The ultimate goal of metallographic sample preparation is to prepare a flat mirror surface for observation after corrosion or direct observation. The importance of grinding and polishing is obvious. Polishing is the last step in the sample preparation stage, and it is also the most important and critical step.

A key measurement indicator of the grinding and polishing step is without scratches.And scratches are actually an indicator of the surface finish of the sample. Scratches can only be divided into coarse and fine. Absolute scratches do not exist. What we usually call scratches generally refers to scratches within 1 micron, which can’t be basically observed under an optical microscope.

How to achieve scratch-free in the conventional sense is a question that many metallographic practitioners are very concerned about. Of course, it is also a very abstract question, and there is no single answer. Eliminating scratches is a systematic problem, which requires starting from the details of grinding and polishing, as follows:

1. Reasonableness of the particle size matching in the grinding and polishing process

The grinding and polishing process is the process of gradually reducing scratches. The particle size span between each process should be set appropriately. If it is too large, it cannot be effectively eliminated, and if it is too small, it will cause unnecessary waste of consumables. The more classic combination is the rough grinding and fine grinding of sandpaper, 9 micron grinding disc, 3 micron rough polishing, and 1 micron fine polishing. Of course, according to their respective needs, processes are also added or deleted to achieve tailor-made.

2. Quality reliability of grinding and polishing fluid

The material removal on the sample surface is completed by abrasive particles. The diamond particles in the grinding and polishing fluid play two roles, removing the rough scratches of the previous process and leaving scratches for the next process. In other words, fine scratches replace rough scratches. Therefore, the particle size control requirements of the abrasive particles in the grinding and polishing fluid are very high, and the particle size distribution must be controlled within a very narrow range, which is also a characteristic of quality suspension.

3. Cross-contamination of grinding and polishing discs

The grinding and polishing disc is the carrier of the suspension abrasive particles and is reused. There will be residual diamond abrasive particles on the surface after each process. The particle size of the grinding and polishing disc must be clearly defined to prevent the possible mixing of large abrasive particles, and cross-mixing is even more prohibited, which will cause abnormal scratches on the surface.

4. Thorough cleaning of each step

Cleaning is the most effective way to prevent scratches. Large particles left over from the previous process may exist on the sample surface, sample gaps, sample holders and other parts. The residues in these places will be potential sources of risk and must be thoroughly cleaned. Ultrasonic cleaning is also required if necessary.

It is a complicate process of removing scratches from above several points.It needs to be equipped with equipments and consumables and also need development of rigorous and meticulous sample preparation habits. At the same time, it is also very important to learn from the methods of professionals, and obtaining relevant experience from professional metallographic solution suppliers can achieve twice the result with half the effort. Domestic professional companies such as Shanghai Truer have more than ten years of experience in commissioned sample preparation, accumulated a large amount of sample preparation information, and established a special database, which can quickly obtain the best sample preparation plan.

All microscopic analyses are the accumulation and crystallization of countless details, and the same is true for metallographic analysis. Even the most insignificant errors may create obstacles for subsequent observations. Industry practitioners must be in awe and pursue perfection.

Shanghai Truer Company has been deeply involved in the metallographic testing industry for decades, and has long practiced the concept of exquisite metallographic. It is a leading metallographic solution provider in China. Truer takes international giants as benchmarks, faces difficulties, concentrates on research, overcomes key equipment and consumables that restrict the development of the industry, and creates a complete metallographic industry chain integrating equipment, consumables and sample preparation training; the company is equipped with a cutting-edge metallographic laboratory and has a team of highly qualified experts. For more than ten years, it has provided metallographic analysis and sample preparation training services to thousands of customers, and provides customized metallographic laboratory solutions.

If you have any metallographic questions, you can get in touch with them to get the information you want.