SIC-BOUND HARD MATERIAL PARTICLES, POROUS COMPONENT FORMED WITH SIC-BOUND DIAMOND PARTICLES, METHOD OF PRODUCING SAME AND USE THEREOF

Abstract

The invention relates to SiC-bound diamond hard material particles, a porous component formed with SiC-bound diamond particles, methods for producing same and the use thereof. Diamond hard material particles and components have a composition of 30 vol. % to 65 vol. % diamond, 70 vol % to 35 vol. % SiC and 0 to 30 vol. % Si, and a component has a porosity in the range of 10% to 40%

Claims

1. SiC-bound hard diamond material particles having a composition of 30%-65% by volume of diamond, 70%-35% by volume of SiC and 0% to 30% by volume of Si, and diamond particles in individual hard material particles are cohesively bonded to one another by the SiC and Si formed in a thermal treatment and have a particle size in the range of 50 m-5000 m.

2. The SiC-bound hard diamond material particles as claimed in claim 1, wherein a median particle size d.sub.50 of diamond particles in the hard material particles in the range of 5 m to 500 m is maintained.

3. The SiC-bound hard diamond material particles as claimed in claim 1, wherein not more than 90% of the surface area of the diamond particles is cohesively bonded to SiC.

4. A process for producing SiC-bound hard diamond material particles as claimed in claim 1, comprising the steps of admixing diamond particles with an organic binder and shaped into granules by drying and granulation process; subjecting the granules to a thermal treatment in an oxygen-free atmosphere, in which organic constituents are pyrolyzed and carbon is formed in situ from the organic binder in the course of pyrolysis and deposited in vitreous form on surfaces of the diamond particles; performing a silicization during the thermal treatment or in a subsequent second thermal treatment with admixed pulverulent silicon and particulate spacers; forming silicon carbide at the same time by chemical reaction with the carbon deposited on surfaces of diamond particles and/or with the diamond particles, to form hard material particles, wherein the diamond particles in the individual hard material particles are cohesively bonded to the SiC formed by reaction in the course of thermal treatment and the silicon so that the shaped granules are predominantly or fully separated or kept at a distance from one another at their surface by means of the added silicon and/or the spacers.

5. The process as claimed in claim 4, wherein the spacers used are chemical elements or compounds that are not easily wetted by Si, do not form any alloy with Si and/or do not react with Si, in order to minimize any firm bonding of the granules to one another, where these chemical elements or compounds are selected from hexagonal BN, Si.sub.3N.sub.4, AlN, Al.sub.2O.sub.3, SiO.sub.2, ZrO.sub.2 and a nitride, carbide of the transition metals, of groups 4 and 5 of the Periodic Table.

6. The process as claimed in claim 4, wherein the organic binder and the amount thereof is chosen so that the organic binder used is a carbon source with a proportion between 1.5% and 20% by mass relative to the total mass of diamond particles used.

7. The process as claimed in claim 4, wherein the diamond particles are used in at least two different particle size fractions, one coarse and one fine particle size fraction.

8. The process as claimed in claim 4, wherein the pulverulent silicon has a median particle size d.sub.50 in the range of 5 m-1000 m, and in this range with a volume of 10%-200%, of the content of the diamond particles is added to the granulated particles prior to the silicization.

9. The process as claimed in claim 4, wherein the hard material particles are formed with at least one further phase which is selected from B.sub.4C, TiC and TiB.sub.2.

10. The process as claimed in claim 4, wherein the diamond particles having h an average particle size of 10 m-50 m.

11. The process as claimed in claim 4, wherein the hard material particles are brought into a defined spherical, cylindrical, prismatic, or pyramidal shape, by extrusion or casting methods.

12. The process as claimed in claim 4, wherein the incorporation of the diamond particles and/or possible partial breakout of the diamond particles into/out of a matrix formed with the SiC and Si formed by reaction is/are influenced during mechanical/tribological stress by the maximum temperature in the silicization and the purity of the diamond particles used.

13. The process as claimed in claim 4, wherein the hard material particles that are hollow on the inside are produced by applying a suspension including not only diamond particles but also an organic binder to silicon particles having a particle size in the range of 50 m-150 m or by mixing in particles of a pulverulent organic substance that breaks down in the course of thermal treatment, and subsequent thermal treatment in which a pyrolysis, the mixing with Si powder and the spacer and reactive formation of SiC are effected; wherein the proportion of the added pulverulent silicon volume of 10%-200% by volume, of the content of diamond particles is added.

