Method of producing coatings of high melting nitrides on metals

Abstract

Abstract Coatings of high-melting point nitrides of elements E are formed on metals or alloys M which have a reducing action on the halide of the element E and of which the halides are readily volatile below the melting-point of the metal M, by pre-casting from a nitrogen atmosphere containing at least one halide of the element E at a temperature at which the reaction is not intensely retrogressive, followed by deposition on the pre-coated metal surface at above 400 DEG C. from a nitrogen-hydrogen, ammonia, ammonia-hydrogen, ammonia-nitrogen or ammonia-hydrogen-nitrogen atmosphere containing at least one halide of E. Titanium nitride coatings may be formed on iron using titanium tetrachloride. Coatings of nitrides of one or more of Zr, Hf, V, Nb, Ta and B may also be formed and by including hydrocarbons in the gas mixtures, mixtures of nitrides and carbides may be produced. To avoid deposition on the object of nitrides formed in the gas space of the reaction chamber, the object to be coated may be heated directly by resistance or induction heating, and/or may be continuously turned; preferably, however, the object is enclosed in a shell closely conforming to the shaft of the object, to provide as little gas space as practicable around it; such shell may itself be of iron coated with titanium nitride.

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