High Temperatures Wear And Oxidation Resistant Electrodeposited Composite Coatings

The wear characteristics of electrodeposited composite coatings containing chromium carbide and alumina at temperatures up to 5007 ¢ have been investigated. Both chromium carbide and alumina improve the wear resistance in the temperature range 120°to 3507C. ‘The wear resistance of electrodeposited cobalt at elevated temperatures is determined by the ability to form an adherent glaze-like layer of compacted oxide. The presence of a particulate phase promotes the formation of a glaze in the temperature range 120°— 350°C (where the amount of oxide present would otherwise be insufficient), and the retention of’ the glaze which would normally spall as a result of thermal cycling. ‘The inclusion of alumina in cobalt-chromium carbide deposits did not result in an improvement in wear resistance. Alumina did however affect the size and volume fraction of chromium carbide code posited. The oxidation characteristics of cobalt-chromium carbide have also been studied between 600°C and 1,000° Cc. The oxidation rate of Co/CrzC5 is less than that of cobalt and decreases with increasing carbide content. Chromium involvement, as result of carbide breakdown, in the oxidation process is observed after prolonged exposure or at high temperatures. The presence of a particulate phase also results in the inward growth and reduction in stress of the oxide. Cobalt—chromium solid solutions produced as a result of complete breakdown of chromium carbide by heat treatment in an inert atmosphere possess comparable oxidation characteristics to those of conventional cobalt-chromium alloys. The influence of both agitation and current density on the composition of composite coatings have been investigated to aid control of the production of composites, particularly in obtaining a desired particle content. The limitation of particle contents obtainable from the conventional agitation systems has led to the development of a rotating barrel technique for producing high particle loadings. This is currently being used for the development of oxidation resistant coatings.