A few weeks ago, I wanted to try electro polishing to expedite polishing for some difficult to polish alloys. As a result, I needed to make my mounts conductive while maintaining good edge retention to prevent bleed out during evaluation. To
do this, I used a hot mounting press to make the mount, then drilled into the backside of the mount, and used a conductive epoxy to glue a copper contact to the sample. The electro polishing technique did not work for that specific
application as well as I would have hoped. However, I did have some leftover copper so I was curious what the structure would look like considering a .125” round piece of drawn wire must have seen significant reduction and the structure maybe rather interesting.
The sample was hot mounted in epoxy with views in the longitudinal and transverse orientation. The sample was then ground and polished to a sub-micron finish and then vibratory polished to ensure a scratch free surface. The sub-micron polishing step used a solution of colloidal silica (100 mL) which was augmented by the addition of 5 mL of ammonia and 1 mL of hydrogen peroxide (30%) to act as a chemical polishing agent. The sample was vibratory polished on a high nap cloth using a colloidal silica suspension. The sample was then etched using a acidified dichromate etchant.
The photomicrographs below show the copper sample in both the longitudinal and transverse orientation at various magnifications. In the transverse orientation, heavily elongated disintegrated grains are seen. In the longitudinal orientation, heavily elongated grains are seen.
Acidified Dichromate:
4 grams Potassium Dichromate, 8 mL Saturated Sodium Chloride (0.1 molar), 16 mL Sulfuric Acid, 200 mL Water
