RATE EFFECTS IN METAL CERAMIC INTERFACE SLIDING FROM THE PERIODIC FILM CRACKING TECHNIQUE

The periodic film cracking technique [Agrawal and Raj, Acta metall. 37, 1265 (1989)] was used to characterize sliding mechanisms at the copper-silica interface of silica films on a copper substrate at temperatures up to 550-degrees-C and at strain-rates ranging from 1.7 x 10(-3) to 1.6 x 10(-5) s-1. Two regimes of behavior were observed. The sliding was strongly rate sensitive in the high temperature/Low strain-rate regime, with a power law stress component of n = 1.00 +/- 0.04. At low temperatures and/or high strain-rates, the crack-spacing was strain-rate independent. These results, when analyzed in terms of the global mechanisms of deformation in crystalline materials, Lead to the following interesting ideas: (a) the diffusional accommodation mechanism of sliding which assumes that diffusional transport can be applied to sliding at a wavy metal-ceramic interface shape, is consistent with the phenomenology of the strain-rate sensitive regime; (b) the non-linear power law creep mechanism (n almost-equal-to 4.5) is not observed for deformation near the interface, presumably because the width of the deformation zone near the interface is smaller than the characteristic subgrain size required in power law creep; (c) in the low temperature regime, interface sliding occurs by dislocation slip in the metal at or near the interface. We extend the concept of "deformation mechanism map" first introduced for bulk crystalline materials by Ashby [Acta metall. 20, 887 (1972)] to sliding at metal-ceramic interfaces.