Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Patent
1994-06-06
1996-03-05
Owens, Terry J.
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
118723E, H05H 124, C23C 1650
Patent
active
054965942
DESCRIPTION:
BRIEF SUMMARY
REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/DE92/01005 filed Nov. 30, 1992 and based, in turn, on German national application P41 40 158.1 of Dec. 5, 1991, under the International Convention.
FIELD OF THE INVENTION
The invention relates to a process for coating substrate bodies with hard substances by using a corona effect activated chemical vapor deposition (hereafter referred to as CVD) process at temperatures above 300.degree. and pressures below 10000 Pa.
Further the invention relates to a device for carrying out the mentioned process with a reactor having at least one gas inlet and at least one gas outlet connected with a pump, and in whose inner space there are one or more substrate bodies and one or more electrodes arranged at a distance therefrom and connected with a voltage source.
BACKGROUND OF THE INVENTION
High-temperature coating processes have the disadvantage that tenacity losses in the composite body consisting of a substrate body and the thereto applied coating of hard substance cannot always be avoided. So, for instance in the case of indexable inserts coated with titanium carbide used in the continuous machining of high-alloy steel, generally a higher degree of wear has been found when the coating was applied by a high-temperature process at approximately 1000.degree.. However at sufficiently low temperatures, such negative effects of the coating process on the substrate body can be avoided. Among the coating processes which can be carried out at low temperatures, besides the PVD process, the plasma-activated CVD process is important. If on the reaction gas in a low-pressure corona effect an unbalanced plasma is superimposed, the charged particles are accelerated under the influence of the existing electric field. Depending on particle density or pressure, the free path length between two impacts is also determined. If the particle energy is sufficient at the applied voltage, molecules or atoms can be excited for dissociation or ionization. In this way chemical reactions become possible which otherwise take place only at relatively high temperatures. The low-pressure plasma can basically be produced by applying a constant direct voltage at a workpiece connected as a cathode, by a high-frequency alternating current or by a pulsed direct voltage.
The high-frequency excitation, wherein the energy can be introduced inductively or capacitively from the outside into the reaction vessel, is often used for the deposition of very pure layers, e.g. in microchips. Since it works with electrodes which are not directly connected with the substrate, it does not matter whether the material itself is conductive or nonconductive. The drawback is that this process is very expensive.
The simplest way to produce a low-pressure discharge is to connect the workpiece as a cathode and to use the vessel or its walls as the anode or ground potential. The temperature of the substrate is thereby a function of the voltage and the current.
Further the direct voltage can be pulsed in which case the substrate temperature is a function of the peak voltage, as well as the peak current and also of the pulse duration and pulse frequency. The advantage of this process is that the coating temperature can be set independently of the parameters of the low-pressure discharge, the voltage and the current.
Basically CVD reactors have to meet two requirements: on the one hand they have to allow the coating of as many substrates as possible, which means they must have a high capacity, on the other hand shading effects or irregular coatings have to be avoided.
With regard to the second above-mentioned requirement it has already been proposed in DE 22 51 571 C3 to circulate the reactive gases in the reactor from the entire marginal area of the substrate support inwards over the substrate support and the substrate bodies supported thereon, from where the gases are then centrally evacuated. In this way a laminar radial flow is meant to be achieved. The reactor has a cover plate which is connecte
REFERENCES:
patent: 4633809 (1987-01-01), Hirose et al.
patent: 4648348 (1987-03-01), Fujiyama
patent: 4676195 (1987-06-01), Yasui et al.
Ko/ nig Udo
Tabersky Ralf
van den Berg Hendrikus
Dubno Herbert
Owens Terry J.
Widia GmbH
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