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Appendix E
Manufacturing Technologies of Coating Processes

   DIFFUSION COATING PROCESSES
Pack Cementation
    ...........
Out-of-Pack Methods
  For the above-the-pack process, the parts to be coated are fixtured out of contact with the pack mixture. The coating vapors are transported to the parts by an inert carrier gas or purge gas and, through the use of two packs, both internal and external surfaces can be separately coated (Levine and Caves, 1973; Benden and Parzuchowski, 1979; Bianco and Rapp, 1993). Other variations are also in use, such as pulse aluminizing and SNECMA vapor phase aluminizing (Gauje and Morbioli, 1982). As with pack cementation, for pulse aluminizing and SNECMA vapor phase aluminizing, the retorts are loaded into an appropriate furnace for the thermal cycle. Because of the increased path length for vapor transport, the out-of-pack methods favor an increased tendency for outward growth and a generally reduced deposition rate.
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