| 摘要 |
A base metal of the group consisting of molybdenum, tantalum, tungsten, niobium, and alloys thereof including other metals such as 0.5% titanium or zirconium, is heated in a non-oxidizing atmosphere in contact with a powdered mixture containing an inert diluent, a silicon and boron source and a halogen source, to diffuse silicon and boron into the surface of the base metal to form a continuous protective coating rendering the metal resistant to oxidation in such parts as nozzles, blades, vanes and shells which are required to operate in air at 1800 DEG to 3600 DEG F. The silicon and boron, which may be elemental and powdered to 60-325 mesh (Tyler) size or of other source such as ferro-silicon and ferro-boron, are preferably heated and alloyed together. Both alloying and diffusion may occur at 1600 DEG to 2200 DEG F. The inert diluent may be a refractory material of grain size 50-350 mesh (Tyler), e.g. clay, kaolin, zirconia, beryllia, alumina. The halogen source may be fluorine, chlorine, bromine or iodine, or metal or ammonium halides, preferably ammonium bifluoride. An example of a diffusion pack composition by weight is: Si 5-70%, B 1/8 -10%, halogen source 0.1-1%, inert diluent 25-75%. A molybdenum alloy containing 0.5% Ti and 0.07% Zr is specified. |
