A 3D print method for providing a sic ceramic preform using sic particles with a specific roundness

Abstract

The invention relates to the use of SiC particles (grains) in a powder bed print method for providing a SiC ceramic preform (green body), wherein the SiC particles (grains) are characterized by - an average grain size (d50) of 2 to 70 µm, preferably 3 to 65 µm, more preferably 5 to 50 µm, such as 25 to 60 µm, preferably 40 to 55 µm, - a roundness of > 0.55, preferably > 0.58, more preferably > 0.6 (as described in experimental section), - bulk density of > 1.6 g / cm3, preferably > 1.65 g / cm3, more preferably > 1.7 g / cm3, even more preferably > 1.75 g / cm3 (according to DIN EN 725-9 ISO 23145-2).

Description

[0001] A 3D print method for providing a SiC ceramic preform using SiC particles with a specific roundness

[0002] The present invention relates to the use of SiC particles (grains) with a specific roundness in a powder bed print method for providing a SiC ceramic preform, and a 3D print method for providing a SiC ceramic preform using said SiC particles.

[0003] Description

[0004] Ceramic substrates or components are used in different technical areas, such as electronic industries, automotive industry and in medicinal industry.

[0005] Ceramic components are obtained in a multistep process, wherein a suitable starting material (such as AI2O3, SiC, SiaN4 or mixtures thereof) is provided as a powder. The powder is shaped into a desired form by pressing, moulding or extrusion providing a preform or a so called “green body”.

[0006] This involves compacting the powder particles (which are optionally mixed with an organic binder) and moulding them into a coherent shape that has sufficient strength for subsequent handling. Depending on the requirements, this moulded, unfired powder body (green compact or green body) can still be processed cost-effectively before firing, as the corresponding work steps after firing are much more complex.

[0007] With the various moulding processes, care must be taken to ensure that there are no noticeable density gradients and textures in the green body, as these may be intensified during firing, lead to deformation and cause internal mechanical stresses. The selection of a suitable moulding process is usually based on economic aspects (rational production).

[0008] In addition to the ceramic powder mixtures (including the permanent additives), the green bodies produced using the original shaping processes of casting, plastic moulding and pressing usually also contain moisture and mostly organic liquefying, plasticising and binding agents or other auxiliary materials. All components that are volatile at high temperatures, i.e. evaporate or burn, must be removed from the ceramic green body before firing, which requires special care so that they can leave the body without being damaged. Recently, 3D print methods were developed as an alternative for providing such preforms, as for example described in WO 2018 / 206250 A1. However, a disadvantage of the printing method is that SiSiC compounds obtained from 3D printed SiC preforms have a low density, coarser SiC grain size and a higher Si content. These factors reduce the mechanical properties and have an influence on the electrical properties.

[0009] WO 2019 / 063833 A1 discloses a method for providing a ceramic component containing silicon carbide (SiC) with the steps of a) providing a green body based on SiC which has been produced by means of a 3D-printing method, b) impregnating the green body with a solution selected from the group consisting of a sugar solution, a starch solution or a cellulose solution, or a resin system comprising a mixture containing at least one resin, at least one solvent and at least one curing agent, the at least one resin and the at least one solvent being different, c) drying or curing the impregnated green body, d) carbonising the dried or cured green body, wherein a fine-pored, foam-like carbon skeleton is produced from the dried solution or a fine- pored, sponge-like carbon skeleton is produced from the cured resin system, e) siliconising the carbonised green body by infiltrating with liquid silicon. In the event of siliconisation of such a green body, the carbon skeleton is converted into silicon carbide and the pores of the green body are filled with silicon. As a result of this filling of the pores, the proportion of relatively large lakes or regions of free silicon is significantly reduced. The free silicon is therefore no longer present in the form of large lakes or regions, and instead silicon carbide structures are present in these pores. The presence of these silicon carbide structures which fill the pores leads to a higher chemical stability and to a greater temperature resistance of the ceramic component and to improved mechanical properties. In any case, this method requires the application of an impregnation solution as an additional process step.

