New nanometer coating and its equipment
Among high performance tool coatings, the market share of (ti,al)n coatings is about 25% ~ 55%. This is due to the excellent properties of (ti,al)n coating, including high hardness (25 ~ 38gpa) and low internal stress (-3 ~ 5gpa), and the hardness only decreases by 30% ~ 40% at 800℃. In addition, the oxidation rate was about 15 ~ 20 microns /cm at 800℃, which was equivalent to the oxidation rate of ticn coating at 400℃ or tin coating at 550℃. Finally, the coating has a low thermal conductivity, with a 30% lower heat transfer capacity than tin coatings.
At present, the coating industry is still doing a lot of work to further improve the excellent properties of (ti, al)n coating, such as:
The multi-arc technology and sputtering technology are combined. Filter the large droplet produced in the multi-arc process; Optimize process parameters (such as arc flow, bias, partial pressure of n2, etc.); Optimize coating structure (e.g. avoid column structure to improve corrosion resistance); Develop multilayer coatings to improve toughness and thickness; Add other alloying elements such as chromium, yttrium (further increasing oxidation capacity), zirconium, vanadium, boron, hafnium (further increasing toughness), and silicon (further increasing hardness and chemical stability). The main tasks of these optimization (ti,al)n coatings are to develop nano multilayer coatings and improve the content of al.
Develop multilayer coatings and improve al content of coatings
Nano - multilayer coating can be achieved by refining existing multilayer coating processes. In the nanometer multi-layer coating formed by alternating coating of tincrn layer and aln layer, the influence of the distance between layers (alternating period) on hardness is shown as the hardness increases with the decrease of the period. The reason is that the materials that make up the multi-layer have different elastic modulus. When the spacing becomes smaller, the hardness decreases again, because the interface between the layers becomes unclear. If the interface is clear, the hardness will not decrease. As for the structure of the coating, it has been pointed out that the aln has a hexagonal structure when the layer spacing is greater than 10nm, and a cubic structure when the layer spacing is less than 10nm.
Coated with nano coating must be control of the cathode target and artifacts (tool) rotation to realize precise synchronization, therefore, is suitable for batch processing of the same kind of parts, if processing is different size of workpiece, the layer distance will change, a layer of the tu have changes from nano coated tools, its durability will decrease due to the change of cutting temperature. The cost of coating is high to apply constant spacing to different parts in a single furnace.
At the same time, the world's famous coating companies are studying to improve (ti,al)n coating al content, the purpose is to improve hardness (mainly high temperature hardness), wear resistance, oxidation resistance, to improve the cutting performance of the tool. In order to distinguish from the usual tialn coating, the coating containing more than 50% al content is currently called altin. Thus, coatings containing 67%, 75%, or even 80% of al content are available, but the al content is limited, and beyond this limit, the properties of the coating will deteriorate. It has been proved that it is difficult to improve the effective aluminum content and maintain the same spacing at the same time. As a result, breakthroughs can only be made with new principles, and the nanocomposite coatings described below will do just that
By depositing several materials with very different properties (such as ti, al, si) at the same time, and the formed tissue components are not completely decomposed, two-phase structure will be formed -- tialn nanometer grains embedded in amorphous si3n4 matrix, forming honeycomb structure, whose grain boundary can block the further extension of cracks. In addition to its high hardness, this coating has excellent heat resistance and can be maintained to 1100℃, making it ideal for efficient, dry cutting. In addition, the properties of nanocomposite coatings are better when they are combined with multilayer nanostructures. The layer spacing of the multilayer coating is 35. This coating structure can only be achieved when the cathodes of multi-arc devices are very close to each other.
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