Abstract: There is disclosed a method for producing corrosion and erosion-resistant mixed oxide coatings on a metal substrate, as well as a mixed oxide coating itself. A surface of the substrate metal is oxidized and converted into a first coating compound comprising a primary oxide of that metal by a plasma electrolytic oxidation (PEO) process. One or more secondary oxide compounds comprising oxides of secondary elements not present in conventional alloys of the substrate metals at significant (>2 wt %) levels are added to the first oxide coating. The source of the secondary element(s) is at least one of: i) a soluble salt of the secondary element(s) in the electrolyte; ii) an enrichment of the surface of the substrate metal with secondary element(s) prior to PEO processing; and iii) a suspension of the secondary element(s) or oxide(s) of the secondary element(s) applied to the oxide of the metal after this has been formed by the PEO process.

Abstract: There is disclosed an insulated metal substrate, consisting of a dielectric oxide coatings of high crystallinity (>vol 90%) on aluminium, magnesium or titanium and high thermal conductivity (over 6 Wm?1K?1), formed by plasma electrolytic oxidation on a surface comprising aluminium, magnesium or titanium. There is also disclosed a plasma electrolytic oxidation process for generating dielectric oxide coatings of controlled crystallinity on a surface of a metallic workpiece, wherein at least a series of positive pulses of current are applied to the workpiece in an electrolyte so as to generate plasma discharges, wherein discharge currents are restricted to levels no more than 50 mA, discharge durations are restricted to durations of no more than 100 ?s and are shorter than the durations of each the positive pulses, and/or by restricting the power of individual plasma discharges to under 15W.

Abstract: There is disclosed a method for producing corrosion and erosion-resistant mixed oxide coatings on a metal substrate, as well as a mixed oxide coating itself. A surface of the substrate metal is oxidised and converted into a first coating compound comprising a primary oxide of that metal by a plasma electrolytic oxidation (PEO) process. One or more secondary oxide compounds comprising oxides of secondary elements not present in conventional alloys of the substrate metals at significant (>2 wt %) levels are added to the first oxide coating. The source of the secondary element(s) is at least one of: i) a soluble salt of the secondary element(s) in the electrolyte; ii) an enrichment of the surface of the substrate metal with secondary element(s) prior to PEO processing; and iii) a suspension of the secondary element(s) or oxide(s) of the secondary element(s) applied to the oxide of the metal after this has been formed by the PEO process.