GB895736A - Articles made of heat resistant alloys - Google Patents

Abstract

An article made of a heat resistant alloy comprising one or more of the metals nickel, cobalt, and iron as the principal constituent, and also comprising chromium, has an outer layer containing beryllium, but substantially free of chromium. Gas turbine parts, e.g. rotor or stator blades, and tubes of high temperature boilers, may be coated in order to withstand high temperature and to resist corrosion by vanadium compounds. A powdered eutectic alloy of beryllium with nickel, cobalt, or iron may be applied in suspension in xylene to the article, which is then heated to 1125 DEG C. in vacuo. Another method is to apply a coating of nickel, cobalt, or iron by electroplating, flame spraying, sputtering, vacuum evaporation, or hot dipping, and then to paint on a suspension of beryllium powder in xylene, followed by drying and heating to 1200 DEG C. out of contact with air. Alternatively the surface of the article may be depleted in chromium by heating in air to form a chromic oxide layer, which is removed, or by heating in molten caustic soda or potash; the surface is then cleaned and enriched in beryllium by painting or spraying with a suspension of beryllium or beryllium alloy powder and then heating in vacuo or an inert atmosphere.ALSO:An article made of a heat resistant alloy comprising one or more of the metals nickel, cobalt, and iron as the principal constituent, and also comprising chromium, has an outer layer containing beryllium, but substantially free of chromium. Compositions of various alloys which may be coated are given, other elements present being carbon, titanium, aluminium, silicon, magnesium, tungsten, molybdenum, manganese, niobium, vanadium, and copper. Gas turbine parts, e.g. rotor or stator blades, and tubes of high temperature boilers, may be coated in order to withstand high temperature and to resist corrosion by vanadium compounds. A powdered eutectic alloy of beryllium with nickel, cobalt, or iron may be applied in suspension in xylene to the article, which is then heated to 1125 DEG C. in vacuo. Another method is to apply a coating of nickel, cobalt, or iron by electroplating, flame spraying, sputtering, vacuum evaporation, or hot dipping, and then to paint on a suspension of beryllium powder in xylene, followed by drying and heating to 1200 DEG C. out of contact with air. Alternatively the surface of the article may be depleted in chromium by heating in air to form a chromic oxide layer, which is removed, or by heating in molten caustic soda or potash; the surface is then cleaned and enriched in beryllium (a) by painting or spraying with a suspension of beryllium or beryllium alloy powder and then heating in vacuo or an inert atmosphere; (b) by heating in an atmosphere containing a volatile beryllium halide and argon or helium; (c) by heating in an air-free vessel with beryllium or an alloy thereof, ammonium chloride, and beryllia or magnesia; (d) by dipping in molten beryllium alloy; or (e) by electrolysis from a molten bath containing beryllium fluoride or oxyfluoride and sodium or barium fluoride or oxyfluoride. The Provisional Specification refers also to articles made of alloys containing titanium, aluminium, zirconium, or silicon, in place of or in addition to the chromium, and also to depleting the surface in chromium by heating with lime, magnesia, alumina, nickel oxide, cobalt oxides, or iron oxides.