Deformation and spallation of shocked Cu bicrystals withΣ3 coherent and symmetric incoherent twin boundaries

Abstract

We perform molecular dynamics simulations of Cu bicrystals with two important GBs, Σ3 coherent twin boundaries (CTB) and symmetric incoherent twin boundaries (SITB), under planar shock wave loading. It is revealed that the shock response (deformation and spallation) of the Cu bicrystals strongly depends on the GB characteristics. At the shock compression stage, elastic shock wave can readily trigger GB plasticity at SITB but not at CTB. The SITB can induce considerable wave attenuation such as the elastic precursor decay via activating GB dislocations. For example, our simulations of a Cu multilayer structure with 53 SITBs (~1.5 µm thick) demonstrate a ~80% elastic shock decay. At the tension stage, spallation tends to occur at CTB but not at SITB due to the high mobility of SITB. The SITB region transforms into a threefold twin via a sequential partial dislocation slip mechanism, while CTB preserves its integrity before spallation. In addition, deformation twinning is a mechanism for inducing surface step during shock tension stage. The drastically different shock response of CTB and SITB could in principle be exploited for, or benefit, interface engineering and materials design.

Ductile-to-brittle fracture transition in polycrystalline nickel under tensile hydrostatic stress

“…Similar results regarding an ultra-high strength behind the shock front due to increased dislocation activities were proved by Yuan and Wu [24]. Luo et al [25][26][27][28] studied the spall damage and void growth/collapse induced by a shock wave loading in Cu where the shock waves also induced local and bulk melting associated with anisotropy, premelting, superheating, supercooling and re-crystallisation [29]. Other researches focused on the effect of hydrostatic pressure on deformation.…”

Symmetric and asymmetric tilt grain boundary structure and energy in Cu and Al (and transferability to other fcc metals)

“…Many of the early studies (e.g., [5,6]) focused on understanding the grain boundary structure and energy. However, recent studies have expanded to address grain boundary sliding [7][8][9][10], migration and bulk dislocation slip transfer [11][12][13], grain boundary fracture [14][15][16] or spall [17][18][19][20], grain boundary segregation [21][22][23], phase transformations [24], grain boundary mobility [25,26], etc. In many cases, grain boundary structures have to be recreated in order to assess properties, and it is unclear whether the minimum energy structure was used or a higher energy metastable structure; hence, openly publishing grain boundary datasets in materials repositories can aid in providing a common starting configuration for these studies.…”

A review on atomistic simulation of grain boundary behaviors in face-centered cubic metals

“…Over the past decade, numerous efforts have sought to understand the influence of twin boundary on the behavior of nanocrystalline metals by atomistic simulations, including both the CTB and SITB [125][126][127][128][129][130]. The primary role of twin boundary is the obstacle to dislocation motion, but the blocking is not absolute.…”