Application of Nanocomposite Film in Dry Cutting Tool Coating
It is widely used in tool coatings by reducing wear during tool cutting and significantly increasing tool life.
With the application, popularization and green manufacturing concept of various high-efficiency, high-speed, high-precision CNC machine tools and machining centers, in order to meet the processing needs of various hard and high-hardness difficult-to-cut materials, dry cutting technology is becoming more and more It has received much attention and has placed higher demands on tool coating technology and coating materials. Nano-films meet the new requirements for tools under dry cutting conditions. Therefore, nano-films and their application in dry-cutting tools have become the research hotspots in the field of tool coating preparation and surface engineering.
Research and development of nano-film technology
With the advent of nanomaterials, nanofilm (coating) technology has also been developed accordingly. To date, research has shifted from a single material nano-film to a nano-composite film, and the thickness of the film has also evolved from several micrometers to several nanometers of ultra-thin film. Films which have been prepared at present include Ti(N, C, CN), (V, Al, Nb)N, Al2O3, SiC, and Cu, Ni, Al, Ag, Au, diamond, and the like. Among them, TiN, Al2O3 and TiC are typical superhard films, and their microhardness is HV1950, HV3000 and HV3200, respectively. The anti-wear order is TiC>TiCN>TiN>Al2O3. These films are used in applications in the field of cutting tools, micromachines, and microelectronics as wear resistant, corrosion resistant coatings and other functional coatings. Since the concept of superhard nanocomposite film was proposed by VeprekS, the research on nanocomposite film has attracted extensive attention. The super-hard nano composite film has the effects of surface friction reduction and wear resistance, can improve the motion reliability and life of the friction pair, achieve the same or better use effect as the high alloy material, and achieve the purpose of energy saving, material saving and efficiency improvement. The nanocomposite film is composed of two different materials, which may be nanocrystalline/nanocrystalline or nanocrystalline/amorphous, each having a particle size of 3 to 10 nm. Among the composite film preparation methods, plasma chemical vapor deposition (PACVD) was firstly applied to the preparation of nc-TiN/Si3N4, nc-TiN-BN and nc-TiAlSiN films.
For example, VeprekS and ShizhiL used PACVD method to prepare nc-TiN/α-Si3N4 film at a deposition temperature of 550-600 °C with SiCl4, SiH, TiCl4 and H2 as reaction gases. However, the reaction gas may corrode the membrane and equipment during the preparation process, posing a risk of environmental pollution or even fire. In general, CVD deposition technology requires temperatures of 500-600 ° C to promote the growth of nano-grains, while too high deposition temperature will cause problems such as softening of the substrate and decreased dimensional accuracy, thus severely limiting the application of nano-composite films. Studies have shown that the key to the preparation of nanocomposite films is to rapidly form crystal nuclei while ensuring low-speed growth of grain size. Therefore, in order to ensure that the overall performance of the film is not reduced, reducing the deposition temperature becomes the key technology.
Current experiments show that magnetron sputtering is the most effective method for low temperature deposition. Therefore, the current research mainly focuses on the preparation of nanocomposite films by magnetron sputtering. For example, reactive magnetron sputtering deposition is widely used to prepare MeC/DLC (diamond-like carbon film), and Me is a transition metal such as Ti. With this technique, the deposition temperature can be below 150 °C. KarvánkováP et al. used unbalanced magnetron sputtering technology to prepare ZrN-Ni and CrN-Ni nanocomposite films with matrix temperatures of 300 ° C and 200 ° C respectively. It was also found through preparation experiments that when the substrate temperature was higher than 400 ° C, the synthetic film was obtained. The hardness will decrease. It can be seen that the deposition temperature has a great influence on the hardness of the nanocomposite film.
MusilJ used a spherical spherical unbalanced magnetron with a diameter of 100 mm to sputter the TiAl alloy target in a mixture of Ar and Ar+N2 with a total pressure of 0.5 Pa. The continuous change of N2 partial pressure resulted in significant changes in the structure and microhardness of the film. The nc-TiAlN/AlN nanocomposite film has a microhardness of up to 47 GPa and a high elastic recovery (74%).
At the same time, the combination of various technologies also shows unique advantages in the preparation of nanocomposite films (such as the combination of magnetron sputtering and pulsed laser technology). VoevodinAA et al. used pulsed laser deposition (PLD) and magnetron sputtering techniques to prepare TiC/DLC and WC/DLC/WS2 nanocomposite films. Since this composite technique is used to make the substrate temperature during deposition lower than 100 ° C, the method is the main method for preparing the WCS series nanocomposite film. MengWJ et al. used radio frequency coupled assist (ICP) PVD/CVD technology combined with reactive magnetron sputtering to prepare Ti/α-C:H nanocomposite film and achieved good results.
