Exploring Plastic Deformation Mechanism Of Multilayered Cu/Ti Composites By Molecular Dynamics Modeling

Multilayered metallic composites have been widely used in the field of high technology due to their high strength,hardness,excellent thermodynamic stability,impact resistance and radiation damage resistance.This kind of material is often subjected to large strain deformation during processing and subsequent service,which puts forward a high requirement for its ability to resist deformation damage.Therefore,the study of its mechanical behavior has become one of the hot topics in materials science.At present,researchers at home and abroad mainly focus on the microdeformation of ultrafine scale layered complexes in fcc and bcc systems.Although the superfine scale laminated composites with hcp structure is revealed the mechanism of plastic deformation to some extent,the mechanism of plastic deformation at atomic scale is still unclear.In this thesis,the nanocrystalline multilayer Cu/Ti composites with some characteristic crystal orientations at the fcc/hcp heterostructure interface are considered as the object of study.By means of molecular dynamics simulation of uniaxial tensile and plane strain compression deformation,the microscopic mechanism of starting and spreading of deformation configuration(including dislocation,twinning and shear band)at heterogeneous interface is revealed at atomic scale.The specific model and deformation model are:Employ simulation of plane strain compression deformation with Model Ⅰ(Ti is basal orientation,Cu is Copper orientation.)and Model Ⅱ(Ti is basal orientation,Cu is Goss orientation.).Employ simulation of uniaxial tension deformation with Model Ⅱ(Ti is basal orientation,Cu is Copper orientation.)and Model Ⅳ(Ti is basal orientation,Cu is Goss orientation.).The simulation results are as follows:During plane strain compression deformation,1/6<112>Shockley dislocations are preferentially nucleated at the heterogeneous interface between Cu and Ti,and then slip along {111} plane within the Cu layers.The corresponding mechanism is confined layer slip.After the dislocations run through the Cu layer,the intrinsic stacking faults and deformation twins are formed in Cu layers.The stress concentration at the interface leads to the shear band moving in the hard phase Ti layer.With the increase of the strain load,the grain of the model rotates.In addition,the initial orientation has an important effect on the microscopic deformation process of Cu/Ti composites.With the increase of strain,the degree of atomic disorder in the complex increases.Plastic deformation occurred earlier in Model I than in Model II,which shows that the 1/6<112>Shockley incomplete dislocation in the Cu layer orientation of the copper is easier to nucleate and move under the plane strain compression loading.For the plane strain compression deformation at different temperatures,with the increase of deformation temperature,the stress value of the whole model decreases and the strain corresponding to the peak value of the model stress decreases.The change of temperature has obvious influence on the starting time of deformation system,but there is no obvious difference in plastic deformation mechanism.With the increase of strain rate,the yield point of the model is delayed and the yield strength increases.When the strain rate reaches 1011/s,the model will become amorphous during deformation,and work hardening will occur with the increase of strain.The effect of temperature and deformation rate on Model Ⅰ and Model Ⅱ is consistent.During plane strain compression deformation,1/6<112>Shockley dislocations are preferentially nucleated at the heterogeneous interface between Cu and Ti,and then slip along {111} plane within the Cu layers.The corresponding mechanism is confined layer slip.After the dislocations run through the Cu layer,the intrinsic stacking faults and deformation twins are formed in Cu layers.With the increase of strain load,the grain of the whole model rotates and the stress concentration occurs at the Cu/Ti heterogeneous interface,which leads to the fracture of the complex.Compared with Model Ⅲ,Model Ⅳ occurs plastic deformation earlier than Model Ⅲ.However,with the increasing of load,the ability of uniform plastic deformation is better.For uniaxial tensile deformation at different temperatures,the stress value of the whole model decreases with the increase of deformation temperature,and the temperature has a significant effect on the starting time of the deformation system,but there is no obvious difference in the plastic deformation mechanism.By comparing the deformation process of Model Ⅲ and Model Ⅳ,the maximum elongation of ModelⅢ was higher than Model Ⅳ at 77 K and the maximum elongation of Model Ⅲ at 450 K was lower With the increase of strain rate,the yield point of the model is delayed and the yield strength increases.When the strain rate reached 1011/s,the necking position of the model increased significantly,and the elongation of the model as a whole increased due to multiple necking.The effect of increasing deformation rate on Model Ⅲ is consistent with that of Model Ⅳ.The results show that the mechanism of plastic deformation under different deformation mode,temperature and strain rate is clearly revealed from atom angle,so it can provide theoretical guidance for designing and developing high strength and high toughness hexagonal metal composite material and material safety service.