Grinding and Polishing

Grinding and polishing removes sectioning damage (burning, tearing, plastic flow) and progressively refines scratches until the surface reflects a mirror finish suitable for optical metallography. Each step uses finer abrasive and lighter pressure than the prior step to avoid embedding coarse grit and to keep deformation depth shallow.

Planar grinding on SiC papers establishes coplanarity between mount and specimen. Fine grinding transitions to diamond on composite disks or rigid platens to control flatness. Polishing with colloidal silica or alumina chemo-mechanically removes the last damage layer for grain boundary and inclusion contrast after etching.

Water sensitivity (e.g., aluminum-lithium alloys) or corrosion-prone steels may require oil-based lubricants or short cycles to avoid staining. Automated head pressures improve repeatability across operators.

The final surface must be artifact-free: comet tails, pull-outs, and relief between phases bias automated inclusion ratings and hardness indent placement. Documenting grit sequence and force supports audit trails in accredited labs.