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Discoloration or stain on the sample surface
Discoloration or stains on the sample surface may be caused by drying traces left by residual suspensions, water or ethanol due to inadequate cleaning. This problem is not serious and can be easily resolved by correctly identifying the stain and applying additional cleaning steps.
Sample corrosion may occur when aqueous-based preparation methods are used for corrosion-prone samples or when samples are not dried fast enough. It is recommended that alcohol or oil-based methods be used to prepare extremely corrosive samples.
Rounding is a problem when working with components that have different hardnesses, such as composites or hard materials embedded in softer resins. This results in the soft material being removed more quickly than the hard material. Edge rounding effectively resulted in two levels of samples where transitions occurred at the interface where the material was rounded. Investigation in these areas was very challenging.
Edge rounding is caused by the use of metallographic grinding and polishing media with soft elastic substrates, so pre-polishing with grinding and polishing discs with hard substrates can help **minimize or avoid this problem. **The polishing step should be as short as possible.
Scratches may be found when the sample is not properly polished. Scratches appear in composites from one of the previous polishing steps, when one component is well polished but another component shows scratches due to its different hardness. Scratches may also appear if the sample is not handled properly.
The initial preparation of a new material usually involves some degree of iterative testing. The operator will identify the part and determine its cause throughout the process. To simplify this process, it is important to examine the sample with a microscope after each individual preparation step. This allows the operator to determine which step is causing the problem.