14. A porous component composed of SiC-bound diamond particles is formed, and the porous component has a porosity in the range of 10% to 40%, has an average pore size between 10 m-100 m, and consists of 30%-65% by volume of diamond, 70%-35% by volume of SiC and 0% to 30% by volume of Si, and the diamond particles present have an average particle size in the range of 5 m to 500 m.

15. The porous component as claimed in claim 14, has at least one further phase with a spacer function that undergoes primary wear in the event of tribological or abrasive stress and hence forms pores in the material, wherein the further phase(s) is/are formed by non-diamond carbon, Si.sub.3N.sub.4, which may also be partly sintered, Al.sub.2O.sub.3 or transition alumina, impervious or porous glass beads, high-melting silicide or boride, TiSi.sub.2, MoSi.sub.2, WSi.sub.2, TiB.sub.2, W.sub.2B.sub.5, WB.sub.2 or ZrO.sub.2 with a wide variety of different dopants, at least one other high-melting oxide or silicate, MgO or talc, at least one transition metal carbide, oxycarbide, nitride or boride.

16. A process for producing a porous component as claimed in claim 14, mixing diamond particles with SiC, an organic binder and particles of an organic substance, with pulverulent plastic as a pore former, polystyrene, polymethylmethacrylate, polyurethane, polyethylene or polypropylene or starch, having a median particle size d.sub.50 in the range of 30 m to 100 m prior to the thermal treatment and shaped via a shaping process, then subjecting to a thermal treatment in an oxygen-free atmosphere in which the organic constituents are pyrolyzed and carbon formed in situ from the organic binder in the course of pyrolysis is deposited in vitreous form on surfaces of the diamond particles and a silicization is conducted during this thermal treatment or in a subsequent second thermal treatment with externally supplied silicon and forming silicon carbide at the same time by chemical reaction with the carbon deposited on surfaces of the diamond particles and the diamond, so the porous component has a composition of 30%-65% by volume of diamond, 70%-35% by volume of SiC and 0% to 30% by volume of Si and a porosity in the range of 10%-40%.

17. The process as claimed in claim 16, wherein the organic binder and its amount is chosen such that the organic binder is used as carbon source with a proportion between 1.5% to 20% by mass relative to the total mass of diamond particles used.

18. The process as claimed in claim 16, wherein the diamond particles are used in at least two different particle size fractions, one coarse and one fine.

19. The process as claimed in claim 16, wherein particles of an organic substance, are added with a proportion in the range of 20% to 40% by volume.

20. The process as claimed in claim 16, wherein a further phase(s) comprising non-diamond carbon, B.sub.4C, TiC and TiB.sub.2, Si.sub.3N.sub.4, which may also be partly sintered, Al.sub.2O.sub.3 or transition alumina, impervious or porous glass beads, high-melting silicide or boride, TiSi.sub.2, MoSi.sub.2, WSi.sub.2, TiB.sub.2, W.sub.2B.sub.5, WB.sub.2 or ZrO.sub.2 with a wide variety of different dopants, at least one other high-melting oxide or silicate, MgO or talc, at least one transition metal carbide, oxycarbide, nitride or boride is mixed in homogeneously prior to the shaping.

21. The process as claimed in claim 16, wherein the incorporation of the diamond particles and/or possible partial breakout of the diamond particles into/out of a matrix formed with the SiC and Si formed by reaction is/are influenced during mechanical/tribological stress by the maximum temperature in the silicization and the purity of the diamond particles used.

22. The process as claimed in claim 16, wherein silicon powder having a median particle size d.sub.50 between 20 m-100 m is mixed into the starting material prior to the shaping, and the particle size thereof is maintained during the shaping and hence pores are formed during the silicization.

23. The process of using SiC-bound hard material particles as claimed in claim 1 as abrasive grains, for the production of abrasive media, components reinforced with hard material particles for wear protection and antiwear applications, as abrasive medium, mounted point, or for protection and antiwear applications.

Description

DESCRIPTION OF THE DRAWINGS

[0067] The invention is to be elucidated in detail hereinafter by examples.

