Mr. Guo Guangyu, general manager of coating supplier Kehui Titan Co., Ltd., introduced the coating from the original single layer to the structure of multi-layer and gradient layer (Gradient); among them, TiN, TiCN, TiAlN, AlTiN, CrN and TiAlCN has become a traditional coating. Up to now, nano-multilayers and nanostructures (such as CrTiAlN, TiAlN/SiN, CrAlN/SiN and CrTiN) have been further popularized. Next, the multilayer coating will become the most important coating structure in the future.
He introduced that the multi-layer hybrid structural coating is deposited in three stages, the bottom layer is a thin and hard Adhesion Layer, and the middle is an AlTiN stepped core layer composed of a single layer or a stepped structure. The periphery is a nano-structured layer with a nanohardness of up to 50 GPa and high heat resistance, which maintains the stability of the workpiece at a high temperature of 1,200 °C.
It can be seen that multi-layer hybrid structural coatings have become one of the mainstream developments. But he added that the use of coating types is diversified, and how manufacturers choose, mainly depends on the application. For example, milling tools are suitable for multi-layer hybrid structural coatings, and their multi-layer construction effectively reduces tool cracking.
Coating technology is one of the main means to improve tool performance. The coating improves the resistance of the cutting tool to various wears, prolongs the life of the tool, improves the surface precision of the machined part, and increases the cutting speed and feed rate, thereby improving the metal cutting efficiency. Today, in the cemented carbide of the cutting tool mainstream material, coated carbide tools account for 80%, of which CVD (chemical coating) accounts for 60% to 65%, and the rest is PVD (physical coating).
In the CVD coating, multilayer composite coatings including various compounds such as TiCN, TiC, TiN, ZrCN and Al2O3 improve the overall properties of the coating, such as bonding strength, toughness, wear resistance and abrasion resistance, and corrosion resistance. Sex has a good effect. The typical VCDTiN (outer layer) + Al2O3 (middle layer) + TiCN (inner layer) multilayer structure is now further improved from the coating process and the thickness of the coating film. MTCVD (Medium Temperature Chemical Coating) minimizes brittle η phase at the interface between the coating and the substrate due to lower process temperatures and faster deposition rates, while reducing the high temperature temperatures common in high temperature CVD coatings. Tensile cracking, therefore, MTCVD TiCN coating has become a major component of CVD multilayer coatings, which have been used in α-Al2O3 coatings such as ISCAR's α-IC9150, α-IC9250, α-IC9350 and α-IC4100, etc., improves the bonding strength of the coating to the substrate and the ability to resist back wear, front wear and anti-adhesion.
In the case of PVD coatings, it has also evolved from a single TiN or TiCN or TiAlN coating to the current composite coating, the hard coating + soft coating. In order to meet the requirements of higher cutting speed and dry cutting, the red hardness of coated tools has become a hot spot in the development of PVD technology in recent years. TiAlN's improved coating, AlTiN, increases the Al content of the film (Al content greater than 50%), improving the red hardness, chemical stability and oxidation resistance of the coating, such as ISCAR's Al-IC910 (processed cast iron and steel) , Al-IC900, Al-IC930 (processed steel, stainless steel, hard steel, cast iron, superalloy, etc.).
An important feature of modern tool coating development is composite. In order to improve its comprehensive performance, coating material compounding, coating layer compounding and CVD and PVD compounding, such as ISCAR DT7150 (K05-K25) by MTCVD Al2O3 and PVD TiAlN composite The coating improves the overall properties of the material and is used for high speed machining of grey cast iron and ductile iron. Diversification is another trend in the development of tool coatings, including various nitride and oxide coating materials, as well as TiB, SN coatings, diamond coatings, cubic boron nitride coatings, and the like. The deeper reason for diversification is specialization, that is, different coatings are applied for different needs, and the composition, percentage, structure and thickness of the coating can be controlled and changed to a greater extent to suit different Machining materials and different cutting conditions significantly improve the cutting performance of the tool. For example, CrAlN coating, with Cr element instead of Ti element, has a hardness of 3200 HV and an oxidation temperature of 1100 ° C. It has better toughness than TiAlN, and is more suitable for the processing of interrupted cutting and difficult-to-machine materials; The layer can obtain TiSiN for hard cutting, and can also obtain lubricated CrSiN, which is more suitable for processing materials with strong adhesion such as aluminum and stainless steel. In addition, the miniaturization of coating materials is another interesting trend in the development of modern tool coatings, and nanocomposite coatings are being used in more and more places. In the future, tool coating will be a system concept, that is, the tool coating must be combined according to the changing conditions of modern cutting applications, which is a traditional concept of "coating a film on the tool." "A very different and more complex system engineering approach, which requires us to think systematically.