USE OF A DIAMOND LAYER DOPED WITH FOREIGN ATOMS TO DETECT THE DEGREE OF WEAR OF AN UNDOPED DIAMOND FUNCTION LAYER OF A TOOL

Abstract

A first diamond layer made of polycrystalline diamonds and doped with foreign atoms, is arranged on a metal surface of a machining tool, and is used to detect the degree of wear of an undoped polycrystalline second diamond layer, which is arranged on the doped diamond layer and forms a functional region of the machining tool, wherein at least one physical parameter is detected continuously or periodically during operation of the tool, and wherein a change in the parameter indicates the degree of wear of the undoped second diamond layer. The doped diamond layer forms an intelligent stop layer for the tool because as a result of change in the transition from the undoped to the doped layer, the conductivity of the system changes, for example, and this change can be used to form a stop signal for the machine drive before the tool and the machined workpiece are damaged.

Claims

1. Use of a first diamond layer, which is doped with foreign atoms and which is made of polycrystalline diamonds and which is arranged on a metal surface of a machining tool, to detect the degree of wear of an undoped polycrystalline second diamond layer, which is arranged on the doped diamond layer and which forms a functional region of the machining tool, wherein at least one physical parameter is detected continuously or periodically during the operation of the tool, and wherein a change of the parameter indicates the degree of wear of the undoped second diamond layer.

2. The use according to claim 1, wherein the first diamond layer is an n-type doped or a p-type doped diamond layer.

3. The use according to claim 1, wherein the foreign atoms are selected from the group consisting of: aluminum, boron, silicon, tungsten, iron, molybdenum, cobalt, niobium, tantalum, rhenium, nitrogen, and phosphor, as well as mixtures thereof.

4. The use according to claim 1, wherein at least some of the foreign atoms are boron atoms.

5. The use according to claim 1, wherein at least some of the foreign atoms are nitrogen atoms or phosphor atoms.

6. The use according to claim 1, wherein the at least one physical parameter is/are selected from the group consisting of the electrical resistance, the electrical conductivity, the capacitive resistance, the Hall voltage and the Hall current of a Hall sensor.

7. The use according to claim 1, wherein the physical parameter is detected between the tool and a machined workpiece.

8. The use according to claim 7, wherein the at least one physical parameter is/are selected from the electrical conductivity, the electrical resistance and/o, and the capacitance between machined workpiece and the tool.

9. The use according to claim 1, wherein the doped first diamond layer is applied to a cobalt-containing hard metal surface.

10. The use according to claim 1, wherein the doped and the undoped diamond layer are applied to the metal surface by chemical vapor deposition (CVD) from a methane/hydrogen atmosphere.

11. The use according to claim 1, wherein the doping of the first diamond layer is created by supply of a doping gas, during a CVD method in a CVD chamber.

12. The use according to claim 1, wherein the undoped second diamond layer is created by interruption of the supply of the doping gas into the CVD chamber.

13. The use according to claim 1, wherein the first polycrystalline diamond layer is produced by CVD, and the obtained layer is irradiated with an ion beam of the desired foreign atom for doping the first diamond layer; and then a tempering step is carried out; and the undoped second diamond layer is then deposited on the doped first diamond layer.

14. A method for continuously detecting the degree of wear of an undoped diamond layer, which forms a functional region of a machining tool, and which is arranged on a diamond layer doped with foreign atoms, during operation of the tool; wherein a) the doped diamond layer is arranged directly on the substrate surface of the machining tool; b) at least one measurement parameter, which results from both diamond layers, the tool, and a workpiece machined with the tool, is detected continuously or periodically during the operation of the tool; c) a predefined threshold value for the measurement parameter is specified; and wherein d) a change of the measurement parameter above or below the predefined threshold value indicates the degree of wear of the undoped diamond layer.

15. The method according to claim 14, wherein the measurement parameter is selected from the electrical conductivity, the electrical resistance, and the capacitance between machined workpiece and the tool coated with doped and undoped diamonds.

16. The method according to claim 14, wherein the foreign atoms are selected from the group consisting of: aluminum, boron, silicon, tungsten, iron, molybdenum, cobalt, niobium, tantalum, rhenium, nitrogen, and phosphor, as well as mixtures thereof.

17. The method according to claim 14, wherein the foreign atoms comprise at least one of boron, nitrogen and phosphorus.

18. The method according to claim 14, wherein the doped diamond layer is applied to a cobalt-containing hard metal surface.

19. The method according to claim 14, wherein the doped diamond layer and the undoped diamond layer are applied to a metal surface by chemical vapor deposition (CVD) from a methane/hydrogen atmosphere in a CVD chamber, wherein a coating temperature of between 800 C. and 1100 C. and a coating pressure of between 1 kPa and 100 hPa is set.