[0010] CN 116409997 A discloses a preparation method for silicon carbide composite ceramics that includes S1) providing silicon carbide powder that has undergone a pre-treatment step with acid, S2) mixing the pre-treated silicon carbide powder raw material with a curing agent to obtain a silicon carbide curing agent mixture, S3) selecting a suitable binder and performing 3D-printing using said silicon carbide curing agent mixture to obtain a silicon carbide ceramic material blank (or green body), S4) degreasing the green body at high temperatures (about 900°C), S5) densifying the degreased silicon carbide ceramic green body by impregnation with a precursor polymer solution, subsequent cross-linking and degreasing at high temperature (about1000°C), and S6) performing high-temperature sintering (1450-2200°C) to obtain a high- strength silicone carbide composite ceramics with a density of 2.72 - 3.15 g / cm3. The process described in CN 116409997 A requires a multitude of process steps making the whole process laborious and expensive.

[0011] Thus, it was an object of the invention to provide a more economical process that would allow to obtain SiC preforms (green bodies) by powder bed printing (also known as binder jetting) that have a high (green) density and subsequently SiSiC compounds with a high final density.

[0012] This object was solved by using SiC particles with a specific roundness in a powder bed printing method as described in the claims.

[0013] Accordingly, a method for obtaining a SiC green body (or preform) by powder bed printing is provided, wherein the method comprises the steps of:

[0014] Providing a composition, in particular as a powdery composition, comprising at least 80 wt%, preferably at least 85wt%, more preferably at least 90wt% (based on the overall weight of the composition) of SiC particles having o an average grain size (dso) of 2 to 70 pm, preferably 3 to 65 pm, more preferably 5 to 50 pm, such as 25 to 60 pm, preferably 40 to 55 pm, o a roundness of > 0.55, preferably > 0.58, more preferably > 0.6 (as described in the experimental section), o bulk density of > 1.6 g / cm3, preferably > 1.65 g / cm3, more preferably > 1.7 g / cm3, even more preferably > 1.75 g / cm3(according to DIN EN 725-9 ISO 23145-2), and spreading or printing the SiC particle composition to form at least one first layer while being simultaneously vibrated, applying at least one binder to the at least one first layer of the SiC particles containing composition and consolidating the at least one first layer, in particular chemical, thermal and / or light induced consolidating the at least one first layer to obtain a silicon carbide ceramic material green body; and curing the silicon carbide ceramic material green body to obtain a cured green body. Subsequently, in further steps the cured silicon carbide ceramic green body may be subjected to an infiltration step with silicon to obtain a SiSiC ceramic material as will be described in more detail below.

[0015] It is to be pointed out that the present method does not require: any pre-treatment of the raw SiC particles with an acid or any other substance to improve the flowability of the particles,

[0016] No mixing of the raw SiC particles with any curing agent and / or binder or any further additive before printing, no impregnation of the green body obtained after printing before curing with any sugar or starch solution, as for example required in WO 2019 / 063833 A1.

[0017] In an embodiment of the present method, the composition used as starting material comprises 80- 100 wt% , preferably 85- 100 wt%, more preferably 90-100 wt%, even more preferably 95- 100 wt% of SiC particles. A high content of SiC particles of at least 80 wt%, more preferably at least 85 wt%, more preferably 90 wt% (based on the overall weight of the composition) leads to a high purity of the resulting 3D-printed SiSiC ceramic part. A high purity of the 3D-printed SiSiC ceramic part is required for reasonable mechanical and / or electrical properties.

[0018] In an embodiment of the present method, the composition used as starting material may comprise 0-20 wt%, preferably 0-15 wt%, more preferably 0 - 10 wt%, even more preferably 0 - 5 wt% of Carbon. Thus, carbon, for example carbon black or graphite, can be added to the SiC powder before the preforms are produced, so that the carbon content required for the secondary SiC is already introduced. However, it is preferred not to add carbon to the starting SiC particle composition.

[0019] As mentioned above, SiC particles (grains) are used in the present print method for providing a SiC ceramic preform (green body), wherein the SiC particles (grains) are characterized by an average grain size (dso) of 2 to 70 pm, preferably 3 to 65 pm, more preferably 5 to 50 pm, such as 25 to 60 pm, preferably 40 to 55 pm, a roundness of > 0.55, preferably > 0.58, more preferably > 0.6 (as described in experimental section), bulk density of > 1.6 g / cm3, preferably > 1.65 g / cm3, more preferably > 1 .7 g / cm3, even more preferably > 1 .75 g / cm3(according to DIN EN 725- 9 ISO 23145-2).

