subject: Coating technology and development tools - Tool coating - the machine tool industry [print this page] Coating technology and development tools - Tool coating - the machine tool industry
Abstract: Modernization Metal Cutting Processing, the tool requirements are high cutting speed, high feed rate, high reliability, long life, high accuracy and good cutting controlled. Coated tools have enabled cutting tool with a major breakthrough, it will tool thin film substrate surface with the combination of hard, because the substrate to maintain a good toughness and high strength, rigid film surface but also has high wear resistance and low friction coefficient, thus greatly improving the performance of cutting tools.
1 on the modern metal-cutting tool requirements
Modern metal machining, the tool requirements are high cutting speed, high feed rate, high reliability, long life, high accuracy and good cutting controlled. Coated tools have enabled cutting tool with a major breakthrough, it will tool thin film substrate surface with the combination of hard, because the substrate to maintain a good toughness and high strength, rigid film surface but also has high wear resistance and low friction coefficient, thus greatly improving the performance of cutting tools.
Since the early 20th century, 70 since the advent of hard coated tools, chemical vapor deposition (CVD) techniques and physical vapor deposition (PVD) techniques have been developed for performance improvement tool to create a new chapter in history. Coated tool compared with the uncoated tool with significant advantages: it can improve processing efficiency, higher precision and extend tool life, machining parts to ensure quality and reduce processing costs.
2 tool hard coatings and new materials
2.1 Multiply the development of hard coatings
Tool hard surface film on the material the following requirements: high hardness, good wear resistance; chemical stability, not a chemical reaction with the workpiece material; thermal oxidation resistance, low coefficient of friction, and substrate adhesion firmly so. All single coating material is difficult to achieve the above technical requirements. The development of coating materials, from the first single TiN coating, TiC coating, through the TiC-Al2O3-TiN composite coating and TiCN, TiAlN coatings such as multiple stages of development, and the current development of the TiN / NbN, TiN / CN, and other multi-composite thin films, the performance of the tool coating greatly improved.
Hard coating materials, process the most mature and most widely used is TiN. At present, the industrial countries TiN coated high speed steel tool usage accounts for 50% of high-speed steel cutting tools -70%, some of the complex can not be re-grinding tool usage has exceeded 90%. As the modern metal-cutting tools are high on the technical requirements, TiN coating increasingly unable to meet. TiN coating poor oxidation resistance, the use temperature of 500 , the film was obviously oxidized ablation, and its hardness can not meet needs.
TiC has high hardness, good wear resistance and therefore the material. At the same time it's attached to a solid matrix, in the preparation of multi-resistant coating would often TiC as a substrate in contact with the bottom membrane, the coating is very commonly used tool in the coating material.
TiCN and TiAlN development, but also to the performance of the coated tool to a new level. TiCN coating can reduce the internal stress and improve the coating toughness, to increase the thickness of the coating to prevent the spread of crack, reducing tool chipping. TiCN coated tools will set the main wear-resistant layer can significantly improve tool life. TiAlN chemical stability, oxidation and wear resistance, processing high-alloy steel, stainless steel, titanium alloy, nickel alloy, the ratio of TiN coated tools to improve life 3? 4 times. If the TiAlN coatings have a higher Al concentration in the cutting surface will generate a thin coating of non-product state of Al2O3, form a hard protective layer of inert, the coated tools can be used more effectively High-speed machining. Oxygen in nitrogen-doped titanium carbide TiCNO high hardness and chemical stability, can produce the equivalent of TiC + Al2O3 composite coating effect. Some transition metal nitride, carbide, boride, and their multi-complex compounds, some with very high hardness, these materials can be developed, used cutting tools, coated cutting tools will make new breakthroughs in performance .
2.2 Low Pressure Synthetic Diamond Thin Film Gas
Hard in the film material, more than 50GPa hardness HV can have three kinds: diamond films, cubic boron nitride CBN, carbon nitride -C3N4. The few ultra-high hardness emergence of thin film materials for hard coating film development tool to open up a very rare and expensive natural diamond far from meeting the needs of modern industry. 50 mid-20th century, the U.S. General Motors synthetic diamond, are granulated and powdered diamond. As the granular diamond processing difficulties, it is difficult to tool the surface coating. Polymer materials commonly used in machinery industry, diamond blade (PCD) and because the geometric shape of a single, non-chip-breaker geometry parameters and reasonable limits the performance of the play. The early 70s by low pressure chemical vapor deposition synthesis of diamond films, after 20 years of technology research, low-pressure gas synthetic diamond technology finally has a major breakthrough in research of diamond become a hot topic worldwide.
Diamond and graphite are allotropes, diamond is the cubic body product lines, an Fd3m space group; while graphite is a hexagonal lines, the space group is R3m. Because the bonding between atoms is different, so the performance difference is huge. From the thermodynamic theory point of view, graphite is more stable than diamond. Low pressure vapor growth of diamond, the phase diagram of carbon is in graphite and diamond stable region for the metastable conducted. However, two-phase chemical potential is very close to the two phases can be generated. Low-pressure gas is the key technology of diamond synthesis inhibition of graphite phase, and promote the growth of diamond phase. Synthetic methods used hot wire method, plasma enhanced chemical vapor deposition (PECVD), including microwave PCVD, electron cyclotron resonance ECR? PCVD, such as DC and RF PCVD method, DC and high frequency thermal plasma arc discharge method. Reaction in the energy input (such as RF power, microwave power, etc.), the reaction gas activation status and the best ratio, deposition of the nucleation mode, for the formation of diamond films have a decisive role. Substrate materials, crystal type and lattice constant of the diamond film nucleation and growth effects, and when the diamond phase and the graphite substrate at the same time in the nucleation, the graphite will grow rapidly. If there are high concentrations of hydrogen would be on the original in the graphite phase grow from corrosion and to remove the graphite phase, although it can also play on the diamond with corrosion, but the speed is much slower, and thus to inhibit the growth of graphite phase purpose. Many diamond film deposition temperature required for the 600 -900 , so the technology used
