SiC-bonded diamond hard material particles, porous component which is formed with SiC-bonded diamond particles, processes for their production and their use

The invention relates to SiC-bonded diamond hard material particles, porous construction part, which is formed with SiC-bonded diamond particles, methods for de Ren production and their use.

Usually a wide variety of hard material particles are used alone or in the form of granules or in a material matrix, for a wide variety of applications, in particular for machining in the form of grinding. Among other things, Diamantpar particles are used as hard material particles, which are known to have a very high hardness. However, diamond alone can have disadvantages in various applications, which can be disadvantageous, for example, in the case of thermal shock loads or the bonding behavior in a matrix material. In addition, diamond particles can also chemically under certain environmental conditions

decompose or dissolve from a matrix or a composite material.

It is therefore the object of the invention to provide granules or components which have improved properties compared to pure granules formed from pure diamond particles, which can be adapted to specific areas of application.

According to the invention, this object is achieved with hard material particles that have the features of claim 1, a component that has the features of claim 14. Claim 4 defines a manufacturing method for hard material particles and claim 16 for components. Claim 23 relates to uses of hard material particles and components. Advantageous refinements and developments can be implemented with features identified in the subordinate claims.

With the invention, super hard abrasive materials made of SiC bonded diamond can be made available.

The hard material particles according to the invention are formed from SiC-bonded diamond and can be obtained in particle sizes between 20 μm and 5 mm. The hard material particles are formed with 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 vol .-% to 30 vol .-% Si. 40 vol .-% -60 vol .-% diamond, 60 vol .-% -40 vol .-% SiC and 2 vol .-% to 20 vol .-% Si are preferred.

The particle size distribution of the diamond particles can be multimodal in order to increase the packing density of interconnected diamond particles in hard material particles.

A fine fraction is advantageous which is 0.1 to 0.3 times the size of the diameter of a coarse diamond particle fraction and has a proportion of 5% by volume - 50% by volume of the coarse particle size fraction. Advantageously, 5% by volume to 30% by volume of the coarse particle size fraction should be used in the case of a multimodal particle size fraction.

In this case, diamond particles on surface areas in individual hard material are particles with the SiC and Si formed during the thermal treatment

firmly connected to each other.

In this case, the entire surface areas of diamond particles with the reactively formed SiC do not have to and should advantageously not be materially bonded to one another. As a result, predetermined breaking points can be formed at which a break can occur if the mechanical load is sufficiently high. For example, during grinding, diamond particles and / or areas of SiC can break out of the material bond, which can have an advantageous effect during grinding.

The mean particle size d 50 of diamond particles in the material should be kept in the range from 5 pm to 500 pm, preferably from 5 pm to 100 pm. The particle size distribution of the diamond particles in a hard material particle can be multimodal in order to increase the packing density. So at least two different particle size fractions can be used.

A fine and a coarser particle size fraction of diamond particles is particularly advantageous; the finer particle size fraction should be 0.1 to 0.3 times the diameter of the coarse particle size fraction and with a proportion of 5 vol .-% - 50 vol .-% of the coarse

Particle size fraction be contained in a hard material particle. Very particularly advantageously 5% by volume to 30% by volume of the coarse particle size fraction are adhered to.

In the production of the granulate, the procedure is that a suspension containing diamond particles and an organic binder or diamond particles with a suspension or dispersion containing an organic binder are used. During the granulation and drying process, the diamond grains are partially or completely coated. As a result, these are held together as granules.

In the case of thermal treatment in an oxygen-free atmosphere, pyrolysis takes place, in which components of the organic binder are thermally decomposed and in the pyrolysis carbon formed in situ from the organic binder is deposited in vitreous form on the surfaces of diamond particles.

During this thermal treatment or during a subsequent second thermal treatment with added powdered silicon, siliconization is carried out. The powdered silicon can be added before the siliconization.

With the carbon deposited on the surfaces of diamond particles, silicon carbide is formed by chemical reaction, so that hard material particles containing 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 to 30 vol Vol .-% Si are formed can be obtained.

The diamond granules obtained should be mixed with powdered silicon and or possibly additionally with particulate spacers in such a way that the granules are not or only minimally destroyed and they separate the diamond particles at least in some areas. This simplifies or enables the SiC-bonded diamond hard material particles thus obtained to be separated without intensive grinding or the like, which would lead to severe wear on aggregates.