20. The method according to claim 19, wherein a W-wire is used as a heating wire in a hot wire method in carrying out said chemical vapor deposition.

21. The method according to claim 14, wherein the doping of the doped diamond layer is created by supply of a doping gas during chemical vapor deposition in a CVD chamber.

22. The method according to claim 14, wherein the undoped diamond layer is created by interruption of supply of a doping gas into a CVD chamber.

23. A system comprising: a) a machining tool comprising the layer sequence: i) metallic substrate layer, ii) diamond layer of polycrystalline diamonds doped with foreign atoms, iii) undoped polycrystalline diamond layer, wherein there is a differentiation between the doped diamond layer ii) and the undoped diamond layer iii) with regard to a physical measurement parameter, and wherein the undoped polycrystalline diamond layer forms a functional region of the machining tool, and b) a workpiece.

24. The system according to claim 23, wherein the physical measurement parameter is the electrical resistance or the electrical conductivity.

25. The system according to claim 24, wherein the workpiece is an electrically conductive workpiece.

Description

EXAMPLE 1

Production of Tools with Doped and Undoped Diamond Layers

[0083] After cleaning and degreasing the surface with acetone or a different organic solvent, hard metal spiral drills of a 10M % Co hard metal comprising an average WC grain size of 0.6 m (Ghring trade name DK460UF) and after particle blasting, the tools to be coated with quartz particles were subjected to an acidic etching step for removing Co from the surface. According to WO 2004/031437 A1, a mixture of HCl/HNO.sub.3 was used for this purpose. After rinsing and drying, the tools, which were pretreated in this way, were introduced into the vacuum chamber of a commercially available hot wire CVD system (CemeCon CC800/5). The tungsten wires (99.99% purity) of the CVD system are arranged parallel to one another at a distance of approx. 4 mm. The drills were circumferentially surrounded by the filaments parallel to their longitudinal axis. The temperature of the filaments was set to approx. 2100 C. The temperature was measured by means of optical thermometers. The distance of the filaments to the tool to be coated was 5 mm.

[0084] First of all, a doped diamond layer was produced on the surface of the tools by supplying H.sub.2/CH.sub.4 as material gas and B.sub.2H.sub.6 as doping gas. In the exemplary case, the following mass flows were used thereby after preliminary tests: [0085] H.sub.2 600 sccm [0086] CH.sub.4 5 sccm [0087] B.sub.2H.sub.6 2 sccm

[0088] sccm hereby stands for standard cubic centimeters per minute. Regardless of pressure and temperature, a defined streaming gas quantity per time unit is thus described with this unit, a mass stream is thus specified.

[0089] The standard cubic centimeter is thereby a gas volume of V=1 cm.sup.3 under standard conditions (T=0 C. and p=1013,25 hPA), the so-called physical standard conditions according to DIN 1343.

[0090] The specified mass streams were applied for 80 hours. The supply of the dopant diborane was then blocked and the mass streams for H.sub.2 and CH.sub.4 were maintained for further 180 hours. The temperature of the tools to be coated was 970 C., the pressure in the CVD chamber was approx. 13 kPa.

[0091] A layer thickness measurement (REM with focused ion beam [FIB], Helios NanoLab 600 by FEI) of the doped diamond layer resulted in values of between 70 and 90 pm. The total layer thickness in the present exemplary case was approximately 220 m, which results in a layer thickness of approximately 130 m for the undoped diamond layer.

[0092] The concentration of boron was determined by the Curcumin method. The boron-containing diamond material with oxygen is thereby removed from the metal surface according to DE 101 17 867 A1 by heating to 700 C. The diamond carbon thereby burns to CO.sub.2, and boron is oxidized into boron trioxide and borates, which are infused with curcumin in the acidic range, which, with borates, forms a red complex of Rosocyanine, which is analyzed photometrically at 540 nm and is compared to standard borate solutions. In the doped diamond layer according to this method, the boron content was between 7 and 10 atomic percent, based on C+B in the doped diamond layer.

[0093] The electrical properties of the doped and of the undoped diamond layers were initially measured as part of the present invention.

[0094] After measurement of the absolute layer resistance of the boron-doped layer (four-point method according to Vogel 2005), the specific resistance of the obtained boron-doped diamond layers (p-type doping) was determined by multiplication with the layer thickness and, at room temperature and a degree of doping of 10 atomic percent, based on C+B in the doped diamond layer, is 1.58 cm, whereas the specific resistance of a pure undoped diamond layer (produced on the tool as described above, but without doping gas supply) is 5.610.sup.13 cm. It is thus shown that the conductivity of diamond can be changed by many orders of magnitude by doping in generalin the exemplary case with boronwhich can be used metrologically for the purposes of the present invention to detect the degree of wear of an undoped polycrystalline diamond layer.

