Abstract
We performed molecular dynamics simulations for uniaxial tension of Cu/Fe nano-multilayered films with different modulation periods (λ) using Kurdjumov-Sachs (K-S) relationship to investigate their interfacial morphologies and the effects of λ on their mechanical properties. It shows that the mismatch dislocation lines at the interfaces are periodic. At the Cu side of the interface, triangles distribute with the smallest period; while at the Fe side, parallelograms distribute with the smallest period. There are two yield points, except the case of λ=2.10 nm where there is only one yield point, in the stress-strain curve of Cu/Fe multilayer film under tension, corresponding to the sequential nucleation of dislocations in the Cu and Fe layers from interface, respectively. We further found that there is a critical modulation period, λc, and the flow stress decreases with the increases of λ if λ > λc while increases with the increases of λ if λ < λc. The possible mechanisms are discussed.
Highlights
Copper-iron (Cu/Fe) nano-multilayers is a kind of FCC/BCC type multilayers which have been found to have a variety of applications, such as in magnetic devices and nuclear reactor structures, etc
It was reported that the thicknesses of Cu and Fe layers, and the grain size strongly influence the strength of Cu/Fe multilayers,[2] and in the Fe layer the lattice may change from BCC to FCC as its thickness is reduced to below 0.75 nm
The lattice mismatch at the interface can affect the nucleation of dislocations and the direction of dislocation propagation.[26]
Summary
Nano-multilayered films have attracted worldwide attention in recent years due to their extraordinary mechanical properties.[1,2,3,4] FCC/BCC interface is a kind of common interface in metallic multilayers, where there are two types of orientation relationships: 1) Kurdjumov-Sachs (K-S) relationship, (1 ̄11 ̄)fcc/(110)bcc and [011]fcc/[1 ̄11]bcc ; 2) Nishiyama-Wasserman (N-W) relationship, (1 ̄11 ̄)fcc/(110)bcc and [011]fcc/[001]bcc.[5,6] Copper-iron (Cu/Fe) nano-multilayers is a kind of FCC/BCC type multilayers which have been found to have a variety of applications, such as in magnetic devices and nuclear reactor structures, etc. Some experimental studies have been made on the mechanical properties and the microstructures of Cu/Fe nano-multilayered films.[2,7,8] Wang et al.[8] conducted compression tests on Cu/Fe multilayers and found that plastic deformation mainly takes place in Cu layers but cracks mainly appear in Fe layers. The effects of interface structure and modulation period on deformation mechanisms in Cu/Fe nano-multilayered films remain unclear
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