[0068] The figures show:

[0069] FIG. 1 in schematic form, means of production of SiC-bound hard diamond material particles, and

[0070] FIG. 2 in schematic form, means of production of a component.

DETAILED DESCRIPTION OF THE INVENTION

[0071] The left-hand drawing of FIG. 1 shows the granules consisting of diamond particles and a pyrolyzed binder (thick black outline of the diamonds). They are separated by the Si and the spacers S. This is the state prior to the silicization and reactive formation of SiC.

[0072] The silicization forms an SiC matrix incorporating the diamond particles from the pulverulent Si and vitreous carbon that has been formed in a pyrolysis at surfaces of diamond particles and partially from diamond. Even after silicization, they are separated by the spacers and therefore easily individualized.

[0073] The left-hand drawing of FIG. 2 shows a shaped body composed of a mixture consisting of diamond particles having a vitreous carbon layer at their surface by means of pyrolyzed binder. Additionally present are particles P of polyurethane as pore former.

[0074] The right-hand drawing of FIG. 2 shows the state after silicization. The diamond particles are embedded in a matrix formed with SiC formed by reaction. The matrix includes islands of Si and pores Po. Si and pores Po effectively form intended fracture sites, such that, under mechanical and/or tribological stress, diamond particles can also break out of the component material together with SiC residues and hence can achieve adaptation to abrasive or tribological requirements during use. At the same time, the pores can serve as a reservoir for abrasives or coolants or additional abrasive media.

Example 1

[0075] For the production, diamond powder having a median particle size d.sub.50 of 50 m is granulated together with an organic binder. The diamond powder is mixed here with the organic binder in aqueous form or in a solvent and agglomerated by means of a granulation technique (e.g. spray granulation, fluidized bed granulation, buildup granulation, etc.). Granular material thus obtained has an average particle size of 500 m. The granules produced are subsequently pyrolyzed under Ar atmosphere at 800 C., with the conversion of the organic constituents of the binder to a vitreous carbon. This vitreous carbon functions as binder phase between the granular diamond in the agglomerates or a bed thereof, and reacts further during the reactive silicon infiltration to give silicon carbide. The silicization is conducted under vacuum conditions at 1550 C. as bulk material. For this purpose, the carbon-coated diamond granules produced are mixed with a mixture of coarse silicon powder having a median particle size d.sub.50 of about 200 m and a further fine fraction of pulverulent silicon having a median particle size d.sub.50 of 10 m. The fine fraction of the silicon powder acts here primarily as spacer, in order to prevent bridge formation between the individual granules formed with crystallized silicon and SiC. As a result, it is easily possible to individualize the SiC-bound hard diamond material particles in a jaw crusher and then to classify them once again by sieving. In this way, it is possible to produce a narrow grain size band, for example with particle sizes between 450 m and 550 m.

[0076] The SiC-bound hard diamond material particles consist of diamond and silicon carbide formed by reaction, and residual silicon that has not reacted to give silicon carbide.

Example 2

[0077] For production of hollow granular bead material, a buildup granulation is to be utilized. For this purpose, diamond powder having a median particle size d.sub.50 of 50 m is dispersed with an organic binder in a suspension. Subsequently, a two-component agglomerate is obtained by means of buildup granulation, by spraying the diamond particle-containing suspension during the granulation onto coarse silicon particles having a median particle size d.sub.50 of 100 m during the granulation (fluidized bed granulation).

[0078] The granules obtained had a median particle size d.sub.50 of 500 m. The granules thus produced are subsequently pyrolyzed under a nonoxidizing atmosphere at 800 C., with the conversion of the organic constituents of the binder to a vitreous carbon. This vitreous carbon functions as binder phase between the diamond particles at the surfaces of which a coating of this vitreous carbon has formed, and this carbon reacts further during the reactive silicon infiltration to give silicon carbide.

[0079] During the final heat treatment under vacuum conditions at 1550 C., the granular material thus obtained is sylicized from the inside outward. The silicization can be assisted by adding a further fine fraction of pulverulent silicon having an average particle size of 10 m. The fine fraction of the silicon powder acts primarily as a spacer in order to prevent bridge formation between granules consisting of diamond, crystallized silicon and SiC.

