Metallography Evaluation

[vcduramais]

Dear all,

hope you are doing fine.

I made asked a new company (due to covid-19 the one I used to do is not opperating) for a metallografy analisys of my WC 10Ni (-45/+15) coating sprayed with HVOF air cooled (GTV 720.000 - propylene). I'm having porosity problem resulting in cylinder rods "undermining oil" when they leave the cylinder. I'm doing this test so I can find the problem and to compare the coating from this equipment with the one I'm going to do with the new equipment our company is acquiring (MEC 2700).

I'm ataching the microphtografy so you can se what is going one. I can't tell if there was a poor preparation or if this is actually what is going on.

If our coating is this poor, can you please tell me if it could be due to compressed air contaminated with oil?

Thank you and best regards

[EmilAV]

Hi Vcduramais,

Since the major failure is observed quite a distance from the substrate, you should not expect the preparation of your substrates to be the major source for this type of failure. I have seen similar failures, but slightly more homogenous, in water cooled kerosene guns when there has been small water leaks present. If there is oil or other hydrocarbons in the compressed air used for cooling the substrate you could expect failures similar to the image presented. However, It will highly depend on amount and consistency of the contaminants coming to your sample.

In addition, I will add that hot mounting of brittle coatings could cause mid layer failures due the the high pressure and temperature during the embedding. Hard to determine embedding technique from the image. If this is likely for you coating, I cannot tell.

I acknowledge that my input is a bit late. Therefore I ask, is the problem solved and root cause eliminated? Would be interesting to hear development moving to a new system.