Heterogeneous gradient nanostructured metals have been shown to achieve the strength-ductility synergy, thus potentially possessing the enhanced tribological performance in comparison with their homogeneous nanograine...Heterogeneous gradient nanostructured metals have been shown to achieve the strength-ductility synergy, thus potentially possessing the enhanced tribological performance in comparison with their homogeneous nanograined counterparts. In this work, a facile laser surface remelting-based surface treatment technique is developed to fabricate a gradient nanostructured layer on a TiZrHfTaNb refractory highentropy alloy. The characterization of the microstructural evolution along the depth direction from the matrix to the topmost surface layer shows that the average grain size in the ~100 μm-thick gradient nanostructured layer is dramatically refined from the original ~200 μm to only ~8 nm in the top surface layer. The microhardness is therefore gradually increased from ~240 HV in matrix to ~650 HV in the topmost surface layer, approximately 2.7 times. Noticeably, the original coarse-grained single-phase bodycentered-cubic TiZrHfTaNb refractory high-entropy alloy is gradually decomposed into TiNb-rich bodycentered-cubic phase, TaNb-rich body-centered-cubic phase, ZrHf-rich hexagonal-close-packed phase and TiZr Hf-rich face-centered-cubic phase with gradient distribution in grain size along the depth direction during the gradient refinement process. As a result, the novel laser surface treatment-introduced gradient nanostructured TiZrHfTaNb refractory high-entropy alloy demonstrates the significantly improved wear resistance, with the wear rate reducing markedly by an order of magnitude, as compared with the as-cast one. The decomposed multi-phases and gradient nanostructures should account for the enhanced wear resistance. Our findings provide new insights into the refinement mechanisms of the laser-treated refractory high-entropy alloys and broaden their potential applications via heterogeneous gradient nanostructure engineering.展开更多
Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass(BMG) components. In this study,the influences of machining parameters(i.e.,depth of cutting,feed rate,and spindle rate) on the...Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass(BMG) components. In this study,the influences of machining parameters(i.e.,depth of cutting,feed rate,and spindle rate) on the turned surface of a Zr-based BMG after observing the 3D morphologies of this surface were characterized.The results showed that the influence of the spindle rate on the surface morphologies is more substantial as compared to the depth of cutting and the feed rate. Nanoscratch tests were conducted to further characterize the separation mechanism of the chips,which revealed that the chips are torn off the surface of a BMG because of inhomogeneous localized maximum shear stress.展开更多
The deformation behavior in Zr36 Cu64 metallic glasses with pre-introduced indent-notches has been studied by molecular dynamics simulation at the atomic scale.The indent-notches can trigger the formation of densely-p...The deformation behavior in Zr36 Cu64 metallic glasses with pre-introduced indent-notches has been studied by molecular dynamics simulation at the atomic scale.The indent-notches can trigger the formation of densely-packed clusters composed of solid-like atoms in the indent-notch affected zone.These denselypacked clusters are highly resistant to the nucleation of shear bands.Hence,there is more tendency for the shear bands to nucleate outside the indent-notch affected zone,which enlarges the deformation region and enhances both the strengthening effect and the plastic deformation ability.For indent-notched MGs,when determining the initial yielding level,there is a competition process occurring between the densely-packed clusters leading to the shear band formation outside the indent-notch affected zone and the stress-concentration localizing deformation around the notch roots.When the indent-notch depth is small,the stress-concentration around the notch root plays a dominant role,leading to the shear bands initiating from the notch root,reminiscence of the cut-notches.As the indent-notch depth increases,there are many densely-packed clusters with high resistance to deformation in the indent-notch affected zone,leading to the shear band formation from the interface between the indent-notch affected zone and the matrix.Current research findings provide a feasible means for improving the strength and the plasticity of metallic glasses at room temperature.展开更多
Shear-banding behavior in metallic glasses plays a key role in the operation of plastic deformation,which is associated with yield strength.In a micro-scale,the shear-banding behavior must be affected by many factors ...Shear-banding behavior in metallic glasses plays a key role in the operation of plastic deformation,which is associated with yield strength.In a micro-scale,the shear-banding behavior must be affected by many factors from the test machine and the substrate.Therefore,in this study,comprehensively considering a machine compliance,a geometry imperfection of micro-pillar,and a substrate sink-in the machine-sample-substrate system,we developed a plastic-strength model at a micrometer scale in this study,which is evidenced by the microscale compressive properties of 18 kinds of metallic glasses.The the-oretical model provides a guidance for the elastic limits and shear-banding dynamics of metallic glasses at the micro-scale,which can be applicable to characterize the microscale deformation behavior of other amorphous materials.展开更多
