Precision Ceramics
A commonly used hardness representation method for precision ceramics materials:
- Scratch method
A commonly used hardness expression method for industrial precision ceramics and mineral materials is Mohs hardness. It is a scratch test to indicate the order of hardness from small to large. That is, the latter minerals can scratch the surface of the front minerals, but there is no specific value. There are fifteen grades of Mohs hardness.
- Press-in method
The chemical bonds of ceramic materials mainly include ionic bonds and covalent bonds. Due to the large elastic modulus of advanced ceramic materials, the directionality of their bonds is strong. Moreover, the density is small, so the plasticity is small. The microstructure of ceramic materials is different from that of metal materials, which compose a single phase. The crystal phase structure composed of them is also more complex. To obtain the specific value of the hardness of ceramic materials, commonly used expressions are Vickers hardness, Knoop hardness, and Rockwell hardness.
- The conversion relationship between Rockwell hardness HRA and HRC
For harder materials (such as 95 alumina ceramic, SiC ceramics, etc.), the Rockwell hardness representation use more. It has high precision and a small error. But it has many scales, there are nine kinds of A, B, C, D, E, F, G, H, and K. Conversion between hardness is more difficult, and there is no uniform standard.
GB/T230-91 is the standard for test methods for metal Rockwell hardness, and is also suitable for ceramic materials.
Precision Ceramics are generally based on HRA (scope value: 20~88). Harder ceramics can use HRC as a scale (scope value: 20~70). Rockwell hardness calculate according to the depth of indentation.
HR = (K-h)/0.002
As can be seen from the formula, the larger the h, the smaller the HR value.
There are many methods of assessing hardness for precision ceramics materials. Different methods are suitable for different ceramic categories. Tests are only comparable between the same hardness methods. If simple and fast is required, the Mohs hardness method can be used for comparison. If more accuracy is needed, the Rockwell or Vickers hardness can be used for testing.
The hardness of industrial precision ceramics material depends on its crystal phase composition and structure. Grain size is the most sensitive factor. The smaller the grain size, the higher the ion electricity price. This results in greater binding energy. There is also a stronger ability to resist external friction scratching and pressing, leading to greater hardness.