The organic binder and / or its amount with which the diamond particles are coated or which is contained in the suspension should be selected so that the organic binder as a carbon source with a proportion between 1.5% by mass to 20% by mass in Relation to the total mass of a set diamond particles is used. The SiC used to bind the diamond particles is essentially obtained from the chemical reaction of the carbon released during pyrolysis with silicon. This improves the properties of the hard material particles obtained in this way, as follows:

Increased thermal stability,

- Specifically adjustable fracture behavior of the hard material particles (if diamonds that contain larger residues of catalyst (Fe, Ni) are used, these are weakened internally and the siliconizing temperature can vary between 1425 ° C and 1650 ° C The breaking of the diamond particles can be controlled under application conditions (higher temperatures lead to breaking

under less load)

The integration of the diamond particles in the SiC matrix can be influenced by lengthening the holding time during siliconization at temperatures> 1525 ° C. Longer times at higher temperatures lead to faster breakout of the diamond particles under severe tribological stress. During the siliconization at 1650 ° C and a holding time of 20 min, interfaces of non-diamond carbon form with a thickness of> 50 nm. This means that the diamond particles are released when the SiC bond is partially worn. With siliconization <= 1600 ° C and siliconization times of <60 min, the diamond particles are firmly integrated so that the diamond particles do not fall out, even if the hard SiC bond is partially worn. Integral Knoop hardnesses of>

The associated reduced strength of the connection between the diamond particles and the SiC as well as the Si sometimes has a positive effect when the hard material particles are used for grinding.

In addition to the bond with the reactively formed SiC, the diamond particles in hard material particles can also be bonded with Si that has not been reactively converted. This free Si is, however, typically separated from the diamond by a nm to pm thick SiC layer.

A maximum of 90%, particularly advantageously a maximum of 80%, of the surfaces of the diamond particles should advantageously be bonded to SiC and Si in a materially bonded manner. For this purpose, the amount and type of organic binder and silicon added can be selected accordingly. The organic binder forms the essential carbon source for the reactive in situ formation of the SiC. In addition, there is a superficial reaction of the diamond particles with the Si during the infiltration to form SiC. This ensures the solid chemical bond between the diamond particles and the SiC. The carbon from the binder reduces the proportion of reactive diamond, which means that higher diamond proportions can be achieved.

The reaction preferably results in the formation of β-SiC. A SiC (usually the inexpensive a-SiC) that may be mixed into the granulate can also be incorporated into the SiC matrix / network that is formed. However, this reduces the density of the diamond particles, so that there is usually no advantage in mixing them in. For special applications, in particular to reduce the price, a-SiC could be added.

The hard material particles can be produced by means of granulation with minimal proportions of organic binder and solvent content

Plate granulator or, for example, in an Eirich mixer or by means of fluidized bed or spray granulation. It is also possible to compress the granulate and then to crush it. You can use higher

Diamond particle densities can be achieved.

The organic binder, which is pyrolyzed in an inert atmosphere at 400 ° C - 1400 ° C, can lead to a content of non-diamond carbon of 1.5% - 20% by weight, based on the diamond content in the pyrolized state.

The particle size distribution of the individual siliconized hard material particles can be refined by means of classification / comminution, for example by sieving, and adapted to requirements. Before classification, mechanical separation, for example with a jaw crusher, can be carried out.

The organic binder which can be used in the invention can be an organic chemical compound or a mixture selected from polyvinyl alcohol, acetate, polyethylene glycol, a sugar, cellulose, and phenolic resins. The term binder is used here as a collective term for the organic components used, since the bond between the diamond particles in the granulated state is the main function. The organic components can also be used in addition to the actual binder,

Contain dispersants, wetting agents, plasticizers (eg PEG), defoamers.

Hard material particles are infiltrated with silicon. For this purpose, the granules formed with diamond particles and the organic binder can be used before or preferably after the pyrolysis in the thermal treatment with Si powder with an average particle size d 50 in the range of 5 pm-1000 pm, preferably in the range 10 pm-150 pm and with this Area with a volume of 10 vol .-% - 200 vol .-%, preferably 20 vol .-% - 100 vol.% Of the content of diamond particles are added and mixed.

The silicon powder should preferably have a particle size between 5 μm and twice the particle size of the granules of the granules formed with diamond particles and the organic binder in order to ensure sufficient distance between the individual granules. The distances are beneficial for problem-free comminution after siliconization. The silicon content should not exceed twice that which is necessary to carry out the reactive bond. 1.5 times or even only 1.1 times is better.

The infiltration can be carried out during the thermal treatment, in which the pyrolysis is also carried out, but also during a second thermal treatment carried out subsequently. For further thermal treatment, a maximum temperature of 1650 ° C and particularly preferably vacuum conditions should be maintained.

Coarse silicon powder can also be used. In addition, however, a particle size fraction of fine silicon powder in the range from 5 μm to 20 μm with a volume of 10% by volume to 30% by volume of the SiC diamond granulate should then be used. Due to the remaining porous oxide / SiC surface layers of the original Si grains, this finer fraction enables the problem-free separation of the SiC-bonded diamond hard material particles.

