For a long time, "nanotechnology" has been a buzzword in many industries. But what does nanotechnology mean in the field of tool coating materials? What is the current development of nanostructured tool coatings? Defining the nanoscale may be a good starting point. The generally accepted definition of nanoscale refers to the order of magnitude of 100 nanometers (or less) (1 nanometer is one-billionth of a meter). However, for tool coatings, the problem is not that simple. Although the feature sizes of nano-coated materials do meet the 100 nm or smaller scale, new coating processes and coating materials are being used to produce cutting tools for many difficult processes. In some cases, these coated tools are Service life and processability may be far superior to conventional tools. Dr. Ajay Malshe, founder and chief technology officer of NanoMech, believes that the use of nanotechnology to develop tool coatings requires a completely different way of thinking based on the concept of chemical synthesis, in the last century or longer, The development of materials science is mainly driven by chemical synthesis technology. Dr. Malshe said, “We basically use size effects in the opposite way to chemical methods. The traditional thinking about material properties is not applicable to nanoscale. For example, for tool coatings, it may mean more than traditional materials. New materials with higher hardness and better strength may mean a new surface structure on the coating that can act as a micro chip breaker during processing.†New developments in CBN coatings as NanoMech Subsidiary, Duralor has developed a nanotechnology coating process for depositing CBN composite coatings on tool surfaces and is commercializing them. In 2008, this CBN nanocomposite coating was still in the early stages of development. In the following two years, Duralor focused on the processing of CBN coated tools and selected users – according to Bob, President of Duralor According to Reed, there are about a dozen companies working together to commercialize CBN coated tools. Reed said, “At present, we focus on the use of CBN coated tools to process hardened steel with hardness up to HRC54. The effect of processing pre-hardened steel and powder metallurgy materials with this coating is also very good.†Duralor currently focuses on CBN coatings. Continuous turning, however, in the coming months, the company expects to make progress in the development of interrupted cutting with CBN coated inserts and round cutters. The Tufftek process, developed by Duralor and researchers at the University of Arkansas, consists of two steps: first, electrostatic deposition of CBN submicron particles on a cemented carbide substrate; then, using chemical vapor deposition (CVD), TiN, TiCN, TiC Or other conventional tool coating materials penetrate into the CBN particles. This technique is capable of depositing relatively thick (100 μm or more) coatings, but more typically coating thicknesses below 20 μm. According to Reed, CBN coated tools offer a greater cost advantage than tools with PCBN tips, and because CBN coatings have the potential to extend tool life by 3-4 times, they are traditionally coated with multiple layers. The processing cost of the layer blade is also quite competitive. In addition to extending the application of CBN coatings to milling and, if possible, drilling, Duralor's research has focused on the infiltration of electrostatically deposited CBN particles with different coating materials. The company is investigating the use of CVD Al2O3 as a possible composite coating material and investigating the addition of lubricious materials to composite coatings. Dr. Malshe explains, “The tool coated in this way combines CBN nanoparticles with a lubricant that provides lubrication for the cutting edge, such as molybdenum disulfide. Therefore, our deposition process is actually a kind of Technology platform that combines different coating materials and coating structures in ways that are not possible with conventional CVD or PVD processes.†HPPD Nanocoating Applications Another nanocoating process is Rushford Hypersonic The supersonic plasma particle deposition process (HPPD) developed by LLC. The company's president, Daniel Fox, explains, "The basic principle of this deposition process is to separate the material molecules into their basic forms, thereby generating reactants in the plasma stream. Then, by nucleating the process, recombining these materials, and The combined material molecules are accelerated to 8 times the speed of sound (about 6,000 miles per hour) and deposited on the substrate.†Fox pointed out that nanoparticles with a particle size of 2-20 nm will occur when the substrate hits the substrate at high speed. The phase change is chemically combined with the matrix, and as a result, a single-layer thin coating layer having excellent adhesion, high hardness, and high fracture toughness is formed. “Our coatings typically have hardnesses above 37 GPa and fracture toughness of over 3.1 MPa. Moreover, the more precise we control the particle size distribution of the nanoparticles, the higher the fracture toughness and hardness of the coating obtained. Within 6 months, we expect the coating to have a fracture toughness of 6 MPa and a hardness of over 50-60 GPa.†Rushford is using the HPPD coating process to produce SiC coatings while preparing to add titanium and boron to this deposition process. Thereby obtaining TiC, TiN, BN and BC coating materials. Similar to Duralor, Rushford is also working with users to study the practical application of HPPD coated tools. Fox said, “We have been working with our customers to use this coating on a variety of high speed steel substrates that are primarily used for drilling, but we are also investigating it on carbide inserts and milling inserts. The company is also conducting quantitative research on the role of HPPD coatings in improving tool life and other aspects. Fox believes that one of the main advantages of HPPD coated tools is their ability to expand the range of dry machining. “This processing capability that does not require coolant can make the machining process greener in nature,†he said. “At present, this is crucial in Europe where environmental regulations are strict, and in the US, it will become more and more The more important we are working with the user, combining this coating with tool geometry and matrix material optimization to meet the requirements of dry machining.