Introduction to tool coating materials Which is the best tool coating material?

1. Diamond, diamond-like (DLC) coating

Diamond coating is one of the new tool coating materials. It uses low-pressure chemical vapor deposition technology to grow a layer of diamond film composed of polycrystalline on the cemented carbide substrate, with which the processing of non-ferrous metals such as silicon-aluminum alloys and copper alloys, engineering materials such as glass fibers and cemented carbide, etc., the life of the tool is 50-100 times that of the ordinary cemented carbide tool. Diamond coating uses a number of diamond synthesis techniques, the most common being the hot wire method, microwave plasma method and DC plasma jetting method. By improving the coating method and the bonding of the coating, diamond coated tools have been produced and applied in industry.

In recent years, the United States, Japan and Sweden and other countries have launched a succession of diamond-coated taps, reamers, milling cutters, as well as for the processing of printed wiring boards on the small holes diamond-coated carbide drills and a variety of indexable inserts, such as Sweden Sandvik's CD1810 and the U.S. Kennametal's KCD25 and other grades of products. American Turchan company developed a new process of laser plasma deposition of diamond, with this method of deposition of diamond, due to the plasma field surrounded by the entire tool, the coating on the tool is uniform, and its deposition speed is 1000 times faster than the conventional CVD method. The diamond coating made by this method produces a real metallurgical bond with the substrate, and the coating is of high strength, which prevents defects such as coating peeling, cracking and crazing, etc. CemeCon has a distinctive CVD diamond coating technology, and set up a production line in 2000 to make the diamond coating technology reach the level of industrialized production, which is of high technological content, and allows for the mass production of diamond coatings.

Diamond-like coatings have obvious advantages in the mechanical processing of certain materials (Al, Ti and their composite materials). The microstructure of diamond-like coatings deposited by low-pressure vapor deposition is still quite different from that of natural diamond. In the nineties, low-pressure vapor deposition of DLC in the presence of activated hydrogen was often used, and the coatings contained a large amount of hydrogen. Excessive hydrogen will reduce the bonding strength and hardness of the coating and increase the internal stress, and the hydrogen in the DLC will be released slowly at higher temperatures, causing the coating to work unstably. DLC without hydrogen has higher hardness than DLC with hydrogen, and has the advantages of uniform organization, large area deposition, low cost, and flat surface, etc. It has become the hot spot of DLC coating research in recent years. American scientists A.A. Voevodin proposed the deposition of super-hard DLC coating structure designed for Ti-TiC-DLC gradient transition coating, so that the hardness of the softer steel matrix gradually increased to the surface layer of super-hard DLC coating. This type of composite coating maintains high hardness and low coefficient of friction, while reducing brittleness and improving load carrying capacity, bonding and wear resistance. Sumitomo Japan has introduced the DL1000 coating with diamond DLC on carbide inserts for cutting aluminum alloys and non-ferrous metals, which is bond-resistant and can effectively reduce the roughness of the machined surface.

After years of research shows that: due to the diamond-like coating of high internal stress, poor thermal stability and the catalyst effect with the ferrous metal between the SP3 structure to the SP2 transformation and other shortcomings, decided it can only be applied to the processing of non-ferrous metals, thus restricting it in the machining of further applications. But in recent years, research shows that the SP2 structure based diamond-like coating (also known as graphite-like coating) hardness can also reach 20 ~ 40GPa, but there is no problem with the ferrous metal catalyst effect, its coefficient of friction is very low and has a very good resistance to moisture, cutting can be used as a coolant can also be used for dry cutting, the life of its uncoated knife than the exponential increase in the processing of iron and steel materials, and thus cause Coating companies, tool manufacturers are very interested. In time, this new diamond-like coating will be widely used in the cutting field.

2. Cubic boron nitride (CBN) coating

CBN is the emergence of another super-hard material after the synthetic diamond, it has many similar to diamond in addition to excellent physical and chemical properties (such as ultra-high hardness, second only to diamond, high wear resistance, low coefficient of friction, low coefficient of thermal expansion, etc.), while also having some better than the characteristics of diamond. CBN has the characteristics of iron, steel and oxidizing environment. For iron, steel and oxidizing environment is chemically inert, in the oxidation of the formation of a thin layer of boron oxide, this oxide for the coating provides chemical stability, so it is in the processing of hard iron, grey cast iron, heat resistance is also extremely good, in a fairly high cutting temperature can also be cut heat-resistant steel, hardened steel, titanium alloys, etc., and can be cut with high hardness of the cold hardened rolls, carburized quenched materials, as well as very serious wear of cutting tools, silicon, aluminum alloys and other difficult to machine materials. Aluminum alloy and other difficult to machine materials.

Since 1987, Inagawa and other successful preparation of pure CBN coating, in the international set off a CBN hard coating research boom. Low-pressure vapor-phase synthesis of CBN coatings are mainly CVD and PVD methods. CVD includes chemical transport PCVD, hot-wire-assisted heating PCVD, ECR-CVD, etc.; PVD has a reactive ion-beam plating, reactive reactive vapor deposition, laser vapor deposition ion-beam assisted deposition method. The research results show that: progress has been made in the synthesis of CBN phase, good bonding to the cemented carbide substrate and suitable hardness, etc., the current deposition of cubic boron nitride on the cemented carbide is only a maximum of 0.2 ~ 0.5 μm, if you want to achieve commercialization, it is necessary to use a reliable technology to deposit high-purity and economical CBN coatings, which should be in the thickness of 3 ~ 5 μm, and in the actual metal cutting machining to confirm Its effect.

3.CNx coating

Twenties eighties, American scientists Liu and Cohen designed a similar β-Si3N4 new compound β-C3N4, using solid state physics and quantum chemistry theory, calculated that its hardness may reach diamond, which has attracted the attention of scientists around the world. The synthesis of carbon nitride has become a hot topic in the field of materials science in the world. Japan Okayama University FFujimoto using electron beam evaporation ion beam assisted deposition method to obtain carbon nitride coating reached 63.7Gpa. Wuhan University synthesized carbon nitride hardness of 50GPa respectively, and deposited into the high-speed steel twist drill, to obtain very good drilling performance. The main methods of synthesizing carbon nitride are true-flow and radio frequency reaction sputtering method, laser evaporation and ion beam assisted deposition method ECR-CVD method, dual ion beam deposition method.