To the SiC bonded diamond hard material particles easier after the

To be able to separate siliconization, components can be added as placeholders before siliconization or pyrolysis, which are difficult to wet by Si, do not form an alloy with Si and do not react with Si. Such rule chemical elements or compounds can be used for coating, reindeer each other to minimize a fixed connection (bonding) of the granules. For this purpose, chemical elements or compounds may be preferably selected to be from BN, Si 3 N 4 , AlN, Al 2 0 3 , Si0 2 , Zr0 2 and a nitride, carbide of the transition metals, in particular groups 4 and 5 of the periodic table (in particular of Ti, Zr, Hf, V, Nb).

This method is particularly effective if the Si necessary for reaction bonding has already been added to the granulate and does not have to be fed from the outside to the granulate during the siliconization.

Since SiC or SiC-Si0 2 shells can remain around the silicon particles, the siliconized granulate heaps can easily be crushed and then classified (eg jaw crusher, sieve, air classifier, etc.) when the Si particles have been mixed into the granulate .

The SiC-bonded hard material particles obtained can still be agglomerated after the siliconization. Therefore, they should usually be mechanically crushed and then classified (e.g. jaw crusher, ball mill, sieve,

Air separator, etc.). With the measures described above, this can also be done without great wear and tear on the units.

In addition, excess Si can be partially or completely dissolved out with alkaline solutions (eg 20% ​​NaOH) at room temperature or at elevated temperatures in the range from 60 ° C. to the boiling point. This can also be used to separate the hard material particles.

The hard material particles obtained can be used as abrasives, but they can also be introduced as hard material particles into other matrix materials and thus new types of abrasive bodies / discs bonded with plastic, metal or ceramics can be produced.

The SiC-bonded diamond hard material particles can be processed into grinding wheels with a glass matrix or a metal matrix, for example.

In addition to the advantage of better grinding behavior, the hard materials according to the invention also have the advantage of greater thermal stability compared to pure diamond.

The introduction of the SiC-bonded diamond hard material particles into a matrix material can take place in accordance with typical ceramic technologies. These hard material particles can also be mixed separately with a dried granulate before shaping. They can, however, also be added to the initial composition and then processed further using conventional ceramic shaping technologies such as granulating, pressing, slip casting, extrusion, injection molding, hot casting or using additive manufacturing processes.

Since the SiC-bonded diamond hard material particles essentially consist of diamond and SiC, they have a different fracture behavior than pure diamond granules. As a result, the grinding wheels, which can be formed with a granulate according to the invention, are more effective than those formed with pure diamond under certain conditions.

The fracture behavior of the SiC bonded diamond hard material particles can be adjusted. In addition, different diamond qualities can be used to adjust the fracture behavior of the hard material particles.

The bond between diamond particles and SiC can be adjusted by means of thermal treatment. If diamond particles that contain larger amounts of catalyst (Fe, Ni) are used, these can be weakened internally and, due to the variation in the siliconizing temperature between 1425 ° C and 1650 ° C, the diamonds can break under application conditions controlled (higher temperatures lead to breakage under lower load).

By extending the holding time during siliconization at temperatures> 1550 ° C, the integration of the diamond particles in the SiC matrix can be influenced. Longer times and higher temperatures lead to faster breakout of the diamond particles under severe tribological stress. In the case of siliconization at 1650 ° C. and a holding time of 20 min, interfaces made of non-diamond carbon with a thickness of> 50 nm can form. This means that the diamond particles are released when the SiC bond is partially worn. With siliconization <= 1600 ° C and siliconization times of <60 min, the diamond particles are firmly bound, so that the diamond particles cannot fall out, even if the SiC bond is partially worn. Integral Knoop hardnesses of>

For certain grinding applications, SiC-bonded diamond hard material particles of a defined shape are advantageous. By means of ceramic molding processes, such as extrusion or casting processes or pressing, the particles can be brought into any desired shape before siliconizing, preferably spherical, cylindrical, prismatic, pyramidal, in particular by extrusion or by casting processes.

The hard material particles can also be used as an additive to other materials to increase stiffness, hardness or wear resistance. This can be used, for example, in metals as particle reinforcement or in other materials that are supposed to have a burglar-resistant function (e.g. concrete) or to create extremely durable, rough surfaces, for example to prevent slipping when wet in security-relevant areas.

As a result of the siliconization, an agglomerate formed with diamond particles can be enclosed with SiC. As a result, an abrasive grain has a higher thermal stability or is much more stable when interacting with oxidic or metallic matrices. This improves the installation of the hard material particles in critical matrix materials such as hard metal, Al 2 0 3 , etc ..

Hard material particles that are hollow inside can be applied to silicon particles with a particle size in the range 50 μm - 150 μm by applying a suspension containing diamond particles as well as an organic binder or by using a suspension in which, in addition to diamond particles, organic binder is also used during the thermal treatment decomposing powdery polymer material, preferably polyurethane, and subsequent thermal treatment in which pyrolysis and reactive formation of SiC takes place, are produced. Polystyrene, polymethyl methacrylate, polyethylene or polypropylene or starch can also preferably be added as polymeric material. Polymeric material should have a medium

Particle size d 50 in the range from 30 μm to 100 μm is added before the thermal treatment and pyrolyzed during the thermal treatment.