†Advantages of nanocomposite coatings NanoMech and Rushford use non-traditional A coating process to deposit some relatively unconventional coating materials. However, the innovative concept of combining two or more coating materials to form a nanocomposite coating material with superior properties has also been applied to some of the more traditional tool coating materials. Platit is one of the leading developers of such composite coatings, deposition processes and coating equipment. The PVD nanocomposite coating developed by the company combines nanocrystalline TiN, CrN, TiAlN or AlTiN coatings with amorphous SiN materials. The coating comprises a tie layer, a core layer of a single material or a graded material, and a top layer of a nanocomposite. The total thickness of the coating system was 2.72 μm. This nanocomposite coating has a wide range of applicability, but is especially beneficial for efficient cutting. The coating is characterized by embedding nanocrystalline TiAlN, AlCrN or AlTiCrN particles in an amorphous SiN substrate. This arrangement prevents grain growth during deposition and keeps the coating hardness above 50 GPa. Tool coatings deposited with Platit's PVD coating equipment using side or central rotating cathode technology have been extensively tested in milling, drilling, hobbing and other types of machining. The results proved that the coating was the most successful in drilling operations due to the increased coating thickness. In the cutting test of drilling a D-2 tool steel with a solid carbide drill having a diameter of 5.2 mm, the drill using a nanocomposite coating is compared with a drill using a conventional TiAlN, AlTiN and Al-CrN coating. Tool life has more than doubled. Swiss Tek Coatings is a coatings service provider using Platit coating equipment. Peter Bartos, president of the company, said the company uses its Nano-Tek and Nano-Tek/Cr processes to deposit two nanocomposite coatings: AlTiN/Si3N4 composite coatings deposited using the Nano-Tek process; using the Nano-Tek/Cr process An AlCrN coating was deposited on the Si3N4 substrate. He explained, "In either of these processes, amorphous Si3N4 is filled with voids between AlTiN or AlCrN nanocrystals." Bartos says nanocomposite coatings for monolithic round tools as well as threading and milling. And turning inserts, they are increasing in the company's coating business. “The main advantage of this coating is its very high hardness and excellent heat resistance,†he said. “There are considerable limitations in these properties when using traditional AlTiN coatings, but nanocomposite coating materials break through these. Barriers. Bartos pointed out that the oxidation temperature of the nanocomposite coating - the temperature at which the coating oxidizes in the air and begins to decompose - is 1,100 ° C -1,200 ° C. This temperature is much higher than the oxidation temperature of the best performing conventional PVD coating and is very close to the initial sintering temperature of the cemented carbide substrate. This excellent heat resistance makes nanocomposite coatings ideal for a variety of high efficiency or high speed processes. Bartos said, "We found that this chromium-based coating is more versatile than titanium-based coatings, and it seems to be more suitable for hard milling of hardened steel." However, compared to conventional coatings, nanocomposite coatings The cost is more expensive. “The price of any nanocomposite coating may be about 20% higher than traditional AlTiN or TiAlN coatings,†Bartos said. However, depending on the type of coating, the cost of the coating may only be 5 of the total cost of the tool. %-15%, therefore, there is not much difference in the cost of purchasing nano-composite coated tools compared to conventional coated tools.†The prospect of nano-coated tools has been clear to tool suppliers and coating service providers for many years. The multilayer structure coating has better strength and wear resistance than a single layer coating. Harvey Tooling has applied this concept to the field of nano-coating for small diameter end mills and drill bits. Jeff Davis, vice president of design at the company, said, “Multilayer structures can effectively control the generation of cracks, and even if cracks or flaking occur, it spreads much more slowly across the entire coating structure.†Harvey Tool Development The nano-coating thickness is usually 1-4 μm, compared to the conventional AlTiN coating thickness of 2-5 μm or more. According to Davis, due to the finer grain size of nano-coated materials, coatings with thinner thickness, better adhesion and better structural consistency can be produced. Coatings deposited with nanocrystalline materials also have higher hardness and better heat resistance. Harvey Tooling claims that its nano-AlTiN coating has a hardness of 45 GPa and a maximum operating temperature of 1,150 ° C. Compared to its traditional AlTiN coated grade, it has a hardness of 35.5 GPa and a maximum operating temperature of 760 ° C. The improved coating properties make nano-coated tools have a longer service life than traditional coated tools in the processing of difficult-to-cut materials. Davis said, “Perhaps the best application area for nano-coatings is the milling of hardened steels – the hardness of such materials starts at HRC45 and can reach extremely high hardness levels. Traditional TiN coated tools are powerless. The AlTiN coating advances in the right direction, and the nano-coating – plus the right tool cutting edge preparation, matrix and geometry optimization – allows the user to increase tool life from a few seconds to perhaps A few minutes.†Davis said that the company will also apply nano-coating to drilling. “If you need to machine a hole with a depth of more than 4 times, it is always a critical issue to get the coolant to the tip. You can take 'sniper' processing or other means, but the ability of nano-coatings to withstand higher cutting temperatures will benefit this process." Despite this, Davis still offers some advice on the application of nano-coated tools. "Nano-coating is different from TiN coating. TiN coating can be used on any tool and it can improve its cutting performance. Nano-coating is a special coating. It has a narrow range of applications. We use it for hard milling tools, several finishing tools and some variable spiral groove tools. In addition, we must emphasize again that it is not only the coating but also the cutting edge that needs to be optimized. Preparation, tool base, relief and helix angles, core diameters, etc. can be optimized to extend tool life in very difficult processes.†Bartos of Swiss Tek Coatings believes that the range of applications for nano-coatings will be further expanded. These coatings have now taken a big step towards the ultimate development of a magical universal coating that improves tool life and productivity in almost all types of cutting operations. “Everyone wants to develop a 'all-in-one'-type nano-coating – one that can be applied to milling and drilling tools, turning inserts, carbide and high-speed steel substrates, and Excellent coatings in processing. Of course, this coating does not exist yet, but this is our efforts to develop nano-coating technology and materials."
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