The Cu foil was first electroplated with a layer of Ni, then the alloy foil was annealed in quartz tube under H2/Ar atmosphere at 1040℃ for 2 hours. But when I open the furnace and cool the tube rapidly, all of the alloy foils were crimped.
Did anyone encounter this problem before? How can I resolve this problem?
Thanks!
Copper and nickel, have different thermal expansion coefficients. This results in strong, uneven warming and cooling to irreversible plastic deformations.
At even (slowly) warming/cooling the bimetal films are only reversible elastically deformed.
Vadim is correct, you have created a bi-metallic foil. The difference in thermal expansion causes the foil to bend in response to changes in temperature.
You may be able to produce a flat foil by clamping the foil between two rigid plates during heat treatment and cooling. Alternatively, if you plate both sides of the Cu foil the stresses would be balanced.
Thanks for all of your answers. As far as I know, the Nickel and Copper can form substitutional solid solution, hence, the bi-metallic foil will be uniform after annealing. So the deformation process can only be occurs in the process of heating. Is my reasoning correct? Thanks again.
I guess this might result from unequal thickness of Ni plating on the double sides of Cu foil.
During heating, the thermal expansion and dilatation due to hydrogen absorption was thermodynamic equilibrium on the two surfaces. Upon cooling, the absorbed hydrogen would evolved faster on the side with thinner Ni plating. The difference of residual hydrogen concentration induced an unbalanced stress. The foil curved. The curved foil can be easily flattened out by employing vacuum annealing.
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