[0080] Owing to the technique of buildup granulation used, the silicization from the inside outward results in formation of hollow granular material. The granules produced consist of diamond and silicon carbide formed by reaction, and possibly residual unreacted silicon. They may be classified and used after silicization.

[0081] Residual adhering unreacted Si could be dissolved in 20% NaOH at 60 C. within 1 h while stirring.

Example 3

[0082] Porous abrasive diamond media are produced on the basis of a diamond-containing suspension. In this suspension, a bimodal diamond particle size fraction consisting of median particle sizes d.sub.50 of 50 m and 5 m is used. In addition, a further solid-state component present in the suspension is a silicon powder having a median particle size d.sub.50 of 100 m. The spacer used is a polystyrene powder having a median particle size d.sub.50 of 200 m. The solids ratios of diamond to silicon to polystyrene are 2:2:1 by volume.

[0083] The binder used in the aqueous suspension is an aqueous polyvinylacetate dispersion that crosslinks on drying.

[0084] The suspension is processed and shaped by slip casting. During the final heat treatment, the diamond-containing shaped article is pyrolyzed under a nonoxidizing atmosphere at 800 C. and then reactively bound under vacuum conditions at 1550 C. In the course of pyrolysis, the organic binder is converted to a vitreous carbon with outgassing of volatile constituents. This vitreous carbon functions as binder phase between the diamond particles in the agglomerates and reacts further during the subsequently conducted reactive silicon infiltration to give silicon carbide. The polystyrene spaces are split almost completely into volatile constituents, such that these take the form of pores in an abrasive medium formed with the granular material. In the reactive binding, the silicon present in the material melts and reacts with the carbon present that has been formed from the pyrolyzed organic binder, and is deposited on diamond particle surfaces. This forms a porous diamond-SiCSi-containing material composite that can be used as abrasive medium.

Example 4

[0085] Porous abrasive diamond media are produced here on the basis of a diamond-containing suspension. A bimodal diamond particle size fraction having diamond particles having a median particle size d.sub.50 of 50 m and 5 m is used therein. Additionally present in the suspension as a second solid-state component is a silicon powder having a median particle size d.sub.50 of 100 m. The mass ratios of the diamond and silicon solids are 2:1.

[0086] The organic binder used in the aqueous suspension is a polyvinylacetate dispersion that crosslinks on drying. Also added to the suspension is a surfactant as foaming agent.

[0087] The suspension is foamed by means of a high-speed stir and then cast in a nonabsorptive mold and freeze-dried. The demolding is followed by the heat treatment steps. This involves pyrolyzing the diamond-containing shaped article under nonoxidizing atmosphere at 800 C., followed by reactive binding under vacuum conditions at 1550 C. The pyrolysis converts the organic constituents of the binder, with outgassing of volatile constituents, to a vitreous carbon with which surfaces of the diamond particles are coated. The reactive binding during the heat treatment melts the silicon present, and it reacts with the carbon present in the pyrolyzed binder and the diamond particle surfaces. This forms a porous diamond-SiCSi-containing material composite.

Example 5

[0088] Porous abrasive diamond media are produced on the basis of a diamond-containing granular material. The granular material is agglomerated by means of a customary granulation technique (e.g. spray granulation, fluidized bed granulation, buildup granulation, etc.) and has an average size of 200 m-1000 m. The granules produced include a diamond particle size fraction having a median particle size d.sub.50 of 50 m, a silicon particle size fraction having a median particle size d.sub.50 of 50 m, and a particle size fraction of a polystyrene powder having a median particle size d.sub.50 of 100 m. The granular material is bound by means of a sugar-based organic binder in aqueous suspension. The solids ratios of diamond to silicon to polystyrene are 1:1:1 by volume.

[0089] The granules produced are subsequently shaped to a shaped body by a pressing operation (for example by isostatic pressing or uniaxial pressing). This is followed by pyrolysis under nonoxidative atmosphere at 800 C. This converts organic constituents of the binder, with outgassing of volatile constituents, to a vitreous carbon with which surfaces of diamond particles are coated. The polystyrene particles as spacers are split almost completely into volatile constituents, such that these are present as pores in the finished product. In the subsequent reactive binding, the silicon present in the material melts and reacts with the carbon present that has been obtained from the pyrolyzed binder, and diamond particle surfaces are coated with silicon carbide. This forms a porous diamond-SiCSi-containing material composite.