Unraveling the Role of Interfaces on the Spall Failure of Cu/Ta Multilayered Systems

Jie Chen,Naresh Thadhani,Avinash M Dongare,Suveen N Mathaudhu

doi:10.1038/s41598-019-57048-9

Jie Chen, Naresh Thadhani + Show 2 more

Open Access

https://doi.org/10.1038/s41598-019-57048-9

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Abstract

Molecular dynamics (MD) simulations are carried out to investigate the effects of the type and spacing of FCC/BCC interfaces on the deformation and spall behavior. The simulations are carried out using model Cu/Ta multilayers with six different types of interfaces. The results suggest that interface type can significantly affect the structure and intensity of the incoming shock wave, change the activated slip systems, alter dislocation slip and twinning behavior, affect where and how voids are nucleated during spallation and the resulting spall strength. Moreover, the above aspects are significantly affected by the interface spacing. A transition from homogeneous to heterogeneous dislocation nucleation occurs as the interface spacing is decreased to 6 nm. Depending on interface type and spacing, damage (voids) nucleation and spall failure is observed to occur not only at the Cu/Ta interfaces, but also in the weaker Cu layer interior, or even in the stronger Ta layer interior, although different mechanisms underlie each of these three distinct failure modes. These findings point to the fact that, depending on the combination of interface type and spacing, interfaces can lead to both strengthening and weakening of the Cu/Ta multilayered microstructures.

Highlights

Nanoscale multilayered materials are an emerging class of materials that render a unique combination of high thermal stability, strength, and damage resistance[1,2]
A systematic study of the role of length scales of interfaces on the deformation and spall failure behavior is currently missing. It is not clear if a decrease in layer spacing will modify the deformation twinning/de-twining behavior of the Cu layers and the Ta layers. This raises the questions: (a) Will the spall failure always be observed in the weaker Cu layers, or is this determined by the structure and spacing of the interfaces wherein voids can be observed to nucleate and grow in the Ta layers? (b) Does the observed length scale dependence of spall strength values for the multilayered structures exist for all interface structures? While the current state-of-art experimental capabilities use in situ femtosecond XRD for characterization of deformation mechanisms under shock loading conditions[23,24,25], such questions are still very challenging to explore experimentally, given both the small length scales of the phenomena and the short time scales over which they occur
The entire simulation duration is divided into four stages and marked here for analysis: Stage I (SI) – shockwave compression generated by driving the piston for a www.nature.com/scientificreports given pulse (10 ps); Stage II (SII) – release of the compression wave starting at 10 ps and ends when the compression wave reaches the rear surface at ~20 ps; Stage III (SIII) – starts at the expansion of the rear surface, interaction of release waves and creation of triaxial tensile pressures that results in onset of spall failure; and Stage IV (SIV) – corresponds to void nucleation, growth and spallation

Summary

Introduction

Nanoscale multilayered materials are an emerging class of materials that render a unique combination of high thermal stability, strength, and damage resistance[1,2]. The shock compression behavior (dislocation slip vs deformation twinning) and spall failure (void nucleation and growth) behavior of multilayered microstructures are observed to vary with interface structure and spacing. For multilayered FCC/BCC microstructures, the current studies investigating the shock response have largely focused on the wave propagation behavior[42,43], dislocation nucleation behavior[44] and spall failure[45] in Cu/Nb composites. This work, aims to carry out a systematic study of the role of the structure (orientation) and spacing of Cu/Ta FCC/BCC interfaces on the atomic scale deformation mechanisms during shock compression and spall behavior of the multilayered microstructures using MD simulations. The study uses six Cu/Ta multilayered microstructures with six commonly occurring FCC/BCC interfaces with layer spacing ranging from 6 nm to 47 nm for each layer as model systems

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