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. If cutting and mounting are the preliminary steps of sample preparation, then grinding and polishing are the most important steps in the sample preparation process. Friends who are fortunate enough to avoid the cutting and mounting processes should be more cautious and careful in the grinding and polishing stage, otherwise the work will fail.

Grinding and polishing are divided into two stages: flat grinding and polishing. The purpose of flat grinding is to quickly remove the rough surface left by cutting and obtain a flat fresh surface. Polishing is to gradually increase the roughness of the sample surface until it reaches the mirror level of optical observation.

For high-end equipment, both grinding and polishing can be done on one machine. For consumables, grinding and polishing are very different.

The grinding stage is equivalent to the rough processing of the sample preparation stage, which requires rapid grinding of coarse abrasive grains. Silicon carbide sandpaper or diamond grinding discs are usually used. Basically, no external abrasive grains are required. Just add a large amount of water.

Polishing is the finishing stage of sample grinding. It is very sensitive to the surface affinity of the material and the difficulty of material removal. Usually, the polishing disc is the carrier and the polishing liquid is the abrasive carrier. The two are used together. For example, the materials of the polishing disc are silk, cashmere, chemical microscope, rubber, flannel, etc. Different materials and textile characteristics determine their storage characteristics and grinding characteristics of abrasive grains; for polishing liquid, diamond abrasive grains are mostly used, polycrystalline diamond has rich cutting edges, fast grinding speed, effectively avoids edge rounding, single crystal cost is low, and ordinary applications can cope with it. For fine final polishing, there are many oxide polishing liquids, and the particle size can be less than 1 micron.

It is worth mentioning that diamond grinding discs have been used more and more, especially in the fine grinding stage. They are fast and simple, can be used repeatedly, and have a long lifespan, so the overall cost performance is very high.

Generally speaking, the diameter of the abrasive in the flat grinding stage is above 100 microns, so the basic scratches are naturally around 100 microns. The polishing process is to reduce the size of the scratches step by step, and finally within 1 micron, which is invisible under the conventional optical magnification, suitable for direct observation and analysis, or observation and analysis after corrosion. It can be seen that grinding and polishing is a fine material surface grinding process. The grinding medium has two sources, grinding discs and suspensions. Especially in the initial stage of polishing, the abrasive source is the grinding disc. The grinding disc surface can be sandpaper or a grinding disc with diamond or other types of abrasives. This process can also be supplemented by suspensions to enhance the grinding effect. In the later stage of polishing, the grinding disc is a different type of fabric. It does not contain abrasives itself, but can store abrasives from the suspension.

The goal of grinding and polishing is to eliminate scratches step by step. Macroscopically, it is a physical process of material grinding. In fact, due to stress, the surface of the sample is in a high-energy state and it is easy to undergo electrochemical reactions with water, air, grinding media, etc. Therefore, the matching of grinding and polishing consumables for samples of different materials is very particular, and it requires a lot of trial and error to find an effective and simple method.

In summary, the main task of a metallographic technician is to constantly explore and optimize various combinations, and then solidify them and share them with others. This process is destined to be repeated exploration and trial, and it is inevitable to take detours and waste time and energy. The most worry-free way is to outsource this work to a professional company. 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 to 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 metallography. 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.