On the physics of moisture-induced cracking in metal-glass (copper-silica) interfaces

Environmentally dependent subcritical crack growth, or stress-corrosion cracking, along ceramic-metal interfaces is studied for the silica glass-copper system. Tests were conducted in various gaseous and liquid environments in order to determine their relative effects on stress-corrosion cracking and to gain some insight into the mechanisms that control interfacial crack growth. In agreement with previous studies, interfacial crack-growth rates were found to vary by orders of magnitude depending on the moisture content in gaseous environments. Water and several organic liquids, namely n-butanol, methanol, and N-methylformamide, were also found to promote stress-corrosion cracking. Specifically, crack-growth behavior was found to be largely dependent on the molecular structure of the test environment. Crack growth at high velocities was limited by either transport of the reactive species to the crack tip or by viscous drag contributions. Results are discussed in the context of the current mechanistic models proposed for the stress corrosion of bulk silica.