This form of hard material particles also has advantageous properties when used for grinding processing, since it also reduces the strength of the material connection between diamond particles and in particular the SiC and possibly with the Si. As a result, an improved breakout of diamond particles can be achieved during the grinding process, which has a favorable effect because of the formation of new cutting edges.

The effect is similar to that when using reduced surface areas on which material connections have been formed, as has already been described.

However, grinding wheels as porous components can also be produced directly from SiC bonded diamond. Such components have a porosity in the range 10% to 40%, preferably between 10% and 30%, an average pore size between 10 μm-100 μm, preferably between 20 μm-50 μm. They consist of 30 vol .-% - 65 vol .-% diamond 70 vol .-% - 35 vol .-% SiC and 1 vol .-% to 30 vol .-% Si, preferably 40 vol .-% - 60 Vol .-% diamond, 60 vol .-%

40% by volume SiC and 2% by volume to 20% by volume Si, and the diamond particles contained have an average particle size in the range from 5 μm to 500 μm, preferably in the range from 30 μm to 100 μm, particularly preferred > 50 pm - 200 pm.

A material formed with the SiC bonded diamond particles can contain, for example, 20 vol .-% - 50 vol .-% of at least one soft phase that primarily wears in the event of tribological or abrasive loads and thus creates pores in the material, with an average particle size of 10 pm

- 50 pm, preferably 15 pm - 30 pm or 10 pm - 20 pm be formed by hard material particles. This design is particularly advantageous for grinding wheels made of SiC bonded diamond.

This soft phase (s), which has / have a lower mechanical strength compared to the diamond particles and the SiC, can / can non-diamond carbon, BN, Si 3 N 4 , which can also be sintered, Al 2 0 3 , or transition alumina, dense or porous glass spheres, high-melting silicide or boride (e.g. TiSi 2 , MoSi 2 , WSi 2 , TiB 2 , W 2 B 5 , WB 2 , Zr0 2) with a wide variety of dopings, at least one other high-melting oxide or silicate (e.g. MgO, talc, ...), at least one transition metal carbide or oxicarbide or nitride or boride, in particular from groups 4 and 5 of the periodic table (in particular from Ti, Zr , Hf, V, Nb). A porosity can also be understood as a phase in this sense, as it can lead to the same result in the product.

Preferably, 20% by volume - 30% by volume of this phase (s) (in addition to diamond; SiC and Si) can be contained in a material. .

A component can also be manufactured in such a way that diamond particles with SiC, an organic binder and with particles of an organic substance, preferably powdered plastic, as pore-forming agents, in particular polystyrene, polymethyl methacrylate, polyurethane, polyethylene or polypropylene or starch, preferably with an average particle size d 50mixed in the range from 30 pm to 100 pm before the thermal treatment and shaped via a shaping process. This shaped body is then subjected to a thermal treatment in an oxygen-free atmosphere, in which pyrolysis of the organic components takes place and in the pyrolysis carbon formed in situ from the organic binder is deposited in vitreous form on surfaces of diamond particles. Siliconization is carried out during this thermal treatment or during a subsequent second thermal treatment with silicon, preferably in powder form, which is supplied from the outside. In this case, silicon carbide is formed by chemical reaction with the carbon deposited on the surfaces of diamond particles and the diamond, so that

the component material has a composition of 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 to 30 vol .-% Si and a porosity in the range 10% - 40% having.

Particles of an organic substance, in particular powdered plastic, should be added in a proportion in the range from 20% by volume to 40% by volume.

Silicon powder with a mean particle size d 50 between 20 μm - 100 μm can be added to the starting material for the production of the components before shaping, the particle size of which is retained during shaping and thus pores can be formed during siliconization.

Otherwise, the same parameters and procedures can be selected for the production of components as can also be used for the production of hard material particles, which relates in particular to the features of claims 5 to 7, in some cases from claims 8 to 11 and 13.

In order to produce grinding wheels, the granulate should be subjected to a shaping process, such as pressing, isostatic pressing, extrusion or casting molding, before siliconization, and also before pyrolysis. Then the siliconization takes place, which leads to a three-dimensional binding of the diamond particles in an SiC matrix / framework, as in the hard material particles described above within the particles. The introduction of the pore-forming agents or the soft phase, which primarily wears when subjected to tribological or abrasive loads and thus creates pores in the material, into a matrix material, can be carried out in accordance with typical ceramic technologies. These can also be mixed separately with a dried granulate before pressing.

The granulate formed at least with diamond particles and organic binder can be supplied with silicon or silicide particles in a number and size that corresponds to the number of desired pores. Capillary forces can then cause in-situ infiltration of the material during a heat treatment, preferably in a vacuum, and no silicon has to be added from the outside.

