Modifications were made on the traditional split Hopkinson pressure bar （SHPB） system to conduct dynamic shear tests. The shear response of Ti-6A1-4V was acquired at a shear strain rate of 104 s-1 by using this modi...Modifications were made on the traditional split Hopkinson pressure bar （SHPB） system to conduct dynamic shear tests. The shear response of Ti-6A1-4V was acquired at a shear strain rate of 104 s-1 by using this modified apparatus. The geometry as well as the clamping mode of the double-notch specimen was optimized by commercial FEM software ABAQUS, and the feasibility of the experiment set-up was validated. A shear stress calibration coeff^cient of γT = 1.03 and a shear strain calibration coefficient of γT- = 0.50 were obtained.We have employed high- speed photography to record the deformation process, especially the initiation and propagation of adiabatic shear band （ASB）, during the dynamic shear test. The frames show that the time duration from ASB initiation to its completion is less than 2 μs, from which we can estimate that the propagation speed of ASB within Ti-6A1-4V is more than 1250 m/s under such loading conditions. The temperature rise within ASB is also estimated to be △T2 ≈ 1460 ℃ based on energy balance. Such high temperature has led to softening of the material within the ASBs, and has intensified the shear localization and finally resulted in fracture of the material.展开更多
A light-weight high-entropy alloy （LWHEA） A120Be20Fe10SilsTi35 has been developed to have unique mechanical properties and oxidation resistance. One major and two minor phases are observed in the as-east microstruct...A light-weight high-entropy alloy （LWHEA） A120Be20Fe10SilsTi35 has been developed to have unique mechanical properties and oxidation resistance. One major and two minor phases are observed in the as-east microstructure. The density of the alloy is 3.91 gcm-3, and its hardness is HV 911, which is higher than quartz. The hardness and hardness to density ratio are the highest of all light-weight alloys reported before. In addition, it has excellent oxidation resistance at 700℃ and 900℃, which far exceeds that of Ti-6A1-4V. Thus, the combination of properties is promising for high-temperature applications, which require light weight, wear-resistant and oxidation-resistant components.展开更多
分别在800℃、825℃、850℃焊接温度、30 m in保温时间,3 MPa焊接压力下,进行Ti-6A l-4V钛合金板与304L不锈钢网的真空扩散焊接。对接头组织结构与化学元素扩散进行了扫描电镜与能谱分析,并测试了接头的剪切强度。结果表明:不添加中间...分别在800℃、825℃、850℃焊接温度、30 m in保温时间,3 MPa焊接压力下,进行Ti-6A l-4V钛合金板与304L不锈钢网的真空扩散焊接。对接头组织结构与化学元素扩散进行了扫描电镜与能谱分析,并测试了接头的剪切强度。结果表明:不添加中间过渡层金属,可以成功地实现钛合金板与不锈钢网的扩散焊接,并使接头的剪切强度达到90 MPa以上。不锈钢网中的Fe、N、iCr扩散并固溶到钛合金中,稳定了β相,使钛合金在一定深度上,其组织由原来的α+β双相结构转变为单相的β相。不锈钢中的Cr,由于钛合金中Ti的扩散进入,而在界面发生了上坡扩散现象。这种Cr在不锈钢一定深度内的富集,形成窄长的富Cr区域,冷却后转变为硬脆的σ相。但在焊接接头中没有发现明显其它的金属间化合物或氧化物相的生成,使得接头的机械性能得到了很好的保证。展开更多
Three friction welding processes are compared for temperature, stresses and strains, as well as strain rates developed in the early phases of the processes, which are essential in their successful development. These a...Three friction welding processes are compared for temperature, stresses and strains, as well as strain rates developed in the early phases of the processes, which are essential in their successful development. These are friction stir welding （FSW）, linear friction welding （LFW） and rotary friction welding （RFW）. Their common characteristic is the use of friction to generate adequate energy and raise temperature locally in order to create favorable conditions for welding at the interface between two parts. Although the mode of movement is different for each one of them, welds are produced through plastic deformation. The Lagrangian and coupled Eulerian-Lagrangian numer- ical models developed have produced results which are in qualitative agreement with experiments and have shed a light on the commonalities of these friction welding processes展开更多
