1 Introduction Cutting tool surface coating technology […]
Cutting tool surface coating technology in recent decades should be developed in response to market demand for surface modification of materials technology. The use of coating technology can effectively improve the life of cutting tools, cutting tools to obtain good comprehensive mechanical properties, thereby greatly improving the efficiency of machining. Therefore, the coating technology and materials, cutting technology together and known as the field of cutting tool manufacturing three key technologies. In order to meet the requirements of high efficiency, high precision and high reliability of modern machining, the development of coating technology and its application in tool manufacturing have been paid more and more attention in the world. China's tool coating technology after years of development, is currently in a critical period, that is, the original technology has been unable to meet the increasing demands of cutting, the domestic major tool factory coating equipment to the replacement period must also be. Therefore, the full understanding of the status of domestic and international tool coating technology and development trends, aimed at the international advanced level of coating technology, a planned, step by step to develop tool coating technology (especially PVD technology), to improve China's cutting tool manufacturing level Significance.
Tool coating technology can be generally divided into chemical vapor deposition (CVD) technology and physical vapor deposition (PVD) technology, two categories, respectively, as described below.
2.1 The development of CVD technology abroad
Since the 1960s, CVD technology has been widely used in the surface treatment of carbide indexable tools. The preparation of TiN, TiC, TiCN, TiBN, TiB2, Al2O3 and other monolayer and multi-layer composite coatings can be realized by the relatively easy preparation of the metal source needed for the vapor deposition of CVD process. The bonding strength of coating and substrate is relatively high, The thickness of up to 7 ~ 9μm, so the late eighties, the United States has 85% of the carbide tools used in the surface coating treatment, which accounted for 99% of CVD coating; to the mid-1990s, CVD coating Carbide blade in the coating of carbide cutting tools still account for more than 80%.
Although the CVD coating has good wear resistance, but the CVD process also has its inherent shortcomings: First, high processing temperature, easy to cause a decline in bending strength of the tool material; Second, the tensile stress within the film state, easily lead to the use of tools The CVD process emissions, waste liquid will cause greater environmental pollution, and now strongly advocated the concept of green manufacturing conflict, so since the mid-nineties, the development and application of high-temperature CVD technology by a certain Constraints.
At the end of 1980s, the low temperature chemical vapor deposition (PCVD) technology developed by Krupp.Widia reached the practical level, its processing temperature has been reduced to 450 ~ 650 ℃, effectively inhibited the η phase, can be used for thread cutter, cutter , TiN, TiCN, TiC and other coatings, but so far, PCVD process in the field of tool coating is not widely used. In the mid-1990s, the advent of new technologies of intermediate temperature chemical vapor deposition (MT-CVD) revolutionized CVD technology. The MT-CVD technique is a new process for the decomposition of TiCl4, H2, N2 at 700 ~ 900 ℃ with the C / N-containing organic substance acetonitrile (CH3CN) as the main reaction gas. By MT-CVD technology can be dense fibrous crystal morphology of the coating, the coating thickness of up to 8 ~ 10μm. This coating structure has high wear resistance, thermal shock resistance and toughness, and by high temperature chemical vapor deposition (HT-CVD) process in the blade surface deposition Al2O3, TiN and other high temperature oxidation resistance, and be processed Material affinity small, self-lubricating properties of good material. MT-CVD coated blade is suitable for high speed, high temperature, heavy load, dry cutting conditions, its life can be doubled than ordinary coated blade. At present, CVD (including MT-CVD) technology is mainly used for carbide cutting tools surface coating, coating tools for medium and heavy cutting of high-speed roughing and semi-finishing. CVD technology can also achieve α-Al2O3 coating, which is difficult to achieve PVD technology, so in the dry machining, CVD coating technology still occupies a very important position.
2.2 The development of foreign PVD technology
PVD technology appeared in the late 1970s, because of its processing temperature can be controlled below 500 ℃, it can be used as the final treatment process for high-speed steel-like tool coating. As the use of PVD technology can greatly improve the cutting performance of high-speed steel cutting tools, so the technology has been rapidly since the eighties to the late eighties, the industrial developed countries, high-speed steel tool PVD coating the proportion of more than 60% .
PVD technology in the field of high-speed steel tool for the successful application of the world's manufacturing industry has attracted great attention, people competing to develop high-performance, high reliability coating equipment, but also the expansion of its applications, especially in cemented carbide, Ceramic tools in the application of a more in-depth study. The results show that the temperature of PVD process is lower than that of CVD process, and it has no effect on the bending strength of the tool material when the temperature is below 600 ℃ (the test results are shown in Table 1). The internal stress state of the film is compressive stress, Carbide cutting tool complex sophisticated coating; PVD process on the environment without adverse effects, in line with the development of modern green manufacturing. With the advent of the era of high-speed machining, the application of high-speed steel cutting tool gradually declined, carbide cutting tools and ceramic tools to increase the proportion of applications has become an inevitable trend, therefore, industrial developed countries since the early nineties began committed to carbide cutting tools PVD coating technology has made a breakthrough in the mid-nineties, PVD coating technology has been widely used in carbide end mills, drill bit, step drill, oil hole drilling, reamer, tap, indexable Milling cutter, profiled tools, welding tools, such as coating treatment.
At present, PVD technology not only improves the bonding strength between the film and tool matrix, but also from the first generation of TiN to TiC, TiCN, ZrN, CrN, MoS2, TiAlN, TiAlCN, TiN-AlN and CNx. Floor. ZX coating (ie TiN-AlN coating) and other nano-coating the emergence of the PVD coating tool performance has been a new breakthrough. This new coating and substrate bonding strength, coating hardness close to the CBN, good oxidation resistance, anti-stripping strong, and can significantly improve the tool surface roughness, effective control of precision cutting tool edge shape and accuracy of its precision Processing quality and uncoated tool compared favorably.
After several decades of research and development, all kinds of tool coating process has been widely used in high-speed steel and carbide cutting tools.
The development trend of the coating technology in the world is as follows: the coating composition will tend to be diversified and compounded because the single coating material can not meet the requirement of improving the comprehensive mechanical properties of the cutting tool; in order to meet different cutting processing requirements, Will be more complex and more targeted; in the composite coating, the coating thickness of the single component will become increasingly thinner, and gradually tend to nanocrystallization; coating process temperature will become increasingly low, the tool coating process Will be more reasonable direction, is expected PVD, MT-CVD process will become the mainstream technology.
Present Situation and Development Trend of Tool Coating Technology in China
3.1 China's CVD technology development
China since the early 1970s began to study the CVD coating technology, because of the strong technical specificity, the research unit is not much. In the mid-1980s, China's CVD tool coating technology to achieve the level of practical development, technology and the international level at the same level, but in the next 10 years, the development of more slowly (similar to foreign research); The research and development of MT-CVD technology and equipment is expected to be completed in 2001. According to the research objectives, the technology and equipment will reach the international advanced level. The research of PCVD technology in China will start at the end of this year. In the early nineties, PCVD process technology is mainly used for mold coating, cutting tools in the field of application is still very limited. Overall, the overall level of development of domestic CVD technology and the gap between the international level is not until the MT-CVD technology successfully developed, China's CVD tool coating in the field of the overall level will be able to keep pace with the international advanced level.
3.2 China PVD technology development
China's PVD coating technology research and development work began in the early eighties, to the mid-eighties successfully developed small and medium hollow cathode ion coating machine, and the development of high-speed steel cutting tool TiN coating technology.