Posted by Gordon England (62.252.0.12) on 12:15:43 22/02/05
In Reply to:Re: 410 SS HVOF Application posted by john winne
: What we found is that by changing the PSD to -38um (from -53), we were able to achieve the necessary microstructure. The specification we have been attempting to achieve makes no mention of unmelt count, but we have been informed that ours was unacceptable. The specification further indicated that an increased presence of oxides was preferred. We have attempted to apply this with Plasma, HP/HVOF and HVOF. All three have produced acceptable microstructures, none have passed 10Ksi bond testing, and only the Plasma has met the <37Rc requirement @ 27Rc
:
: Any thoughts on how to drop the hardness numbers? 36 with HVOF. 45 with HP/HVOF.
:
: We have also been informed that the FM1000 adhesive we have been using produces 'true' results, and that others (like EP15) produce artificially higher results, as much as 2Ksi higher. It is unknown which adhesive was used to determine the 10Ksi specification. We have made a number of tests with the FM1000 and various application methods.
Hi John
1. Failure on bond strength testing - is it adhesive or coating failure?
2. High hardness may be due high oxide content or overheating.
3. All adhesives should give 'true' results except in cases where adhesive penetrates porosity to the coating/substrate interface and acts as a strengthener (should not be a problem with good HVOF coatings). If we are talking about adhesive failure rather than coating failure, then
you can only assume that the 'true' result is greater than the adhesive strength. So a result of 8 Kpsi with a glue failure does not mean the coating fails a 10 Kpsi minimum specification. You just need to find a glue with a 10 Kpsi minimum strength to test the coatings to this specification. Unfortunately, most adhesives give up at this point.
Please, can anybody advise on adhesives which can consistently give over 10 Kpsi strength for tensile bond strength testing?
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