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STRESS-CORROSION CRACKING AT CERAMIC-METAL INTERFACES J. C. CARD, R. M. CANNON, R. H. DAUSKARDT and R. 0. RITCHIE Center for Advanced Materials, Materials Sciences Division, Lawrence Berkeley Laboratory, and Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720. ABSTRACT It is known that the fracture resistance of glass-copper interfaces depends strongly on the water content in ambient gaseous environments. In the present study, subcritical crack growth stimulated by water and other environmental species is investigated for such interfaces. Tests were conducted in various liquids, namely water, N-methylformamide, and n-butanol. All were found to accelerate fracture with the greatest effects from liquid water. Results are considered in the context of current models for stress-corrosion crack growth. INTRODUCTION Understanding the mechanical behavior of ceramic-metal interfaces is vital to predicting the performance and reliability of numerous components for advanced technologies. Composite materials, microelectronic devices, wear and corrosion resistant coated components all have mechanical properties that critically depend on the ceramic-metal interfaces contained within them. The integrity of such bimaterial interfaces is often characterized in terms of their resistance to fracture, as defined by a critical fracture energy Gc, or fracture toughness Kc [1]. However, since components often fail at stresses far below those required for such catastrophic failure, it is necessary to consider additionally subcritical crack growth [2] and cyclically induced fracture [3] at or near these interfaces when predicting in service life. It has previously been observed that glass-copper interfaces exhibit environmentallyassisted subcritical crack growth at rates that vary by orders of magnitude depending on the water content of the gaseous environment [2]. Accordingly, the purpose of the present ongoing study is to determine the accelerating effects of various liquid environments on such stress-corrosion crack growth relative to that in water. Results are being compared with those for bulk glass, rather than copper which is immune to stress corrosion in these environments [4], with the objective of providing some insight into the micro-mechanisms of stress-corrosion cracking along glass-copper interfaces. BACKGROUND A schematic crack velocity-driving force (u-G) curve for stress-corrosion cracking along a glass-copper interface (Fig. 1a) displays four distinct regimes of behavior which should be anticipated based on reported behavior [2,5]. Three of the regions, labeled I, II, and III, are analogous to the three regions readily observed for stress corrosion in bulk glass [6,7] (Fig. lb). Models for these regions, developed largely for glass, are described briefly. However, it is recognized that for interface cracks, a stress field rotation is introduced by elastic discontinuities [8] which makes the relationships among strain energy release rate, G, stress intensity factor K, and c