DE19722728A1 - Composite body consisting of a hard metal, cermet, or ceramic substrate body and method for its production - Google Patents

Abstract

The invention concerns a composite body consisting of a hard metal, cermet or ceramic substrate body and at least one layer of a mechanically resistant material, a ceramic substance, a diamond-like layer, amorphous carbon and/or hexagonal boron nitride. The invention also concerns a method of producing this composite body, wherein, when the green compact has been dewaxed, with its pores still open and whilst it continues to be heated as from a temperature of between 600 DEG C and 1100 DEG C, it is acted upon by sublimable solids and/or reaction gases which are necessary for coating purposes. The temperature of the green compact is then further increased and the latter is fully compressed by sintering, before one or more layers of the above-mentioned type is/are applied.

Description

The invention relates to a method for producing coated cermet, hard metal or ceramic substrate bodies, in which a green body is pre-selected from a starting powder mixture presses, waxed and then in a microwave field sintered and with a hard material coating or a corro sion protection or wear protection coating from one or is coated in several layers.

The invention further relates to a composite body from a Substrate body of the type mentioned and at least one layer from a hard material.

Composites of the type mentioned are in particular as Inserts for machining or as a high temperature materials used. Composites concerned who which, as a rule, according to the prior art by sintering Compacts made from the corresponding mixtures of Hart substances and metal powders (binders) are made. The Sintering takes place in furnaces, for example with graphite heating elements are equipped, whereby the heating of the samples indirectly by means of the radiation emitted by the heating elements as well as by convection or heat conduction. The disadvantage This process engineering is that the choice of furnace atmosphere due to the chemical properties of the heating elements is severely restricted. In addition, the heating takes place of hard metals, cermets or ceramics from the outside in and is essentially due to the thermal conductivity and Controlled emissivity of the samples. Depending on the thermal conductivity of the samples is the range of variation of the heating and Cooling rates are severely limited, which is why they are sometimes complex  Measures such as a high level of equipment and process engineering Effort is required, for example, to Sintering hard metals satisfactorily.

To eliminate this disadvantage, is proposed in WO 96/33830 beat, pre-pressed green compacts from a cermet or a Sinter carbide in a microwave field. The pre-pressed Green body can already continuously during the heating be irradiated or pulsed with microwaves, whereby plasticizers, such as wax, are expelled during heating will.

If necessary, the finished sintered body can then using PVD, CVD and / or a plasma-activated CVD one or more hard material layers are coated.

Suitable microwave sintering furnaces and sintering processes Microwave radiation is described, for example, in DE 195 15 342 described.

In addition to the choice of material for the substrate coating, in particular carbides, nitrides and / or carbonitrides of the elements of the IVa to VIa group, diamond-like substances, ceramic substances such as Al ₂ O ₃ and / or ZrO ₂ and boron nitride come into question , the adhesion of the coating on the sintered body as a substrate body is of crucial importance.

It is an object of the present invention, a method as well a coated substrate body of the type mentioned specify where specifically the liability of the only or first Layer on the substrate body can be improved. The Ver Driving should be easy to handle without great technical effort and be energy-saving.

This object is achieved by the method according to claim 1, which is characterized according to the invention in that after  Dewaxing of the green body with still open porosity at Tempe temperatures between 600 ° C and 1100 ° C, preferably between 800 ° C and 1100 ° C, the green compact not for hard material coating agile reaction gases and / or sublimable solids then the temperature of the green body continues increased and this is completely compressed by sintering, after which one or more layers of hard material, Ceramics, diamond-like layers, boron nitride or the like be applied. The main idea of the invention is in that the outer pores are not yet closed Substrate body surface is relatively rough. Will now be in this Phase with the CVI (chemical vapor infiltration), CVD or PCVD coating started, the coating material partially fill the existing open pores so that an intimate bond of the coating during final sintering materials with the substrate body material, which also a gradient transition from the substrate material to the layer material. The desired first or only layer does not need up to the desired one during the heating phase Thickness can be applied, it is sufficient if the Substrate surface with the relevant coating material is wetted in thin layers. In contrast to the conventional Sintering in an oven heated with heating elements, in which the Sintered bodies are heated from the outside to the inside the microwave radiation already contributes to the substrate body low temperatures. Because in a microwave field Substrate body or the batch formed therefrom are hotter than the cavity is the substrate body (s) inside warmer than outside; in a corresponding manner Sintering process from the inside out. The one in the heating phase applied layer or layers if the gas phases composition is changed, thus affect or disrupt not the sintering process. Overall, the sintering and Coating can also be shortened to the same extent as in the Warm-up phase a first coating on the substrate body has been deposited on the after sintering  if necessary, add more layers after cooling to the usual CVD, plasma CVD temperature can be applied "in one heat" can.

