Spray Aluminum on Ceramic
03-07-2008, 10:32 AM,
#1
Spray Aluminum on Ceramic
please help, how can i spray aluminum on ceramic (Al2O3), i tried arc spray, but the bond strength is not good.
coating thickness about 0.15mm, roughness 700 microinch
Please advice on this.
thank you!
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03-07-2008, 11:08 AM, (This post was last modified: 03-07-2008, 12:29 PM by ycwbycwb.)
#2
RE: Spray Aluminum on Ceramic
Maybe you can consider cold spray or cold gas dynamic spray method.
You can download a file from the following link. In page 9 of the pdf file, there is pic showing Al, Ti, Cu coating on Al2O3.
[Image: Al%20on%20Al2O3.jpg]

(link dead)
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03-07-2008, 12:04 PM, (This post was last modified: 03-07-2008, 12:09 PM by Alexangel1226.)
#3
RE: Spray Aluminum on Ceramic
Hi Skymoon,

Just to share, I had experience previously spraying Al on Ceramic parts. And these are microelectronic equipments that used for PVD or CVD processes esp in Thin film Technology or wafer fabrication industry. Not sure if your job piece is of similar discipline.

I was working on the thing called a deposition ring, exact application not so sure, but part returned always show delamination & flake-off prob esp at areas recieve thick deposition in the working process.

I was then using the Arc Spray process, the tensile strength is always a prob as metallic coating does not bond well with ceramic, unless you apply some bond coat. To achieve the high roughness profile, I use a fan cap. Tensile has no test requirement then, so I can not comment much. But remember I have done some test on that, the tensile hopping at low reading, which is 1~2k psi.

But preheating is a crucial step so as the masking part of it esp at edges where during the demasking process, have to be extremely careful not to pull out masking tape together with the Al overhang coating on it.

Regards
Alexangel1226
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03-09-2008, 05:35 AM,
#4
RE: Spray Aluminum on Ceramic
Quote:i tried arc spray, but the bond strength is not good.

Just a quick query, what is the bond strength required?

And how are you checking the bond strength? using a portable pull-off type Question
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03-09-2008, 01:26 PM,
#5
RE: Spray Aluminum on Ceramic
Hi Skymoon

Sign0016 to the Surface Engineering Forum.

Have you experimented with preheating of the ceramic substrate before arc spraying?
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03-10-2008, 01:52 AM,
#6
RE: Spray Aluminum on Ceramic
Alexangel1226 Wrote:
Quote:i tried arc spray, but the bond strength is not good.

Just a quick query, what is the bond strength required?

And how are you checking the bond strength? using a portable pull-off type Question

I did not check the bond strenght, the coating just peel off buy itself.

So you mean i can try 2 layer of spray? first layer as bond coat, second layer to provide roughness?
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03-10-2008, 01:53 AM,
#7
RE: Spray Aluminum on Ceramic
Gordon Wrote:Hi Skymoon

Sign0016 to the Surface Engineering Forum.

Have you experimented with preheating of the ceramic substrate before arc spraying?

I preheat it at 150 degree c only, my masking jig is not able to withstand high temperature.
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03-10-2008, 04:25 PM,
#8
RE: Spray Aluminum on Ceramic
What sort of prep are you doing to the pc. before you coat? Have you tried to grit blast the part. I have arc sprayed the 1188Al wire on many ceramics with good result.
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03-11-2008, 01:44 AM,
#9
RE: Spray Aluminum on Ceramic
I did beadblast it to around 150 microinch Ra. and arc spray.
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03-11-2008, 01:23 PM,
#10
RE: Spray Aluminum on Ceramic
This may just be a terminology issue but you really need to use a sharp, angular grit prior to metal spraying. As you use the term beadblast, it makes me think that you are using smoother blast medium.

Ideally, your blast profile should typically be between 50 and 100 microns but of most importance is the shape of the blast. This is difficult to specify but using simple terminology, you are looking to acheive a rough, sharp edged profile that when magnified, looks like mountains as opposed to a smooth, hilly profile. On steels, this would normally be acheived by using a G17 or G24 chilled iron grit or an Al Oxide grit.

Hope this helps.
Stuart Milton
Metallisation Ltd
https://www.metallisation.com
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03-11-2008, 03:33 PM, (This post was last modified: 03-11-2008, 03:39 PM by Alexangel1226.)
#11
RE: Spray Aluminum on Ceramic
Just some comments on grit blasting as mentioned...

I guess ceramic physical properties is very diferent from normal metallic substrate. For metal, when being grit blasted, an abrasive particle strikes the surface adjacent to the previously cut pit, at the microstructure level, the surface is cut, pushing molecules side way or plastically displaced in a manner that provides rough asperities, and form multiple " holding" dovetails. Dovetails are the holding hands or anchors, that provides mechanical interlocking to the molten powder particles. And the depth and amount of dovetails created, depends very much on the surface and the grit size and pressure applied on it.

Generally, metal surface is softer, and dovetails are easily formed compared to a hardened surface like hard metal surface. That's the reason why bond strength is poor on hardened surface because grit blasting would not be able to create a roughened surface. Depending on the grit type used, sometimes it is hard to cut deep enough to profile the effective dovetails.

And hard surface is also lack of dutility that makes the displacement or structure deformation impossible or difficult. Excessive blasting may instead break away the shape edges (dovetails) which is brittle as it fractures. These are the prob with hardened metal or steel.

Bare in mind that with all these attributes to hard surface, and we are now dealing with Ceramic, which appears to be even harder than hardened steel, but exemplifies much higher brittleness. That is why 1st no dovetails can be effectively created, 2nd, sharp cut key or edges are all fractured and broken easily, and the non-ductile surface make deposition of any metal on it, extremely lose, without proper interlocking mechanism.

Thus, I suggest a bond coat to be used as the solution(if permitted), else, you have to really take care of the surface preparation, as mentioned, preheating, proper degreasing, and proper blasting by corundum(Al2O3), and avoid over blasting as all sharp edges will be flatened, surface will appear fatigue and smooth and leads to debonding effect.

Regards,
Alexangel
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03-12-2008, 05:28 PM,
#12
RE: Spray Aluminum on Ceramic
Hi Skymoon

If you are in fact bead blasting, I would stronly recommend changing to an angular aluminium oxide grit for grit blasting.

Try higher pre-heat temperatures, this should be no problem for alumina substrates, although you will probably need to change to mechanical masks if you are presently using adhesive masking tapes. Take care bridging between coating and mask can be a problem.

Let us know how you get on.
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