| Due to its ascendant high temperature properties, superalloy occupies an important position in the fields of aviation, aerospace and many other industries. In order to adapt to the increasing requirements for properties, more alloying elements have to be added into the superalloy, leading to many harsh problems such as severe segregation, complicated processing course and formation difficulty of materials. The traditional powder metallurgy, hot canned deformation may overcome the machining difficultiy and the disadvantage of easy occurrence of cracks to some extent, but the difficulty in the working process has not been solved. So the exploration of new plastic processing theories and methods should be particularly important.The phenomenon of electroplastic effect has attracted wide attention as soon as it was found. A lot of achievements have been obtained in the research of plastic working of some metallic materials such as magnesium alloy and stainless steel utilizing the electroplastic effect of pulse current. The phenomena of recrystallization of pure copper, brass, magnesium alloy and aluminum-lithium alloy with pulse current were studied, and it was found that the pulse current can bring the effect of the reduction in starting temperature, the improvement of nucleation rate and the refinement of grains in recrystallization. So far, there are few reports about the recrystallization behavior of hard-deformation superalloy with pulse current. The results that have already obtained concentrate on the specific technologies of deformation resistance decrease too much, and the corresponding micromechanisms of electroplasticity has not been sufficiently invested, especially for the superalloys with high-content alloying elements and complex phases. A thorough study on the discipline and mechanisms of electroplastic effect is more representative. Therefore the deformation tests of GH4169 alloy were carried out at high temperatures with or without pulse current. In present research, the processability and dynamic recrystallization were discussed under pulse current with different parameters.Based on present research, it is found that the deformation resistance decreases with temperature increase in a certain range. The results of tensile tests at 850℃ and compressive tests at 950 ℃ show that the pulse current can reduce deformation resistance and promote dynamic recrystallization. In addition, this kind of decline and promotion shows a larger degree with pulse current density increases constantly. Analysis on the specimens of tensile tests at 850℃ for 14% deformation indicates that the bulge of grain boundaries is more obvious with pulse current density increase. When the pulse current density increases to 4.5 kA/mm2, the bulge of grain boundaries of new grains produced by dynamic recrystallization can be observed. The new round of dynamic recrystallization is caused by the rise of deformation energy with deformation increase.The heat activation and the kinetic energy of atoms increase, while the critical resolved shear stress of slip systems, leading to the decrease of deformation resistance. The cross-slip and climb of dislocations as well as the dynamic recrystallization contribute to the decline of deformation resistance. The movement of dislocations is accelerated by electron wind force and mechanical force with pulse current during deformation process. In addition, The pulse current can also reduce the binding energy between dislocations and obstacles or the energy barrier in the lattice containing defects, thus causing the further reduction of deformation resistance and the promotion of plasticity. The mobility of dislocations and the diffusion of atoms are promoted by pulse current. The process of entering into sub-boundaries for dislocations climb and the growth of boundaries angle also gets promoted, so the recrystallization nucleation time is shortened. Meanwhile, the energy barrier of atoms transition and dynamic recrystallization activation energy are also reduced by pulse current. |
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