Factors affecting growth defect formation in cathodic arc evaporated coatings

The origin of the conical features on the surfaces of arc evaporated hard compound coatings was investigated. A simple metallographic technique was employed to show that these conical features are growth defects made of the coating material (TiN in our case) precipitated by macroparticles of the cathode material, and not the macroparticles themselves. The effect of bias voltage characteristics, such as the amplitude (for d.c. voltage), frequency and duty cycle (for pulsed voltage), on the evolution of defects was also investigated. An increase in the amplitude or duty cycle resulted in a decrease in the defect density, R_a and the surface area covered with the defects. A simple explanation for the phenomena observed is suggested.