DE1521570

1,150,006. Diffusion coating; dispersion strengthened nickel alloys. UNITED AIRCRAFT CORP. Aug.11, 1966 [Aug.16, 1965], No.35965/66. Headings C7A and C7F. A Ni-, Co- or Febase heat resistant alloy article, e.g. a gas-turbine blade or vane, is protected against oxidation, corrosion and erosion at operating temperatures above 1200‹C. while subjected to combustion gases by contacting it first with a finely divided mixture comprising Cr powder and a halogen-bearing compound as activator and heating between 982‹ C . and the melting point of the alloy (1454‹C. for Ni-base alloy) to provide an adherent Cr layer, then with a similar mixture, but additionally containing Al powder, and heating between 538‹C. and the melting point of the alloy to provide an adherent Cr-Al (aluminide) layer on the Cr layer. The diffusion heating is conducted in the absence of deleterious gas, e.g. under vacuum or in an atmosphere of He, A and/or H 2 . The mixture may be in powder pack form and the article immersed therein, or the article may be coated with an aqueous slurry of the mixture and dried, prior to diffusion heating. Either mixture may also contain an inert filler powder such as alumina, zirconia, titania, ceria, magnesia, hafnia or rare earth metal oxide. The activator powder may be CrCl 3 , CrBr 3 , CrI 3 , CrF 3 , NaCl, KCl, KF, NH 4 Cl, NH 4 I or NH 4 Br. The article may be of dispersion strengthened Ni-base alloy containing at least 60% Ni, 0À02 to 20% of dispersed ThO 2 , Al 2 O 3 , ZrO 2 , TiO 2 , MgO, HfO 2 or rare earth metal oxide, and balance Fe, Co, Al, Cu, Cr, Mo, W, Ti, Ta and/or Re; e.g. 2% ThO 2 20% Cr and/or 15% Mo, balance Ni. Where a Ni-base alloy article is chromized at a rate in excess of that at which Cr diffuses in the Ni, a discrete body-centered-cubic Cr layer is formed; this layer is absent where the Cr is deposited at the same rate as the diffusion rate. In either case, outer layers comprise a layer of Ni 3 Al + Cr (bonded over the layer of Cr containing Al and/or Ni, or a layer of Al + Ni - Cr) over which is bonded a layer of NiAl + Cr. The chromium layer may have a thickness of 2.54.10-3 to 2.54.10 2 cm.