DGO-1: A metal coating/surface treatment resistant to cathodic delamination

Finding coatings/surface treatments that are resistant to cathodic delamination is not an easy task. Both the materials used and the inter-material bonds must be able to survive exposure to a very high pH (13-14) environment. During the last two years, the U.S. Navy has been testing non-conductive ceramic (NCC) coatings and a proprietary polymeric coating made by Teledyne/D.G. O'Brien called “DGO-1” for resistance to cathodic delamination. These experiments utilized an elevated temperature accelerated life test (ALT) in which solid, cylindrical monel 400 alloy samples were placed in a 66°C salt solution (3.5% sodium chloride) with zinc sacrificial anodes attached to simulate cable connectors subjected to an environment conducive to cathodic delamination. The DGO-1 coated samples were overmolded with PR-420 primer and PR-1547 polyurethane (PRC-DeSoto). The Arrhenius time-temperature correlation for this ALT was based upon the rate of cathodic delamination observed on bare metal monel 400 flat coupon samples made with the same primer and polyurethane encapsulant. One equivalent year (EY) of exposure was calculated to be 31.2 days in the ALT tank. Circumferential peel test data from the DGO-1 coated samples indicate that cable connectors of similar dimensions could be expected to last for 18 EYs under environmental conditions that promote cathodic delamination. DGO-1 coated samples lasted much longer than bare-metal samples made with PR-420 primer and PR-1547 polyurethane, and they also survived significantly longer than monel 400 samples with NCC coatings and standard seal coats overmolded with the same primer and polyurethane encapsulant.