Void Evolution Of Cu/Al/Cu Three-layer Film Prepared By Casting Under Cyclic Loading And Uniaxial Tension Was Studied By Molecular Dynamics Simulation

Two dissimilar metal of Cu and Al are combined to form a composite material,which can combine the high electrical conductivity and high thermal conductivity of Cu with the light weight,corrosion resistance and economic characteristics of Al.At present,it has great applications in various fields such as electronics,electric power,automobiles,and energy.Cu and Al composite materials have become an important research direction of people.In this paper,molecular dynamics methods are used to study the void evolution mechanism of the Cu/Al/Cu three-layer film under cyclic loading.At the same time,the effect of the void shape on the mechanical properties of the Cu/Al/Cu three-layer film under uniaxial tension is analyzed.The results of the study are as follows:(1)Molecular dynamics method is used to simulate the deformation process of the Cu/Al/Cu three-layer film prepared by the casting method under cyclic loading,and is also used to analyze the evolution mechanism of the voids.The results show that the voids appear at the middle of the Al film and the interface near the Al film side.The evolution process of the void at the middle of the Al film is as follows: Hirth dislocation and Stair-rod dislocation at the middle of the Al film are overcome,resulting in a gap.The two newly formed Hirth dislocations are overcome and the gap grows.The nucleation of the void emits dislocation loop several times,and the vacancy group grows and forms the void.Detwining crystal forms a stacking fault to release the stress and then the void grows.The stress concentration and release make the stacking fault disappear and reappear,and then the void further grows.The newly formed stacking fault intersects with the previous stacking fault,and by emitting dislocations,the void grows to the maximum.Under the compressive force,the void is filled with atoms of OTHER structure,which shrinks into a vacancy cluster along the strain loading direction,and the atoms of OTHER structure around the void are converted into atoms of FCC structure.The void is filled with atoms of OTHER structure,and closes;The evolution process of the void near the Al side at the interface is as follows: Hirth dislocation and Stair-rod dislocation are overcome,and a gap appears.As strain increases,the atoms of the HCP structure at the nucleation of the void are converted to the atoms of the OTHER structure,and the gap grows along the strain loading direction to form the void.Continue to load,and the void slightly increases along the strain loading direction.Subsequently,the void follows the vertical strain loading direction.Stacking faults appear,stress is released,and then void grows along the direction of strain loading.Continue to load,and the void shrinks into vacant cluster along the strain loading direction,and atoms of OTHER structure fill the void.The atoms of OTHER structure around the void are converted to atoms of FCC structure,so void closes.(2)Molecular dynamics simulation was used to study the deformation process of the Cu/Al/Cu three-layer film with square and spherical voids under tensile load,and the evolution mechanism of the voids was analyzed.The tensile deformation process of the Cu/Al/Cu three-layer film with square voids is similar to that of the Cu/Al/Cu three-layer film with spherical voids.In the process of uniaxial stretching along the[001] crystal direction,the deformation process can be divided into three stages: elastic deformation stage,plastic deformation stage and fracture stage.The voids along the direction of the direction of strain loading,and then grows along the direction perpendicular to the strain loading.Finally,the Cu/Al/Cu three-layer film with voids is fracture at the Al-based Cu film.The Cu/Al/Cu three-layer film with square voids has higher yield strength and lower tensile strength.Under the same loading conditions,the Cu/Al/Cu three-layer film with square voids fails earlier than those with spherical voids.It shows that the shape of the void has a greater impact on the mechanical properties of the Cu/Al/Cu three-layer film.