COATED NICKEL-BASE AND COBALT-BASE ALLOYS HAVING OXIDATION AND EROSION RESISTANCE AT HIGH TEMPERATURES

摘要

1,174,483. Coating with metals. UNITED AIRCRAFT CORP. Jan.26, 1967 [Jan.27, 1966], No.3991/67. Headings C7D and C7F. A Ni base or Co base alloy substrate is coated with a first layer of Ta and then with a layer comprising Al powder which is bonded by sintering and then an outer layer of Al 2 O 3 is formed on the Al coating. The Ta coating 0À2-1À5 mil thick is preferably formed by thermal decomposition of Ta halide vapour or by pack cementation in a powder mixture of Ta, a halide salt such as NaCl, KF, NH 4 I or NH 4 Cl, a filler such as Al 2 O 3 , SiO 2 , BeO or MgO and heating at 1400‹ -2200‹F. under vacuum. The coated article is then preferably reheated at 1600‹-2200‹F. under vacuum. The Ta may alternatively be applied electrolytically or by plasma spraying. The Al coating is preferably applied as an Al/Co powder mixture containing 5-40% by weight Co. The mixture in the form of a dispersion in an alcohol, ester or ketone with or without a binder such as naphthalene, nitro cellulose and stearates, is applied by dipping, painting or spraying and then sintered at 1600‹- 2100‹F. in dry hydrogen, argon or under vacuum. The coating contains 0À1 to 1% by weight of Ta and the coating has a thickness of 2-6À5 mil. The final Al 2 O 3 coating is formed by heating the coated substrate in air.