Patent Application
20050081599
The present invention relates to a method and a device for determining the wear resistance of abrasively or adhesively strained surfaces, for example thin layers. Methods of this kind are necessary for all types of technical surfaces, which are strained abrasively or adhesively, in particular for tribologically-coated surfaces, for measuring their wear resistance.
The determination of the wear resistance of very thin surface layers is gaining importance very quickly as considerable miniaturization efforts are made in many technical areas, and innovative technologies are growing, like for example the micro-system technique. Micro-Iribological optimisations of rails, bearings and sliding contacts require for example the use of extremely thin layers, which thickness is very often on the sub-micrometer scale and which have to be investigated and optimised by measuring techniques concerning their mechanical wear resistance. Currently there are no appropriate procedures for this problem.
The known micro-scratch tester based on the AFM method is not suitable for the determination of practically usable and transferable results since the scratch results, which are gained with the help of a thin needle, permit no conclusion about the actual areal wear in practice.
For the local resoluted examination of wear characteristics on material surfaces the ball wear method is used. Here calotte shaped grindings are produced by the 3-body-contact on the surface, which is to be measured. Optically measured the grindings allow conclusions about the wear resistance. The grinding is produced by a ball turning on the material surface, which is moistened with a polishing slurry.
It is disadvantageous, that the polishing medium can change its grinding characteristics by being soiled with abraded material, by deposit of particles and by evaporation losses of the fluid. The polishing slurry can furthermore operate as wear passive when particles deposit in soft surfaces and it is unevenly spread over the counter-body's contact route. The surface of the ball is also altered. A frequently change of balls is necessary.
Furthermore this method of load variation is limited by a reduction of the calotte radius. Also the pressure force of the ball can only be used restrictively. When evaluating the measurement, failures of the calotte form (especially rounding of the edges) can falsify the measurement results.
Altogether it is to say, that all the mentioned testing methods supply only limitedly transferable results for each application (scratch-test) or that they cannot be restricted to smaller lateral analyse areas (sand trickle test).
Using the refection method for testing lacquers, the results show great dispersion, while the Taber test does not allow an analysis of extremely thin surface areas.
A further testing device for determining the abrasive wear resistance of magnetic heads in video recorders is published in Bushan, B. et al. “Tribology and Mechanics” Sp. 22, ASLE Spec. Publ., Park Ridge, 1987 from van Groenou et al. In this so-called “Sphere-on-Tape-Test” a tape with an abrasive effect is run between a sample surface and a lateral fixed, weight loaded counter-body ball. The abrasive tape is pressed on the sample by the pressure of the counter-body ball, so that a wear calorie is formed on the sample surface. The sample is now taken out of the device at different points of time and the depth of the calotte is measured.
With this device for example deviations of the tape thickness or complicated topographies of the samples are leading to damping difficulties. Furthermore no exact sample positioning control is possible and due to the removal and fixing of the sample in the device an automation of the measurement is not feasible. So no in situ wear measurement is possible.
The purpose of the present invention is it, to create a device and a method for determining the mechanical wear resistance of a sample surface, which can also be used for determining the wear resistance of extremely thin surface installations and coatings reliably, at favourable costs and quickly.
This purpose is fulfilled by the method as per patent claim 1 and by the device as per claim 17. Advantageous further descriptions of the method according to the invention and the device according to the invention are presented in the claims subject.
According to the invention the present method differs from the prior art by determining the position of the counter-body at at least two different points of time. The advantage of this is now, that not the depth of the wear calotte after removing the counter-body, but directly the position of the counter-body in situ during the wear test is measured. So that then the depth of the wear calotte in the sample's body can be determined from the position of the counter-body.
The increase of the depth is correlated to the wear resistance of the sample surface. With this a simplified measurement and interpretation of the wear measurement is possible.
The used appliances can be constructed small and mobile, although a measurement is possible on big and on small objects.
Measurements of surface areas up to a dimension of 10 nm respectively local measurements on surfaces down to 10 μm2 are possible. Wear measurements on the edges of a sample are feasible with this method. By an appropriate controlled load on the counter-body, standardized work parameters as well as an elimination of the influence of thickness variations of the wear belt are practicable.
