IMPROVED PROTECTION AGAINST CORROSION AND FRETTING CORROSION FOR AIRCRAFT MATERIALS BY PVD-COATINGS

To substitute the ecologically critical cadmium as corrosion and fretting-corrosion protecting coating for aircraft materials aluminium-based PVD-coatings were tested. Apart from pure Al-coatings, Mg- or Li-alloyed Al-platings, in some cases additionally covered with a tribologically active top-coat (AlN; CrN). were deposited by IBAD- and Arc-techniques on the mild steel 1.7734, the martensitic chromium-steel 1.4548 and the titanium-based alloy 3.7164. In the condensed water- and salt-spray-test the corrosion protection for 1.7734 by Al-, Al/AlMg3- or AlLi-IBAD-coatings was not satisfactory because of the relatively high porosity of these coatings and an inhomogeneous Mg- and Li-distribution in the Al/AlMg3-IBAD- and AlLi-IBAD-platings. By depositing the more homogeneous Arc-coatings AlMg3 and above all AlLi a long-time corrosion protection could be achieved. In comparison to a Cd-plated 1.7734 the fretting-corrosion resistance was slightly improved by an AlLi/AlN-Arc-coating. The corrosion resistance of the electrochemically noble materials 1.4548 and 3.7164 in the condensed water- and the salt-spray-test was not affected by the deposited platings. In comparison to a Cd-coating, the fretting-corrosion resistance was improved by a TiC/i-C-IBAD-plating.