Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-06-03
2001-06-19
Turner, Archene (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C264S603000, C264S610000, C264S667000, C264S669000, C264S674000, C427S532000, C427S553000, C427S561000, C427S585000, C427S598000, C427S249300, C427S255120, C427S255290, C427S255360, C427S307000, C427S309000, C427S314000, C427S331000, C427S337000, C427S419100, C427S419300, C427S419700, C427S419800, C428S304400, C428S306600, C428S307300, C428S310500, C428S312800, C428S312800, C428S319100, C428S408000, C428S457000, C428S698000, C428S704000
Reexamination Certificate
active
06248434
ABSTRACT:
The invention relates to a method for the production of a coated cermet, hard metal or ceramic substrate body, whereby from an initial powder mixture a green compact is precompressed, dewaxed and subsequently sintered in a microwave field and coated with a coating of hard materials, respectively with a coating for protection against corrosion and wear, consisting of one or several layers.
Further the invention relates to a composite body consisting of a substrate body of the mentioned kind and at least one layer of a hard material.
Composite bodies of the mentioned kind are used especially as cutting plates in machining operations, or as material capable to resist high temperatures. According to the state of the art, as a rule the respective composite bodies are produced through sintering of pressed bodies, which consist of the corresponding mixtures of hard materials and metal powders (binders). The sintering takes place in ovens, which for instance are equipped with graphite heating elements, whereby the heating of the samples is done indirectly by means of the radiation emitted by the heating elements, as well as through convection, respectively heat conductivity. The drawback of this process technology consists in that the selection of the oven atmosphere is considerably limited by the chemical properties of the heating elements. Furthermore the heating of hard metals, cermets or ceramics takes place from the outside in, and is substantially controlled by the heat conductivity and the emission capability of the samples. Depending on the heat conductivity and the emission capability of the samples, the variation range of the heating and cooling rates are strongly limited, which is the reason why expensive steps, such as a high expenses for the apparatus and the process technology, have to be taken in order to satisfactorily sinter ultra-fine hard metals.
In order to eliminate this drawback, the WO 96/33830 proposes to sinter precompressed green compacts of cermet or a hard metal in a microwave field. The precompressed green compact can thereby be irradiated with microwaves in a continuous or pulsed manner, already during heating, whereby during heating plastifiers such as wax, are eliminated.
Optionally the finished sintered body can also be subsequently coated with one or several layers of hard material by means of PVD, CVD and/or a plasma-enhanced CVD process.
Suitable microwave sintering ovens and sintering processes by means of microwave radiation are described for instance in DE 195 15 342.
Besides the selection of the materials for the substrate coating, which include carbides, nitrides and/or carbonitrides of elements of the Groups IV to VI, diamond-like materials, ceramics such as Al
2
O
3
and/or ZrO
2
, as well as boron nitride, the adhesion of the coating to the sintered body as a substrate body is of decisive importance.
It is the object of the present invention to indicate a method, as well as a coated substrate body of the kind mentioned in the introduction, wherein the adhesion of the sole or first layer to the substrate body can be controlledly improved. The method has to be able to be carried out without great technical effort, to be easily handled and to conserve energy.
This object is achieved due to the process defined in claim
1
, which according to the invention is characterized in that after the dewaxing of the green compact, while the pores are still open, at temperatures between 600° C. and 1100° C., preferably between 800° C. and 1100° C., the green compact is treated with the reaction gases necessary for the coating with hard materials and/or sublimable solid substances, then the temperature of the green compact is further increased and the latter is completely densified through sintering, after which finally one or more layers of hard material, ceramic, diamond-like layers, boron nitride or the like are applied. The basic concept of the invention consists in that when the outer pores are not yet completely closed, the surface of the substrate body is still relatively rough. If the CVI (chemical vapor infiltration), CVD or the PCVD coating is started in this phase, the coating material can partially fill out the existing open pores, so that during the finishing sinter process an intimate bond between the coating material and the substrate body results, which in addition allows for a gradient transition from the material of the substrate body to the material of the coating. The desired first or sole layer does not have to be applied up to the desired thickness during the heating phase, it is enough to superficially wet the surface of the substrate body with a thin layer of the respective coating material. The difference between the conventional sintering in an oven heated by heating elements, wherein the sintered bodies are heated from the outside in, and the invention is that the microwave radiation penetrates the substrate body already at low temperatures. Since substrate bodies, respectively a charge thereof placed in a microwave field are hotter than the cavity, the substrate bodies, respectively a charge thereof, are, respectively is hotter inside than on the outside; correspondingly the sintering process takes place form the inside out. The layer or layers applied during the heating phase do not influence or disturb the sintering process, in case the composition of the gas phase is changed. Generally the sintering and coating can also be shortened to the extent that already during the heating phase a first coating was deposited on the substrate body, on which then after the finished sintering optionally further layers can be applied after a previous cooling at the usual CVD, plasma-enhanced CVD temperature “in one heat”.
Further developments of the process of the invention are described in the dependent claims.
In the case of hard metals the introduction of the gases required for the reactive deposition of the mentioned materials starts when the volume proportion of the open pores with respect to the total volume of the hard metal substrate body amounts to >10%, preferably 35 to 60%.
The same applies to ceramic or cermets with regard to the open pores, preferably they should amount areawise in ceramics to 35 to 70%, respectively 50 to 60% and in cermets 35 to 60%, preferably 40 to 60%.
Depending on the desired penetration depth of the infiltration, it can be especially advantageous in ceramics to first subject the green compacts to a preliminary densification at high temperatures, before the green compact, after a cooling period between 600° C. and 1100° C., is treated with the reaction gases and/or sublimable solid substances required for the hard material coating. As an alternative, particularly in the case of hard metals and cermets, the mentioned treatment can take place during the heating of the green compact after dewaxing (binder removal).
Preferably already at the beginning of the treatment with reaction gases and/or sublimable solid materials with the use of carrier gas (argon, etc), the temperature is kept constant over a period of time up to an hour, or the heating speed is slowed down to maximum 200° C./h until it reaches at least 1000 to 1100° C. This procedure insures that there is sufficient time in a temperature interval suitable for CVI, respectively for CVD deposition for the deposition of a first thin layer. As already mentioned, the further layers of hard material, ceramic, diamond, boron nitride or similar substances are applied directly by CVD or PCVD in the cooling phase.
For the final CVD/PCVD coating an essential advantage of microwave sintering comes to bear, namely the possibility to keep a part of the open porosity up to high densities. This insures a good anchoring of the layers applied by CVD-PCVD during the cooling phase, at a porosity of <10%. The preliminary treatment of the surfaces, as required by conventional CVD/PCVD is here eliminated.
Furthermore due to a controlled setting of the (partial) pressure and selection of the temperature, the process of the invention makes it possible to fill the margi
Dreyer Klaus
Gerdes Thorsten
Rodiger Klaus
Westphal Hartmut
Willert-Porada Monika
Dubno Herbert
Turner Archene
Widia GmbH
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