Metals sticking. I need a Chemical Engineer or a Physicists

[calexanian]

So I was cleaning cleaning nickel strips about .750" wide, 6" long, and .010 thick in my hydrogen reducing tube furnace, which on the previous load I was cleaning .035 nickel rod of the same alloy which proceeded as normal. The strips however came out in an unexpected manner. Several of them stuck together at various points. Almost as if lightly spot wended. They were clean and degreased before loading in the furnace. It got nowhere near the melting temperature of the material. Strange. I know things get very clean in that style furnace, but I don't believe the conditions are right for a cold weld or other molecular welding.

Anybody have any ideas what may have happened? I thought perhaps a foreign metal may have gotten in and perhaps formed some lower melting temp spots, but i see no other evidence of that. All perfectly clean nickel.

conditions were 100% dry hydrogen at a light flow, and approximately 950 to 1000 degree celsius over the length of the furnace. Strange.

[Ian.M]

Nickel powders can reliably be sintered in a 5% Hydrogen, 95% Nitrogen reducing atmosphere at temperatures as low as 600°C.

[T3sl4co1l]

IIRC, diffusion bonding is effective at about half the melting point, which sounds reasonable here.

Tim

[calexanian]

Thanks. I dd not know both processes could be performed at such low temperatures. I see reference that wet hydrogen can be used to avoid this where it is not detrimental to the process. 

[woodchips]

Possibly the molecular bonding you get with very smooth surfaces such as slip gauges?