Kirigami, the ancient Japanese paper cutting technique, has been applied to achieve high stretchability and low energy loss of designed metallic glass. Despite the exploration of the underlying deformation mechanism o...Kirigami, the ancient Japanese paper cutting technique, has been applied to achieve high stretchability and low energy loss of designed metallic glass. Despite the exploration of the underlying deformation mechanism of kirigami-inspired structures from the energy point of view, the morphable responses of the kirigami patterns and the origin of the kirigami response are yet to be fully understood. This study reveals the mechanical driven-forms of the kirigami structure with the corresponding deformation stages. Based on the beam deflection theory, the elastic buckling behavior of kirigami metallic glass is manifested and a critical force prediction model is developed. Moreover, a force concentration parameter is introduced in the rigid-plastic deformation stage, predicting the nominal ultimate force. The kirigami-inspired facture force is firstly proposed. The findings of these models are in good agreement with the experimental sizedependent kirigami responses, and expected to provide significant insights into the understanding of the deformation behavior and the design of kirigami metallic glasses.展开更多
Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnac...Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α＂ m phase which aooears as directional rods and the round precipitates. The other was the fcc α＇m phase. 〈101〉. The orientation relationship between the a phase and transitional phase α＇m was determined as （022）α＇m （fcc）//（022^-）α（fcc）, [1^-11]α＇m, （fcc）//[2^-33]α（fcc）. The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships.展开更多
利用电弧熔炼/水冷铜模吸铸技术制备了块体非晶合金(Zr_75-Cu_25)_78.5Ta_4Ni_10A_l7.5和第二相形态为颗粒状的块体非晶基复合材料(Zr_75Cu_25)_74.5Ta_8Ni_10A_l7.5.利用Instron力学性能实验机研究了块体非晶和复合材料在过冷液态区内...利用电弧熔炼/水冷铜模吸铸技术制备了块体非晶合金(Zr_75-Cu_25)_78.5Ta_4Ni_10A_l7.5和第二相形态为颗粒状的块体非晶基复合材料(Zr_75Cu_25)_74.5Ta_8Ni_10A_l7.5.利用Instron力学性能实验机研究了块体非晶和复合材料在过冷液态区内的单向压缩变形行为.结果表明:两种材料在过冷液态区内的形变行为都强烈依赖于温度和变形速率.随着应变速率的增加,两种材料的流变特征都由牛顿流变转变为非牛顿流变.用基于自由体积模型的过渡态理论(transition state theory)对两种材料的压缩形变行为进行了阐释和比较.展开更多
基金supported by the joint Ph D project between the Hong Kong Polytechnic University and Southern University of Science and Technologythe grant from the Research Committee of Poly U under student account code RK2N+1 种基金supported by the National Natural Science Foundation of China Projects (Nos. 51701171 and 51971187)the Fundamental Research Program of Shenzhen (Grant No. JCYJ20170412153039309)。
文摘Heterogeneous gradient nanostructured metals have been shown to achieve the strength-ductility synergy, thus potentially possessing the enhanced tribological performance in comparison with their homogeneous nanograined counterparts. In this work, a facile laser surface remelting-based surface treatment technique is developed to fabricate a gradient nanostructured layer on a TiZrHfTaNb refractory highentropy alloy. The characterization of the microstructural evolution along the depth direction from the matrix to the topmost surface layer shows that the average grain size in the ~100 μm-thick gradient nanostructured layer is dramatically refined from the original ~200 μm to only ~8 nm in the top surface layer. The microhardness is therefore gradually increased from ~240 HV in matrix to ~650 HV in the topmost surface layer, approximately 2.7 times. Noticeably, the original coarse-grained single-phase bodycentered-cubic TiZrHfTaNb refractory high-entropy alloy is gradually decomposed into TiNb-rich bodycentered-cubic phase, TaNb-rich body-centered-cubic phase, ZrHf-rich hexagonal-close-packed phase and TiZr Hf-rich face-centered-cubic phase with gradient distribution in grain size along the depth direction during the gradient refinement process. As a result, the novel laser surface treatment-introduced gradient nanostructured TiZrHfTaNb refractory high-entropy alloy demonstrates the significantly improved wear resistance, with the wear rate reducing markedly by an order of magnitude, as compared with the as-cast one. The decomposed multi-phases and gradient nanostructures should account for the enhanced wear resistance. Our findings provide new insights into the refinement mechanisms of the laser-treated refractory high-entropy alloys and broaden their potential applications via heterogeneous gradient nanostructure engineering.
基金supported by the National Natural Science Foundation of China (Nos.51171098,and 51222102)the Research Grants Council of Hong Kong (No.Poly U511211)+2 种基金the Innovation Program of Shanghai Municipal Education Commission (No.12ZZ090)the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learningthe "085 Project" in Shanghai University
文摘Cutting behavior exerts a considerable influence on the fabrication of bulk metallic glass(BMG) components. In this study,the influences of machining parameters(i.e.,depth of cutting,feed rate,and spindle rate) on the turned surface of a Zr-based BMG after observing the 3D morphologies of this surface were characterized.The results showed that the influence of the spindle rate on the surface morphologies is more substantial as compared to the depth of cutting and the feed rate. Nanoscratch tests were conducted to further characterize the separation mechanism of the chips,which revealed that the chips are torn off the surface of a BMG because of inhomogeneous localized maximum shear stress.
