CrC-25NiCr coating layer observed by optical microscope
04-28-2015, 06:00 AM, (This post was last modified: 04-28-2015, 06:07 AM by Roy.)
#1
Question  CrC-25NiCr coating layer observed by optical microscope
Dear All,

I would like to hear your kind advice on my coating specimen.
I sprayed CrC-25NiCr(PSD: -45+15 micron) by using JP-5000 gun with 6" barrel. Feed rate was 60g/min and spray distance was 360mm.

After getting 350 um thickness, I made an specimen -cut the coating coupon and polished - to measure microhardness and to observe coating structure.

Please see the following photo which was taken by optical microscope(X100).

   

Is all the dark colored sections porosities?
I am confused about what ther are. The microhardness of the coating is around 870~950 HV0.3.
When magnified to X500, it looked like dark green colored particles.

Please advise me whether my specimen has too much porosities or not.
Reply
05-01-2015, 05:34 PM,
#2
RE: CrC-25NiCr coating layer observed by optical microscope
Normally CrC almost never has a true porosity problem. The problem is that very fine round globular particles are formed which do not like being polished as they are round and are easily separated during the grinding and polishing procedures. Your problem really is globular particles and not true porosity.


(04-28-2015, 06:00 AM)Roy Wrote: Dear All,

I would like to hear your kind advice on my coating specimen.
I sprayed CrC-25NiCr(PSD: -45+15 micron) by using JP-5000 gun with 6" barrel. Feed rate was 60g/min and spray distance was 360mm.

After getting 350 um thickness, I made an specimen -cut the coating coupon and polished - to measure microhardness and to observe coating structure.

Please see the following photo which was taken by optical microscope(X100).

[attachment=439]

Is all the dark colored sections porosities?
I am confused about what ther are. The microhardness of the coating is around 870~950 HV0.3.
When magnified to X500, it looked like dark green colored particles.

Please advise me whether my specimen has too much porosities or not.

Reply
06-20-2015, 05:36 PM, (This post was last modified: 06-20-2015, 05:42 PM by Johnny_Blaze.)
#3
RE: CrC-25NiCr coating layer observed by optical microscope
(04-28-2015, 06:00 AM)Roy Wrote: Dear All,

I would like to hear your kind advice on my coating specimen.
I sprayed CrC-25NiCr(PSD: -45+15 micron) by using JP-5000 gun with 6" barrel. Feed rate was 60g/min and spray distance was 360mm.

After getting 350 um thickness, I made an specimen -cut the coating coupon and polished - to measure microhardness and to observe coating structure.

Please see the following photo which was taken by optical microscope(X100).

[attachment=439]

Is all the dark colored sections porosities?
I am confused about what ther are. The microhardness of the coating is around 870~950 HV0.3.
When magnified to X500, it looked like dark green colored particles.

Please advise me whether my specimen has too much porosities or not.

Hi Roy,
I have to agree with Kevin's assessment. I think your coating looks relatively good and if I remember the typical hardness specs for CrC you are in the normal hardness range.

I would try a slightly closer spray distance if I were to offer you some other tests ideas...start at 230mm and move back from there, this may increase your density slightly, although I do admit to having no experience with the JP5000.


Just a guess but chromium oxide is typically a dark shade of green, maybe its oxide inclusions?

Regards,
John
Reply
06-21-2015, 12:56 PM,
#4
RE: CrC-25NiCr coating layer observed by optical microscope
(04-28-2015, 06:00 AM)Roy Wrote: Dear All,

I would like to hear your kind advice on my coating specimen.
I sprayed CrC-25NiCr(PSD: -45+15 micron) by using JP-5000 gun with 6" barrel. Feed rate was 60g/min and spray distance was 360mm.

After getting 350 um thickness, I made an specimen -cut the coating coupon and polished - to measure microhardness and to observe coating structure.

Please see the following photo which was taken by optical microscope(X100).

[attachment=439]

Is all the dark colored sections porosities?
I am confused about what ther are. The microhardness of the coating is around 870~950 HV0.3.
When magnified to X500, it looked like dark green colored particles.

Please advise me whether my specimen has too much porosities or not.

Dear Mr.Roy
If you want to get a real picture of porosity then you need to use an electron microscope. Optical microscope gives a lot of artifacts and can mislead you.

Reply




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