Since the 1930s, diamond abrasives have been a valuable tool for metallographic sample preparation. Diamond can polish the widest range of samples as it is the hardest known material.
Buehler provides a broad range of diamond products to suit customers’ requirements.
Products with polycrystalline diamond (Metadi® Ultra Diamond Paste and MetaDi® Supreme suspension) and monocrystalline diamond (MetaDi® II Paste and MetaDi® suspension) are available from Buehler.
For ductile materials including most metals, polycrystalline diamonds are usually preferred, as they contain more cutting surfaces, resulting in a quicker polish along with less deformation and the best surface finish.
Monocrystalline diamonds are cheaper, but can polish slowly and their use results in an inferior finish on ductile materials. Monocrystalline diamonds work best with hard materials, although they can be an option when wastage is expected or polishing quality and time are not a major concern.
Paste or Suspension
The material in which the diamond is carried is very important to polishing results. Buehler provides diamonds carried in wax pastes, oil, and water-based suspension.
Water-based suspensions such as MetaDi® Supreme Polycrystalline and MetaDi® Monocrystalline suspension are easy to use, multipurpose, and effective. The suspensions contain a unique formulation to ensure that the diamond stays in suspension, and provide better lubrication during polishing. They are commonly used in applications where water sensitivity and embedding are not an issue.
Paste has a high diamond concentration, and is ideal when applied on a new cloth to ensure that there is enough diamond and lubricity for the cloth to be working at 100% right from the start.
Polishing suspension can be used subsequently to replenish diamond and provide lubrication. If only suspension is used on a previously unused cloth, polishing times can be extended by ~1 minute to allow the diamond concentration to rise to an effective level.
Problems with Embedding and Water Sensitivity
Diamond in the water-based suspension may become embedded in very soft materials. In such cases, paste is favored as the wax carrier enables the diamond to be more 'fixed' to the polishing cloth, helping to prevent embedding. Pastes need to be used with a lubricating fluid – water-based (Metadi Fluid) or oil-based (Lapping Oil). For best results, enough fluid should be added to keep the polishing cloth moist.
Oil-based suspensions are valuable for the preparation of water-sensitive materials, and have better lubricity. However, their polishing rates are slower and they create difficulties when cleaning samples and equipment, so they are usually only used when necessary.
Several of Buehler’s diamond products are dyed according to abrasive size (e.g. red = 9 micron, green = 3 micron, blue = 1 micron). When dyes are used, they also color the cloth, helping to prevent accidental contamination. Buehler also offers dye-free products for those who may need to conduct analysis thatcould possibly be affected by the dye.
This information has been sourced, reviewed and adapted from materials provided by Buehler.
For more information on this source, please visit Buehler.