The pores or the faster-wearing particles that replace them can be generated as follows:

1) Pore formers (organic particles such as PMMA, starch, polypropylene, polystyrene) can be added, which pyrolyze and can form dense surface layers during the siliconization, which the

Prevent silicon infiltration or form poorly wetting surfaces for the Si, such as BN or Si0 2 .

2) Si or silicide particles can be added to the granulate in a number and size corresponding to the number of pores. Capillary forces then cause in-situ infiltration of the workpiece during a heat treatment, preferably in a vacuum, and no Si has to be added from the outside.

3) The introduction of faster-wearing particles into the component material can take place in accordance with typical ceramic technologies. These particles can be mixed dry, for example, between the granulated diamond granulate or hard material particles, or they can also be mixed with the starting suspension. This is followed by shaping and further processing by means of pyrolysis / siliconization.

4) It is also possible to mix the SiC-bonded diamond hard material particles according to the invention in the finished form with diamond particles and binder and then to shape them and then pyrolyze and siliconize them accordingly. The Si required for this can either be supplied from the outside or be introduced directly into the diamond particle-binder mixture or suspension. In the latter case, the Si particle sizes should approximately correspond to the desired pore size.

In addition, excess Si can be partially or completely dissolved out with alkaline solutions (eg 20% ​​NaOH) at room temperature or at elevated temperatures (60 ° C - boiling temperature) in order to clear the pores.

The porosity of SiC-bonded hard material particles can be achieved in the same way.

The SiC-bonded diamond granules according to the invention and porous construction parts can also be used in multiple layers on / in a component. A substrate made of SSiC or SiSiC or short or long fiber reinforced SiC ceramic in order to achieve higher rigidity or better connection to tools can form a base on which hard material particles can be arranged and fixed.

SiC-bonded hard material particles or components can advantageously be used as abrasive grains, for the production of grinding wheels, components reinforced with hard material particles for protection and applications for wear protection, as grinding elements, grinding pins or for protection and applications for wear protection.

The invention is to be explained in more detail below with the aid of examples.

Show:

FIG. 1 shows, in schematic form, possibilities for the production of SiC-bonded diamond hard material particles and

Figure 2 in schematic form possibilities for producing a

Component.

In the left representation of Figure 1, the granules, consisting of diamond particles and a pyrolysed binder (thick black border of the diamond) are shown. They are separated from Si and spacers S. This is the state before the siliconization and reactive formation of SiC.

During siliconization, the powdery Si and vitreous carbon, which has been formed on surfaces of diamond particles during pyrolysis, and partially from diamond, form an SiC matrix in which the diamond particles are bound. Even after siliconization, they are separated by the placeholders and are therefore easy to separate.

In the illustration on the left in FIG. 2, there is a shaped body made of a mixture consisting of diamond particles which have a vitreous carbon layer on their surface by means of a pyrolyzed binder. In addition, particles P made of polyurethane are contained as pore formers.

The right-hand illustration of FIG. 2 shows the state after siliconization. The diamond particles are embedded in a matrix that is formed with reactively formed SiC. Islands of Si and pores Po are contained in the matrix. Si and the pores Po form, so to speak, "predetermined breaking points", so that in the event of mechanical and / or tribological stress, diamond particles break out of the component material together with SiC residues and can be achieved by adapting them to abrasive or tribological requirements during use The pores can serve as a reservoir for abrasion or cooling or additional abrasives.

example 1

Diamond powder with an average particle size d 50 is used for productiongranulated from 50 pm together with an organic binder. The diamond powder is mixed in water or in a solvent with the organic binder and agglomerated using a granulation technology (e.g. spray granulation, fluidized bed granulation, build-up granulation, etc.). The granulate obtained in this way has an average particle size of 500 μm. The granules produced are then pyrolyzed under an Ar atmosphere at 800 ° C., the organic components of the binder being converted into a glass-like carbon. This vitreous carbon acts as a binding phase between the diamond granules in the agglomerates or a bulk of them and reacts to silicon carbide during the reactive silicon infiltration. The siliconization is carried out 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 with an average particle size d50 of approx. 200 μm and a further fine fraction of powdered silicon with an average particle size d 50 of 10 μm. The fine fraction of the silicon powder acts primarily as a spacer to prevent bridging between the individual granules, which are formed with crystallized silicon and SiC. As a result, the SiC-bonded diamond hard material particles can simply be separated in the jaw crusher and then classified again by sieving. As a result, a narrow grain size range, for example with particle sizes between 450 μm and 550 μm, can be produced.

The SiC-bonded diamond hard material particles consist of diamond and reactive silicon carbide and the remaining silicon that does not react to form silicon carbide.

