CORROSION PROPERTIES OF ALUMINA COATINGS ON STEEL AND ALUMINUM DEPOSITED BY ION-BEAM-ASSISTED DEPOSITION

Hard and corrosion-resistant ceramic coatings like Al2O3 have shown pr omising protective properties in previous investigations. The aim of t his work is to deposit optimized Al --> Al2O3 layers on tool steel (Ck 45) and a common aluminum alloy (AlMgSi0.5). The major consideration i s to examine the influence of a graded metal-ceramic interface on inte rnal stress, adhesion and corrosion properties. For this purpose the w idth of the Al --> Al2O3 interface was varied by controlling the proce ss parameters during deposition. The electrochemical and corrosion beh aviour was determined by potentiodynamically controlled current-potent ial measurements under conditions of uniform corrosion attack and pitt ing corrosion. Further examinations of the local surface conditions we re made by scanning-micro-electrode (SME) microscopy. The adhesion was determined by scratch and pull-off tests and the internal stress was recorded in situ during the deposition process. The results show that optimized Al --> Al2O3 graded interfaces increase the hardness and imp rove the corrosion resistance in comparison with pure Al2O3 coatings. The adhesion is very good in all cases. (C) 1998 Elsevier Science S.A.