Interface mediated deformation and fracture of an elastic-plastic bimaterial system resolved by in situ transmission scanning electron microscopy

A wide variety of today's engineering material systems consist of multiple layered constituents to satisfy varying demands, e.g. thermal barrier-or hard coatings, thermal-or electrical conduction or insulation lay-ers, or diffusion barriers. However, these layers are commonly only of the order of a few hundred nanome-ters to microns thick, which renders conventional mechanical investigation of interfacial failure quite challenging, especially if plastically deforming constituents are involved. Herein, we present an in situ study of the mechanical deformation of a WTi-Cu model interface, commonly encountered in the micro-electronics industry, utilizing transmission scanning electron microscopy. This approach elucidated the interplay between plastic deformation and fracture processes when loading either perpendicular (mode I) or parallel to the interface (mode II). Under mode I purely ductile failure in the Cu phase, exhibiting dis-location slip facilitated void nucleation and coalescence, was observed with an initiation value for dislo-cation propagation of Jdislocation.:.15 J/m2. Mode II loading exhibited nucleation and propagation of an interface crack, with the initiation value for crack extension as Jcrack.:.8.8 J/m2. The results are discussed with respect to the frameworks of classical fracture mechanics and dislocation plasticity, providing funda-mental insight into the failure behaviour of elastic-plastic interfaces with respect to loading orientation. CO 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Automated summary

This study investigates the mechanical deformation behavior of a WTi-Cu model interface commonly found in the micro-electronics industry using in situ transmission scanning electron microscopy. The interplay between plastic deformation and fracture processes under different loading modes is observed. The results provide fundamental insights into the failure behavior of elastic-plastic interfaces under different loading orientations.