Our parts need to be checked for using penetrants and coated by HVOF,but we don't know which one should be first?Penetrants Check is for base material or coated material?Thanks!
I am assuming that the penetrant check is to detect surface cracks. If this is true, then the penetrant must be used and read prior to coating. The coating will obscure surface defects, and render the penetrant test useless.
It is indeed the purpose of a penetrant inspection to check for cracks before coating (with hvof or any other thermal spray technique).However, there have been case were a crack that initiated in a hvof applied WC coating progressed into the base material due to the fact that it's a very dense coating and has a high bond strength. So it might be the intention of the designer to check the coating also for cracks. The sensitivity level has then to be selected carefully to avoid excessive background.
The first step in the HVOF process is to roughen up the surface with a 60 grit Aluminum Oxide blast. This in itself would make Penetrant examination impossible. The whole point of the inspection is to assure the quality of the base material prior to covering it up. Hope this helps.
Sincerely,
DJ Kallhof
Quality Engineer
NDT Level III
