One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm ...One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.展开更多
Transverse crack often occurs in the trailing edge region of the bladewhen subjected to the excessive edgewise fatigue load.In this paper a refined model was established through local mesh refinement methods in order ...Transverse crack often occurs in the trailing edge region of the bladewhen subjected to the excessive edgewise fatigue load.In this paper a refined model was established through local mesh refinement methods in order to investigate the initiation mechanism of crack and its extension in blade trailing edge.The material stress around the crack in trailing edge region under different thicknesses is calculated based on the fracture mechanics theory.The factors affecting the fatigue robustness of blade trailing edge are concluded by investigating the results of finite element analysis and coupons test.Compared with the laminate,the lower fatigue strength of the adhesive is the cause of the transverse crack of the adhesive joint at the trailing edge.The increase of the adhesive thickness at the adhesive joint will significantly increase the stress concentration factor at the crack region and accelerate the crack extension of the laminate.In final,a practical design scheme to prevent crack initiation is given for the manufacture of the wind turbine blade.展开更多
Direct alloying is difficult to be realized in an immiscible Mo-Ag system with a positive formation heat due to the absence of thermodynamic driving force at equilibrium.In this work,a direct alloying method is develo...Direct alloying is difficult to be realized in an immiscible Mo-Ag system with a positive formation heat due to the absence of thermodynamic driving force at equilibrium.In this work,a direct alloying method is developed to realize the direct alloying between Mo and Ag and construct Mo-Ag interface.The direct alloying method was mainly carried out through a direct diffusion bonding for Mo and Ag rods at a temperature close to the melting point of Ag(Tm Ag).Then the microstructure and phase constitution of the as-constructed Mo-Ag interface are characterized.The results show that Mo-Ag metallurgical bonding interface has been constructed successfully,indicating that a direct alloying in the immiscible Mo-Ag system has been realized.Additionally,mechanical tests are carried out for the Mo-Ag joints prepared through the direct alloying method.The test results show that the average maximum tensile strength of the joints is about 107 MPa.The effect of alloying parameters on the tensile strength is also discussed,which shows that there is an effective temperature range for the direct alloying between Mo and Ag.Lastly,an improved thermodynamic model that considers the formation of Mo-Ag crystalline and amorphous phase is presented to reveal the thermodynamic mechanism of the direct alloying.Combining the calculation and differential scanning calorimetry(DSC)tests results,the Gibbs energy diagram for the direct alloying is obtained.It is confirmed that the co-release of storage energy and surface energy can serve as the thermodynamic driving force to overcome the effect of positive formation heat and lead to direct alloying for Mo-Ag systems.展开更多
对被粘接件为钢板和铝板的刚度平衡、非平衡搭接胶接接头进行不同温度下的拉伸载荷剪切强度试验,分别得到各种类型搭接件在3种温度下的最大拉伸力值。以Goland和Reissner的一维梁模型为基础,参考Wu Z J提出的接头解析方法推导出求解刚...对被粘接件为钢板和铝板的刚度平衡、非平衡搭接胶接接头进行不同温度下的拉伸载荷剪切强度试验,分别得到各种类型搭接件在3种温度下的最大拉伸力值。以Goland和Reissner的一维梁模型为基础,参考Wu Z J提出的接头解析方法推导出求解刚度不平衡接头端部载荷的相关公式,并且通过有限元仿真对试验中各种类型接头进行胶层应力分析,最后针对刚度非平衡结构对接头强度的影响进行了讨论。展开更多
Solid-liquid state bonding of Si3N4 ceramics with TiN-modified Ag-Cu-Ti brazing alloy was used'- to enhance joint strength. The effects of the TiN particles on the microstructures, interfacial reactions, and roo...Solid-liquid state bonding of Si3N4 ceramics with TiN-modified Ag-Cu-Ti brazing alloy was used'- to enhance joint strength. The effects of the TiN particles on the microstructures, interfacial reactions, and room-temperature properties of the joints were investigated. The results show that the TiN particles are gen- erally well dispersed in the Ag-Cu eutectic base and the interface between them is both clean and com-pact. Changes in the TiN volume fractions from 0 to 20% exert no noticeable effect on the interfacial reac-tion between Ag-Cu-Ti and the substrates. Other bonding parameters being constant, the TiN volume frac-tion in the filler material plays a key role in the joint properties. For TiN volume fractions below 20%, the joints are reinforced, especially joints with 5% and 20% TiN. The average shearing strength of joints with 5% TiN is 200.8 MPa, 30% higher than that of joints with no TiN (154.1 MPa). However, for TiN volumes frac- tions above 20%, the joint strengths decrease.展开更多
Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temper...Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.展开更多
文摘One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.
基金This research was funded by Natural Science Foundation of Shandong Province(Grant No.ZR2019MEE076)National Natural Science Foundation of China(Grant No.52075305).