Further developments of the method according to the invention are in the Subclaims described.

In the case of hard metals, preference is given to letting in the gases, required for the reactive separation of the substances mentioned are then started when the volume fraction of the open pores of the total volume of the hard metal base body <10%, preferably is 35 to 60%.

The same applies to ceramics and cermets with regard to the open pores Corresponding, preferably in the case of ceramics, 35 to 70% or 50 to 60% and in the case of cermets 35 to 60%, preferably 40 up to 60% are adhered to in certain areas.

Depending on the desired penetration depth of the infiltration, it can get into the be particularly advantageous for ceramics, first the green body pre-compress at higher temperatures before after Cooling of the green compact to 600 ° C to 1100 ° C for the hard necessary reaction gases and / or subli miable solids is applied. Alternatively can, especially in the case of hard metals and cermets Application during the heating of the green body after the Dewaxing (debinding) take place.

It is preferred to start with the application of Reaction gases and / or sublimable solids (under Use of carrier gases (argon etc.) the temperature above kept constant for up to one hour or the heating rate up to a maximum of 200 ° C / h until reached slowed down by at least 1000 to 1100 ° C. This  Measure is used in one for CVI or CVD deposition suitable temperature interval enough time for separation to give a first thin layer. As already mentioned, the other layers of hard material, ceramic, diamond, Boron nitride or similar substances immediately in the cooling phase applied by CVD or PCVD.

For the final CVD / PCVD coating an essential comes cher advantage of microwave sintering to bear, namely the Possibility up to high densities a part of the porosity to keep open. This is a good anchoring of the in the Cooling phase with total porosity of <10% applied CVD / PVD layers guaranteed. Pretreatment of the waiter areas that are often required with conventional CVD / PCVD is not applicable.

The method according to the invention also enables through a targeted adjustment of the (partial) pressure and the temperature raturwahl, the filling of the near-edge pores of the substrate body pers with those from the reaction gases and / or sublimable Solids formed substances (coating material), whereby in the substrate body from the outside in to a maximum Penetration depth of 200 µm an inwardly decreasing gradient these substances are created. Unlike the state of the art nik basically known complete infiltration of Ceramic materials by coming out of the gas phase or ent standing connections, which are essentially homogeneous extend the infiltrated body with the invention According to the method, only those close to the edge during the heating phase pores not yet closed to an inwardly decreasing extent filled up by the substances forming from the gas phase, before the substrate body finally ver during sintering is sealed.  

Depending on the batch size, the preferred micro is used shaft power between 10 W and 100 kW. The set pressure during the said heating phase, which off at the Reaction separation gases, carrier gases and other process attendants is formed by Separation during the heating phase between 0.1 kPa and 100 kPa. The depth of penetration of the coating can vary depending on the pressure tion material in the near-edge pores of the substrate body varies will. Reaction gases can be used in all CVI and CVD deposits known gases are used, esp special with metal halides, methane, nitrogen, gases with Cyanide content, where between carbon and nitrogen there is a triple bond, such as with the Aceto nitrile, alcoholates, β-diketonates and carbonates. Come into question but also molecular precursors, the elements to the desired Provide reaction separation or pore filling, for which purpose include special organometallic compounds.

Preferred materials which are deposited on the substrate body in one or more layers are in particular carbides, nitrides or carbonitrides of the metals of the IVa to VIa group of the periodic table, Al ₂ O ₃ , ZrO ₂₁ carbon as a diamond-like layer, amorphous carbon and / or cubic or hexagonal boron nitride.

According to a further embodiment of the invention, it is possible to deposit a ceramic layer with infiltrated ZrO ₂ and / or one or more further layers, in particular TiC, on ceramic substrate bodies made of Al ₂ O ₃ . In a corresponding manner, however, single or multi-phase layer layers, which are formed from hard materials, cermet, ceramics and / or metals, can also be applied directly to the substrate body as an intermediate layer or as an outer layer.

If a first thin layer of 0.1 µm to 10 µm, preferably 1 µm, is applied after a preferred further development of the invention after Fer sintering through the thin-layer coated substrate body corresponding admission of the same reaction gases as in the Heating phase the "started" coating until it is reached the desired thickness of this single or first layer set.

