Low-Melting point metals such as zinc, lead and tin are not always easy to prepare. These metals are very soft and malleable, and attaining a scratch free finish can be challenging. One of the more common problems during preparation of these specimens is embedding. Embedding occurs when hard abrasive particles (or other contaminant) becomes fixed in the surface of the softer specimen. Embedded abrasives can introduce more damage. They can also be misidentified as a feature of the material. Here are a few remedies for preventing embedding.
When grinding with Silicon Carbide discs (SiC), the abrasives particles fracture and break free from the disc during use. These particles can embed into soft specimens. Coating the SiC discs with paraffin wax can remedy this problem. The wax helps hold the SiC to the paper and adds lubricity.
For polishing steps, diamond embedding becomes a more significant problem at around 3 microns and smaller. The use of diamond paste such as MetaDi Ultra instead of suspensions can greatly reduce embedding. The waxy paste used as a carrier for the diamond helps hold the diamond to the cloth. Oil based diamond can also be used effectively, but can be more difficult to clean.
Other factors that reduce the occurrence of embedding are:
Use compressed fiber (not napped or woven) cloths such as TexMet C
Use Complementary rotation for semi-automatic preparation
Maintain minimal fluid on the cloth surface, keeping the surface lubricated but not wet
Figure 1: SiC from grinding embedded in a weld in 6061-T6 aluminum (0.5% HF etch)
Figure 2: 6-µm diamond embedded in a lead specimen (shown after the 6-µm step, unetched).