The high surface hardness of the coating is one of the best ways to improve tool life. In general, the higher the hardness of a material or surface is, the longer the life of the tool will be.
The titanium carbonitride (TiCN) coating has a higher hardness than the titanium nitride (TiN) coating. Due to the increased carbon content, the hardness of the TiCN coating is increased by 33%, and its hardness varies from approximately Hv 3000 to 4000 (depending on the manufacturer).
The application of CVD diamond coating with a surface hardness of up to Hv9000 on cutting tools has become more mature. Compared with PVD-coated tools, the lifetime of CVD diamond-coated tools has increased by 10 to 20 times. The high hardness and cutting speed of diamond coating can be increased by 2~3 times than that of the uncoated tool, making it a good choice for machining non-ferrous materials.
2. Abrasive resistance
Abrasion resistance refers to the ability of a coating to resist abrasion. Although the hardness of some workpiece material may not be too high, the elements added during the production process and the adopted process may cause the cutting edge of the tool to crack or blunt.
3. Surface lubricity
High friction coefficient will increase the cutting heat, resulting in shortened service life and even failure. Lower friction coefficient can extend tool life. The delicate smooth surface of the coating helps to reduce the cutting heat, because the smooth surface allows the chips to quickly slip off the rake face and reduce the heat generation. Compared with the uncoated tools, the better surface lubricity of the coating tools can be processed at a higher cutting speed, thus further avoiding the high temperature welding of the workpiece material.
4. Oxidizing temperature
The oxidation temperature refers to the temperature at which the coating starts to decompose. The higher the oxidation temperature, the better the cutting process is under high temperature conditions. Although the hardness of TiAlN coating at room temperature may be lower than that of TiCN coating, it is proved that it is much more effective than TiCN in high temperature processing. The reason that the TiAlN coating can still maintain its hardness at high temperature is that a layer of alumina can be formed between the cutting tool and the chip, and the alumina layer can pass the heat from the tool to the workpiece or chip. Compared with high speed steel tools, the cutting speed of cemented carbide tools is usually higher, which makes TiAlN the preferred coating for cemented carbide tools.