Due to the complicated process and high cost of PVD, CVD and other methods, it is not suitable for large-area preparation of nanocomposite films. Therefore, in the past decade, foreign countries have done more research on the preparation of nanocrystalline materials by electrodeposition, and domestically began in recent years. Research in this area. Electrodeposition is gradually gaining attention due to its outstanding advantages such as simple equipment, mature technology, low temperature and controllable parameters. The electrodeposition process has undergone the development of direct current, pulsed, and selective jet electrodeposition, and films of various thicknesses have been prepared. The electrodeposited nanomaterials studied have been nickel, copper, cobalt, etc., and the composite deposition of nickel and nickel-based alloys is the most concerned. The deposited materials are Ni-P, Ni-Fe, Ni-Cu, Ni-Mo. , Ni-SiC, Ni-Al2O3, Ni-ZrO2, and the like. Electrodeposition of a thin metal layer (less than 100 μm thick) on the substrate to improve surface properties is the most widely used electrodeposition technique. Electrodeposited nanostructured thin layer with high wear resistance and corrosion resistance, high hardness and excellent adhesion to the substrate, can be used as an ideal protective coating; low wear rate and low The coefficient of friction can be used in applications where high wear resistance is required while low friction coefficient is required, such as tool materials, surface coatings for automotive engines and hydraulic pistons.
It has been reported that in recent years, many researchers have prepared nano-films by sol-gel method. Since the precursor of sol can be purified and its sol-gel process can be formed into a liquid phase at normal temperature, the equipment used is simple, easy to operate, and has the advantages of easy control of stoichiometric ratio, uniform composition, large film formation area, etc. Used in film preparation. At present, the nanocomposite films prepared by the method mainly include Co(Fe, Ni, Mn)/SiO2, CdS(ZnS, PbS)/SiO2 and the like. Chen Yuanchun et al. studied the preparation of alumina-coated cemented carbide tools by sol-gel method, and obtained a single-layer gel film with a thickness of several hundred nanometers. The test results show that the life of the coated tool produced by the sol-gel method in the dry cutting state is about double that of the uncoated tool.
Application of nano film in dry cutting tools
The development of coating technology is one of the important conditions for the popularization and application of dry cutting. In the dry cutting process, the tool coating with nano-film can play a significant role: 1 to form an isolation layer between the tool and the material to be cut; 2 to reduce thermal shock by suppressing heat conduction from the cutting zone to the blade; Friction and friction heat. The tool is coated to provide solid lubrication, reduce friction and adhesion, and reduce heat absorption by the tool to withstand higher cutting temperatures.
At present, B4C/W multilayer nano-coatings can be applied to cemented carbide tools and HSS drill bits using closed field unbalanced magnetron sputtering (CFUMS) technology. The total number of layers of the coating was 100 layers, and each layer consisted of a B4C coating material having a thickness of 13 angstroms and a W coating material of 18 angstroms. B4C/W multilayer nano-coated and uncoated tools, ordinary single-coated (TiAlN) tools, and three-coat (TiC/TiCN/TiN and TiC/Al2O3/TiN) at a cutting speed of 105 m/min The tool performs a dry cutting comparison test on medium carbon steel. The test results show that the flank wear of nano-coated tools is much smaller than that of uncoated tools and the commonly used TiC/Al2O3/TiN three-coating tools. In addition, as the cutting time is extended, the cutting force of nano-coated tools is significantly reduced compared to uncoated tools, TiC / TiCN / TiN three-coated tools and TiAlN coated tools. The test further demonstrates that the tool coating produced by the closed field unbalanced magnetron sputtering technology has the characteristics of good repeatability, higher bond strength between the coating and the substrate, and low friction coefficient, so it has a longer use in dry cutting. life.
The layered crystalline molybdenum disulfide has a small coefficient of friction and is a commonly used solid lubricant. The combination of MoS2 and heat resistant metal Mo into a composite coating MoS2/Mo has an excellent antifriction and heat resistance effect. The researchers used a MoS2/Mo dual-material coating structure to prepare a nano-coating layer with a thickness of 80 angstroms and a total thickness of 3.2 μm (400 layers in total) on the surface of the HSS drill bit. The dry cutting test of TI6Al4V alloy workpiece was carried out with the coated drill bit and the uncoated HSS drill bit. The test drill has a diameter of φ9.5 mm and a nominal drilling speed of 2200 rpm. The test results show that when the uncoated drill bit is drilled, the drill bit is stuck into the workpiece due to the sharp increase of the drilling force; the drilling force when measuring the multi-layer nano-coated drill bit is reduced by about 33%, the same Drilling time guarantees normal drilling and drilling performance is significantly better than uncoated drills. It is indicated that the nano-coated tool with MoS2/Mo double-material coating structure is an ideal tool for dry cutting.
In addition, after the tool surface is coated with four nano-composite coatings of nano (Ti50Al45Si5)N, (Ti50Al45Si5)N+(Ti80Al15Si5)N and Ti-BN, the cutting test is performed on ASTM1043 standard steel workpiece (cutting speed is 150-310m/min). The depth of cut is 2mm and the feed rate is 0.219mm/rev. It also shows that these nanocomposite coatings have excellent wear resistance in high-speed cutting tests and can be used as coating materials for dry cutting tools.
Outlook
At present, the thin film technology is developing rapidly, and the prepared thin film is getting thinner and thinner. The thin film with a grain size of 1 nm is the research target for preparing the nano ultrathin film; since the single coating material is difficult to meet the requirements for improving the comprehensive mechanical properties of the tool, it is satisfied The requirements for coating on the cutting process have led to diversified preparation processes, and the development of various technologies, multi-component chemical components, etc.; coating process temperature will be lower and lower, tool coating The layer process will develop in a more rational direction. Undoubtedly, the research and development of these new film technologies has a very broad application prospect in tool coating preparation, but PVD and MTCVD processes are still the mainstream technology for tool coating preparation.
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