Method for coating temperature-sensitive substrates with polycrystalline diamond

Abstract

A method for coating temperature-sensitive substrates with polycrystalline diamond by a hot-wire CVD method, in which hydrogen and at least one carbon carrier gas are fed into a coating chamber. The fed gases are split at an electrically heated wire in such a way that carbon is formed and deposits on the temperature-sensitive substrate in the form of the diamond modification thereof. The substrate is arranged in the coating chamber, which is at a reduced pressure, and electrical power to electrically heat the wire is adjustable. The method is performed cyclically in respect of the electrical power that is fed to electrically heat the wire. A basic power is fed as lower threshold value for a predetermined time (basic load phase) and is increased for a further predetermined time to a maximum power as an upper threshold value (pulse phase) and is then reduced again to the basic power.

Claims

1. A hot-wire CVD method for coating a substrate with polycrystalline diamond, wherein hydrogen and at least one carbon carrier gas are fed into a coating chamber, wherein the fed gases are split at an electrically heated wire in such a way that carbon is formed, which is deposited on the substrate in the form of diamond, wherein the substrate is arranged in the coating chamber, which is at reduced pressure; and wherein an electrical power required to electrically heat the wire is adjustable, wherein the method is performed cyclically with respect to the electrical power that is fed in order to electrically heat the wire, wherein a basic power P.sub.Bas is fed as lower threshold value for a predetermined time t.sub.1 in a basic load phase, and is increased for a further predetermined time t.sub.2 to a maximum power P.sub.max as upper threshold value in a pulse phase, and is then reduced again to the basic power P.sub.Bas.

2. The method according to claim 1, wherein the basic power P.sub.Bas during the basic load phase is 50-75% of the power in the pulse phase.

3. The method according to claim 1, wherein the duration t.sub.1 of a basic load phase lies between 1 μs and 120 s.

4. The method according to claim 1, wherein the duration t.sub.2 of a pulse phase lies between 1 μs and 60 s.

5. The method according to claim 1, wherein the method is performed in a total duration tees between 5 and 100 h.

6. The method according to claim 1, wherein in the pulse phase, the temperature of the wire lies between 2000° C. and 3000° C.

7. The method according to claim 1, wherein the temperature of the substrate to be coated lies between 500° C. and 600° C. in the basic load phase and between 600° C. and 650° C. in the pulse phase.

8. The method according to claim 1, wherein in the pulse phase, the diamond deposition rate lies between 100 nm/h and 200 nm/h.

9. The method according to claim 1, wherein the basic power P.sub.Bas is 1-15 KW during the basic load phase, and the maximal power Pmax is between 18 and 30 KW during the pulse phase.

10. The method according to claim 1, wherein the method is performed for a total duration t.sub.Ges between 50 and 60 h.

11. The method according to claim 1, wherein in the pulse phase, the diamond deposition rate is approximately 150 nm/h.

Description

EXAMPLE

(1) For an exemplary diamond coating by means of the hot-wire CVD method, a PCD cutting insert is introduced into the reaction chamber of a commercially available coating plant, e.g. of a CemeCon CC800/5 Dia plant, in the present example. The PCD cutting insert is a sintered body of diamonds with a grain size distribution of between 0.1 and 50 μm. A solid PCD of this type must not exceed a substrate temperature of 650° C., because a reconversion of the cubic crystalline diamond into a hexagonal crystalline structure of the carbon takes place otherwise, which is generally referred to as “graphitization”. Such graphitizations of the PCD are inevitably associated with a loss of strength and also with the destruction of the structure of the PCD.

(2) To coat a solid PCD cutting insert of this type, the heating wire assembly of the used HD-CVD coating plant must not exceed a fed power of 14 kW. According to the invention, the power introduction with a basic power of approx. 13.5 kW is increased to 20 kW for a time period of between 0.5 s and 5 s in a sequence of pulse phases, so that the filament temperature of the used tungsten wire increases to 2500° C. for this short period of time. In the constantly conducted continuous operation, this would lead to a diamond deposition rate of approx. 300 nm/h, but whereby the substrate temperature of 900° C. would also be reached, but which would then lead to the above-described graphitization effects and lattice conversions.

(3) According to the invention, the introduction of the electrical power is shortened to the above-mentioned time window t.sub.2, and the substrate temperature thus does not rise above 650° C., wherein the deposition rate is still approx. 150 nm/h. Diamond films can be deposited economically—in the case in point within approx. 60 h—on temperature-sensitive substrates with this diamond deposition rate.

(4) In the case of the practical performance of the method according to the invention, basic powers P.sub.Bas of between 10 and 15 KW can appear during the basic load phase depending on the substrate, and the maximal power P.sub.max can be between 18 and 30 KW during the pulse phase depending on the substrate.

(5) Functional areas of chip-removing tools or cutting inserts, which were diamond-coated by means of the method according to the invention, display large strengths and long service lives and are thus optimally suited for the industrial production of chip-removing tools with diamond coating.