The effect of interfacial reactions on the fracture toughness of the bond between a reactive metal, Ti, and a relatively stable oxide αAl2O3, was studied for heat treatments at different temperatures. The microstructure, chemistry and fracture toughness of the interfaces were characterized using transmission electron microscopy and a continuous microscratch test. The formation of intermetallic compounds resulted in a deterioration in the interfacial fracture toughness, relative to an unreacted interface. The decrease in fracture toughness was related to the presence along the interface of a brittle intermetallic phase and cavities. The cavities were produced as a result of the volume change and the oxygen released during the formation of intermetallic compounds at temperatures of 600°C and above. The strongest interface exhibited little if any reaction between the Ti and the Al2O3.
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Acknowledgements--This research was supported by the U.S. Office of Naval Research under Grant No. N00014-91-J-1660. Q. Bai, D. L. Kohlstedt and W. W. Gerberich would like to thank the 3M company for financial support under ONR contract No. N00014-92-J-1962. The use of the Micromechanical Testing Facility of the Center for Interfacial Engineering at the University of Minnesota is kindly noted. The use of the Electron Microscopy Facility of the Materials Science Center at Cornell University, which is supported by the National Science Foundation under Award No. DMR-9121564, is gratefully acknowledged. The assistance of R. Keyse, J. Hunt, M. Thomas, B. Addis, R. Shewchuck and M. Rich is greatly appreciated.