Quote:
Originally posted by murray13
Thx 8-ball for digging into this!!! Very informative.
One question, all this talk about 'cold working' copper decreasing thermal conductivity does it really apply to the extent suggested at the start of the thread? What I mean. Most of what we do to a piece of copper is to a surface. We are not bending, skieving, or compressing to an extent that would cause significant deformation. Yes the surfaces will be deformed to some depth depending on the method used. But the bulk of the mass will not have sufficient stress applied to cause crystal deformation. Or am I out in left field?
Since most copper bar stock people buy is of the cold drawn type I think annealing would be good at some point during the making of a WB. I guess my question is do you have to wait until it's complete (except for final lapping) before you anneal and to what extent machining and lapping will actually have on thermal conductivity?
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Sorry, I didn't really read your post thoroughly.
If you are using cold drawn copper, it will have an incredibly high defect density. This is the material compared with soft copper which had only 90% of the conductivity. The machining and lapping will have little effect on the overall defect concentration of cold drawn copper, as it is already high. (The local concentrationaround the milling surfaces may increase)
However, milling a soft copper will raise the defect density several orders of magnitude above the normal. So you will have to recrystallise again.
In summary, machine your cold drawn copper bar stock and then lap the base. Then recrystallise, either 140 degrees C for 15 minutes in the oven or 2 hours in boiling water. Once you've finished the recrystallisation, you could give it another quick lap on 2000 grit wet and dry paper, though I don't think it would be necessary.
8-ball
PS, I'm thinking of writing this up properly when I get the time, along with anything else I can find out relating to materials science in extreme cooling and overclocking. Any suggestions are welcome. (This won't be till the summer)