Improvements in Oxidation-Resistant Coatings for Refractory Metals and Alloys

摘要

1,192,740. Electro-plating refractory metal with iridium and/or rhodium. IMPERIAL METAL INDUSTRIES (KYNOCH) Ltd. Nov. 3, 1967 [Nov. 16, 1966], No.51412/66. Heading C7B. [Also in Division C1] An article of a refractory metal of M. P. at least 2000‹ C. or an alloy based thereon is provided with an oxidation-resistant coating by applying an underlayer of Ir, Rh, or Ir-Rh alloy and at least one upper layer of siliceous glaze. Preferably the alloy underlayer contains at least 50% Ir and an intermediate layer of alumina, hafria, zirconia or zircon is applied beneath the glaze. Typically the metal or alloy underlayer is electro-deposited from a hydrobromic acid bath containing also ammonium bromide, typically at 75‹ C., the refractory metal being cleaned and surface roughened by jet-blasting with a dispersion of alumina powder. Examples are given of coating N6-11%W-3%Mo-2%Hf with 1 to 5 mils Ir or Ir-50%Rh followed by spraycoating with the intermediate layer material, least desirably zirconia, and of coating Ta-10%W with Ir followed by zirconia as the intermediate layer. Preferably two layers of glaze powder are successively applied from suspensions in toluene containing a methacrylate polymer, each glaze layer being vacuum fired at 1450 to 1600‹ C.