[0020] The term "dso" is understood to mean that 50% of the particles are smaller than the specified value. The dso value was determined with the aid of a method based on laser granulometry (ISO 13320).

[0021] By using the particularly round grain or particle a significantly higher bulk density can be achieved compared to standard grain with a roundness of less than 0.55. For example, the bulk density of standard grain is about 1.55 g / cm3, whereas the bulk density of the round grain can be more than 1.75 g / cm3, e.g. 1.79 g / cm3.

[0022] The elongation EL (as the a / b ratio as explained in the experimental section) of the SiC particles is less than 1.45, more preferably less than 1.40, more preferably less than 1.35.

[0023] In order to be able to process fine powders in powder bed printing, a narrow particle size distribution is necessary. The particle size distribution can be quantified by the percentage difference between D90 and D10: the value (D90-D10) / D50. The modality and distribution range for the round particles is less than 0.55, preferably less than 0.52, more preferably less than 0.5, even more preferably less than 0.48, for example 0.46. For comparison: the modality of standard particles is about 0.6.

[0024] The higher bulk density results in a density increase of the SiC preform (or green body) obtained by 3D print using said round particles.

[0025] For example, as will be explained further below in more detail, when using the SiC particles with a roundness of > 0.55, preferably > 0.58, more preferably > 0.6 (as described in experimental section), SiC ceramic preform (green body) with a density of 1.59 g / cm3is obtained. In contrast, when using the SiC particles with a roundness of less than 0.55, such as 0.5, a SiC ceramic preform (green body) with a density of 1.46 g / cm3is obtained; i.e increase of density by about 10% in the SiC preform (green body) is achieved using the rounder particles. Such increase in green density of 10% is currently only possible by means of soot impregnation, the use of multimodal printing powder or inks consisting of liquid resin containing SiC particles. The SiC particles containing powders can also have a multimodal particle size distribution, in particular a bimodal or trimodal particle size distribution, i.e. from fractions of powders of different particle sizes. The packing density can be optimised by using an even finer fraction to fill the gaps in the next coarser powder fraction. To achieve a high packing density the particle size distribution can be optimised so that the fine powder fills the gaps in the gaps in the bulk of the coarser powder.

[0026] In a preferred embodiment, the ceramic powder with an average grain size in the range of 25 to 70 pm, preferably of 30 to 60 pm, more preferably 40 to 55 pm, can be a fraction, preferably the main fraction, and can be mixed with one or more further fraction(s), for example with an average grain size of 2 to 15 pm, preferably 5 to 12 pm, more preferably 8 to 10 pm.

[0027] The SiC particles of the main fraction have a roundness of > 0.55, preferably > 0.58, more preferably > 0.6, whereas the roundness of the smaller SiC particles of the minor fraction can be of any desired value.

[0028] In case of the bimodal composition, the composition comprises 65-95 wt%, preferably 70 - 90 wt%, more preferably 75 - 85 wt% of larger particles of the main fraction and 5-35 wt%, preferably 10 to 30 wt%, more preferably 15 to 25 wt% (based on the overall weight of the composition) of the smaller particles of the minor fraction.

[0029] In a specific embodiment the bimodal mixture was composed of 70 to 80 wt% of the round grain with a particle size d50 of 25-70 pm and 20 to 30 wt% (based on the overall weight of the composition) of the small grain with a particle size d50 of 8 to 10 pm. The minor fraction of smaller particles has a very narrow size distribution of (d3-d95 5pm).

[0030] The bulk density of the described bimodal composition is more than 1.8 g / cm3, preferably more than 1.85 g / cm3, such as 1.9 g / cm3.

[0031] The SiC particles used according to the invention may be obtained in different ways.

[0032] In one embodiment the SiC particles are obtained from SiC waste products. The SiC particles and methods for obtaining the same are described in WO 2023 / 217706 A1. Accordingly, SiC waste products are crushed by mixing, grinding, e.g. autogenous grinding, or by using eddy currents and / or ultrasound or by grinding, hammering, crushing or by means of electrical discharges or shock waves. The energy input during the mechanical stressing and comminution of SiC waste products into SiC particles is between 0.1 and 5 MJ / kg.

