Interplay between bond breaking and plasticity during fracture at a nanomolecularly-modified metal-ceramic interface

Abstract

International audienceWe reveal the roles of moisture and temperature on the interplay between interfacial work of adhesion gamma(a) and metal plasticity gamma(p) for copper-silica interfaces modified with an organosilane nanolayer. We find that gamma(p) not equal 0 for interfaces with metal thicknesses h(cu) > 12 nm, and increases with ha, before it saturates at h(cu) similar to 165 nm. For a fixed h(cu), gamma(p) increases due to temperature-induced yield stress decrease despite a decrease in gamma(a) with temperature because of water-induced siloxane bond weakening. These findings should be valuable for understanding the fracture mechanics of, and designing, nanomolecularly-functionalized interfaces subject to thermomechanical and chemical stresses. (C) 2016 Elsevier B.V. All rights reserved

Frequency-tunable toughening in a polymer-metal-ceramic stack using an interfacial molecular nanolayer

“…We prepared polymer-metal-MNL-ceramic structures sandwiched between two silica-capped Si(001) wafers for four-point-bend mechanical tests 19 (Fig. 1a ).…”

“…Without breaking vacuum, we also deposited a 100-nm-thick Ta layer to facilitate metal-polymer bonding 17 . We glued the metal-MNL-silica structures to a dummy Si wafer with a System Three Resins ® T88 epoxy polymer to obtain beams comprised of layered Si-polymer-Ta-Cu-MPTMS-SiO 2 -Si structures for four-point-bend mechanical tests 19 (Fig. 1a ).…”

“…We extracted the Γ Fatigue from strain energy release rate-crack velocity ( Γ - u crack ) plots by recognizing that Γ = Γ Fatigue at u crack = 0. We also determined the stress corrosion fracture energy Γ Static from static load tests 19 to explicitly separate the effects of chemical attack and load-cycling. The fracture surfaces were examined by X-ray photoelectron spectroscopy (XPS) and polarized-light microscopy.…”

“…Since moisture weakens siloxane bonds, our results indicate a minimum interface bonding strength, attainable below a threshold , is a prerequisite for fatigue toughening. This is reminiscent of static toughening at Cu-MPTMS-SiO 2 interfaces below a threshold that provides adequate siloxane bonding strength to enable metal plasticity 18 , 19 .

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“…But, loading-frequency-dependence of interfacial fatigue, and related phenomena, remain largely unexplored. Our prior work has shown that introducing an interfacial molecular nanolayer (MNL) in model polymer-metal-ceramic structures can yield multifold increases in fracture energy under static loading 16 – 19 , enhance thermal 20 and electronic 21 – 25 transport, inhibit diffusion 26 – 28 , and alter phase formation 29 . However, the effects of cyclic loading on the fracture behavior of such molecularly modified model systems are not known.…”