Adhesion in Metal-Ceramic Systems
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ADHESION IN METAL-CERAMIC SYSTEMS SHANKAR K. VENKATARAMAN, WILLIAM W. GERBERICH* AND DAVID L. KOHLSTEDT** *Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455. **Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455. ABSTRACT The adhesion of Pt thin films to NiO substrates has been studied using the continuous microscratch technique. Films of Pt ranging from 65 to 1080 nm in thickness were sputter deposited onto single crystals of NiO. Continuous microscratch experiments were performed by driving a conical diamond indenter, with a nominal radius of 5 grm, simultaneously into and across the film until a load drop was observed indicating that the film had delaminated. The practical work of adhesion was calculated using a theoretical model developed for metal-ceramic systems. The practical work of adhesion increases from 0.03 to 4.7 J/m 2 as the film thickness increases from 65 to 1080 nm. The practical work of adhesion includes the true work of adhesion -- the energy to produce two new surfaces -- and terms involving the plastic deformation of the film and substrate. Extrapolation of the practical work of adhesion versus film thickness data to zero thickness yields a first order estimate of the true work of adhesion. The true work of adhesion for the as-sputtered Pt/NiO system is determined to be 0.025 J/m 2, a value of the same order as the Van der Waal's energy. INTRODUCTION In the past few years, continuous microindentation and microscratch techniques have become powerful tools in the determination of the mechanical properties and adhesion strengths of thin films [1-31. These techniques are relatively simple, and samples can be tested in the same thin-film configuration as they are used in the particular application. Various properties such as hardness, elastic modulus, fracture toughness and adhesion strengths can be easily determined. Thin films have been used in a variety of electronic, engineering, optical, biomedical, and other applications. Thin films are used for various purposes: to provide resistance to abrasion, wear, corrosion and oxidation or to provide special magnetic or dielectric properties [4]. Whatever their intended use, the properties, structure, functional characteristics and performance all depend on the adhesion between the film and the substrate. There are a number of experimental techniques which measure adhesion between films and substrates. However, most of these techniques are only qualitative and serve as relative comparisons between samples. The peel test, bulge test and scratch tests, however, have been made quantitative and yield estimates of adhesion strengths [5-7]. The term adhesion, however, has been defined in different ways depending on the application. Mittal[4] has treated adhesion in three different forms: i) basic or true adhesion; ii) thermodynamic or reversible adhesion; and iii) experimental or practical adhesion.
Mat. Res. Soc. Symp. Proc. Vol. 308. ©1993 Materials Research Society
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