PVD technology by SHM
There are two methods in principal used for PVD coating of tools and indexable inserts. There are CVD (Chemical Vapour Deposition) and PVD (Physical Vapour Deposition). CVD uses a mixture of chemically reactive gasses such as TiCl4, CH4, AlCl3, etc. heated up to a rather high temperature of 900 – 1000°C for deposition. PVD technology is based on physical principles, evaporation or sputtering of materials included in a coating (eg. Ti, Al, Si, Cr, …) and their subsequent deposition on tools.
SHM technology is based on evaporation by means of low voltage arc.
Low voltage arc evaporation
Low voltage arc is advantageous for its high speed of evaporation and high plasma ionization. Its parameters are highly interesting. It burns in a place of a cathode spot of 10 μm diameter, where it reaches approx. 15 000°C. Under those conditions it is possible to evaporate practically every electrically conductive material...
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| cathode spot movement | cathode spot schema |
The principle of a coating process can be easily explained on a PVD unit schema. The material is evaporated and concurrently ionized by the arc from electrodes. The ionized material (eg. Ti+, Ti2+, etc.) is accelerated towards the substrates by negative bias, which is applied to them. While traveling it ionizes atoms of gas atmosphere (eg. N2, Ar, …) as well. The ionized atoms create the actual deposited coating by surface reaction when reaching the substrate.
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| PVD unit schema |
Why are we successful in industrial preparation of the unique nanocomposite coatings?
The preparation of a nc-(Ti1-xAlx)N/a-Si3N4 requires an evaporation of a great volume of ionized particles and their large ionization. This condition stands in not only for the electrode material but for the atmosphere particles, too. Both can be achieved by using a relatively strong magnetic field, which in a needed way influences the arc burning.
Simple, but…
Conventional PVD units are equipped with so-called planar electrodes (they are flat, in a shape of a plate or a small ring), on which excessive and centralized erosion and substantially earlier wear occurs when applying a strong magnetic field.
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| planar and cylindrical target |
We have found a very elegant technical solution to this problem, which are rotating cylindrical electrodes, whose effective area is in essence _-times larger and thanks to their rotation the static erosion mentioned does not occur. The cylindrical cathode solution met the condition for nc-(Ti1-xAlx)N/a-Si3N4 coatings preparation, while prolonging the target life as well.
MARWIN® technology
The characteristic feature of MARWIN® technology is the application of rotating cylindrical electrodes. The electrodes are positioned in a pair in the center of the unit chamber, centrally towards to the coated tools. A combination of Ti and eutectic AlSi (approx. 11,9 wt%) electrodes is used for nc-(Ti1-xAlx)N/a-Si3N4 coatings preparation..
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| MARWIN unit chamber schema |
(in principal the same schema applies also for the ORM coating unit)
Application of the two electrodes is very important. It is possible to change stoichiometry, growth speed and partially even the roughness of a coating without a physical exchange of the electrode material by setting different values of current applied on the electrodes. Thus the basic structure of mono-, multi- and gradient coatings is prepared.
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| multilayer macrostructure |
The substrates rotation mentioned above (they move planetary) is also a very important parameter influencing the coatings cutting performance. By synchronizing the rotation speed in relation to the current on the electrodes it is possible to obtain nanolayer (nano-multilayer) thickness of approx. 5 – 7 nm witch is optimal from the hardness point of view.
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| TEM – nanocomposite structure |
