interface usually promotes the adhesion between the film and substrate [13], and is a likely cause of the increased interface fracture toughness exhibited by the IBAD samples. SUMMARY Although results of interface fracture toughness measured from different tests, and sometimes within the same test, are not always consistent, general trend of the effect of silver has be established where the interface fracture toughness decreases with the amount of silver at the niobium/sapphire interface. Furthermore, the microscratch test results showed that the interface fracture toughness was related to the work of adhesion through a power law relation with the exponent equals to 3, supporting the result of Elssner et al. [2]. The ability to produce interface delamination depends on the test technique, but the values of interface fracture toughness obtained from different techniques fall into the same range (tens of J/m2 to tenth of J/m2). Ion bombardment during film deposition (IBAD) significantly increased the interface fracture toughness. Both ion mixing and development of an orientation relationship at the interface enhance the adhesion. The high interface adhesion of the IBAD niobium-sapphire system can be attributed to either one of the two factors or a combination of the two. Ion mixing is believed to be the primary cause. ACKNOWLEDGMENTS The authors would like to thank Dr. W. W. Gerberich and Dr. J. Nelson for providing help on microwedge scratch test. Qiong Zhao helped on preparing the samples used in the microwedge scratch test. The authors acknowledge the Michigan Ion Beam Laboratory for Surface Modification and Analysis and the Electron Microbeam Analysis Laboratory at the University of Michigan for the use of their facilities. This work was supported under NSF grant #DMR-9411141. REFERENCES 1. H. Ji, G. S. Was, J. W. Jones, and N. R. Moody, (1997) Mat. Res. Soc. Symp. Proc., Vol. 458, p 191. 2. G. Elssner, D. Korn, and M Rühle, (1994) Scr. Metall. et Mater. 31, no. 8, 1037. 3. M. P. Seah, (1980) Acta Metall., 28, 955. 4. J. R. Rice, Z. Suo, and J. S. Wang, (1989) In: Metal-Ceramic Interfaces, M. Rühle, M. F. Ashby, A. G. Evans, and J. P. Hirth, (Eds), Pergamon Press, Oxford. 5. H. Ji, G. S. Was, J. W. Jones and N.R. Moody, (1997), Proc. Mater. Res. Soc., Materials Research Society, Pittsburgh, vol 458, p. 191. 6. G. Elssner, T. Suga, and M. Turwitt, (1985) J. Phys. (Orsay), 46-C4, 597. 7. D. Korn, G. Elssner, H. F. Fischmeister, and M. Rühle, (1992) Acta. Metall. Mater. 40, suppl., S355. 8. M.G.Nicholas, (1989) In: Surfaces and Interfaces of Ceramic Materials’, p. 393, L.-C.Dufour (Ed), Norwell, MA, Kluwer Academic. 9. M. P. dE Boer, M. Kriese, and W. W. Gerberich (1997), J. Mater. Res. 12, No. 10, 2673. 10. M. P. dE Boer, H. Huang, and W. W. Gerberich, (1995) Mat. Res. Soc. Symp. Proc., Vol. 356, p. 821. 11. J. W. Hutchinson and Z. Suo, (1992) Advances in Applied Mechanics 29, 63. 12. H. Ji, G. S. Was, J. W. Jones, and N. R. Moody, (1996) Mat. Res. Soc. Symp. Proc. Vol. 434, p. 153. 13. J. E. E. Baglin, (1986) In: Ion beam modification of insulators, p. 585, P. Mazzoldi and G. W. Arnold (Eds), Amsterdam, Elsevier.
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