Hard coating refers to the coating of wear-resistant tic or tin, HFN, Al2O3 on the surface of cemented carbide blade by chemical vapor deposition (CVD).


Advantages of cemented carbide coating:
Coated carbide inserts are generally made into indexable patterns. It can be clamped on the cutter bar or cutter body by machine clamping method. It has the following advantages:
1) Due to the high hardness and wear resistance of the coating material on the surface, the coated cemented carbide is allowed to use higher cutting speed compared with the uncoated cemented carbide, thus improving the processing efficiency; Or it can greatly improve the tool life at the same cutting speed.
2) Because the friction coefficient between the coated material and the processed material is small, the cutting force of the coated blade is lower than that of the uncoated blade.
3) When the coated blade is machined, the machined surface quality is better.
4) Because of the good comprehensive performance, the coated blade has good versatility. The blade with a coating brand has a wide application range.
The common method of cemented carbide coating is high temperature chemical vapor deposition (htcvd). In the deposition system of atmospheric pressure or negative pressure, pure gases or vapors such as H2, CH4, N2, TiCl4, AlCl3 and CO2 are mixed evenly according to the composition of the deposit, In this way, tic, tin, Ti (C, n) or Al2O3 or their composite coatings are deposited on the surface of cemented carbide inserts. The reaction equation is summarized as follows:
TiCl4+CH4+H2TiC+4HCl+H2TiCl4+ ½ N2+2H2TiN+4HClTiCl4+CH4+ ½ N2 + H2 → Ti (CN) + 4hcl + h22a1cl3 + 3co2 + 3h2 → Al2O3 + 3Co + 6hcl, PCVD (plasma chemical vapor deposition) method is also used to coat the surface of cemented carbide inserts °～ eight hundred °)， Therefore, the reduction of bending strength of the insert is small, which is suitable for milling insert.
Before coating, the surface of the base blade should be cleaned and the cutting edge should be passivated. After coating, because of the difference of the coefficient of linear expansion between the coating material and the base material, the residual tensile stress will inevitably appear on the surface of the coated blade, which will reduce the bending strength of the blade. Usually, tic thin layer is applied on the surface of the substrate first, because the coefficient of linear expansion of tic is close to that of the substrate; Tin and Al2O3 are applied on the outside. In the past, tic was used for single coating, TiC / tin and TiC / Al2O3 were used for double coating, TiC / Ti (C, n) / tin and TiC / Al2O3 / tin were used for three coating. In recent years, with the improvement of the substrate materials, the coating materials are also backed by tin, that is, tin / TiC / tin and other coating materials, as well as HFN, MoS2 and so on.