GB681250A - Coated metal machine parts, particularly jet engine parts - Google Patents

Abstract

A machine part e.g. a jet engine part, has a main body formed by a powder metallurgical process from one or more of the metals molybdenum, tungsten, tantalum, zirconium and titanium or alloys thereof, a thin coating layer consisting of one or more of the metals cerium, lanthanum, thallium, tin, copper, silver and gold and an impervious outer layer of one or more oxides solid and stable up to at least 1400 DEG C bonded to the thin coating layer. The oxides may be those of aluminium, chromium, cerium, lanthanum, thallium, titanium and zirconium. The metallic coating may be applied by a hot dip method, electroplating or vapour-plating and may be followed by heat treatment to form a superficial diffusion alloy; the oxide coating may be formed by heat treatment of the coating metal in oxygen (in the case of cerium, lanthanum or thallium), by anodization or by additional electrodeposition of the oxides of the coating metal or of another oxide or by baking on a ceramic coating. Alternatively, a second metallic layer (or several layers) may be formed e.g. by electroplating, and the outer layer, which may be of aluminium, oxidized by heating or anodization. In an example, molybdenum is cleaned electrolytically, treated with aqua regia, washed and dried, coated with cerium electrolytically using molten cerium p chloride at 800-850 DEG C, coated with aluminium electrolytically using 40-60 per cent potassium chloride and 60-40 per cent cryolite at 700-800 DEG C, washed, induction heated, and treated electrolytically to form a coating of mixed aluminium and titanium oxides using an aqueous solution of aluminium citrate and titanium potassium oxalate. In another form, the oxide may form part of a ceramic outer coating produced by firing thereon a frit containing e.g. titanium and/or zirconium oxides and a vitreous binder e.g. calcium, magnesium, aluminium and/or sodium silicates. The Specification as open to inspection under Sect. 91, comprises also references to the use of aluminium as the coating metal and thorium oxide as the oxide and to coating by a mist plating method. This subject-matter does not appear in the Specification as accepted.ALSO:A machine part e.g. a jet engine part, has a main body formed by a powder metallurgical process from one or more of the metals molybdenum, tungsten, tantalum, zirconium and titanium or alloys thereof, a thin coating layer consisting of one or more of the metals cerium, lanthanum, thallium, tin, copper, silver and gold, and an impervious outer layer of one or more oxides solid and stable up to at least 1400 DEG C. bonded to the thin coating layer. The oxides may be those of aluminium, chromium, cerium, lanthanum, thallium, titanium and zirconium. The oxide coating may be formed by heat treatment of the coating metal in oxygen (in the case of cerium, lanthanum or thallium), by anodisation or by additional electrodeposition of the oxides of the coating metal or of another oxide or by baking on a ceramic coating. Alternatively, a second metallic layer (or several layers) may be formed e.g. by electro-plating and the outer layer which may be of aluminium, oxidised by heating or anodisation. In an example, molybdenum is cleaned electrolytically, treated with aqua regia, washed and dried, coated with cerium electrolytically using molten cerium chloride at 800-850 DEG C., coated with aluminium electrolytically using 40-60 per cent potassium chloride and 60-40 per cent cryolite at 700-800 DEG C. washed, induction heated, and treated electrolytically to form a coating of mixed aluminium and titanium oxides using an aqueous solution of aluminium citrate and titanium potassium oxalate. In another form, the oxide may form part of a ceramic outer coating produced by firing thereon a frit containing e.g. titanium and/or zirconium oxides and a vitreous binder e.g. calcium, magnesium, aluminium and/or sodium silicates. The Specification as open to inspection under Sect. 91, comprises also references to the use of aluminium as the coating metal and thorium oxide as the oxide. This subject-matter does not appear in the Specification as accepted.