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Process for forming nitride protective coatings

  • US 5,599,404 A
  • Filed: 04/25/1995
  • Issued: 02/04/1997
  • Est. Priority Date: 11/27/1992
  • Status: Expired due to Term
First Claim
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1. A method of forming a specific reactive element barrier layer on a surface of a substrate material, said substrate material being essentially free of free sulfur and other contaminants capable of segregating to said substrate material surface, and further containing specific reactive elements selected from the group consisting of aluminum, titanium, zirconium, tantalum, columbium, silicon, beryllium, manganese, uranium, vanadium, magnesium, thorium, calcium, barium, rare earth elements, and combinations thereof, and elements whose nitrides are less stable than a corresponding nitride of the specified element said method comprising the formation of a nitride barrier layer wherein said barrier layer is formed by:

  • a) placing at least the surface and contiguous region of said substrate material in contact with a static or flowing process medium at a temperature from about 1000°

    F. to about 2000°

    F. and containing a specified process medium nitrogen concentration;

    b) monitoring and controlling the temperature and concentration of said process medium to maintain the same within the specified ranges;

    c) reducing said less stable atom nitrides at the substrate surface and reacting said specific reactive element atom at said substrate surface, said reaction occurring only with said nitrogen provided by said process medium to form a specific reactive element, such formation causing a specific reactive element atom concentration gradient between the surface and interior of said substrate material; and

    d) continuing to maintain said substrate material surface in contact with said process medium within said specific temperature range such that said specific reactive element concentration gradient causes said specific reactive atoms in the substrate material interior to diffuse to the surface of said substrate material, where they react with the nitrogen provided by said process medium until a uniform, lateral growth of specific reactive element barrier layer is formed, said barrier layer being strongly bonded to said substrate material surface,wherein said process medium is selected from the group consisting of;

    1) a hydrogen/ammonia atmosphere having a nitrogen concentration from about 0.01 ppm to about 10 ppm; and

    2) liquid lithium having a lithium nitride concentration from about 1 ppm to about 500 ppm.

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