The invention further relates to that described in claim 13 Composite body made of a hard metal cermet, or Kera micro substrate body and at least one layer of a hard fabric, a ceramic, a diamond layer, amorphous Koh lenstoff and / or boron nitride and the invention is characterized in that in the coating Remove the adjacent zone of the substrate body with the inside the gradient in the substrate body hard materials of the same type as the first hard material layer is embedded, preferably until to a penetration depth of maximum 200 µm and / or the limit between the substrate body surface and the first layer has a roughness that roughly corresponds to the surface roughness of a partially compacted green body with an open porosity at 600 ° C to 800 ° C before sintering. Regarding the advantages of this composite body and the special design The same applies as described above.

In a specific embodiment, there are six indexable inserts plates have been coated at normal pressure and sintered.

The paraffinized WC-CO green bodies (cobalt content 6% by mass) are waxed in a first sub-step in a 2.45 Ghz multi-mode applicator under an Ar atmosphere with a low microwave power of less than 250 W for about 20 minutes, the green linge for thermal insulation in an insulating box made of micro-wave-transparent Al ₂ O ₃ fiber plates are arranged. After dewaxing, the green bodies are further heated to 850 ° C. At this temperature, a TiC precursor is deposited on the samples from the gas phase for 20 minutes. At this temperature, the samples have an open porosity of 45% of the theoretical density. Titanium (diisopropoxide) BiS (pentanedionate) (TDP) serves as the TiC precursor. The atmosphere is loaded with TDP using an argon flow of 1 l / min which is passed through a TDP receiver preheated to 100 ° C. The gas stream loaded with TDP is fed through ceramic microtubes directly into the microwave-transparent insulation box. In this first coating stage, in which the temperature is kept at 850 ° C., the inner surfaces accessible through the open porosity are only partially coated in the zones near the edge, while the edge zone is completely coated. After the holding time has ended, the green body is heated to the sintering temperature of 1400 ° C. in 30 minutes by increasing the microwave power. The sintering temperature is held for 15 minutes, after which the fully compacted sintered bodies (indexable inserts) are cooled to 850 ° C. and coated again with TiC at this temperature for 20 minutes under the conditions described above.

In another embodiment, six turns inserts of the same composition as described above coated in microwave plasma and sintered. The difference to the above-described method, after reaching 850 ° C. in the warm-up phase began with the introduction of the Ar-TDP mixture NEN and at the same time the pressure lowered so far that within the Isolation box at the given microwave field strength plasma bed conditions can be achieved. The set pressure is between 5 kPa and 30 kPa in the set microwave plasma  Coating carried out for 20 minutes and then the printing again increased to 100 kPa to the indexable inserts as in first embodiment described in the microwave field sinter. In the cooling phase, the pressure is again at 850 ° C while introducing the Ar-TDP mixture until the Plasma conditions lowered to a closed in 20 minutes Apply TiC layer.

In a third exemplary embodiment, the procedure was as for the first two variants described, in addition, one or more further layers are applied to the first TiC layer by changing the gas atmosphere or the precursor, namely as a second layer TiCN or TiN or the layer sequence TiCN and TiN. As an alternative to this, a carbide and / or nitride of Zr and ZrO ₂ , Al ₂ O ₃ or combinations thereof have been deposited as the second layer.

In a further exemplary embodiment, Al ₂ O ₃ green bodies were debinded in a first partial step in a 2.45 GHz multi-mode applicator under normal pressure at a low MW output of 300 W for about 30 minutes. For thermal insulation, the green compacts were arranged in an insulating box made of MW-transparent Al ₂ O ₃ fiber plates. After the debinding, the green bodies were heated to 800 ° C. At this temperature, a ZrO ₂ precursor is deposited on the samples for 30 min from the gas phase. Zirconium tetrapropylate (ZTP) serves as a precursor. The atmosphere is loaded with ZTP with the aid of an argon flow of 1 l / min, which is passed through a ZTP receiver preheated to about 200 ° C. The gas stream loaded with ZTP is fed through ceramic tubes directly into the MW-transparent insulation box. After coating, the green bodies are heated to the sintering temperature of 1600 ° C in 50 min by increasing the MW output. After a holding time of 30 minutes, the compressed Al ₂ O ₃ bodies are cooled.

In the arrangement described above, the Al ₂ O ₃ green bodies were initially debinded and heated to a sintering temperature of 1400 ° C. in 90 minutes. After a holding time of 20 minutes, the bodies which have not yet been completely compressed are cooled to 800 ° C. and coated with ZrO ₂ in the manner described above for 30 minutes. After this coating, which is limited to the area near the surface, the samples are heated to 1600 ° C. and, after a holding time of 30 minutes, cooled back to room temperature.

