In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling du...In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process.Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy.Quasi-static tensile experiment was carried out at temperatures ranging from 750–900℃and strain rates of 0.0001–0.1 s^(-1).The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s^(-1)and temperatures of 750–850℃.At strain rates of 0.0001–0.001 s^(-1)and tempera-tures of 850–900℃,the flow stress of joint presented steady-state characteristics.Different defor-mation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal,but the flow stress in elastic and strain hardening stages exhibited similar behavior.The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively.The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained.The models have shown good correlation,with correlation coefficient values of 0.984 and 0.99.The percentage average absolute relative error for the models were found to be 10%and 9.46%,respectively.展开更多
In the present study, corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel （MDSS） and Ti6AI4V alloy （TiA） （at 900 ~C for 60 min under 4 MPa uniaxial pressure in vacuum） was i...In the present study, corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel （MDSS） and Ti6AI4V alloy （TiA） （at 900 ~C for 60 min under 4 MPa uniaxial pressure in vacuum） was investigated in 1 mol/L HCI and 1 mol/L NaOH solutions using various electrochemical measurements such as open circuit potential （OCP）, electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization （PD）. For comparison, corrosion behavior of base metals （MDSS and TiA） was also evaluated. Bonded joint was characterized by light optical microscopy and scanning electron microscopy using backscattered electron mode. The layer wise σ phase and λ ＋ FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were - 556.4 MPa and -420.2 MPa, respectively.展开更多
A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel（DSS） has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain f...A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel（DSS） has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope（OM）, the scanning electron microscope（SEM）, the electron backscatter difraction（EBSD） and the transmission electron microscope（TEM）. The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ → γ and/or δ → γ ＋ σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization in δ-grains. During the second aging treatment, σ-phase mainly nucleated at δ/γ interfaces and further grew along those interfaces into various morphologies（e.g., butterfly and granule）. A novel precipitation behavior was found in this study that the γ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into the σ-phase precipitates without the prior precipitation of the isolated secondary austenite γ2or another phases.展开更多
基金supported by the National Natural Science Foundation of China(No.51675029).
文摘In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process.Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy.Quasi-static tensile experiment was carried out at temperatures ranging from 750–900℃and strain rates of 0.0001–0.1 s^(-1).The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s^(-1)and temperatures of 750–850℃.At strain rates of 0.0001–0.001 s^(-1)and tempera-tures of 850–900℃,the flow stress of joint presented steady-state characteristics.Different defor-mation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal,but the flow stress in elastic and strain hardening stages exhibited similar behavior.The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively.The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained.The models have shown good correlation,with correlation coefficient values of 0.984 and 0.99.The percentage average absolute relative error for the models were found to be 10%and 9.46%,respectively.
基金the support provided by the INDO US Science&Technology Forum,New Delhi,India
文摘In the present study, corrosion behavior of diffusion bonded joints formed between micro-duplex stainless steel （MDSS） and Ti6AI4V alloy （TiA） （at 900 ~C for 60 min under 4 MPa uniaxial pressure in vacuum） was investigated in 1 mol/L HCI and 1 mol/L NaOH solutions using various electrochemical measurements such as open circuit potential （OCP）, electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization （PD）. For comparison, corrosion behavior of base metals （MDSS and TiA） was also evaluated. Bonded joint was characterized by light optical microscopy and scanning electron microscopy using backscattered electron mode. The layer wise σ phase and λ ＋ FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were - 556.4 MPa and -420.2 MPa, respectively.
基金support by the Project of Investigation on Fundamental Issues of Stainless Steels from Shenyang National Laboratory for Materials Science(SYNL)Institute of Metal Research(IMR),Chinese Academy of Sciences(CAS)(No.KGCX2-YW-221)
文摘A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel（DSS） has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope（OM）, the scanning electron microscope（SEM）, the electron backscatter difraction（EBSD） and the transmission electron microscope（TEM）. The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ → γ and/or δ → γ ＋ σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization in δ-grains. During the second aging treatment, σ-phase mainly nucleated at δ/γ interfaces and further grew along those interfaces into various morphologies（e.g., butterfly and granule）. A novel precipitation behavior was found in this study that the γ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into the σ-phase precipitates without the prior precipitation of the isolated secondary austenite γ2or another phases.
