The current development of PVD coating technology in the world has the following four major trends.
1. The coating composition will tend to be diversified and composite
The first generation of PVD coatings was mainly TiN. On this basis, TiC, TiCN, ZrN, CrN, WC and other single metal coatings were developed. With the further development of PVD deposition technology, aluminum-based multi-metal alloy coatings such as TiAIN and TiAICN were developed one after another. The wear resistance and red hardness of these coatings are much higher than single metal coatings, and they can be used for higher cutting speeds situation such as hobbing (up to 150m/min). Later, people considered the possibility of layering different kinds of coatings on the tool to exert the advantages of different coatings, such as TiN+TiCN+TiN, TiN+TiAlN, TiAIN+WC/C, etc.
In recent years, PVD coating technology has taken another step forward. Many coating companies have developed and applied pulsed coating technologies, such as P3E (Pulse Enhanced Electron Emission) technology from Balzers, Switzerland. And H.I.P_ (High Ion Pulse) technology from Cemecon, Germany. Both of these new technologies use pulsed electrons to activate the arc evaporation target. As the process can operate in oxygen atmosphere, so theoretically, almost any metal oxide (eg, A12O3, ZrO2, Cr2O3, Ta2O5, etc.) and their compound coatings can be deposited by this process.
2. Application development of coatings is more targeted
In order to meet different application requirements, the design and development of coatings are increasingly targeted. In order to meet the characteristics and requirements of different areas of application, such as drilling, milling, dry hobbing, stamping, drawing, etc., coatings with relative advantages in this respect are developed. After continuous efforts and trials, successes have been achieved in certain fields, such as the application of high-aluminum TiX (Al:Ti-2:1) coatings on milling, non-Ti coating AICrN on high-speed dry hobbing, the composite coating CrN + TISIN on drilling, composite coating TIN + TCX on drawing mold. The surface lives of them are significantly better than other coatings. In addition, various targeted coatings for corrosion resistance (Crx coating), "self-lubricating (WC/C coating), soft material processing (MoS2 coating), and high hard material processing (CBN, Dimond coating) are all widely applied. And with the continuous development of PVD coating technologies, new targeted coatings will continue to be developed to replace them.
3. The deposited particles of the coating tend to be nano-sized
With the development of nanotechnology and advances of coating technology, nano-tool coating has also attracted the attention of a large number of researchers and PVD coating service companies. The nanocrystallization of the deposited particles of the coating can enhance the bond strength between the coating and the substrate, at the same time it can reduce the surface roughness of the coating. At present, most of the coating's deposited particles are still large. Although there are so-called nano-scale coatings, larger particles can still be found on their final surface, and the coating surface is still rough. Reducing the size of the deposited particles of the coating and maintaining the process stability to avoid the large abnormal particles will become another development direction of the coating. Especially for the application on mirror face, although some companies developed mirror coating, the quality and stability are poor and the process is too complex. In the future, the nanocrystallization of the coating particles and the nanometerization of the coating layer thickness will be the main development direction, which is of great significance for improving the overall performance of the coating and reducing the stress between layers, and it will increase the smoothness of the mirror face and further expands the application of coatings in the precision forming industry.
4. The coating process temperature is getting lower and lower
From the deposition temperature around 1000°C for general CVD coating layer to about 500°C for the PVD and PECVD coatings, the deposition temperature of the coating has been reduced. Therefore, the application range of the coating layer is also enlarged, but the deposition temperature around 500°C still have an adverse effect on workpiece, such as deformation and reducing hardness of the substrate. Therefore, special requirements are demanded for the pre-heat treatment of the coated workpiece. For example, the temper temperature of the workpiece may not be lower than the coating temperature. Lower temperature coatings, such as coating temperatures below 200°C, will eliminate these limitations, which make more types of materials available for coating, and the selection of early heat treatment more flexible. At the same time, the application of low-temperature coatings will also reduce the energy consumption of coating equipment, and have a certain environmental protection effect in energy conservation. In addition, the reduction of the coating temperature will reduce the heating and cooling time and then shorten the delivery cycle of the coating. So the low-temperature coatings will promote the application and popularization of the coating and it will become an important direction of PVD coating development. At present, some coating companies have developed cryogenic coating (coating temperatures is as low as 250°C). However, due to process instability and poor adhesion between the coating and the substrate, no substantial applications have been made and it needs more improvements.