There are many treatments on surface to improve hardness. One of them. tungsten-carbide coating by H.V.O.F has good hardness and wear resistance. But after rotating shaft(Al) coated tungsten-carbide to seal rotating surface operates in sea water, corrosion occurs on sealing surface coated WC H.V.O.F.
Considering corrosion, hardness, roughness of surface and porductivity, hard anodizing apply on sealing surface by verification test and research.