The method according to the invention can be utilized manifoldly. It can be used, for instance during the quality control and in the field of research and development, for example for lacquer coatings, for the sealing of floors, for the quality control of micro-edifice elements (MEMS) or in the micro-system technique. Particularly, a fast assessment of wear hard-material-layers in the field of coating techniques (galvanizing, varnishing, material coating procedures in general) is possible. It also can be used as optimisation tool during the layer process development (e.g. in the field of galvanic, CVD, PVD).
Since the determination of the position of the counter-body can be made in situ, the tape thickness variation can be eliminated from the measurement by running back the belt into the same position at the respective measurement points of time. So the position of the counter-body is always determined with the same tape thickness. The measurement of the counter-body's position can be made when the tape is stopped at one patch of the tape, which has not been used for generating wear. This has a particular importance, when calotte-depths are measured in a range of 10 nm, while the tape thickness is usually >10 μm (typically 10-20 μm) and amounts so up to a thousand times of the produced calotte-depth. This also enables the resolution of calotte-depths of a scale of 1 nm. Customary magnet tapes can be used as tapes, which enable the marking and recognizing of a certain tape position, so that the belt can be run back into the marked position for the single measurement points of time without pressure or load and, if applicable, without further contact to the counter-body and/or the sample surface. Of course, also a position, which is relatively staggered to the measurement position of the tape, can be marked. The utilized grinding belts are in this case advantageously conventional audio or videotapes with a RMS roughness of 10 to 30 nm. In the case of magnetic tapes the marking of the tape position used for the measurement can be made and/or recorded magnetically. As holding and transport device for this belts customary tape transporting units like VCR or MC drives can be used like for instance from mobile devices.
The measurement of the counter-body's position can be made capacitative, inductive or interferometric. In the last case the counter-body itself can be equipped as reflector. The force on the counter-body for pressing the tape against the sample surface can be produced capacitatively (AFM), magnetically or also inductively (touch method). The adjustment of the force can be done very flexible using this method, so that the damping behaviour is controllable and even with higher belt speeds micro-calottes with an extraordinarily good surface smoothness without grind grooves are produced. For the magnetic generation of force, permanent and/or electro magnets are suitable.
The counter-body can be a ball or a cylinder. When using a rolling ball or a rolling cylinder the damage on the back of the tape is reduced by the abrasion of the ball and the grinding belt. Also the abrasion of the ball is reduced. The counter-body can also be tribologically optimal coated for reducing the friction and the abrasion between the counter-body and the grinding belt.
Further advantageous coatings refer to the adjustment of the nano/micro topography of the grinding belt surface, which gets in contact to the sample surface, for instance through plasma or ion corrosion. The grinding belt can also be adhesively coated on the abrasive side, e g. by CVD or PVD methods like steaming or sputtering for being able to record an adhesive abrasion as well.
For evaluating the measurement a depth criterion can be used for example. In this case the abrasive belt runs until a certain depth criterion for the produced calotte in the sample surface is achieved. The depth criterion can be controlled by measuring the position of the counter-body after certain time distances or continuously. If the depth criterion is reached, the required space of time or the length of the belt, which was producing this calotte running through between the counter-body and the sample, can be determined. The space of time or the belt length now correlate with the wear resistance of the sample surface.
In the following an example of a device and a method according to the invention is described.
The only
The hemisphere 4 is now fixed by a holding 5 referring to movements in the plane surface 10, although a holding 5 makes vertical movements of the hemisphere 4 to the surface 10 possible. The hemisphere 4 is furthermore connected to a unit 7, which puts a load on the hemisphere 4 and contains a measurement unit for determining the vertical position of hemisphere 4.
By unit 7 the hemisphere 4 is now pressed with a defined force on the magnet belt 3, so that it gets in friction contact to the surface 10 of the sample body 1 and produces a wear or abrasion calotte 2 during the run of the belt. On
The measuring unit 7 contains here for example an interferometer, which sends a ray of light on the plane surface of the hemisphere 4, which is turned away from the grinding belt. The ray of light is reflected from that surface and measured in the interferometer 7. From this measurement the position of the hemisphere 4 and, with timely distanced measurements, even the depth respectively the change of depth of the calotte 2 can be determined.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 05 435.5 | Feb 2002 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP03/01243 | 2/7/2003 | WO |
