Preparation Of Gradient Nanocrystalline Ni Foil And Its Micro Bending Properties Assisted By Pulse Current

Nanocrystalline metal materials have very small grain size,and containing lots of grain boundaries and other interfaces,it has different physical,chemical and mechanical properties from other ordinary metal materials,they are very important research objects in the new material field.Micro plastic processing of nanocrystalline metal foil is one of the main methods to prepare micro parts,and is widely applied in the fields of microelectronics,MEMS and other fields.But compared with traditional metal materials,nanocrystalline material has poor plasticity at room temperature,which makes the forming cost of nanocrystalline materials too high,and greatly limits its application and popularization.To solve these problems,gradient nanocrystalline Ni foil was prepared by pulse electrodeposition,and high density pulse current was introduced into the micro forming process as an auxiliary forming method to improve the micro forming performance of nanocrystalline metal foil.The metal nanocrystalline materials prepared by pulse electrodeposition have the advantages of homogeneous composition,low porosity,small and compact tissue and high surface hardness,So,by using pulse electrodeposition method,the nanocrystalline Ni foil with a gradient distribution of grain size in the thickness direction was prepared with the dynamic adjustment of electrodeposition parameters.Through the brittleness test and the cross section hardness test,the difference between the toughness of the gradient nanocrystalline nickel foil and the nanocrystalline Ni foil with ordinary uniform grain size was analyzed.The results show that the nanocrystalline Ni foil with the grain size distribution has a higher surface hardness and better toughness,so it is more beneficial to the microforming.To investigated the micro-bending properties of two different nanocrystalline Ni foils,we designed the "U" type and "V" type micro-bending die with different bending fillet and bending angle.The bending results show that the graded nanocrystalline Ni foils have better micro-bending properties.In order to further improve the formability of materials,a high density pulse current was introduced into "V" micro-bending test to study the influence of pulse current density on bending rebound.In order to deeply analyze the effect mechanism of impulse current on micro-bending rebound of material,the stress relaxation experiment under impulse current was designed and the effect of impulse current on micro-forming of nanocrystalline Ni foil was further analyzed by TEM micro-analysis mechanism.The results show that the high density pulse current can promote the elastic deformation to plastic deformation to a certain extent,so as to improve the micro-bending forming ability of nanocrystalline metal foil and reduce the bending rebound.The greater the current density,the more obvious the promotion effect.