SUBSTRATE SURFACE FINISH EFFECTS IN DUPLEX COATINGS OF PAPVD TIN AND CRN WITH ELECTROLESS NICKEL-PHOSPHORUS INTERLAYERS

The ability to deposit hard coating materials on to a wide range of su bstrate surface finishes and still maintain adequate structural and fu nctional properties is a very desirable objective in the quest to opti mise product economics. A better surface finish requires longer and mo re elaborate finishing processes which will result in substantial addi tional costs. In this investigation two different groups of substrate surface roughnesses were prepared for a number of appropriate testing procedures. The tests involved in this study were microhardness, surfa ce profilometry, scratch adhesion and the wet sand rubber wheel abrasi ve test. Electrochemical corrosion testing was also carried out. The r esults reveal that the substrate roughness can be optimised to achieve the best compromise in terms of cost and performance. The addition of an electroless nickel-phosphorus (ENiP) interlayer, in particular, is beneficial in isolating the substrate from near-surface effects and i n permitting the use of rougher surface finishes.