Sample preparation for testing in optical microscope using VR
Note : This is a VR experiment, so idea is to play with the variables. Suggested steps, to utilize the simulation and learn from the changes, are:
Grinding : The purpose of grinding is to obtain a flat surface and remove damage caused during sectioning of sample.
Begin the process of surface abrasion using coarsest (i.e. 120 grit or 180 grit) abrasive paper. Do utilize coolant/lubricant to precent the specimen from overheating, which may change its microstructure.
Sample should be flat with a uniform/distributed force in order to avoid any tapering and rendering uniform material removal from sample surface. Typically one-direction movement (or generating eight-pattern) ensures uniform material removal.
When using the subsequent finer grit (i.e. 240, 320, 400, 600), rotate the sample by 90° relative to previous scratch direction, and continue grinding until all the earlier scratches (in orthogonal direction) disappear.
Keep the water running, and do ensure to wash and thoroughly clean the sample after each grinding step. This process removes any embedded/hanging abrasive particles and or coarser debris that may hamper the finer scratch removal in subsequent grinding cycle.
After the final grinding stage (i.e. 600 grit), the next step in sample preparation is polishing.
Polishing : Purpose of polishing is to result a mirror-finish surface free from any scratches.
Change to a polishing wheel with a velvet cloth (hard-woven/nap-cloth) and use very coarse (say 9 μm) abrasive (diamond) suspension with a lubricant.
Press the sample firmly against the wheel and move it against wheel’s rotation direction to protect the edges from smearing. After the scratches tend disappear, clean the sample to prevent retention of any coarse abrasive particle.
Progressively follow the steps using finer diamond paste/suspension (say 6 μm followed by 3 μm diamond) along with compatible lubricant. Cloth should remain just damp and should neither be flooded wet nor complete dry.
Final polishing proceeds with even softer cloth (high-nap) using 1 μm diamond suspension, followed by 0.3 μm and 0.05 μm alumina/colloidal silica till a mirror-finish is obtained. The surface should be free from any scratch to be observed under microscope.