基金supported by the National Natural Science Foundation of China under Grant 51801174the Program for the Top Young Talents of Higher Learning Institutions of Hebei under Grant BJ2018021+2 种基金the National Key R&D Program of China under Grant 2018YFA0703602the Hong Kong Scholars Program under Grant XJ2017049support from the National Science Foundation under grant number CMMI 17-026。
文摘The deformation behavior in Zr36 Cu64 metallic glasses with pre-introduced indent-notches has been studied by molecular dynamics simulation at the atomic scale.The indent-notches can trigger the formation of densely-packed clusters composed of solid-like atoms in the indent-notch affected zone.These denselypacked clusters are highly resistant to the nucleation of shear bands.Hence,there is more tendency for the shear bands to nucleate outside the indent-notch affected zone,which enlarges the deformation region and enhances both the strengthening effect and the plastic deformation ability.For indent-notched MGs,when determining the initial yielding level,there is a competition process occurring between the densely-packed clusters leading to the shear band formation outside the indent-notch affected zone and the stress-concentration localizing deformation around the notch roots.When the indent-notch depth is small,the stress-concentration around the notch root plays a dominant role,leading to the shear bands initiating from the notch root,reminiscence of the cut-notches.As the indent-notch depth increases,there are many densely-packed clusters with high resistance to deformation in the indent-notch affected zone,leading to the shear band formation from the interface between the indent-notch affected zone and the matrix.Current research findings provide a feasible means for improving the strength and the plasticity of metallic glasses at room temperature.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51925103,51801027)the program 173(No.2020-JCIQ-ZD-186-01)+1 种基金China Postdoctoral Science Foundation(No.2022M713334)the Research Grants Council of the Hong Kong Special Administrative Region,China(No.PolyU 15222017).
文摘Shear-banding behavior in metallic glasses plays a key role in the operation of plastic deformation,which is associated with yield strength.In a micro-scale,the shear-banding behavior must be affected by many factors from the test machine and the substrate.Therefore,in this study,comprehensively considering a machine compliance,a geometry imperfection of micro-pillar,and a substrate sink-in the machine-sample-substrate system,we developed a plastic-strength model at a micrometer scale in this study,which is evidenced by the microscale compressive properties of 18 kinds of metallic glasses.The the-oretical model provides a guidance for the elastic limits and shear-banding dynamics of metallic glasses at the micro-scale,which can be applicable to characterize the microscale deformation behavior of other amorphous materials.
基金fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region,China(Project No.PolyU 15222017)。
文摘Kirigami, the ancient Japanese paper cutting technique, has been applied to achieve high stretchability and low energy loss of designed metallic glass. Despite the exploration of the underlying deformation mechanism of kirigami-inspired structures from the energy point of view, the morphable responses of the kirigami patterns and the origin of the kirigami response are yet to be fully understood. This study reveals the mechanical driven-forms of the kirigami structure with the corresponding deformation stages. Based on the beam deflection theory, the elastic buckling behavior of kirigami metallic glass is manifested and a critical force prediction model is developed. Moreover, a force concentration parameter is introduced in the rigid-plastic deformation stage, predicting the nominal ultimate force. The kirigami-inspired facture force is firstly proposed. The findings of these models are in good agreement with the experimental sizedependent kirigami responses, and expected to provide significant insights into the understanding of the deformation behavior and the design of kirigami metallic glasses.
文摘Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α＂ m phase which aooears as directional rods and the round precipitates. The other was the fcc α＇m phase. 〈101〉. The orientation relationship between the a phase and transitional phase α＇m was determined as （022）α＇m （fcc）//（022^-）α（fcc）, [1^-11]α＇m, （fcc）//[2^-33]α（fcc）. The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships.
文摘利用电弧熔炼/水冷铜模吸铸技术制备了块体非晶合金(Zr_75-Cu_25)_78.5Ta_4Ni_10A_l7.5和第二相形态为颗粒状的块体非晶基复合材料(Zr_75Cu_25)_74.5Ta_8Ni_10A_l7.5.利用Instron力学性能实验机研究了块体非晶和复合材料在过冷液态区内的单向压缩变形行为.结果表明:两种材料在过冷液态区内的形变行为都强烈依赖于温度和变形速率.随着应变速率的增加,两种材料的流变特征都由牛顿流变转变为非牛顿流变.用基于自由体积模型的过渡态理论(transition state theory)对两种材料的压缩形变行为进行了阐释和比较.
