Spray-fuse rapid "mushroom" growth NiCrSiB

[jasonpbond]

We are currently sprayfusing a large number of chipper wear plates with a 50HRC NiCrBSi alloy.

After fusing in a furnace, when the furnace has cooled down to around 200^oC, the furnace is opened to remove the parts. At this stage, there is rapid growth of mushroom-like formations all over the sprayed surface. This happens within a matter of minutes. I understand that leaving the parts in the furnace to cool to below 100 degrees avoids the problem, but for us this will be an extremely expensive option, due to having to rent the furnace time.

These growths are easy to remove with a chisel, but there are many hundreds of them on every surface, and when you have many hundreds of surfaces to do this can be a time consuming operation.

Does anyone know what causes these rapid growths, and how to avoid them? Your help is much appreciated!

I have photos of these growths if anyone can let me know how to attach them. They are approximately round, up to 10-15mm in diameter.

[Gordon]

Hi jasonpbond

to the Surface Engineering Forum.

I can't really understand how this could happen at 200 ^oC as materials should be solid and not fluid enough to flow.

The only thing I can think of that is similar to what you describe, though probably much worse


A furnace fused WC/NiCrBSi coating, unfortunately, I can only guess at what went wrong, as I was not privy to much process information.

If you have problems with attaching your images in your posts, just email them to me at sef@gordonengland.co.uk

[jasonpbond]

Thanks Gordon. Thats exactly what it looks like. I'll email you some photos, hopefully you can post them for me. We've been trying a few different wires from a few different manufacturers, with a few different blends. The interesting thing is that the growth happens extremely quickly, looking almost bacterial in nature. The WC/NiCrBSi wire seems to not produce the same problem, its just the straight NiCrBSi at this stage!! Will keep pondering.

[Joris Kraak]

We observed exactly the same recently with a WC nicrbsi (36C material) after heating it too 200 degrees this blistering started.

[Stephen Booth]

Hi Jason,

A couple quick questions/ notes:

a) you mentioned using wire? I think most wires that have NiCrBSI are in a Fe tube?
b) Have you done this fusing before on the wire?
C) have you tried powder metal spaying of NiCrBSi for the fusing