Natural and synthetic single crystal diamonds Natural and synthetic single crystal diamonds are generally classified according to the application field and can be used as cutting tools, dressing machines and wire drawing dies. They are all designed for precision machining applications where surface finish, geometry and size are critical. The surface of the workpiece cut by the single crystal diamond tool is continuous, and the surface of the workpiece cut by the polycrystalline diamond tool exhibits a discontinuity of the order of micrometers. The condition of the surface of the workpiece is more or less related to the grain size of the diamond tool material, although The precise characteristics of the workpiece and the machining tool need to be carefully considered, but there is a general principle that the requirement for a metal surface finish of better than 0.025 μm requires a single crystal diamond tool and a machining tool with high rigidity and high quality bracket. .
Natural diamonds have long proven to be successfully applied in these areas. However, the current development of high temperature and high pressure technology has made it possible to prepare synthetic single crystal diamonds with a certain size, and the current maximum size is up to 8 mm. A typical example of the preparation of diamond using high pressure technology is the De Beers MONODITE series. The blank of the synthetic single crystal diamond tool is produced by a plane sawing provided parallel to the (100) face of the 1b type synthetic diamond or along a sheet having a thickness of 2 mm and an edge length of 8 mm. The advantage of this engineering material is its good consistency in size, shape and performance, which is not possible in natural products. In addition, the lack of various sizes, especially the large size of natural diamond, the difference in the quality of different diamonds, and the requirements for the selection of diamonds, orientation and pretreatment of the tool tip, have an important impact on the price factor of natural diamonds, thus greatly limiting Its application in a wider range of fields. The application of synthetic single crystal diamond tool materials has been rapidly developed.
Polycrystalline diamond (PCD)
The application of diamond tools has rapidly expanded to many manufacturing industries, especially in the automotive and wood processing industries, becoming a high-performance alternative to traditional WC tools. As a recognized product that is inexpensive and has a blade length of 70 mm, PCD applications are growing rapidly.
The performance of a PCD depends primarily on the processing involved in its application, but choosing the right grade or grain size will also affect its performance. The standard grades include 002, 010 and 025, and their initial grain average sizes are 2, 10, 25 μm. In general, the larger the grade, the better the wear resistance; the smaller the grade, the better the quality of the cutting edge.
The application of diamond tools in the processing of layered wood flooring In recent years, a new application area for synthetic single crystal diamonds is the wood processing industry, which is mainly because of its high wear resistance. PCD tools have long been used in the machining of MDF and chipboard in wood processing. Currently, there is a growing demand for highly wear-resistant layered wood flooring with alumina coating on the surface, but when grinding the edge of the board Special tools, including PCD, have special requirements because the wear-resistant layer of the board can cause passivation of the cutting edge, resulting in cracking of the alumina wear layer. Therefore, the tool must be trimmed frequently until it is reground or replaced, which will inevitably lead to a long downtime. It has been reported that the performance of synthetic single crystal diamond is superior to PCD when applied in this field.
Chemical vapor deposition diamond
PCD, PCBN and synthetic single crystal diamond are synthesized at high temperature and high pressure, while CVD diamond is prepared at low pressure. The mixture of carbon-based gas and hydrogen decomposes at a high temperature and a pressure below atmospheric pressure to form a diamond deposited on the substrate. What is deposited is a polycrystalline diamond with excellent inter-growth, which is columnar and very dense. CVD diamonds also exhibit different grain sizes and structures depending on the growth conditions. CVD diamond does not require a metal catalyst, so its thermal stability is close to that of natural diamond.
The grain size and deposition technique can be selected as needed. For example, in non-tool applications such as thermal control and optical windows, the performance requirements for CVD diamonds are significantly different from those of cutting tools. According to different application needs, different CVD deposition processes can be used to synthesize polycrystalline diamond with different grain size and surface morphology. Since the performance requirements of the tool are varied, it is possible to have a variety of CVD diamonds of different grain sizes to meet the needs of various applications.
In fact, CVD diamond knives come in two forms: the first is to deposit a thin layer (film) having a thickness of less than 30 μm on a suitable substrate. For example, the edges of ISO blades and twist drills are two typical thin coatings. The second is to deposit a substrateless diamond layer (thick film) up to 1 mm thick, which can be soldered to the substrate if desired.
The properties and preparation of the matrix material are very important if the CVD diamond film is to a satisfactory degree of deposition and bonding strength to the CVD film. Until now, this technology has still limited the equipment for CVD coating, so most of the work in the field of CVD film preparation is currently devoted to its research. The good base material is WC because its mechanical properties match diamonds, and the tool manufacturer is familiar with WC-based tool materials and would like to use it as a matrix material.
A second limitation of the coated tool material is that the coating on the substrate necessarily forms a rounding on the cutting edge, which limits the thickness of the coating and makes it necessary to treat the coated edge (eg Grinding). So far, the market for thin film diamond products is not very large.
In contrast to CVD diamond thick films, CVD diamond thick films can be soldered to the desired substrate by special, easy-to-use techniques. However, the strength of such brazed joints is by no means equivalent to the strength of the PCD, which is fragile when used in the highly demanding machining process of interrupted cutting. Otherwise, CVD diamond thick films will compete with PCD throughout the machining application. Compared with PCD, its main advantage is that it has better thermal stability, and its disadvantages are higher brittleness and non-conductivity. The lack of electrical conductivity hinders its use in discharge corrosion (EDM) cutting and machining technology, which is widely used in the diamond tooling industry, especially in the production and finishing of woodworking tools. However, thick CVD tool materials that can be cut with EDM have been fabricated and are currently being evaluated. Its potential application areas are also the machining of highly wear-resistant workpieces, in which the high purity of the diamond in the CVD diamond thick film and the resulting increase in wear resistance and thermal stability are utilized.
At present, the cost of CVD diamond thick film is relatively high. With the development of technology, the manufacturing cost will gradually decrease, and eventually it will enter the field of superhard tool industry.
CVD CBN
CVD CBN Unlike diamond, diamond consists of a single element, and it is a compound, and many problems, including stoichiometry, make its growth process more complicated. Despite years of research, virtually all CVD CBN coatings are multiphase microcrystalline materials. CVD CBN is more like "Diamond-like Carbon" (DLC) than high quality CVD diamond. It is quite possible to develop applications coated with DLC coated tools, although the application prospects have not been apparent so far.
Conclusion In summary, various forms of diamond cutting tools can complement each other very well. However, there are also cross-cutting applications where rational selection of tooling products is required. There are two types of products that are most likely to cross-apply: 1 natural and synthetic single crystal diamond; 2PCD and CVD diamond thick film.
Synthetic single crystal diamond has been developed to a more advanced level, and the quality of the product has been identified by international standards. In natural diamonds, large-size diamonds are rare, and the success of synthetic large-size diamonds opens up new possibilities for applications such as the wood processing industry.
The processable grade CVD diamond thick film has high mechanical strength and good thermal properties, and its rapid development indicates that CVD diamond will play an active role in the tool industry.
The degree of development of replacing natural diamond with synthetic diamond and replacing PCD with CVD diamond depends on both technical and economic factors. The relationship between price and performance, the degree of trust of tool manufacturers and end users in CVD diamonds, especially the ease of forming, grinding and brazing processes, will affect the end result of their development. But one thing is certain, that is, it must develop toward higher productivity and higher cutting speed. With the increasing wear and more difficult workpiece materials, the application of various types of diamond tools will continue to increase.
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