GB2176809A - Process for applying hard coatings and the like to metals and resulting product - Google Patents

Abstract

Hard coatings are applied to substrate metals by coating the metal surface, e.g. by dipping the substrate metal in a molten alloy of the coating metals, and then exposing the coating at an elevated temperature to an atmosphere containing a reactive gaseous species which forms a nitride, a carbide, a boride or a silicide. The coating material is a mixture of the metals M1 and M2 of which M1 forms a stable nitride, carbide, boride or silicide under the prevailing conditions and of which M2 does not form a stable nitride, carbide, boride or silicide. M2 serves to bond the nitride, etc. of M1 to the substrate metal. Mixtures of M1 and/or M2 metals may be employed. This method is much easier to carry out than prior methods. Figure 1 shows a substrate alloy (10) with a laminar coating (11). Laminar coating (11) consists of intermediate metallic layer (12) and outer M1Xn layer (13). Figure 1A shows the substrate alloy (10), the outer M1Xn layer (13), a diffusion zone (D), and an intermediate zone (I). The diffusion zone (D) may be an alloy of one or more substrate metals and the metal M2 or it may be an interdiffusion layer resulting from diffusion of substrate metal outwardly away from the substrate (10) and of the metal M2 inwardly into the substrate. The intermediate zone (I) may be a cermet formed as a composite of M1Xn and M2.