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Cemented carbide diamond coating tools are less expensive to manufacture than polycrystalline diamond tools and diamond thick film welding tools, and can deposit coatings on tools of any shape. Therefore, it has better market application prospects and development potential. Countries such as Europe and the United States successively invested a large amount of manpower, material resources, and financial resources to research and develop diamond thin film coating tools. At present, SP3 companies in the United States, Cemecon companies in Germany, and Balzers companies in Liechtenstein have commercialized products. Many colleges and universities and research institutes in China have done a lot of work in this area, but no substantive breakthroughs have been made.
The key to restricting the industrialization of diamond coating tools is the low adhesion of the coating. The problem stems from the binding of cobalt in the cemented carbide matrix.
Cobalt can easily cause the diffusion and dissolution of carbon in the diamond deposition process, inhibit diamond nucleation and promote the growth of graphite, and make the quality of diamond coating worse and adhesion lower. According to reports on the untreated cemented carbide diamond coating of the substrate, no matter which deposition equipment is used or which deposition process is applied, its adhesion is low, and the critical load is less than 300N; the cemented carbide liner treated by other methods At the end, the optimized deposition process, the critical load value of the coating adhesion is only up to 600N. This research through a series of technologies such as vacuum metalized carbide inserts, manual grinding, ultrasonic treatment of seed crystals, implementation of an optimized deposition process, etc. The measures eliminated the adverse effects of cobalt on the deposition of the diamond coating, roughened the surface of the cemented carbide, improved the quality of the diamond, and significantly improved the adhesion of the coating (with a critical load value of 1500 N).
1, the use of ordinary boron workpieces after the surface of boron after the emergence of glue-like objects, and difficult to clean, poor surface quality. The surface of the workpiece before and after vacuum boronizing no significant change, no attachments appear, the surface quality is high, do not need to carry out complicated cleaning.
The results of the X-ray diffraction analysis of the surface of the vacuum boride sample are shown below. Boronizing phase is WC + CoB + CoWB + CW2B2, and the surface of the same batch of samples treated with the same vacuum boronizing process is the same, and the process repeatability is good. The boriding phase obtained by the ordinary boronizing process is WC+CB+CB2 and WC+CW2B2. Furthermore, the Boron products produced by the two researchers using the same process to treat different batches of workpieces are not the same. Boronizing process has poor reproducibility.
It is the cross-section X-ray energy spectrum scan result of the surface layer of hard alloy insert after 950T vacuum boronization. As shown in the figure, the content of B and C in the surface layer is significantly higher than that of the matrix, while the content of Co element is significantly lower than that of the matrix. In addition, it can be seen from the figure that the thickness of boronized layer is about 15-20|xm, while under the same process conditions, the thickness of ordinary boronizing layer is 10-16pm. , the same original sheet, ordinary boronizing blade, the boronizing time of the surface quality of the vacuum permeation boron blade, and the vacuum boriding layer thickness, which has better effect on preventing the diffusion of C. D The possible reason for these differences is that the ordinary seepage The boron workpiece is in contact with the oxygen-containing atmosphere during the boronizing process and generates various oxides of different thicknesses. This oxide is impervious and has an important influence on the boronizing process. 2.2 Surface morphology and roughness of the boronized blade before and after manual grinding are the SEM images of the boronized blade before and after grinding with 50% W5+50% W2 diamond powder.
It is very significant to improve the adhesion of the diamond coating 1 The surface profile of the sample before and after grinding.
The open topography of the CVD diamond coating deposited on the surface of the untreated tungsten carbide insert and its Kamati spectrum (above) clearly show that the cemented carbide insert is deposited directly without surface cobalt pretreatment. The coating diamond microstructure of the coating is not complete W, and its corresponding Raman spectrum shows a distinct non-diamond carbon peak, indicating that the cobalt migrated out resulting in the SEM image of CVD diamond deposited on the non-diamond vacuum carburized non-abrasive sample. Raman Spectra (C) Vacuum Boriding + Manual Grinding Specimens Indentation Topography of Three Kinds of Diamond Coatings under 300N, 600Nf1500N Loads i is vacuum drilled and manually ground precoated diamond coating The SEM image of the fracture surface and the partially enlarged SEM image. It can be seen that there is a zigzag interlocking structure between this substrate and the diamond coating. This is actually the reason for the high adhesion of this coating.
In conclusion, when a diamond coating is deposited on an untreated sample, the cobalt migration in the cemented carbide results in the formation of non-diamond carbon and weakens the film/base interface. Therefore, the quality and adhesion of the coating are poor. When depositing a diamond coating on a vacuum boriding non-abrasive sample, due to its boronized layer composition, in which CoB+CoWB+CoW2B2 is a stable compound phase, this inhibits or eliminates the generation of stone carbon and the coating quality is poor See (below). Moreover, this type of coating has poor adhesion and very low strength, and it is severely chipped and peeled off under a 300N load (A).
Boronized non-abrasive sample coating structure is relatively complete diamond microstructure, its corresponding laser Raman spectrum also did not see obvious amorphous carbon peaks, but the gap between diamond grains is more, the organization of dense, poor, The quality of the coating is still poor (see). Moreover, the adhesion of the coating is also poor.
The coating peeled off under 600N load (see B).
Stone coating grain size is moderate, crystal integrity, dense tissue. The corresponding laser Raman spectrum has a sharp peak in the diamond phase, an amorphous carbon peak is not obvious, and the quality is very good ().
(C) is the indentation topography of this sample diamond coating under a 1500N load. It can be seen that, except for the marks left by the indenter, the diamond coating did not crack, and the indentation diameter was about 15 |JLm. The coating has a high adhesion. The SEM images (above) and the partially enlarged SEM images (bottom) of the '0' specimen coating fractures show the migration and diffusion of cobalt, so that a diamond film substantially free of non-diamond carbon can be deposited. However, because the sample has not been ground, the surface is smooth, the nuclear energy of diamond is high, the nucleation density is low, and more voids are formed during deposition, so that the denseness of the coating is poor, and the adhesion of the coating is not high; In the process of diamond deposition by vacuum boronization + manual grinding, on the one hand, the boronized layer can effectively control and block the diffusion and migration of cobalt. On the other hand, surface defects caused by grinding reduce the nucleation energy of diamond and increase the Nucleation density. Shanghai Jiaoda 2 Liu Sha, Yi Danqing. New advances in surface pretreatment of cemented carbide substrates for diamond coatings. Rare Metal Materials and Engineering, 2001, 30 (5): 213 Liu Sha, Yu Zhiming, Research on the two-step erosion method for the surface of high cobalt hard alloy substrate for diamond coating. Technology and Equipment, 2001, 19 (6): 3654 Wang Sigen, Study on Chemical Vapor Deposition of Diamond Thin Film Coating on Cemented Carbide Tools. Ph.D. Dissertation, Beijing: School of Materials Science and Technology, Beijing University of Science and Technology, 1998, 5 Wang Qiang, Preparation of CVD Diamond Coatings for Cemented Carbide Tools, Coating Organization and Bonding. Master's thesis, Beijing: School of Materials Science and Technology, University of Science and Technology Beijing, 2001, 6 Zhang Yuying Born in 1957, female, Qihe, Shandong, teacher of Henan Institute of Education. Mainly engaged in physics teaching and research work.
(Editing Wang Qin)
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