Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N3/40—Investigating hardness or rebound hardness
  • G01N3/42—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/0098—Tests specified by its name, e.g. Charpy, Brinnel, Mullen
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/022—Environment of the test
  • G01N2203/0222—Temperature
  • G01N2203/0226—High temperature; Heating means

Definitions

• the invention relates to indentors for measuring microhardness and layer adhesion of materials, for example for hardness determination according to the Vickers or Knoop method.
• the hardness of a material is often determined using the Vickers method (ISO standard 6507) or the Knoop method (ISO standard 4545). With these methods, a test tip with a given load is pressed into a sample and the resulting depression is measured by operating personnel under a microscope. In order to be able to take precise measurements, there is a requirement that the indentor be very hard. If the indentors are not hard enough, a systematic error will otherwise occur due to the elasticity of the indenter material. For this reason, diamond is well known as an indenter material. These diamond detectors are either made of natural diamond or are crystals synthesized at high pressure and high temperatures.
• the above-mentioned methods have disadvantages if the depression heals automatically due to the elasticity of the material to be examined. In this case, the depth and width of the scratch or scriber immediately after its creation are different than when it was measured. To avoid this systematic source of error, a modification of this method measures the depth immediately at the time of its creation. For this purpose, the depression is no longer evaluated optically after its creation, but the electrical resistance of the pairing of Indentor test material is measured during its creation. However, this requires an electrically conductive indentor, and the workpiece to be tested must also be at least electrically semiconducting. Because of the length dependency of the electrical resistance, the electrical resistance decreases as the depth of penetration of the indentor into the workpiece.
• This method avoids the above-mentioned systematic source of error and advantageously enables an automatable resistance measurement, which can be carried out in situ in a simple manner, particularly in the case of test objects which are difficult to access. Even for test objects with a complicated surface geometry, the method has strengths compared to the conventional variant.
• U.S. 4,984,453 to Enomoto et. al. suggests an indentor made of an electrically insulating holder with an electrically conductive tip.
• the indentor tip can consist of full volume of electrically conductive material such as boron carbide (B 4 C) or of type II diamond.
• B 4 C boron carbide
• type II diamond tip according to US Pat. No. 4,984,453 is diamond, which has become a p-doped semiconductor by adding boron.
• diamond is proposed as an indenter tip, the surface of which has been made electrically conductive by ion implantation.
• indentors Another area of application for indentors is to determine the adhesion of layers to substrates.
• adhesive strength measurements for this.
• a diamond indentor tip is pressed into a relatively moving sample as the load increases.
• the delamination of the layer is determined by a discontinuous jump in acoustic emission or by subsequent optical and / or chemical surface analyzes.
• the latter method is complex and the acoustic measurement method only allows indirect measurement which can only be used with brittle materials. For this reason, the known adhesive strength measurements with diamond indenters can only be used to a limited extent.
• the invention is based on the technical problem of largely avoiding the disadvantages of the prior art and of providing an electrically semiconducting or else electrically conductive diamond indenter which is very hard and wear-resistant.
• This technical problem is solved by the features specified in the independent claims, advantageous refinements being specified by the subclaims.
• an indentor which has a layer of diamond deposited by means of chemical vapor deposition (CVD).
• CVD chemical vapor deposition
• Such coatings have been well known for many years and have the same hardness as natural diamond, since the diamond layer, like natural diamond, is also crystalline.
• the CVD process makes it easy to add other elements in situ and to adjust the electrical conductivity in a customized or defined manner.
• the specific conductivity is preferably between 0.1 ⁇ _l cm "1 and 100 ⁇ _l cm " 1 .
• the indentor as a whole component then has an electrical resistance between 100 ⁇ and 1500 ⁇ .
• the gas phase is activated thermally or by a plasma, and the diamond phase is deposited instead of the thermodynamically stable graphite.
• the macroscopic physical and chemical properties of such layers largely correspond to those of natural crystalline diamond.
• the CVD process enables the diamond to be deposited on chemically different substrates with complex geometries and thus made accessible for numerous applications.
• the CVD process also makes it possible to produce layers with different structures or morphologies through different process controls, such as the application of substrate bias voltages.
• boron-containing precursors (English: precursors) such as, for example, tetramethylborane (TMB) are added to provide the diamond indenter according to the invention.
• TMB tetramethylborane
• the boron content can be specifically adjusted by the amount of boron-containing precursor added. This makes it possible to use lightly doped diamond layers to deposit semiconducting character as well as heavily doped diamond layers with almost conductive character.
• the specific conductivity is preferably between 0.1 ⁇ cm _1 '1 and 100 ⁇ cm _l' 1.
• the boron content lies in this case in the range 10 19 cm "3 to 10 23 cm" 3.
