Polishing and grinding are the most common preparation techniques in metallography. As there are many different types of metals used for inspection in metallography, there are a range of tools and polishing methods appropriate for each job.
Metallography can take a lot of time when going through each process, so it is worthwhile to invest in good quality materials for each stage of material preparation such as quality Polishing cloths. While it is possible to automate these workflows, it can take a considerable amount of capital to do so. Weighing your options dependant on your needs is always a good choice to ensure that you are making an investment that is balanced with the outcome.
Risks during metallography
There are some potential risks that come with the job which is important to consider when preparing materials for inspection:
- Grain boundaries and edges can be unintentionally smoothed or rounded.
- If the cooling element used does not do its job properly, there is a chance that the microstructures in metal samples can be changed or result in thermal
- If the abrasive substance used for polishing is not compatible with the sample degradation. metal, excessive scratching can happen. While scratching is likely to happen with some materials, it is important to look for polishing materials that match the hardness value of the sample metal.
Common metallography methods
There are a wide range of methods used for metallography and with this some common issues may occur. A few popular ones are:
- The pencil effect. In polishing techniques, a commonly applied method is what is known as the ‘pencil effect’. This can happen during both single and manual pressure metal preparations and is caused when the surface of a metal begins to lean towards the middle of the sample. The reasons for this happening include a low contact pressure, a non-cylindrical sample, and a wrong diameter used.
- Comet tails. Comet tails commonly happen with non-metallic pores, phases, and inclusions. If the sample section is held in only one direction when being manually prepared.
- Polishing and grinding errors. Both the position and contact pressure are important to achieve a satisfactory result. If you keep the grinder or pressure too close to the centre there is a chance that you will not achieve the right results.
- Abrasives and polishing agents. Using the correct lubricants can avoid issues such as breaking down materials, excessive abrasion, wrong grain size.