Cracks in WC-12Co coating

[fhyuan]

Hi, everyone:
I have been working on spraying of WC-12Co coating for quite a long time. However, the cracks(about 0.06-0.07 mm, perpendicular to the interface) are invariably present in the cross-sections when viewed at a magnification of 200. I wonder if the cracks resulted from the spraying process or from metallographic preparation processes?
The coatings are sprayed with a Metco Unicoat model sray system.

[DrTofi]

Hi,
if the samples preparation proceeds with correct way according to ASTM wont see cracks founded.
i think that's happen because a a deferential of thermal expansion between substrate and coat materials
select proper substrate with near thermal expansion of coating layer.

Mustafa
Metallurgical Engg.

[fhyuan]

Dr Tofi:
What do you mean by "sample preparation"? the spray or the metallographic preparation? What's the ASTM document?
It is required the coating be sprayed on a titanium alloy.
Thank you!

[Ken59]

Dr Tofi:
What do you mean by "sample preparation"? the spray or the metallographic preparation? What's the ASTM document?
It is required the coating be sprayed on a titanium alloy.
Thank you!

---

Hi
You can stop the cracking by with a thin layer of 5-10 mil of Ni/Cr only (80/20) on the base and the then spray the WC-12. Plus cool the part down slow,and leaving it in the spray lathe at about the same RPMs. but I was using Hvof to spray parts.

[fhyuan]

Hi, the drawing has it that the coating be plasma sprayed directly onto a titanium alloy substrate.