| Superplastic diffusion bonding parts of duplex stainless steel had broad prospects in the field of ship and ocean development machinery. However, due to its short history, there were many problems remain in practical application, such as the need of large cold rolling deformation, require of large pressure during the superplastic diffusion bonding process. Therefore, it was necessary to study the superplastic diffusion bonding conditions and mechanism of duplex stainless steel.In this paper, effects of pretreatments and superplastic diffusion bonding conditions on superplastic diffusion bonding of2205duplex stainless steel was discussed. It proposed to use thermal cycling during superplastic diffusion bonding process to improve interface bonding properties, use duplex stainless steel with different components to improve the interface microstructure. The specimens after superplastic diffusion bonding were analyzed by OM, SEM and TEM, interface microstructure, fracture morphology and elements distribution around the interfacial region were observed. Superplastic diffusion bonding mechanism of duplex stainless steel was explored.Superplastic diffusion bonding of2205duplex stainless steel under different conditions was studied, the results showed that shear bond strength of the joint prepared by specimen with a solution treatment of1350℃and a cold rolling reduction of85% was430MPa after superplastic diffusion bonding experiment, and the experiment parameters were1000℃,5min and10MPa. Using the same specimens of2205duplex stainless steel to do the superplastic diffusion bonding experiment through thermal cycling, the results indicated that when the diffusion bonding time was5min, the specific pressure was10MPa, under the conditions of Tmax=1000℃, Tmin=900℃, cyclic number of heating and cooling was3, shear bond strength of the joint was625MPa. Compared with430MPa after experiment under the constant temperature of1000℃the interfacial strength increased by about45percent.After diffusion bonding experiments of duplex stainless steel with different components, it was realized that the component difference was conducive to the elements diffusion and would improve the interface structure and bonding performance. Under the condition of1100℃,5min and lOMPa, shear bond strength of the joints2205/2507and2205/2906was536MPa and650MPa, respectively. And all the specimens were solution treated under1350℃and cold rolled by80%.As to duplex stainless steel with different components, diffusion bonding experiments had been done in the way of thermal cycling. The results showed that when the bonding time was5min, Tmax=1000℃, Tmin=900℃, cyclic number of heating and cooling was3, shear bond strength of the joints2205/2507and2205/2906was636MPa and748MPa, respectively. And the shear bond strength was18%and15%higher than that of conventional experiment without thermal cycling. All the joints were prepared by the specimens a solution treatment of1350℃and a cold rolling reduction of80%.After solution treated under1350℃and cold rolled by50%, specimens of2205,2507and2906were used to prepared joints in the way of thermal cycling. And the shear bond strength of2205/2507and2205/2906was579MPa and667MPa, which was43MPa and17MPa higher than that of conventional bonding using specimens with the cold reduction of80%. It was closed to that of conventional experiment without thermal cycling in which the joint was prepared using specimens with the cold rolling reduction of80%. As to2205, compared to the shear bond strength of430MPa under the specific pressure of10MPa after conventional bonding, shear bond strength of623MPa was obtained under5MPa in the way of thermal cycling. And the shear bond strength of joint prepard in the mode of thermal cycling using specimens with the cold reduction of60%was15MPa higher than that of conventional bonding using specimens with the cold reduction of85%. All these indicated that the requirements of cold rolling reduction and diffusion bonding pressure were reduced when using thermal cycling during the convetional diffusion bonding process.After diffusion bonding under the condition of1100℃,10MPa,5min in the convetional way using specimens with solution treatment of1350℃and cold rolling reduction of80%, the shear bond strength of the joint,2205matrix and2906matrix were650MPa,740MPa and920MPa, respectively. The joint was then heat treated at the tempreture of1100℃for10min, and its shear bond strength was increased by24%, and the value which was higher than the2205matrix was808MPa.Mechanism of duplex stainless steel using thermal cycling during the superplastic diffusion bonding process was discussed. Under the condition of thermal cycling, activity of atoms and grain boundaries were improved due to the effect of cyclic phase transformation, migration of grain boundaries crossed welding seam was promoted. Furthermore, dislocations were introduced in to the matrix, recrystallization occurred repeatedly, the grain was refined and the interfacial bonding performance was improved. |
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