Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutti...Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutting during the turning of the BMG rod.The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point.The temperature rise caused viscous fluid flow and brought about the deformation of BMGs.This suggested that the deformation of BMGs was derived,at least to some extent,from the adiabatic shear temperature rise.展开更多
The nanoscale shear band operation process of Zr_（55）Pd_（10）Cu_（20）Ni_5Al_（10） metallic glass（MG）was reined in by constant force during well-designed loading-holding-unloading cyclic microcompression test.Th...The nanoscale shear band operation process of Zr_（55）Pd_（10）Cu_（20）Ni_5Al_（10） metallic glass（MG）was reined in by constant force during well-designed loading-holding-unloading cyclic microcompression test.Through the test,it is revealed that the whole shear banding process involves three stages：shear band initiation,shear sliding and shear band arrest.Based on the energy balance principle,the size-affected speed of shear sliding is interpreted.The energy originated from the shear sliding leads to heat-up of the shear plane;therefore,the temperature in shear band increases with the size of shear offset caused by the energy accumulation during shear sliding.Taking the glass transition temperature as the critical temperature of fracture for the Zr-based MG,the critical shear offset is predicted to be approximately 190μm,fully in line with the experimental observation.This directly proved that the fracture of the MG is caused by the temperature rise during shear sliding.展开更多
“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of s...“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys,which brings challenges for studying yield strength.Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators.The yield strength was found to be at least 33%higher than the fracture strength measured with bulk samples for the present brittle MG.The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent,while the required stress for cleavage cracking increases with decreasing sample size.The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition.These findings clarify the physical nature of the strength of“brittle”MG,implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.展开更多
A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treat...A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.展开更多
基金supported by the National Basic Research Program of China (Grant No. 2010CB731600)the National Natural Science Foundation of China (Grant Nos. 50731005,50821001 and 51171163)+1 种基金the Doctoral Fund of Ministry of Education of China (Grant No. 20101333110004)the Nature Science Foundation of Hebei (Grant No. E2010001176)
文摘Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutting during the turning of the BMG rod.The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point.The temperature rise caused viscous fluid flow and brought about the deformation of BMGs.This suggested that the deformation of BMGs was derived,at least to some extent,from the adiabatic shear temperature rise.
基金Item Sponsored by Natural Science Foundation of Guangdong Province of China(2014A030310189)Shenzhen Senior Talent Research Start-up Funding of China(827000056)General Research Fund from Research Grant Council of Hong Kong Government of China(CityU 102013)
文摘The nanoscale shear band operation process of Zr_（55）Pd_（10）Cu_（20）Ni_5Al_（10） metallic glass（MG）was reined in by constant force during well-designed loading-holding-unloading cyclic microcompression test.Through the test,it is revealed that the whole shear banding process involves three stages：shear band initiation,shear sliding and shear band arrest.Based on the energy balance principle,the size-affected speed of shear sliding is interpreted.The energy originated from the shear sliding leads to heat-up of the shear plane;therefore,the temperature in shear band increases with the size of shear offset caused by the energy accumulation during shear sliding.Taking the glass transition temperature as the critical temperature of fracture for the Zr-based MG,the critical shear offset is predicted to be approximately 190μm,fully in line with the experimental observation.This directly proved that the fracture of the MG is caused by the temperature rise during shear sliding.
基金financially supported by the National Natural Science Foundation of China(NSFC)(Nos.51771205 and 52271072)the Natural Science Foundation of Liaoning Province(No.2020-MS-011)the Start-up Program by Northwestern Polytechnical Uni-versity.
文摘“Brittle”metallic glass(MG)usually fractures catastrophically in a shattering mode under macroscopic compression,because cleavage cracking of splitting that originates from extrinsic flaws dominates the failure of such alloys,which brings challenges for studying yield strength.Here we show that the plastic yielding behavior in a brittle Fe-based MG can be successfully activated by decreasing the sample size to micrometer scale to avoid the possible large tensile stress concentrators.The yield strength was found to be at least 33%higher than the fracture strength measured with bulk samples for the present brittle MG.The results further demonstrate that the critical stresses for shear band initiation and propagation are size-independent,while the required stress for cleavage cracking increases with decreasing sample size.The competition of thermodynamic driving forces between the two processes of shear banding and cleavage cracking hence leads to the size-induced brittle-to ductile-transition.These findings clarify the physical nature of the strength of“brittle”MG,implying the great opportunity for using high-strength brittle MGs in devices with small dimensions.
基金supported through the Start-up research grant (No.SRG/2020/000095) of Science and Engineering Research Board,DST,Go INanyang Technological University was supported by the funding from A*STAR via the Structural Metals and Alloys Programme (No.A18B1b0061)+2 种基金Institute of Metal Research CAS was supported by the National Natural Science Foundation of China (Nos.52171164 and 51790484)the National Key Research and Development Program (No.2018YFB0703402)the Youth Innovation Promotion Association CAS (No.2021188)。
文摘A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.
