DEFECTS IN TIN AND TIALN COATINGS GROWN BY COMBINED CATHODIC ARC UNBALANCED MAGNETRON TECHNOLOGY

During the cathodic are enhanced metal ion etching process of steel su bstrates droplets are generated on the cathode which deposit on the su bstrate surface. The concentration of the droplets obviously depends u pon the melting point of the target material. The number of droplets i s much greater for TiAl than for Ti. The composition of the TiAl dropl ets also depends on their size. Large droplets tend to have the same c omposition as the target material, whereas smaller droplets are enrich ed in Ti. The adhesion of the droplets to the substrate is very poor, certainly below L(c) = 20 N. A subsequent coating of the droplet conta minated surface with the unbalanced magnetron leads to growth defects. Nodule-like defects continue to form on the droplet itself, whereas o ther droplets are expelled from the coating surface during film growth , generating craters and dish-like growth defects. A simple explanatio n for the self-expulsion mechanism of droplets is given.