Production Problems Associated with Coating Refractory-metal Hardware for Aerospace Vehicles

Book excerpt: Four coating processes have been scaled up to coat components of aerospace vehicles: (1) slurry, (2) atmospheric-pressure pack cementa tion, (3) vacuum pack cementation, and (4) fluidized bed. The principal advantage of the slurry process is its ability to coat limited access areas such as the interior channels of built-up corrugated panels. This makes the process ideal for coating spot-welded corrugated panels after they have been welded. The other three coating processes, which are vapor-deposi tion processes, are not so suitable for coating limited-access areas. When they are used for parts such as built-up corrugated panels, the individual parts (including rivets) are coated, then riveted together, and then the entire assembly is recoated. This shortcoming is off set by the fact that the coatings applied by the vapor-deposition processes are more protective at higher temperatures than are the slurry coatings.