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Spray and fuse of Colmonoy 5 ( a Ni-Cr-B composition) on 4130 HSLA steel

Q. I'm currently working on a project on thermal spray coating which involves powder coating a layer of Colmonoy 5 on the surface of 4130 quenched and tempered steel. This spray and fuse process seems perfect on stainless steel substrate but when the same process and same parameters being applied to spray-and-fuse 4130, we encounter problems that involves heaps of porosities on the surface of the material. We have tried on 3 work pieces (with the size of DIA 130 x 600 mm) so far, and also ensured that the fusing time is adequate but we still face the same issue.
I have been searching high & low for the root cause of this -- does annealing prior to spraying help? 4130 is known for its hardenability and being case hardened, but why is this surface hardening not working on it?
Would appreciate very much if anyone could help on this issue. Thank you.

Lee Sharon
Engineer - Singapore
June 1, 2008

A. I am retired, so do not have references to go by, and never used that particular material.
Guess 1 is the abrasive blast prior to thermal spray is either not strong enough or is too strong. A variation of this is it is not blasted immediately prior to thermal spray.

Guess 2 is that there is a problem with the bond coat--I assume that there is a bond coat.

Guess 3 is that the part has not been properly warmed up prior to the metal application and is initially forming clumps rather than slightly flowing.

Your vendor for the powder and the spray equipment vendor should be able to help you with this problem. The suggestion of having to go to another powder vendor if they can not help, normally brings a fairly rapid response, especially if you use a fair amount of their product. A new vendor will probably send in a qualified applicator if there is a good possibility of getting all of your account.

I suspect that there is a size/weight difference between the parts as well as possibly a geometry problem causing a slight difference in the spray angle and distance.

James Watts
- Navarre, Florida
June 4, 2008

A. Thermospraying followed by fusion, being basically a physical process, is practically unaffected by chemical differences in the substrates. The reason for your problem must be of a physical nature. Hardness and heat transfer are very different for both substrates you mentioned. Low hardness favors blast media penetration and roughness. Low heat transfer favors superficial temperature rise.

Guillermo Marrufo
Monterrey, NL, Mexico
June 6, 2008

? Did you ever figure this out?

Stephen Gauntt
- Houston, Texas
February 16, 2018

February 2018

thumbs up sign Hi Stephen. Lee's question was from 10 years ago so it's unlikely he'll see your message. But if you are implying that you have an answer, I'm sure the many continuing readers of this page would like to hear it. If you have a question of your own, please post your situation and details. Thanks.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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