Example 2

A build-up granulation is to be used for the production of hollow spherical granules. For this purpose, diamond powder with an average particle size d 50 of 50 μm is dispersed with an organic binder in a suspension for production. In the following, a two-component agglomerate is obtained by means of build-up granulation, the suspension containing diamond particles being deposited on coarse silicon particles with a

mean particle size d 50 of 100 miti is sprayed on during the granulation (fluidized bed granulation).

The granules obtained had an average particle size d 50 of 500 μm. The granules produced in this way are then pyrolyzed in a non-oxidizing atmosphere at 800 ° C., the organic constituents of the binder being converted into a glass-like carbon. This vitreous carbon acts as a binding phase between the diamond particles on the surfaces of which a coating of this vitreous carbon has formed and this carbon reacts further to silicon carbide during the reactive silicon infiltration.

During the final heat treatment under vacuum conditions at 1550 ° C., the granulate obtained in this way is siliconized from the inside. To support the siliconization, a further fine fraction of pulverulent silicon with an average particle size of 10 μm can be added. The fine fraction of the silicon powder acts primarily as a spacer to prevent the formation of bridges between granules, which consist of diamond, crystallized silicon and SiC.

Due to the build-up granulation technology used, the siliconization from the inside out results in the formation of hollow granules. The granules produced consist of diamond and reactively formed silicon carbide and possibly remaining unreacted silicon. They can be classified and used after siliconization.

Remaining adhering unreacted Si could be dissolved in 20% NaOH at 60 ° C. within 1 h with stirring.

Example 3

The production of porous diamond abrasives is based on a diamond-containing suspension. In this one becomes a bimodal

Diamond particle size fraction, consisting of mean particle sizes d 50 of 50 pm and 5 pm, is used. Furthermore, a silicon powder with an average particle size d 50 of 100 μm is located in the suspension as a further solid component . A polystyrene powder with an average particle size d 50 of 200 μm is used as a placeholder . The proportions of the solids diamond to silicon to polystyrene are 2 to 2 to 1 parts by volume. The binder in the aqueous suspension is an aqueous one

Polyvinyl acetate dispersion, which cross-links when drying, is used.

The suspension is processed and shaped by slip casting. During the final heat treatment, the diamond-containing molded part is pyrolyzed in a non-oxidizing atmosphere at 800 ° C and then reaction-bonded under vacuum conditions at 1550 ° C. During pyrolysis, the organic binder is converted into a glass-like carbon with outgassing of volatile components. This vitreous carbon acts as a binding phase between the diamond particles in the agglomerates and reacts during the subsequent reactive

Silicon infiltration further to silicon carbide. The polystyrene placeholders are almost completely split up into volatile components so that these are present as pores in an abrasive body formed with the granulate. During the reaction, the silicon present in the material melts and reacts with the existing carbon, which has been formed from the pyrolysed organic binder, and is deposited on diamond particle surfaces. A porous diamond-SiC-Si-containing material composite is formed, which can be used as a grinding tool.

Example 4

The production of porous diamond grinding media takes place on the basis of a diamond-containing suspension. In this a bimodal diamond particle size fraction with diamond particles is a medium one

Particle size d 50 of 50 pm and 5 pm was used. Furthermore, a silicon powder with an average particle size d 50 of 100 μm is located in the suspension as the second solid component. The mass ratios of the solids diamond to silicon are 2 to 1.

An organic binder is used in the aqueous suspension

Polyvinyl acetate dispersion, which cross-links when drying, is used. A surfactant is also added to the suspension as a foaming agent.

The suspension is foamed by means of a high-speed stirrer and then poured into a non-absorbent mold and freeze-dried. The heat treatment steps follow after demolding. The diamond-containing molded part is pyrolyzed in a non-oxidizing atmosphere at 800 ° C and then reaction-bonded under vacuum conditions at 1550 ° C. During pyrolysis, the organic constituents of the binder are converted into a vitreous carbon with outgassing of volatile constituents, with which the surfaces of the diamond particles are coated. In the reaction bonding during the heat treatment, the silicon present melts and reacts with the carbon present in the pyrolyzed binder and the diamond particle surfaces.

Example 5

The production of porous diamond abrasives is based on a diamond-containing granulate. The granulate is agglomerated using a customary granulation technology (eg spray granulation, fluidized bed granulation, build-up granulation, etc.) and has an average size of 200 μm - 1000 μm. The granules produced include a

Diamond particle size fraction with an average particle size d 50 of 50 μm, a silicon particle size fraction with an average particle size d 50 of 50 μm and a particle size fraction of a polystyrene powder with an average particle size d 50 of 100 μm. The granulate is bound by an organic sugar-based binder in an aqueous suspension. The ratios of the solids diamond to silicon to polystyrene are 1 to 1 to 1 parts by volume.

