Science and Engineering, College of Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Kowloon, Hong Kong SAR, China
^fDepartment of Physics, Institute of Energy Technologies, Center for Research in Multiscale Science and Engineering, Universitat Polit` ecnica de Catalunya, Barcelona 08019, Spain
^gInstitute of Materials Modification and Modeling, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
^hErich Schmid Institute of Materials Science, Austrian Academy of Sciences, A-8700 Leoben, Austria
ⁱState Key Laboratory of Clean and Efficient Turbomachinery Power Equipment, Northwestern Polytechnical University, Xi’an 710072, China

Abstract:

The plastic deformation behavior of metallic glasses is sensitive to the structural states, i.e., as-cast, aged and rejuvenated states. In the current work, Zr₅₀Cu₄₀Al₁₀ metallic glass with different energy states, which were tuned by high-pressure torsion method, is studied by nanoindentation. With the help of the statistical analysis of the first pop-in event, the cooperative shear model is used to describe the size of shear transformation zones (STZs), revealing the variations of STZs influenced by different energy states. The strain rate sensitivity of the metallic glass with various energy states obtained from creep experiments demonstrated that the mechanical softening effect induced by HPT enhances the plasticity of metallic glasses. Within the framework of molecular dynamics simulations, the structural evolution of metallic glasses at the atomic scale under different loading rates is analyzed. The results provide an atomic-scale explanation for the significant enhancement of plastic deformation in metallic glasses with higher energy state and under high strain rate. The research indicates that severe plastic deformation can nucleate STZs with lower energy barriers during the severe plastic deformation in metallic glasses with high-energy states. It also indicated that severe plastic deformation can introduce multiple shear bands during this process. Furthermore, the intersection of shear bands and the presence of multiple shear bands enhance energy dissipation, potentially improving the plasticity of metallic glasses. The underlying physics of the energy state and strain rate independence of plastic deformation is discussed, providing insights into the nucleation and propagation of STZs and shear bands in metallic glasses.