EFFECT OF THE SURFACE-ROUGHNESS OF SUBSTRATES ON THE CORROSION PROPERTIES OF FILMS COATED BY PHYSICAL VAPOR-DEPOSITION

The most important point in coating corrosion-resistant films is to make no pinholes. To research the relationship between the surface roughness and the birth of pinholes, we prepared a carbon tool steel, SK5(JIS), for substrates finished to various kinds of surface roughness (R(max) = 0.2-17-mu-m). Titanium and TiN were deposited on these substrates by the magnetron sputtering method. To detect pinholes, we carried out ferroxyl tests. The number of pinholes was counted by quantitative measurements using an image analyser. Furthermore, we researched the effects of total film thickness and multilayer coatings on the reduction in the number of pinholes. As a result, it was found that for R(max) < 1-mu-m (for titanium films) and for R(max) < 3-mu-m (for TiN films), the numbers of pinholes are less than 10 and 20 respectively in a 400 mm2 area. Also we could reduce the number of pinholes drastically by increasing the number of layers to 10 in multilayer coatings.