| 摘要 |
1. A process for forming a chemical coating in a vapour phase of halogenides, of the surface of metallic parts which must have a high hardness, resulting in the obtainment of monophase superficial layers of carbides of metallic elements of the following series : silicon, titanium, vanadium, chromium, zirconium, niobium, hafnium, tantalum and tungsten, this process, which does not comprise a prior ionic nitriding, being constituted by a gaseous cementation treatment of halogenides of at least one of the aforementioned metallic elements, at temperatures between 800 degrees and 1100 degrees C, during periods between 2 and 20 hours, characterised in that the halogenides of said metallic elements are obtained by using a cement maintained at a distance from the surface to be coated and comprising as sole constituents : at least one of said addition metallic elements, either in the form of ferro-alloy, or in the technically pure state in the metallic form ; an addition of ammonium chloride or fluoride in a proportion between 0.2 and 1.5% by weight of the total mass of the cement ; and an addition of powdered carbon in a proportion between 0.1% and 1.5% of the total mass of the cement, the atmosphere employed being constituted by a neutral gas. |
