Study Gas Blow Forming Process Of Ni Foil On The High-temperature Under Two-dimensional Current

Nanomaterials had broad application prospects due to their unique physical and chemical properties.However,nanocrystalline metal materials had problems such as low forming limit and high brittleness at room temperature.In order to improve the formability of nanocrystalline metal materials,researchers had proposed a method to increase the plasticity of the material by applying an auxiliary current field.However,the traditional current application method made the current present a one-dimensional flow pattern in the blank,which was not compatible with the distribution of stress and strain in the material.Therefore,this paper proposed a two-dimensional controllable current field concept.By applying a controllable two-dimensional current field to the nanocrystalline metal foil,the current flow direction was adapted to the plastic flow trend of the material during the deformation process,thereby improving the plastic deformation ability of the nanomaterial and providing new technical ideas for the nanomaterial forming field.In this paper,the nanocrystalline Ni foil was prepared by electrodeposition method,and the Ni foil high-temperature forming mold under two-dimensional current was designed.The gas blow forming of Ni foil under different temperature,current application method and current density was studied.The test results showed that the ratio of height and diameter of the samples under the condition of pulse current were effectively improved compared with the condition of no current.When the average peak current density was the same,ratio of height to diameter of the samples under the two-dimensional current were larger than the one under the one-dimensional current.Based on the basic geometric relationship in the free bulging process,the strain of the blank in the process of gas blow deformation was described;the electron wind was introduced into the stress balance differential equation to describe the stress in the process of blank deformation;The influence of pulse current on the stress and strain of materials under different current application methods was also analyzed.The study found that the current promoted radial strain better under two-dimensional current.Through the analysis of the TEM morphology under different current densities,it was found that the electron wind could promote the movement of dislocations.As the current density increased,it further promoted the movement of dislocations and grain boundary slip.The dislocation entanglement at the grain boundaries gradually opened,so that the forming ability of the Ni foil material increased as the current density increases.The theoretical electron wind force was deduced and calculated by the energy method,and it was corrected by the test results of the high temperature tensile test of nanocrystalline Ni foil under the condition of pulse current.The MSC.Marc software was used to numerically simulate the high-temperature inflation forming process under two-dimensional current,and the electron wind was loaded on the blank in the form of stress.The simulation results further verified that the electron wind could improve the forming performance of the samples.