05-31-2007, 10:51 AM
I've choosen HVOF NiCrBSi coatings against erosion/corrosion on turbine rotor.
Did anyone have any experience on this topic ?
Thank you for your answer !
06-10-2007, 07:22 AM
to the Surface Engineering Forum.
Knowing the type of turbine and operating environment may make answering your question a little easier.
06-11-2007, 07:52 AM
Hi Gordon !
This is a LP Rotor of a nuclear power plant turbine.
The surface is eroded and corroded because of the droplet splash and steam path.
Temperature is between 75 and 145 ?C.
The rotor is made from a low-alloyed steel.
I've choosen a thin NiCrBSi coating but what is the typical use of NiCrBSi ? Where Is it used ?
Thank you for your answers !
06-12-2007, 05:18 PM
Afraid no direct experience on this particular application. NiCrBSi are fuseable alloys and are most often used in this condition where substrate permits high temperature fusing operation. I suspect you are planning on using the coating in the non fused condition, where the coating should have good corrosion resistance, but somewhat less erosion resistance than the fused variety. If you are planning on fusing the coating, then remember that the ~ 1025 C fusing operation will effect the metallurgy of the steel.
Some alternative HVOF coatings which may be worth consideration and may provide increased erosion resistance, but probably not so economic.
tungsten carbide/cobalt chromium
chromium carbide/nickel chromium
cobalt based alloys (stellite 6, T800)
NiCrBSi with tungsten carbide
06-14-2007, 08:45 AM
Thank you Gordon !
Some more elements :
The fact is that cobalt is forbidden in nuclear powerplant , so no stellite, so coblat alloys, ...
Also, the coating will be machined to get a good enough surface roughness, so if the coating is too hard (carbide) , i'll cannot machine the rotor...
About fusing , you're right ! i won't fuse the coating to avoid effecting the metallurgy of the rotor's steel.
I'm still looking for well-known applications of NiCrBSi, so if you have any idea !
06-14-2007, 12:20 PM
HVOF NiCrBSi coatings (not fused) are used in the glass industry for molds/plungers and in the paper and printing industry for rolls. Typical product data recommends coatings for resistance to wear by hard surfaces, fretting and particle erosion at temperatures up to 815 C. Typical applications suggested include piston rings, cylinder liners, utility fans, thread guides, forging tools and hot forming dies.
What grade of NiCrBSi are you planning on using? Many of these can be around 600 - 800 HV which would be difficult to machine.
06-14-2007, 01:54 PM
Thanks for the answer.
I will probably use Diamalloy 2001 powder by Sulzer; the chemical is : 70,5% Ni ; 17% Cr ; 3.5% Boron ; 4% Silicon ; 1% C ; 4% Fe.
They're known to be about 700 HV.
One of my question is :
I need a surface roughness at about 3 ?m. Before deposit , i'll make a 10 ?m to get a good adhesive strength. So the surface roughness after deposit will be high. (between 5 and 15 ?m) . So why can I machine the piece to get my 3?m ?
The thickness of the coating will be 150 ?m. Have you any comments about that ?
06-14-2007, 02:18 PM
What machining method are you going to use? 150 ?m I assume is the finished thickness, which should be ok, although much thicker coatings are possible if required.
3 ?m Ra is quite a rough finish. Some of the chromium carbide/nickel chromium HVOF coatings are not too far off that as-sprayed (may be with a slightly finer grit blast roughness profile).
07-18-2007, 10:58 PM
I have split this thread so that your post becomes a new thread, as I think this is really a different topic and deserves its own thread.
bhellman Wrote:Dear Colleauges
Moved to http://www.gordonengland.co.uk/sef/-spli...t-245.html
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