Continuous microscratch measurements of the practical and true works of adhesion for metal/ceramic systems

Using a continuous microscratch technique, the adhesion strengths of Pt, Cr, Ti, and Ta₂N metallizations to NiO and Al₂O₃ substrates have been characterized. The practical work of adhesion was determined as a function of both thickness and annealing conditions. For all except the Ta₂N films, the practical work of adhesion increases nonlinearly from a few tenths of a J/m² to several J/m² as the thickness of the thin film is increased, indicating that a greater amount of plastic work is expended in delaminating thicker films. Further, the practical work of adhesion also increases with increasing annealing temperature, indicating stronger bonding at the interface. In the limit that the film thickness tends to zero, the plastic energy dissipation in the film tends to zero. As a result, the extrapolation to zero thickness yields the true work of adhesion for that system.