Regulating The Energy And Mechanical Properties Of Zr-based Metallic Glasses By Triaxial Stress

Metallic glasses(MGs)differ from traditional crystalline materials in that their disordered atom structure prevents precise control of their properties by playing with crystal defects such as dislocations.However,as a metastable material,MGs possess an adjustable energy state,which is a typical characteristic.For MGs,this adjustable energy state has a certain coupling relation with the material’s performance,making the regulation of energy state to become an important method to improve performance.Therefore,developing novel technologies to effectively manipulate the energy state of MGs and studying the properties of MGs with extreme energy states have great theoretical and practical significance for the development and application of highperformance MGs.In this paper,we have successfully fabricated MGs with extreme energy states by adjusting the triaxial stress state.We systematically investigated the intrinsic relationship between the energy state and the mechanical properties of MGs,discovering a new strain hardening mechanism for metallic materials.Moreover,we developed a new method based on tensile stress state control to achieve structural relaxation in MGs,and revealed the effects of different relaxation methods on the microstructure and mechanical properties.These findings aim to provide guidance for the design of highly ductile and stable MGs.For the first time,we have achieved strain hardening of bulk MGs under uniaxial tension and discovered a novel strain hardening mechanism for metal materials.By applying triaxial compressive stress,we successfully prepared highly rejuvenated bulk MGs that exhibit a hardness drop of up to 30%.Our studies on the tensile properties of these highly rejuvenated bulk MGs showed that they exhibit a tensile plasticity of approximately 0.9%and significant strain hardening behavior.Energy analysis revealed a novel strain hardening mechanism for metallic materials.Specifically,strain hardening in metallic glasses is accompanied by a decreasing energy,which is different from the strain hardening behavior observed in traditional crystalline metals,where strain hardening is associated with an increasing energy.Additionally,based on Considere’s analysis,it is revealed that the limit tensile plasticity(<1%)of MGs is closely related to their high yield ratio,high initial strain hardening rate,and the rapid decay of strain hardening rate during deformation.We have systematically investigated the effects of triaxial tensile stress on the structural relaxation of MGs under different loading conditions.The results demonstrate that the degree of structural relaxation in MGs increases with increasing maximum tensile stress.Moreover,it is observed that cyclic elastic loading under triaxial tensile stress can futher promote structural relaxation in MGs.Utilizing this phenomenon,bulk MGs with a lower energy state were successfully fabricated,exhibiting ultrastability comparable to Ce-based MG annealed at room temperature(RT)for 17.7 years and amber annealed at RT for millions of years,and superior to that of ultrastable glasses prepared by vapor deposition.The quantitative analysis based on retrodiction reveals that the energy state of relaxed metallic glass obtained under triaxial tensile stress can only be achieved by annealing at room temperature for at least 100 years.These results indicate that triaxial tensile stress can accelerate the structural relaxation by a factor of 107,providing a new route and idea for producing bulk ultrastable MGs.We have compared the effects of two relaxation methods,triaxial tensile stress and thermal annealing,on the mechanical properties and microstructure of MGs.The findings imply that structural relaxation induced by triaxial tensile stress can enhance the strength and plasticity of MGs,synchronously.Furthermore,the compressive plasticity of relaxed MGs obtained under optimal triaxial tensile stress can reach twice that of as-cast MGs,effectively avoiding the severe plasticity loss caused by thermal annealing.Further analysis revealed that the two relaxation methods have distinct effects on the degree of structure ordering and the size of shear transition zone(STZ)volume despite they both can densify the atom structure of MGs.Structural relaxation induced by triaxial tensile stress does not alter or even decrease the proportion of crystal-like ordering(CLO)structures in MGs but increases the STZ volume.Conversely,structural relaxation induced by thermal annealing significantly increases the proportion of CLO structures and reduces the STZ volume.