文摘Transverse crack often occurs in the trailing edge region of the bladewhen subjected to the excessive edgewise fatigue load.In this paper a refined model was established through local mesh refinement methods in order to investigate the initiation mechanism of crack and its extension in blade trailing edge.The material stress around the crack in trailing edge region under different thicknesses is calculated based on the fracture mechanics theory.The factors affecting the fatigue robustness of blade trailing edge are concluded by investigating the results of finite element analysis and coupons test.Compared with the laminate,the lower fatigue strength of the adhesive is the cause of the transverse crack of the adhesive joint at the trailing edge.The increase of the adhesive thickness at the adhesive joint will significantly increase the stress concentration factor at the crack region and accelerate the crack extension of the laminate.In final,a practical design scheme to prevent crack initiation is given for the manufacture of the wind turbine blade.
基金supported by the National Key Research and Development Program of China(Grant Nos.2018YFB0703904 and 2017YFE0302600)the National Natural Science Foundation of China(Grant No.51471114)。
文摘Direct alloying is difficult to be realized in an immiscible Mo-Ag system with a positive formation heat due to the absence of thermodynamic driving force at equilibrium.In this work,a direct alloying method is developed to realize the direct alloying between Mo and Ag and construct Mo-Ag interface.The direct alloying method was mainly carried out through a direct diffusion bonding for Mo and Ag rods at a temperature close to the melting point of Ag(Tm Ag).Then the microstructure and phase constitution of the as-constructed Mo-Ag interface are characterized.The results show that Mo-Ag metallurgical bonding interface has been constructed successfully,indicating that a direct alloying in the immiscible Mo-Ag system has been realized.Additionally,mechanical tests are carried out for the Mo-Ag joints prepared through the direct alloying method.The test results show that the average maximum tensile strength of the joints is about 107 MPa.The effect of alloying parameters on the tensile strength is also discussed,which shows that there is an effective temperature range for the direct alloying between Mo and Ag.Lastly,an improved thermodynamic model that considers the formation of Mo-Ag crystalline and amorphous phase is presented to reveal the thermodynamic mechanism of the direct alloying.Combining the calculation and differential scanning calorimetry(DSC)tests results,the Gibbs energy diagram for the direct alloying is obtained.It is confirmed that the co-release of storage energy and surface energy can serve as the thermodynamic driving force to overcome the effect of positive formation heat and lead to direct alloying for Mo-Ag systems.
文摘对被粘接件为钢板和铝板的刚度平衡、非平衡搭接胶接接头进行不同温度下的拉伸载荷剪切强度试验,分别得到各种类型搭接件在3种温度下的最大拉伸力值。以Goland和Reissner的一维梁模型为基础,参考Wu Z J提出的接头解析方法推导出求解刚度不平衡接头端部载荷的相关公式,并且通过有限元仿真对试验中各种类型接头进行胶层应力分析,最后针对刚度非平衡结构对接头强度的影响进行了讨论。
基金Supported by the National Natural Science Foundation of China (No. 50075046)
文摘Solid-liquid state bonding of Si3N4 ceramics with TiN-modified Ag-Cu-Ti brazing alloy was used'- to enhance joint strength. The effects of the TiN particles on the microstructures, interfacial reactions, and room-temperature properties of the joints were investigated. The results show that the TiN particles are gen- erally well dispersed in the Ag-Cu eutectic base and the interface between them is both clean and com-pact. Changes in the TiN volume fractions from 0 to 20% exert no noticeable effect on the interfacial reac-tion between Ag-Cu-Ti and the substrates. Other bonding parameters being constant, the TiN volume frac-tion in the filler material plays a key role in the joint properties. For TiN volume fractions below 20%, the joints are reinforced, especially joints with 5% and 20% TiN. The average shearing strength of joints with 5% TiN is 200.8 MPa, 30% higher than that of joints with no TiN (154.1 MPa). However, for TiN volumes frac- tions above 20%, the joint strengths decrease.
基金financially supported by the National Natural Science Foundation of China (Nos.51671017 and 51471024)Fundamental Research Funds for the Central Universities (No.FRFBR-15-078A)
文摘Ti-6Al-4V/Al7050 joints were fabricated by a method of insert molding and corresponding interfacial microstructure and mechanical properties were investigated. The interfacial thickness was sensitive to holding temperature during the first stage, and a good metallurgical bonding interface with a thickness of about 90 μm can be obtained at 750°C. X-ray diffraction, transmission electron microscopy, and thermodynamic analyses showed that the interface mainly contained intermetallic compound TiAl_3 and Al matrix. The joints featured good mechanical properties, i.e., shear strength of 154 MPa, tensile strength of 215 MPa, and compressive strength of 283 MPa, which are superior to those of joints fabricated by other methods. Coherent boundaries between Al/TiAl_3 and TiAl_3/Ti were confirmed to contribute to outstanding interfacial mechanical properties and also explained constant fracture occurrence in the Al matrix. Follow-up studies should focus on improving mechanical properties of the Al matrix by deformation and heat treatment.
