Study On The Evolution And Mechanism Of Comprehensive Performance Of Micro-scale Copper Conductor Materials

In recent years,metal foil sheets have been increasingly used in the electronics industry,microelectromechanical systems,medical and new energy fields.Plastic micro-forming technology has become the first choice for the batch production of micro parts with its advantages of high efficiency,high quality and low cost.However,the comprehensive properties such as mechanical properties and fracture behavior of microscale conductor materials are very different from those of macroscale materials,and not much research work has been done in this area,which restricts the development of microscale conductor materials.Therefore,it is necessary to study the size effect of microscale conductors during plastic deformation.In this paper,pure copper wire and foil were subjected to unidirectional tensile experiments with samples of different macroscopic dimensions and grain sizes to investigate the dimensional effects of parameters such as yield strength,tensile strength and elongation.The microscopic defects affecting their electrical conductivity are quantified,and new ideas are proposed to lift the constraints on the comprehensive performance improvement of microscale conductor materials.The results of tensile experiments show that the yield strength exhibits the dimensional effect of "the smaller the stronger".Under the reinforcing effect of strain gradient,the yield strength of copper foil with thickness less than 70-100?m shows a tendency of"the smaller the stronger" in relation to thickness.After annealing,the orientation of the ultra-fine copper wire is mainly<100>and<111>oriented grains,and as the macroscopic size of the sample decreases,the<100>oriented grains gradually decrease and<111>gradually increase.When the annealing temperature increases the grain growth so that there are only a few grains in the cross section,the growth of the dominantly oriented grains increases the Taylor value significantly with the decrease of the macroscopic size.The tensile strength shows a size effect of "smaller and weaker".Grain size has little effect on the tensile strength of microscale copper wire,which decreases with increasing grain size when the grain size is small.When the grain size is at the same level,the tensile strength is proportional to the macroscopic size,and when the macroscopic size increases to greater than 150-200 ?m,continuing to increase the macroscopic size will not increase the tensile strength.The grains at the surface of the sample have poor ability to accommodate dislocations,and dislocations escape from the sample surface to form slip steps,while dislocations cannot accumulate inside the grains.Using the surface layer model to incorporate surface layer grains and internal grains into the statistical model separately can better predict the changes of flow stress during the tensile process.The elongation of microscale copper decreases with increasing grain size at a certain macroscopic size;at comparable grain size,the elongation is proportional to the macroscopic size and changes from mono-system slip to multi-system slip with increasing macroscopic size,leading to a subsequent increase in flow stress and a change in fracture morphology from slip fracture to slip-tough nest type fracture.The hole growth rate of microscale copper materials under different conditions was calculated using a spherical hole model and the ontological equations giving strain gradient theory.The effect of macroscopic size variation and weave variation on the tensile deformation of polycrystalline wire was simulated using grain plasticity finite element.D/d is 1,it exhibits a single crystal-like nature with elevated strength.D/d is greater than 1,strain starts to appear from the inner grains,forming a unidirectional slip band,which further expands between the grains to form a penetrating slip band.As D/d continues to increase,multiple directional slip systems open up and deformation receives constraints from grain boundaries,forming intersecting slip bands.As D/d decreases,the surface grain increases and the strength value decreases,and the surface grain softening effect is the main reason for triggering the scale correlation.Single crystal copper samples with different dislocation density contents were prepared by the control variable method,and the values of resistance were linearly correlated with dislocation density,and the influence coefficient of residual resistance on dislocation density was about 0.6780×10-25 ?·m3 according to the slope method.copper wire samples with different grain boundary ratios were prepared by the heat treatment method,and the residual resistance for targeting large-angle grain boundaries and small-angle grain boundaries were 0.74×10-15 ?·m2 and 1.87×10-15 ?·m2.The main source of residual resistance is the resistance contributed by grain boundaries,followed by the effect of vacancy density,dislocations and surface scattering have less effect on the resistance,and the contribution of surface scattering to the resistance is not obvious in relation to macroscopic dimensions.