The porous metallic biomaterials have attracted significant attention for implants because their lower young's modulus matches the human bones, which can eliminate the stress shielding effect and facilitate the gr...The porous metallic biomaterials have attracted significant attention for implants because their lower young's modulus matches the human bones, which can eliminate the stress shielding effect and facilitate the growth of bone tissue cells. The porous metallic biomaterials fabricated by selective laser melting (SLM) have broad prospects, but the surface of the SLM-built porous structure has been severely adhered with unmelted powders, which affects the forming accuracy and surface quality. The porous metallic biomaterials face the corrosion problem of complex body fluid environments during service, so their corrosion resistance in the human body is extremely important. The surface quality will affect the corrosion resistance of the porous metallic biomaterials. Therefore, it is necessary to study the effect of post-treatment on the corrosion resistance of SLMed samples. In this work, the mechanical response and the electrochemical corrosion behavior in simulated body fluid of diamond and pentamode metamaterials Ti-6Al-4V alloy fabricated by SLM before and after sandblasting were studied. After sandblasting, the mechanical properties of the two porous metallic biomaterials were slightly improved, and the self-corrosion potential and pitting potential were more negative;meanwhile, the self-corrosion current density and passive current density increased, indicating that its corrosion performance decreased, and the passive film stability of sandblasted samples got worse.展开更多
Constitutive model plays an important role in the numerical simulations of metal forming. However, th~ influence of the models on the calculation is vague. Based on the stress-strain data of A1 7050 and Ti-6A1-4V allo...Constitutive model plays an important role in the numerical simulations of metal forming. However, th~ influence of the models on the calculation is vague. Based on the stress-strain data of A1 7050 and Ti-6A1-4V alloy generated by isothermal compressive tests, the Johnson-Cook （JC） and Arrhenius-type （A-type） hyperbolic sine model were fitted to obtain the constants. Flow stresses directly calculated by the equations were compared with th~ experiment results, and rigid-plastic finite element analyses （FEA） utilizing these models were employed to simulate th~ same compression processes. The results show that A-type model has higher accuracy in the direct prediction of roy stress, even outside of the fit domain. The simulation results using A-type model also have higher agreement with th~ experiment; however, the suitability is affected by the referential parameters employed in the regression process, h terms of the overall deformation and strain distributions, there are slight differences among the simulation results usint these two models.展开更多
基金Project supported by National Natural Science Foundation of China (Nos. 11102166 and 10932008)the 111 project(No. B07050)the Basic Research Foundation of NPU (No. JC201201)
文摘Modifications were made on the traditional split Hopkinson pressure bar （SHPB） system to conduct dynamic shear tests. The shear response of Ti-6A1-4V was acquired at a shear strain rate of 104 s-1 by using this modified apparatus. The geometry as well as the clamping mode of the double-notch specimen was optimized by commercial FEM software ABAQUS, and the feasibility of the experiment set-up was validated. A shear stress calibration coeff^cient of γT = 1.03 and a shear strain calibration coefficient of γT- = 0.50 were obtained.We have employed high- speed photography to record the deformation process, especially the initiation and propagation of adiabatic shear band （ASB）, during the dynamic shear test. The frames show that the time duration from ASB initiation to its completion is less than 2 μs, from which we can estimate that the propagation speed of ASB within Ti-6A1-4V is more than 1250 m/s under such loading conditions. The temperature rise within ASB is also estimated to be △T2 ≈ 1460 ℃ based on energy balance. Such high temperature has led to softening of the material within the ASBs, and has intensified the shear localization and finally resulted in fracture of the material.