The granules produced are then shaped into a shaped body by a pressing process (for example by isostatic pressing or uniaxial pressing). The pyrolysis then takes place in a non-oxidative atmosphere at 800 ° C. In this process, organic constituents of the bin are converted into a vitreous carbon with outgassing of volatile constituents, with which the surfaces of diamond particles are coated. The polystyrene particles as placeholders are almost completely split into volatile components so that these are present as pores in the finished product. During the subsequent reaction bonding, the silicon present in the material melts and reacts with the carbon present, which has been obtained from the pyrolysed binder, and diamond particle surfaces are coated with silicon carbide.

Claims

1. SiC-bonded diamond hard material particles, which have a composition of 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 to 30 vol .-% Si, and diamond particles individually Hard material particles with the SiC and Si formed during the thermal treatment are materially bonded to one another and have a particle size in the range 50 μm-5000 μm, preferably <2000 μm, even more preferably <1000 μm.

2. SiC-bonded diamond hard material particles according to claim 1, characterized in that an average particle size d 50 of diamond particles in the hard material particles in the range 5 pm to 500 pm is adhered to.

3. SiC-bonded diamond hard material particles according to one of the preceding claims, characterized in that a maximum of 90% of the upper surface of the diamond particles are materially bonded to SiC.

4. A method for the production of SiC-bonded diamond hard material particles according to one of the preceding claims, characterized in that diamond particles are mixed with an organic binder and shaped into granules via a drying and granulating process,

be subjected to a thermal treatment in an oxygen-free atmosphere, in which a pyrolysis of the organic constituents takes place and in the pyrolysis of the organic binder formed in situ carbon is deposited in vitreous form on surfaces of diamond particles and

during this thermal treatment or during a subsequent second thermal treatment with mixed powder

silicon and particulate placeholders (S) carried out a siliconization and

silicon carbide is formed by chemical reaction with the carbon deposited on surfaces of diamond particles and / or with the diamond particles, so that the hard material particles are formed, with

Diamond particles in the individual hard material particles with the SiC reactively formed during the thermal treatment and the silicon are firmly connected to one another in such a way that the shaped granules are predominantly or completely separated on their surface using the added silicon and / or the placeholders (S) or in are kept at a distance from each other.

5. The method according to claim 4, characterized in that for placeholder (S) chemical elements or compounds are used that are difficult to wet by Si, do not form an alloy with Si and / or will not react with Si to establish a solid connection To minimize granules with each other, these chemical elements or compounds are preferably selected from hexagona lem BN, Si 3 N 4 , AlN, Al 2 0 3 , Si0 2 , Zr0 2 and a nitride, carbide of the transition metals, in particular group 4 and 5 of the period system.

6. The method according to claim 4 or 5, characterized in that the organic binder and its amount are selected so that the organic cal binder as a carbon source with a proportion between 1.5% by mass to 20% by mass in relation to the total mass of diamond particles used is used.

7. The method according to any one of claims 4 to 6, characterized in that diamond particles in at least two different

Particle size fractions, preferably a coarse and a fine particle size fraction, particularly preferably a fine one

Particle size fraction that is 0.1 to 0.3 times the diameter of the coarse particle size fraction and has a proportion of 5% by volume - 50% by volume of the coarse particle size fraction is used.

8. The method according to any one of claims 4 to 7, characterized in that the granulated particles before the siliconization silicon powder with an average particle size d 50 in the range of 5 pm-1000 pm, preferably in the range 10 pm-150 pm and in this range with a volume of 10 vol .-% - 200 vol .-%, preferably 60 vol .-% - 160 vol .-% of the content of diamond particles is added.

9. The method according to any one of claims 4 to 8, characterized in that the hard material particles are gebil det with at least one further phase, which is preferably selected from B 4 C, TiC and TiB 2 .

10. The method according to any one of claims 4 to 9, characterized in that diamond particles with an average particle size of 10 pm - 50 pm, preferably 15 pm - 30 pm or particularly preferably 10 pm - 20 pm are used.

11. The method according to any one of claims 4 to 10, characterized in that the hard material particles are brought into a defined shape, preferably spherical, cylindrical, prismatic, pyramidal, in particular by extrusion or by casting processes.

12. The method according to any one of claims 4 to 11, characterized in that the incorporation of the diamond particles and / or a possible partial breakout of the diamond particles in / from a matrix formed with the reactively formed SiC and Si during mechanical / tribological stress the maximum temperature during the siliconization and the purity of the diamond particles used is / are influenced.

13. The method according to any one of claims 4 to 12, characterized in that hollow hard material particles on the inside by applying a suspension in which an organic binder is contained in addition to diamond particles, on silicon particles with a particle size in the range 50 pm - 150 pm or

by admixing particles of a powdery organic substance which decomposes during thermal treatment, preferably polymethyl methacrylate, polyurethane, polyethylene or polypropylene or starch and

subsequent thermal treatment in which a pyrolysis, the Mi rule with Si powder and the spacer (S) and a reactive Bil formation of SiC takes place, are produced; wherein the proportion of powdered silicon added volume of 10 vol .-% - 200 vol .-%, preferably 60 vol .-% - 160 vol .-% of the content of diamond particles is added.

