Posted by Gordon England (62.252.0.12) on 16:32:42 09/12/05
In Reply to: Cluster oxide in Inco718 posted by Alex Chan
Hi Alex
Is your problem similar to the message thread below:
:Posted by Gordon England on April 25, 2003 at 12:09:28:
In Reply to: Stripes in plasma sprayed cobalt alloys posted by
Benjamin Russell on April 25, 2003 at 08:19:28:
:: I am working with some plasma sprayed CoCrNiW coatings and am
puzzled by some of the oxide formations i am seeing. Typically
these are stripes all in the same direction and with consitent
angles. Also i have seen some V shaped oxide clusters, generally
originating at a point in the substrate and extending though the
whole thickness of the coating. One theory is that turbulence
effects resulting from defects (eg unmelted particles)
cause vortecies in which oxidised fines accumilate and form these
structure. I would appriciate any liturature on the subject and any
other suggested reasons for this phenomenom.
:Hi Benjamin
Can you describe the spray set-up (with speeds and feeds)
and work piece.
Oxide clusters - Are these effecting the as-sprayed surface texture
of the coating producing small nodules or warts? If you grind
and polish the surface of the coating, can you see oxide clusters
forming a horse shoe shape roughly 1 mm diameter (best view at
about X10). Does the cross-section through oxide clusters
resemble that seen in this photo of Plasma Sprayed NiCr
coating:
http://www.gordonengland.co.uk/pmg6.htm
Ignoring coating lamination effect and bearing in mind that the
oxide clusters appear different depending on sectioning direction.
You need to visualise this effect in 3D as the 2D view from
cross-section can be confusing. This photo is not the best
illustration of this effect, but it is all I have at hand at the
moment.
Generally, I think your theory is on the right track. Give us some
more detail and I will try to explain this phenomenon.
Regards Gordon
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