Inapparent Strengthening Effect of Twin Interface in Cu/Pd Multilayered Films with a Large Lattice Mismatch

Abstract

It has been found that there are two kinds of interfaces in a Cu/Pd multilayered film, namely, cube-on-cube and twin. However, the effects of the interfacial structure and modulation period on the mechanical properties of a Cu/Pd multilayered film remain unclear. In this work, molecular dynamics simulations of Cu/Pd multilayered film with different interfaces and modulation periods under in-plane tension are performed to investigate the effects of the interfacial structure and modulation period. The interface misfit dislocation net exhibits a periodic triangular distribution, while the residual internal stress can be released through the bending of dislocation lines. With the increase of the modulation period, the maximum stress shows an upward trend, while the flow stress declines. It was found that the maximum stress and flow stress of the sample with a cube-on-cube interface is higher than that of the sample with a twin interface, which is different from the traditional cognition. This unusual phenomenon is mainly attributed to the discontinuity and unevenness of the twin boundaries caused by the extremely severe lattice mismatch.in Cu/Pd multilayered film is unquestionable. Since Cu/Pd multilayered films were first found to have excellent mechanical performance, such as an increase of strength and hardness, in this work, it will be selected as a representative to study the mechanical properties of multilayered films [16][17][18][19][20].The modulation period (λ) and modulation ratio (η) are the thickness of a representative unit in a multilayered film and the ratio of the layer thickness of each constituent, respectively [21,22]. The change of λ and η may induce a change of interface proportion and the space for dislocation movement. Moreover, the grain boundary-dominated deformation mechanism may also vary with the variation of λ and η. For example, as λ decreases, the dominant deformation mechanisms in metallic multilayered films may vary from "dislocation pile-up" to "confined layer slip", or to "interface crossing" [21]. With the decrease of λ, the strengthening caused by the dislocation pile-up is weakened due to fact that a large number of dislocations between the interfaces can be stored in layers. However, the strengthening induced by the glide of single dislocations confined by interfaces ("confined layer slip") or the weakening resulting from dislocation crossing the interface ("interface crossing") dominate would play a leading role. Therefore, λ and η have significant effects on the mechanical properties of a multilayered film. This has an essential guiding significance to establish the relationship between the mechanical performance and modulation parameters for the design and development of high-performance multilayered films with excellent mechanical properties. In this work, we will mainly focus on the effects of λ on mechanical properties.Last but not least, interfaces, the transition zone between two components in nanostructured metallic multilayered films, can act as sources of defects, sin...

Effects of Anisotropy and In-Plane Grain Boundary in Cu/Pd Multilayered Films with Cube-on-Cube and Twinned Interface

“…μ = cos φ cos λ , where φ and λ are the Angle between the tensile direction and the normal direction of the slip plane and the Angle between the tensile direction and the slip direction, respectively. Moreover, when the tension is along x , the σ m and corresponding strain ε m of SC COC is slightly higher than that of the SC Twin, which is consistent with the work by Weng et al [ 25 ]. However, when the tension is along y , the σ m and ε m of SC COC are slightly lower than that of SC Twin.…”

“…Unlike the tiny difference in E , σ m and ε m , the difference between the σ f for the different interfacial structures is significant. When the tension is along x , the σ f of SC COC is larger than that of SC Twin, showing the strengthening effect of the COC interface is more obvious than that of the Twin interface, which is consistent with the work by Weng et al [ 25 ]. However, when the tension is along y , the σ f of SC Twin is 15.55% larger than that of SC COC, showing an obvious strengthening of the twin interface, which accords with the traditional cognition of strengthening effect of twin boundary.…”

“…investigated the effect of interfacial structure on the deformation behaviors of Cu/Ni multilayered films with coherent, semi-coherent and coherent twin interfaces using molecular dynamics (MD) simulation and found that the coherent twin interface shows significant strengthening [ 7 ]. However, in our recent work, the inapparent strengthening effect of the twin interface in Cu/Pd multilayered films was observed under tension along 〈110〉 direction [ 13 ]. Besides, the shape of the misfit dislocation network would change during energy minimization and relaxation.…”

“…These jogged dislocations are rarely found in a simulation under an out-of-plane loading [ 7 , 18 , 19 , 24 ]. In available MD simulations of in-plane tensions, the sample is usually stretched along a specific direction, i.e., 〈112〉 or 〈110〉 direction [ 25 ]. However, few comparative studies under tension along these two directions have been conducted.…”

Repeated Thermal Shock Behavior of ZrB2–SiC–Graphite Composite under Pre-Stress in Air and Ar Atmospheres

“…Zhang et al systematically investigated the thermal shock behavior of diboride-based UHTCs with additions such as carbon black, an SiC whisker, and disilicide (TaSi 2 ) [25][26][27][28]. Furthermore, the TSR of composites with additions of graphite, SiC fibers, SiC nanoparticles, carbon nanotubes, and carbon fiber were also extensively investigated [7,[29][30][31][32][33][34][35].…”