Effect Of Interface And Modulation Period On Mechanical Properties Of Nano-twin Fe And Cu/Fe Multilayers

Nanostructured materials have received extensive attention due to their excellent physical and mechanical properties.The mechanical properties of nanostructured materials mainly affected by the two factors:the interface and size of nanostructures.Twin coherent interfaces and incoherent interfaces are two kind of typical interfaces.In this work,we performed molecular dynamics?MD?simulations for the responses of nano-twinned Fe and Cu/Fe metal nano-multilayered films to investigate the effect of twin coherent interfaces,incoherent interfaces and modulation period on their mechanical properties,and made the following progress:?1?The mechanical responses of Nano-twinned Fe under tension and compression were simulated using MD respectively.It was found that implantation of a twin bsoundary in body centered cubic?BCC?Fe does not change the asymmetry of the responses under tension and compression,like face centered cubic?FCC?Cu.Under tensile loading,nano-twinned Fe may transform from BCC structure into FCC structure,and the degree of transformation can reach over 50%.At?=0.157,phase transition reaches the maximum when dislocation nucleation appears at the interface between BCC and FCC and then extends to the FCC layer.The maximum tensile stress of the nano-twinned Fe is smaller than that of pure Fe because of the phase transition,indicating that the implantation of twins in pure Fe may lead to softening,which is different from the conventional hardening mechanism of twins.It can be found that the stress reduction induced by phase transition in the stress of nano-twinned Fe is smaller than that induced by dislocation.Under compression,phase transition does not occur in nano-twinned Fe,and the inelastic deformation can mainly be attributed to the generation and annihilation of point defects.And the point defects are absorbed by the interface and the interface is thickened.Brittle fracture starts on both sides of the interface as the strain increases to 0.172.?2?The simulation of Cu/Fe metal nano-multilayered films?NMLFs?under tension and compression was performed.The influence of the incoherent interface and modulation period???on the deformation of Cu/Fe NMLFs was studied.It showed that the mismatch dislocations at the interfaces are periodic.At the Cu side of the interface,the mismatch image is of triangles distributed with the smallest period,while at the Fe side,it is of parallelograms distributes distributed with the smallest period.When subjected to tension,there are two yield points in the?-?curve of each sample,except the sample of?=2.10 nm where there is only one yield point in the?-?curve,corresponding respectively to the sequential nucleation of dislocations in the Cu and Fe sides of the interface.The two yield stresses increase with the increase of?.?has a critical value of?_cr=6.28 nm,for the cases of?<6.28 nm,the flow stress increases with the increase of?,but for the cases of?>6.28 nm,the flow stress decreases with the increase of?.It was found that the flow stress of the samples of some values of?is even larger than that of pure Fe,exhibiting distinct hardening,e yield stressAnalysis showed that for?>6.28 nm,the inelastic deformation can be attributed to confined layer slip?CLS?,while for?<6.28 nm,local bending occurs to the layers,attributed to the occurence of local instability that results in softening,and the smaller the?,the severer the bending and the smaller the flow stress.When subjected to compression,for the sample of?<6.28nm,the?-?curve has a drop before reaching the peak stress,while for the sample of?>6.28nm,no such a drop can be observed.?has also a critical value of?_cr=6.28 nm.As?<6.28 nm,the maximum stress increases with the increase of?,while as?>6.28 nm,the maximum stress almost keeps constant and the flow stress decreases slightly.