The influence of interfacial wetting and adhesion on the formation of voids at metal-ceramic interfaces

High temperature sessile drop experiments were conducted to evaluate the wetting (contact angle, surface/interface energies) on the basal C and prismatic A surfaces of sapphire by pure liquid Ni, and Ni alloyed with Al or S. After solidification of the drops, inspection of samples showed the presence of millimetre-sized voids at the interface between pure nickel and the basal surface of the sapphire substrate. However, no voids were found at the interfaces of pure Ni with the prismatic surface of sapphire, or at the interfaces of sapphire with Ni alloyed with 0.03at.%S or 2at.%Al, or if the pure Ni drops were significantly smaller in size. It is proposed that the voids form to release strain energy stored in the system, due to the dissimilar thermal expansion coefficients of Ni relative to sapphire. Alloying with Al and/or S retards interfacial void formation by enhancing the metal-ceramic interfacial wetting and adhesion. C 2006 Springer Science + Business Media, Inc.