Study On Grain Refinement Evolution Behavior And Characteristics Of T2 Copper Under Impact

Copper material has good thermal conductivity and ductility.It is widely used in the fields of weapons and equipment,power transmission,electronic devices,vehicles and ships,but it has some shortcomings such as low strength and poor fatigue resistance.By introducing severe plastic deformation layer to prepare gradient nanostructured materials,the serviceability of the materials can be greatly improved,and the production cost is low and the application range is wide.In recent years,scholars at home and abroad have made great progress in the study of surface mechanical treatment preparation,and have also done some research on the microstructure change,but there are many limitations.For example,the influence of contact force,energy absorption and energy absorption on the plastic strain of materials in contact interface dynamics,the evolution law of material microstructure under different strain degrees,and the evolution law of surface quality in the preparation process have not been analyzed in detail.In this paper,T2 copper as the research object,through the use of kinetic impact control test device impact T2 copper surface induced severe plastic deformation layer.By electron backscattering diffraction(EBSD),scanning electron microscopy(SEM),three-dimensional profilometer and transmission electron microscopy(TEM),the evolution law of the surface morphology and microstructure of craters after impact was analyzed.Combined with the dynamic behavior of the material contact interface during impact,The evolution of impact parameters,dynamic behavior of impact interface,microstructure and surface quality are discussed in detail.The main conclusions are as follows:1.A single location,impact velocity as variables:punch in the process of impact energy dissipation(ΔE)and the energy absorption(η)increases with the increase of impact velocity.According to the law of conservation of energy,this part of energy is not only transformed into plastic deformation energy,but also into material wear energy.The wear energy is particularly obvious at low and high speeds.It is easy to form contact fatigue damage between punch and material at low impact speed.At higher impact speed,the punch and the material will form obvious sliding wear,resulting in obvious stripping and cracks in the sliding area.And the increase of impact velocity will lead to the increase of peak impact force(Fmax)and surface hardness of the material.From the perspective of individual craters,the plastic deformation of impact craters is not uniform,resulting in different nanohardness in different regions of the craters.From the inside out,the plastic deformation gradually weakens,resulting in a decrease in hardness.2.In a single position with cumulative impact energy as a variable,appropriate cumulative impact energy can eliminate the initial defects of T2 copper and improve the surface quality of the material.And high cumulative impact energy will cause sliding damage.With the increase of accumulated energy,the crater edge deformation goes through a process from the appearance of resident slip line,resident slip density,surface fold,and finally the formation of "orange peel phenomenon".With the increase of accumulated energy,the volume of craters gradually increases slowly,and the substructure within the grain of craters increases obviously,and the anti-plastic deformation ability of the material increases.Enhanced ability to resist deformation and the material is lead to increased Fmax and ΔE andη decreases,the main reasons for the main way of grain deformation by dislocation proliferation and movement,and a single point of impact effect on the grain size is not obvious.From the perspective of a single crater,the heterogeneous plastic deformation of grain dislocation density around the crater is different,and the dislocation density at the center is higher than that at the edge,resulting in stronger hardness and deformation resistance than that at the edge.At high cumulative energy,material damage will increase energy dissipation and energy absorption during the impact process.3.The two point position,overlapping rate for variables:overlap rate increase will lead to the second position in the craters ΔE and η can decreases,and the enlargement of Fmax.This indicates that the different overlap ratio can significantly change the resistance strength of the material.At a higher overlap rate,the plastic deformation zone of the crater is obviously divided into the secondary impact zone and the extrusion influence zone,and the grain refinement degree of the secondary impact zone is relative to that of the extrusion zone.In addition,there is obvious material accumulation around the crater,and the punch slides obviously,leading to serious wear and tear of the material.Obvious grain refinement occurs in surface grain of craters overlapping area.The evolution of grain refinement is divided into two stages:the first stage is the formation of sub-grain boundary by dislocation movement and entanglement;Dislocation motion and twinning act together in the second order stage,and the twinning process lags behind the dislocation motion,and the deformation caused by dislocation motion is obviously greater than that of the twinning process.