Surface modification of Ti–Al targets during cathodic arc evaporation

Surface modification of powder metallurgical and cast Ti–Al targets during a cathodic arc evaporation process was investigated by using X-ray diffraction, and optical and scanning electron microscopy. It was found that in the near-surface region of the powder metallurgical targets the arc process substantially contributes to the intermixing of the species, so that the worn powder metallurgical targets resemble the cast targets in worn state. At the outermost surfaces of the worn targets, inhomogeneous and partly non-continuous titanium aluminium nitride layers were found. The effect of the target microstructure on the phase formation, residual stress and crystallite size in the cathodic arc evaporated (Ti,Al)N coatings is illustrated on the example of Ti0.5Al0.5N coatings and compared with the effect of the bias voltage. Although the difference in the phase composition of the powder metallurgical and cast targets caused some variations in the microstructure of the coatings, it was shown that the microstructure of the coatings is much more influenced by the bias voltage than by the microstructure of the targets.

Research highlights
► Modification of surface regions in Ti–Al targets during cathodic arc evaporation.
► Interdiffusion of Ti and Al in powder metallurgical targets.
► Formation of additional phases in cast targets containing mainly gamma-TiAl.
► Local concentration gradients in a nitride layer grown at the target surface.
► Effect of the target microstructure on the microstructure of (Ti,Al)N coatings.