文摘A light-weight high-entropy alloy （LWHEA） A120Be20Fe10SilsTi35 has been developed to have unique mechanical properties and oxidation resistance. One major and two minor phases are observed in the as-east microstructure. The density of the alloy is 3.91 gcm-3, and its hardness is HV 911, which is higher than quartz. The hardness and hardness to density ratio are the highest of all light-weight alloys reported before. In addition, it has excellent oxidation resistance at 700℃ and 900℃, which far exceeds that of Ti-6A1-4V. Thus, the combination of properties is promising for high-temperature applications, which require light weight, wear-resistant and oxidation-resistant components.
基金Supported by the Natural Science Foundation of China (50371069)the Basic Defence Research Program of China (K1802060814)+3 种基金the Doctoral Foundation of the Educational Ministry of China (20030699013)the Aviation Science Foundation (04G53044)the Opening Foundation of Jiangxi Materials Engineering Center (ZX200301014) the Doctoral Innovation Foundation of Northwestern Polytechnical University (CX200306)
文摘Three friction welding processes are compared for temperature, stresses and strains, as well as strain rates developed in the early phases of the processes, which are essential in their successful development. These are friction stir welding （FSW）, linear friction welding （LFW） and rotary friction welding （RFW）. Their common characteristic is the use of friction to generate adequate energy and raise temperature locally in order to create favorable conditions for welding at the interface between two parts. Although the mode of movement is different for each one of them, welds are produced through plastic deformation. The Lagrangian and coupled Eulerian-Lagrangian numer- ical models developed have produced results which are in qualitative agreement with experiments and have shed a light on the commonalities of these friction welding processes
基金supported by the Joint Program of the National Natural Science Foundation of China(U1808216)the National Natural Science Foundation of China(Grant No.52275331)+2 种基金the Key Research and Development Program of Hubei Province(No.2022BAA011)the Academic Frontier Youth Team(2018QYTD04)at Huazhong University of Science and Technology(HUST)the Laboratory Project of Science and Technology on Power Beam Processes Laboratory and the Hong Kong Scholars Program(No.XJ2022014).
文摘The porous metallic biomaterials have attracted significant attention for implants because their lower young's modulus matches the human bones, which can eliminate the stress shielding effect and facilitate the growth of bone tissue cells. The porous metallic biomaterials fabricated by selective laser melting (SLM) have broad prospects, but the surface of the SLM-built porous structure has been severely adhered with unmelted powders, which affects the forming accuracy and surface quality. The porous metallic biomaterials face the corrosion problem of complex body fluid environments during service, so their corrosion resistance in the human body is extremely important. The surface quality will affect the corrosion resistance of the porous metallic biomaterials. Therefore, it is necessary to study the effect of post-treatment on the corrosion resistance of SLMed samples. In this work, the mechanical response and the electrochemical corrosion behavior in simulated body fluid of diamond and pentamode metamaterials Ti-6Al-4V alloy fabricated by SLM before and after sandblasting were studied. After sandblasting, the mechanical properties of the two porous metallic biomaterials were slightly improved, and the self-corrosion potential and pitting potential were more negative;meanwhile, the self-corrosion current density and passive current density increased, indicating that its corrosion performance decreased, and the passive film stability of sandblasted samples got worse.
基金Project（2012ZX04010-81） supported by the National Key Technology R＆D Program of China Project （51575066） supported by the National Natural Science Foundation of China
文摘Constitutive model plays an important role in the numerical simulations of metal forming. However, th~ influence of the models on the calculation is vague. Based on the stress-strain data of A1 7050 and Ti-6A1-4V alloy generated by isothermal compressive tests, the Johnson-Cook （JC） and Arrhenius-type （A-type） hyperbolic sine model were fitted to obtain the constants. Flow stresses directly calculated by the equations were compared with th~ experiment results, and rigid-plastic finite element analyses （FEA） utilizing these models were employed to simulate th~ same compression processes. The results show that A-type model has higher accuracy in the direct prediction of roy stress, even outside of the fit domain. The simulation results using A-type model also have higher agreement with th~ experiment; however, the suitability is affected by the referential parameters employed in the regression process, h terms of the overall deformation and strain distributions, there are slight differences among the simulation results usint these two models.
