Common misconceptions about coatings involve inadequate understanding of their hardness characteristics. There are two primary hardness categories: 1. Grain hardness: For instance, tungsten carbide powder consists of numerous sintered and agglomerated micrograins. The commonly used tungsten carbide grains measure 0.8 μm, with typical grain hardness exceeding 2000HV. 2. Alloy hardness: When these micrograins are sintered into a unified tungsten steel alloy, the resulting composite exhibits high hardness. For example, YG10 tungsten steel alloy typically surpasses 92HRA hardness, while tungsten carbide coatings with similar compositions generally exceed 70HRC hardness.

The reason is that the structure is different. Although tungsten carbide powder and tungsten steel alloy are sintered by tungsten carbide grains, tungsten carbide coating is composed of physical bonding of powder particles. Therefore, we must distinguish the hardness of the coating and the hardness of the material, and understand the structure of the coating.

This example uses tungsten carbide to illustrate the issue of hardness, which holds true for other materials as well. To summarize, all coatings are physically bonded to the substrate, and the powder grains within the coating are also physically bonded. This fundamentally differs from common alloys and ceramic products.