Interface mediated deformation and fracture of an elastic–plastic bimaterial system resolved by in situ transmission scanning electron microscopy. (November 2022)

• Record Type: Journal Article
• Authors: Alfreider, Markus; Balbus, Glenn; Wang, Fulin; Zechner, Johannes; Gianola, Daniel S.; Kiener, Daniel
• Is Part Of: Materials & design. Volume 223(2022)
• Publication Date: 2022-11
• Subjects: Mode mixity -- Interface toughness -- Thin films -- Crack extension -- TSEM; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2022.111136
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: A novel push-to-shear testing configuration for in situ transmission scanning electron microscopy is introduced. The failure behaviour of a highly ductile microscale Cu-WTi interface upon mode I or mode II loading are experimentally determined. Characteristics changed from void nucleation and coalescence (mode I) to nucleation and propagation of an interface crack (mode II). Dislocation dynamics and crack propagation combined with theoretical considerations serve to obtain failure parameter estimates. Abstract: 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 layers, or diffusion barriers. However, these layers are commonly only of the order of a few hundred nanometers 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 microelectronics 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 dislocation slip facilitated void nucleation and coalescence, was observed with an initiation value for dislocation propagation of J dislocation ≈15 J/m 2 . Mode II loading exhibited nucleation and propagation of an interface crack, with the initiation value for crack extension as J crack ≈8.8 J/m 2 . The results are discussed with respect to the frameworks of classical fracture mechanics and dislocation plasticity, providing fundamental insight into the failure behaviour of elastic–plastic interfaces with respect to loading orientation.