Measuring deposition efficiency and check the microstructures of the coatings???????

[fahad03092]

Dear all,

I want to measure deposition efficiency of Calcium phosphate coatings sprayed by plasma spray. To measure deposition efficiency, standard technique says that I need to use tube. I am thinking to spray for 1 minute and then check the weight of the coatings on the tube.

After measuring deposition efficiency can I cut the tube in to small piece and then can I check the microstructure of the coatings? or I need to spray on flat substrate again to check the microstructures?


Please help me.Thanks a lot.


with regards
Fahad

[sreenuvundela]

Hi Fahad

Deposition efficiency and bond strength will be less for coating on Tube than Flat surface becausei of radius of curvature of the tube.

Hence, it is always better to carry deposition efficiency calculation and also microstructure analysis on test piece which is identical with your actual component.


Regards,

SREENIVAS

[djewell]

If you cut a small section of your tube, you can do a microstructural analysis of it. There should be no difference if deposit efficiency or bond strength whether the coating is on a tube or a flat coupon. You cannot easily measure the bond strength from the tube.

You only need to spray for 15 seconds on the tube before weighing the coating to calculate deposit efficiency. Make sure the tube is rotating constantly and that you only spray one pass on it. If you know your feed rate, then you can calculate how much powder you used. This will prevent you from consuming more powder than necessary.

[ServiceTech]

Respectfully disagree with djewell that deposition efficiency and bond strength will not change when sprayed on a curved or flat substrate.

Distinctions must be drawn between deposition efficiency and target efficiency. If the tube is too small in diameter to allow full capture of all particles in flight, you will not measure true deposition efficiency. First decide if measuring the deposition efficiency or target efficiency or both is the goal. Measuring on a tube, if not representative of the part geometry will provide inaccurate results

[fahad03092]

Thanks a lot to all for giving their reply.


What diameter and length of tube should be used for measuring deposition efficiency?

I want to analyse the coating and also wants to get deposition efficiency of my powder.I am thinking to spray on tube for 15 second or 30 second for measuring deposition efficiency and spray on flat substrate of 50*30*3 mm to get 200 um thick coatings. Do you think I am thinking right?

If I am wrong please correct me.

Thanks a lot.

[djewell]

The diameter of the tube is not critical for the DE test. However, it should be long enough that you do not run out of tube in the time you are traversing it during the test. It is imperative that the gun traverses across the tube during the test so that you do not overheat the coating.

I do not like the idea of spraying flat DE test coupons. You have unknown losses as you move the gun off of the coupon and change direction. In other words, you have an imprecise target efficiency factor to include in your calculation. You will also use a lot more powder this way. It is unnecessary to continue spraying to achieve a 200 um thick coating. A single pass should be sufficient to measure DE.

[fahad03092]

Thanks a lot for your comments.

I am actually thinking to get 200um coating to analyse the coating.

I am just thinking should i get enough weight of powder in single pass on tube?



If there is any other way could you please help me by giving any any idea.

Thanks a lot

[djewell]

You can calculate how much powder you expect to spray during your test and compare that to the accuracy of your scale. If your scale can read 0.5g differences in weight, then you will want to design your test to deposit at least 5g of powder on your tube, so plan to spray at least 10g of powder. More would be better, but a 10% calculation error of DE is not very significant.