Claims (14)

1. A process for the production of coated cermet, hard metal or ceramic substrate bodies, in which a green compact is pre-pressed from a starting powder mixture, waxed and then sintered in a microwave field and coated with a coating of one or more layers, characterized in that after waxing of the green compact with still open porosity at temperatures between 600 ° C and 1100 ° C, preferably between 800 ° C and 1100 ° C, the green compact is charged with the reaction gases and / or sublimable solids necessary for the coating, then the temperature the green compact is further increased and this is completely compressed by sintering and then one or more layers of hard materials, ceramic, diamond-like layers, hexagonal boron nitride and / or amorphous carbon are applied. 2. The method according to claim 1, characterized in that the green body only then with reaction gases and / or subli miable solids is applied when the volume proportion of open pores in the total volume of the substrate body <10%, preferably 40 to 60% of theoretical Density (for hard metals) or <10%, preferably 35 to 70% or 50 to 60% (for ceramics) or <10% preferably 35 to 60% or 40 to 60% (for cermets) is. 3. The method according to claim 1 or 2, characterized in that with the start of the exposure to reaction gases and / or sublimable solids the temperature above kept constant for up to one hour or the heating rate up to a maximum of 200 ° C / h Reaching at least 1000 to 1100 ° C is slowed down.   4. The method according to any one of claims 1 to 3, characterized characterized that after dewaxing the green body at still open porosity during the further heating of the Grünlings above a temperature between 600 ° C and 1100 ° C, preferably between 800 ° C and 1100 ° C, the Green compact with the reaction necessary for the coating gases and / or sublimable solids then the temperature of the green body is further increased and this is completely compressed by sintering and then one or more layers of hard materials, Ceramics, diamond-like layers, hexagonal boron nitride and / or amorphous carbon are applied. 5. The method according to claim 1 or 2, characterized in that the green compact, especially the ceramic green compact, first pre-compressed at a higher temperature, then to a temperature between 600 C to 1100 ° C, preferably between 800 ° C and 1100 ° C cooled and then with the reaction necessary for the coating gases and / or sublimable solids is increased before the temperature of the green body and this is completely compressed by sintering and finally one or more layers of hard materials, Ceramics, diamond-like layers, hexagonal boron nitride and / or amorphous carbon are applied. 6. The method according to any one of claims 1 to 5, characterized characterized in that the other layers of hard fabrics, ceramics, diamond, hexagonal boron nitride or amorphous carbon immediately in the cooling phase can be applied using CVD or PCVD.   7. The method according to any one of claims 1 to 6, characterized characterized in that by targeted adjustment of a (Partial) pressure and temperature selection the pores near the edge of the substrate body with from the reaction gases and / or sublimable solids formed be, in the substrate body from the outside in to to a maximum penetration depth of 200 µm inwards decreasing gradient of these substances arises. 8. The method according to any one of claims 1 to 7, characterized characterized in that a microwave power between 10 W to 100 kW is set. 9. The method according to any one of claims 1 to 8, characterized characterized in that the set pressure from reaction gases and carrier gases after reaching the temperature of at least 600 ° C, preferably 800 ° C, between 0.1 kPa and 100 kPa. 10. The method according to any one of claims 1 to 9, characterized characterized in that the reaction gases are metal holognides, Methane, nitrogen, gases with C-N groups (cyanides), ins special acetonitrile, alcoholates, β-diketonates, carbonates or molecular precursors, the elements to the desired Deliver reaction separation or pore filling, esp special organometallic compounds can be used. 11. The method according to any one of claims 1 to 10, characterized in that on the substrate body carbides, nitrides or carbonitrides of the metals of the IVa to VIa group of the periodic table, Al ₂ O ₃ , ZrO ₂ , carbon as a diamond-like layer, amorphous carbon and / or deposit hexagonal boron nitride. 12. The method according to any one of claims 1 to 11, characterized in that on the substrate body made of Al ₂ O _3, a layer with infiltrated ZrO ₂ and / or one or more other layers, in particular TiC who deposited. 13. The method according to any one of claims 1 to 12, characterized characterized in that during the heating or holding phase between 600 ° C and 1100 ° C only a thin layer first Layer of maximum 1 µm applied, this thin layer coated substrate body then sintered and finished then in the cooling phase the layer application of the thin layer with the same layer material to the desired thickness of this single or first layer is continued. 14. Composite body consisting of a hard metal, cermet or Ceramic substrate body and at least one layer from a hard material, a ceramic material, a diamond-like union layer, amorphous carbon and / or hexagonal Boron nitride, characterized in that in the to the Coating adjacent zone of the substrate body with inward decreasing gradient in the substrate body substances the same type as the first layer preferably up to a maximum penetration depth of 200 µm and / or that the interface between the substrate body roughness on the surface and the first layer shows that the surface roughness of a part ver sealed green compact with an open porosity at 600 ° C up to 800 ° C before sintering.