14. The porous component is formed from diamond particles bonded with SiC, and the component has a porosity in the range 10% to 40%, preferably between 10% and 30%,

has an average pore size between 10 pm-100 pm, preferably between 20 pm-50 pm and

from 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 vol .-% to 30 vol .-% Si, preferably from 40 vol .-% - 60 vol .-% diamond, 60 vol .-% -40 vol .-% SiC and 2 vol .-% to 20 vol .-% Si, and the diamond particles contained an average particle size in the range 5 pm to 500 pm, preferably in the range 30 pm - 100 pm, particularly preferably> 50 pm - 200 pm.

15. Component according to claim 14, characterized in that at least one further phase with a placeholder function, which primarily wears in the event of tribological or abrasive loading and thus forms pores in the material, is contained, the further phase (s) with non-diamond carbon, Si 3 N 4 , which can also be sintered on, Al 2 0 3 or transition alumina, dense or porous glass spheres, high-melting the silicide or boride, in particular TiSi 2 MoSi 2 , WSi 2 , TiB 2 , W 2 B 5 , WB 2 or Zr0 2 is / are formed with a wide variety of dopings, at least one other high-melting oxide or silicate, in particular MgO or talc, at least one transition metal carbide, oxicarbide, nitride or boride.

16. A method for producing a component according to one of claims 14 or 15, characterized in that

Diamond particles with SiC, an organic binder and particles of an organic substance, preferably with powdered plastic as pore formers, in particular polystyrene, polyemthyl methacrylate, polyurethane, polyethylene or polypropylene or starch preferably with an average particle size d 50 in the range 30 μm to 100 μm before the thermal mixing treatment mixed_and then shaped via a molding process

be subjected to a thermal treatment in an oxygen-free atmosphere, in which a pyrolysis of the organic constituents takes place and in the pyrolysis of the organic binder formed in situ carbon is deposited in vitreous form on surfaces of diamond particles and

During this thermal treatment or during a subsequent second thermal treatment with externally supplied silicon, a siliconization is carried out and

silicon carbide is formed by chemical reaction with the carbon deposited on the surfaces of diamond particles and the diamond, so that

the component material has a composition of 30 vol .-% - 65 vol .-% diamond, 70 vol .-% - 35 vol .-% SiC and 0 to 30 vol .-% Si and a porosity in the range 10% - 40% having.

17. The method according to claim 16, characterized in that the organic binder and its amount are selected so that the organic binder as a carbon source with a proportion between 1.5% by mass to 20% by mass in relation to the total mass of used Dia mantpartikel is used.

18. The method according to any one of claims 16 or 17, characterized in that diamond particles in at least two different particle size fractions, preferably a coarse and a fine particle size fraction, particularly preferably a fine one

Particle size fraction that is 0.1 to 0.3 times the diameter of the coarse particle size fraction and has a proportion of 5% by volume - 50% by volume of the coarse particle size fraction is used.

19. The method according to any one of claims 16 to 18, characterized in that particles of an organic substance, preferably powdered plastic, in particular polystyrene, polymethyl methacrylate, polyurethane, polyethylene or polypropylene or starch with a proportion in the range 20 vol .-% to 40 Vol .-% is added.

20. The method according to any one of claims 16 to 19, characterized in that a further phase (s) with non-diamond carbon, B 4 C, TiC and TiB 2 , Si 3 N 4 , which can also be sintered, Al 2 0 3 or transition alumina, dense or porous glass spheres, high-melting the silicide or boride, in particular TiSi 2 MoSi 2 , WSi 2 , TiB 2 , W 2 B 5 , WB 2 or Zr0 2 is mixed homogeneously with various dopings, at least one other high-melting oxide or silicate, in particular MgO or talc, at least one transition metal carbide, oxicarbide, nitride or boride before shaping.

21. The method according to any one of claims 16 to 20, characterized in that the incorporation of the diamond particles and / or a possible partial breakout of the diamond particles in / from a matrix formed with the reactively formed SiC and Si during mechanical / tribological stress the maximum temperature during the siliconization and the purity of the diamond particles used is / are influenced.

22. The method according to any one of claims 16 to 21, characterized in that the starting material silicon powder with a mean particle size d 50 between 20 pm - 100 pm is mixed before the shaping, the particle size of which is retained during the shaping and thus during form pores during siliconization.

23. Use of SiC-bonded hard material particles according to one of claims 1 to 4 or components according to one of claims 14 to 15 as abrasive grains, for the production of abrasive bodies, components reinforced with hard material particles for wear protection and wear protection applications, as a grinding body, grinding pin or for

Protection and wear applications.