Hi. I expect this to be in standard metallographic books. There you will find expected micrographs of grains that you will see upon etching. In general, one should go from larger grain/powder size (lower grit) to smaller grain size (higher grit). Do not forget to wet the paper or the powder enough to ensure that no change in grain size or shape will occur due to heating (which occurs when you rub/sand the metal). Also do not forget to wash in between sand paper or powder to ensure that there is no mixing of different grain sizes during polishing. Some people sonicate in between to ensure all the powder particles are removed and not embedded. You can also either polish it in one direction or in figure 8. I suggest for the sand papers, sand in one direction for one grit size then sand in the perpedicular direction for the next size so you have an idea that you have sanded the entire surface. Also make sure that you are sanding it such that your surface stays flat on the surface and not lopsided. When you go through the diamond powders, then do an 8 figure as you polish it on the polisher. You will see if it is scratch free enough because it will be shiny. Or you can also examine it under the microscope before etching to get an idea of the maximum scratch size. Ideally, by the end, you will get scratches that are 0.1 microns as this is the smallest size of powder you used. Finally, etch it and check for the amount of time needed for Nital. You do not want to over-etch it so I suggest, removing the acid every certain amount of second and washing with water to check if you have etched it enough. The right etching time is the time that which will give you the best appearance of grains under the microscope. Softer metals will also be easily scratched whereas harder metals would need longer amount of time to get polished. So check the property of your metal to have an idea on how you should handle it. Also, the grain properties you will see depends on what processes your metal has undergone before (such as thermal or mechanical treatment). Hope this helps. Good luck!
Of some possibly interest for your query: J. R. Vilella, D. Beregekoff, "Polishing and etching lead, tin, and some of their alloys for microscopic examination", Ind. Eng. Chem., 19(9) 1927, 1049–1052.
Dear Sunny Sharma,
* You may try 0.05 um colloidal silica and/or alumina suspension finishing in vibratory polisher machine after diamond polishing.
* The second method is to try electrolytic polishing or electropolishing. I haven't carried out any experiments on Tin based alloys but I feel electropolishing will work if suitable electrolyte and other conditions like temperature, voltage or current density, etc.are employed.
Anas
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