High temperature wear-resistant coatings

Abstract

Two families of detonation gun coatings have been developed primarily for use in high temperature wear-resistant applications. One of the coating types is based on a cobalt-chrome-tungsten alloy with a dispersion of chromia particles. The other system is based on cobalt-chromium-tantalum or cobalt-chromium-tantalum-aluminum alloys, with or without a dispersion of alumina. These coatings were studied in static oxidation for periods up to 100 h and in a high temperature fretting wear test at 1066 °C. The addition of about 10 vol.% Cr 2O 3 to the cobalt-chromium-tungsten alloy significantly improves the wear resistance relative to the coating or its welded counterpart without the chromia. Similarly the addition of about 30 vol.% Al 2O 3 to the cobalt-chromium-tantalum system significantly improves the wear resistance compared with the same coating without the alumina. The coatings without aluminum form a continuous protective chromia scale, whereas those with aluminum form, as expected, an alumina protective scale. Surprisingly, vacuum heat treatment at elevated temperature was not necessary to seal the coating effectively in order to prevent internal oxidation. An elevated temperature heat treatment, however, is recommended for some applications to ensure a stronger diffusion bond to the substrate. The results indicate that at intermediate temperatures the cobalt-chrome-tungsten+chromia coating is the preferred coating system but that at elevated temperatures the cobalt-chromium-tantalum+alumina system is superior.