• the indentor according to the invention further allows hardness measurements with a Particularly good signal-to-noise ratio and therefore particularly precise measurements of the material hardness If an undoped diamond was used as an indenter material, its intrinsic electrical conductivity would provide the measurement signal for the measurement method described.
• boron is added to the base material, the boron content makes a second contribution to electrical conductivity.
• the CVD process significantly more boron can be added to a diamond layer than is possible when choosing a diamond with boron doping in its volume, as is the case with US Pat.
• a diamond composite layer is provided for the indentor as a coating, which in addition to diamond also has carbide phase components.
• a carbide-forming metal such as silicon, tungsten or titanium is added to the gas phase in the form of a precursor instead of boron.
• the resulting mechanical properties of the diamond composite layer are composed of the mechanical properties of the individual phases, weighted according to the ratio of the respective phases. In most cases, a proportion of the carbidic phase between almost 0% and 10% is sufficient.
• the specific sheet resistance can be set over several orders of magnitude, namely from approx. 1 ⁇ cm to 10 8 ⁇ cm over the respective proportion of the carbidic phases. It this is no longer a semiconducting layer, as in the case of on-board doping, but an electrically (fully) conductive layer, i.e. a conductive layer with ohmic resistance.
• the coating advantageously has a thickness between 1 nm and 20 ⁇ m. Since very thin layers can be deposited in a reproducible manner, which is more complex, layer thicknesses between 0.5 ⁇ m and 10 ⁇ m are particularly advantageous. The choice of layer thickness is based on the conductivity required for the application. The thicker the layer, the more conductive layers can be deposited. Depending on the application, layer thicknesses of more than 20 ⁇ m are therefore possible. This means that electrical conductivity values up to a few ⁇ "1 cm " 1 can be set continuously. The indentor itself then has an electrical resistance between 100 ⁇ and 1500 ⁇ .
• the indentor consists of a core of electrically insulating diamond with an at least electrically semiconductive coating of diamond.
• the coating adheres particularly well to the substrate, which significantly increases the service life.
• Another area of application of the indenter according to the invention is to determine the adhesion of layers to substrates. If there is an electrically insulating layer on an electrically conductive substrate, the layer failure can be determined with an electrically conductive indentor due to the drastic drop in the electrical resistance between the substrate and the indentor.
• the layers can be deposited using the conventional CVD method and also using the hot filament method.
• the microwave plasma CVD process (MWPCVD) has proven to be particularly advantageous Conditions also allow epitaxial diamond layers to be prepared on a [001] -oriented substrate.
• Fig. 1 shows a MWPCVD reactor (1) with a vacuum stainless steel chamber (2) and a microwave generator (3) with adjustable microwave power up to 1.5 kW.
• the high-frequency heating (4) heats a commercially available diamond indentor on a molybdenum disc (5) as a substrate.
• the molybdenum disk (5) is located on a cooling table (6) which serves to regulate the substrate temperature and which is the subject of DE 199 05980 A1 and with which substrate temperatures of approximately 200 K to 1100 K can be set continuously.
• a pyrometer (7) is used to monitor the plasma temperature.
• the latter is evacuated to a pressure between 10 Pa and 30 Pa and the substrate is heated to temperatures in the range from approximately 600 ° C. to 800 ° C. using microwave powers of 300 to 800 W.
• Hydrogen, methane and tetramethylborane (TMB) were then fed in as process gases via a gas inlet (9).
• the gas flow was between 300 and 1150 sccm for H 2 , between 1 and 10 sccm for methane, and between 0.001 and 0.1 sccm for TMB.
• the substrate bias was between (-) 150 V and (+) 150 V.
• the layer-forming species formed whereby the deposition conditions can be adapted to the desired morphology and the phase purity of the diamond layer.
• the resulting value of the sheet resistance is determined by the bias, the layer thickness and the boron content.
• the bias affects the morphology of the layer and the phase purity has an indirect influence on the resistance.
• the deposited layers having thicknesses of 0.01 ⁇ m to 20 ⁇ m, and wherein particularly good results were achieved with layer thicknesses of 0.5 ⁇ m to 10 ⁇ m.
• a boron content of 0.01% to 0.6% proved to be advantageous, or had a specific electrical resistance of 1 ⁇ cm to 10 8 ⁇ cm.
• FIG. 2 shows a scanning electron microscope image of a diamond indenter tip, on which a boron-doped diamond layer has been grown, and from which the morphology of the layer can be seen.
• FIG. 3 shows the course of the electrical resistance R ( ⁇ ) of the indentor provided in this way when penetrating into a substrate made of HSS steel as a function of the normal force F (N).
• the projected contact area can be calculated from the resistance.
• the hardness of the HSS steel results from this surface and the normal force

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• Physics & Mathematics (AREA)
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• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
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• Crystals, And After-Treatments Of Crystals (AREA)
• Carbon And Carbon Compounds (AREA)

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Citations (6)

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• 2000
  • 2000-01-28 DE DE2000103836 patent/DE10003836C2/de not_active Expired - Fee Related
• 2001
  • 2001-01-25 CN CN 01800695 patent/CN1204390C/zh not_active Expired - Fee Related
  • 2001-01-25 WO PCT/EP2001/000823 patent/WO2001055695A1/de active Application Filing
  • 2001-01-25 AU AU42352/01A patent/AU4235201A/en not_active Abandoned

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