EXAMPLE 2

Measurement Principles and Drilling Tests

[0095] The drilling tools obtained according to Example 1 were tested in highly abrasive test workpieces of AlSi9 and AlSi17. These materials are electrically conductive.

[0096] Cuboid blocks with a surface area of 55 cm and a height of 10 cm as workpiece test specimen were made of these materials. The specimen were clamped into the workpiece accommodation of an industrial drilling device by GHRING KG, Albstadt. A 10 mm drill, to which, according to Example 1, a doped diamond layer and a diamond layer, which is undoped on the chip side, was applied, was clamped into the tool accommodation of the drilling device. The total layer thickness was approx. 220 m. The drilling device was programmed in such a way that a 9 cm deep hole was drilled per specimen, and one then moved on to the next workpiece. For the purposes of the present tests, no coolants or lubricants were used.

[0097] The drilling tests were designed as follows: [0098] Process: drilling into solid material, drilling depth 900 mm [0099] Cutting speed: 100 m/min

[0100] A measurement arrangement for the conductivity measurement of the overall system drill holderdrilling tooldoped diamond layerundoped diamond layertest workpiece was created. The measurement took place in the usual manner of the conductivity measurement of non-ferrous metals without contact (eddy current method according to DIN EN 2004-1) with a commercially available device (SIGMASCOPE SMP350 by HELMUT FISCHER GmbH, Sindelfingen) and corresponding probes having a frequency of 15 kHz, in the case of which the measurement data was read into a computer via a USB interface, was compared to a threshold value, and a switch for turning off the drive device of the drill to be tested was operated by the software when the threshold value was exceeded. The measuring probes of the conductivity measuring device were arranged on the workpiece and on the tool holder, so that the conductivity of the above-defined overall system was detected. In the beginning, a conductivity of the overall system of virtually 0 MS/m was found.

[0101] A conductivity of between approx. 12 and 17 MS/m was determined for this system in preliminary tests when testing drills, which were only provided with a B-doped diamond layer, but did not have an undoped diamond layer. A threshold value of 15 MS/m was formed therefrom. Should this threshold value be exceeded in the case of the test system according to the invention, this means that the undoped diamond layer, which forms the actual functional region of the tool, has worn and that the drill already runs in the emergency mode on the doped diamond layer, but nonetheless fulfills its function. As soon as a value of 15 MS/m is exceeded in the test, the computer outputs a signal for turning off the drill, by means of which it is prevented that the drill, the workpiece or the drive machine are damaged and that the drill can be exchanged at the right time.

[0102] It has been shown in the practical tests that the drills used according to the invention fulfill all expectations on the wear resistance, service lives and reaches of a conventional diamond tool.

[0103] It has further been shown that even though the change of the conductivity occurs gradually, it reaches its maximum within a few minutes at the predetermined cutting speed. It can thus be seen that not only the absolute value can serve as measurement parameter, but that for example the speed of the change or also the edge steepness of the change of a measurement parameter can also be used to accomplish the detection according to the invention of the degree of wear of an undoped diamond layer.

[0104] The doped diamond layer thus quasi serves as intelligent stop layer for diamond-coated tools.

EXAMPLE 3

Ion Beam Pretreatment

[0105] Hard metal spiral drills of a 10M % Co hard metal comprising an average WC grain size of 0.6 m (Ghring trade name DK460UF) were coated as described in Example 1, but no chemical pretreatment of the substrate surface took place, but it was irradiated with an ion stream of nitrogen ions for 3.5 hours, wherein the ion stream was created with a voltage of 30 kV at 3 mA plasma stream at a nitrogen pressure of 110.sup.5 mbar. A commercially available ion generator was used (on generator Hardion by Quertech, Caen) to create the ion beam.

[0106] A temperature of approx. 400 C. was thereby reached on the tool. The tool was then provided with a doped and an undoped diamond layer in a commercially available hot wire CVD system (CemeCon CC800/5), as in Example 1, and the conductivity measurement was carried out as described in Example 2.

[0107] As expected, lower absolute conductivity values of the overall system were reached, because the doped layer was deposited on a more strongly insulating substrate layer.

[0108] The conductivity data, however, could also be used in the case of these diamond-coated tools, which were improved with regard to their service lives, to detect the degree of wear of the undoped diamond layer and to turn off the drilling device at the right time or to reduce the cutting speed.