Industrial developed countries have been working on PVD coating technology for cemented carbide tools since the early 1990s. In the mid-1990s, breakthroughs have been made. PVD coating technology has been widely used in carbide milling cutters, drill bits, step drills, Coating treatment of oil hole drills, reamers, taps, indexable milling inserts, profiled tools, welding tools, etc.
China's PVD coating technology research and development work opened the cathode ion coating machine, and developed the high-speed steel tool TiN coating technology. At the end of the 1990s, the domestic successful development of the TiNTiCNTiN multi-component coating technology of hard alloys reached a practical level. However, compared with the international development level, China's cemented carbide tool PVD coating technology is still behind 10 years. At present, the foreign tool PVD coating technology has been developed to the fourth generation, while the domestic is still in the second generation level, and still dominated by a single layer of TiN coating.
4.PVD, CVD coating technology <br> <br> Comparative currently about 80% of the carbide tools superhard material using a CVD coating techniques. Since the introduction of TiNPVD coated HSS tools in industrial applications in the early 1980s, it has been explored whether PVD can be used to replace cemented carbide inserts instead of CVD. Because of the advantages of CVD coating technology, PVD coating technology has the following advantages: (1) PVD technology has a low deposition temperature, and can deposit super-hard coating such as TiN at about 500 °C, so it does not reduce the original matrix material. It has bending strength, and the η phase is not generated between the coating and the substrate, which expands the application range; (2) The coating has a fine structure, and compressive stress is generated inside the coating, and the crack propagation resistance is strong; (3) Coating The surface is smoother, which is more effective than the CVD coating to prevent the transverse crack propagation on the rake face and reduce the friction coefficient. (4) It is possible to use a sharp-edged tool as the substrate, which is very important for high-speed cutting.
Although PVD coatings have advantages that are difficult to compare with CVD coatings, practice has shown that the performance of TiC/Al2O3 or TiC/Al2O3/TiNCVD coatings for general turning (partially milling) inserts is still superior to PVD coatings, except for CVD technology. In addition to the αAl2O3 coating, the bonding strength of the coating to the substrate is higher than that of the PVD coating, which is also an important factor in the performance of the PVD technology. Scratch test of coated cemented carbide inserts shows that the critical load of PVD coating is generally 30~40N, while the critical load of CVD coating can be >90N; the thickness of CVD coating can reach 8~0μm, while PCD coating The thickness must be controlled at 3~5μm, otherwise the coating is prone to spalling. In addition, the industrial cost of cemented carbide blade CVD coatings is lower than that of PVD coatings, which is one of the reasons why CVD technology is more widely used.
Both CVD and PVD technologies will co-exist and complement each other in cemented carbide tool coatings and have their own share of the tool coating ratio due to their own advantages. In general, steel tools such as high-speed steel, sharp carbide precision-cutting blades, and carbide-based multi-blade tools are ideally coated with PVD technology. Most of the remaining carbide inserts can be coated with CVD technology. Moreover, CVD coatings are also evolving. In addition to the use of medium temperature CVD coatings to reduce the reduction in the strength of cemented carbides, a computer can be used to precisely control the thickness of a single layer of coating to avoid the formation of columnar crystals to meet the coating. Coating requirements for fine-cut carbide inserts.
Carbon content of the cemented carbide substrate surface gradient control <br> <br> control the carbon content of cemented carbide it is a very critical issue. When the alloy is deficient in carbon, a brittle η phase is formed in the alloy, and the occurrence of the η phase greatly reduces the fracture toughness and strength of the cemented carbide. The currently known η phase mainly includes Co6W3C and Co2W4C of M6C type; Co6W6CF, Co6W6C104F and Co3W9C4 of M12C type, in addition to Co2W6C, Co2W8C3 and Co3W10C4. When the carbon in the alloy is excessive, the graphite phase in the alloy will also adversely affect the properties of the alloy. The surface of the gradient alloy substrate is coated with TiC high-hard wear-resistant material by chemical vapor deposition method. At 1000 ° C, the following reaction occurs:
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