[0033] The mechanical comminution of the SiC waste products can take place before and / or after a temperature treatment under vacuum or non-oxidising atmosphere at temperatures of 1400 to 2600°C.

[0034] After one of the last treatment under mechanical stress of the SiC particles, a physical separation of the SiC particles into fractions can be carried out. The separation according to particle size and / or particle shape can be carried out by sieving, sifting and / or cyclone processes. Separation according to the density of the particles can be carried out by flotation and / or cyclone process.

[0035] The SiC particles obtained in this way consist of at least 85 wt% silicon carbide and have a density of 2.89 to 3.20 g / cm3, a compressive strength of > 2500 MPa, a proportion of < 5% of pores with an equivalent diameter of > 1 00 1-1 m and a proportion of open porosity of < 10%.

[0036] The SiC particles according to WO 2023 / 217706 A1 have particle sizes of greater than or equal to 2 mm and an irregular shape with a roundness of 0.5 to 0.8.

[0037] The SiC particles used according to the invention with an average grain size between 2-70 pm and a roundness of > 0.55 are subsequently obtained from the particle mixture by appropriate fractionation, for example by sieving.

[0038] As mentioned above, the SiC particle composition is spreaded or printed to form at least one first layer of SiC particles. The SiC particle powder is printed on a planar bed while simultaneously a vibration frequency (for example of 3000-5000 Hz, in particular 4000 Hz) is applied to the printing device. In a preferred embodiment, a vibrating blade (or recoater) is used in the printing process.

[0039] The density of the powder layer is more than 1.7 g / cm3, preferably more than 1.75 g / cm3, such as 1 .8 g / cm3. When using a bimodal composition as described above the density of the printed powder layer is more than 1.8 g / cm3, such as 1.9 g / cm3. In a further embodiment of the present printing method the at least one first composition layer (and preferably each subsequent composition layer) has a layer thickness between 10 and 250 pm, preferably between 50 and 200 pm, more preferably between 80 and 150 pm.

[0040] The binder may be applied to the SiC powder layer, for example, by means of a print head. The binder should preferably wet the powder well so that the binder material is distributed homogeneously. Consolidation of the printed areas in the layer can be done either by removing the volatile parts of the fixing component or by chemical, thermal and / or light- induced cross-linking (e.g. with an IR or UV lamp). In a preferred embodiment, the fter their consolidation a further layer of SiC powder is applied. The binder is applied and consolidated (i.e. at least partially cured or dried) resulting in the green body having the desired form of the component.

[0041] Thus, in an embodiment of the printing method at least one second layer of the SiC particles containing composition is applied onto the consolidated first layer; followed by applying a binder to the at least second layer of the SiC particles containing composition and chemical, thermal and / or light induced consolidating the at least second layer according to the required next layer of the SiC preform.

[0042] These steps are repeated until the desired form of the component is produced; the individual steps being matched to the desired form of the component.

[0043] The binder used in the printing process can be prepared by chemical, thermal and / or light- induced cross-linking, for example by irradiation of large areas or points with an IR or UV lamp. UV curing components can be radical or cationic curing UV systems or a mixture of both e.g. acrylates, epoxies, enol ethers, vinyls. Thermally curing binder may be a component that is dried over a heat source and / or reaction. Exemplary components are phenolic resins, furan resins, epoxy resins, graphite resins, starch, sugar or cellulose solutions. The binder can also be on an inorganic basis, such as water glass. 3D printing preferably uses a binder that forms a carbon residue after pyrolysis ("coking"). This carbon reacts with silicon to form secondary silicon carbide.

[0044] The choice of the binder for production of the printed green body is not particularly limited. Suitable binders are, for example, phenol resins, furan resins, polyimides, celluloses, starches, sugars, silicates, silicon-containing polymers, water glass, pitch, polyacrylonitrile (PAN) or any mixtures thereof. Solutions of the aforesaid binders are also included herein.

[0045] The binders constituted by phenol resins, furan resins or polyimides are resins and polymers with a relatively high carbon yield. They belong to the class of binders that are transferred by curing into a non-meltable binder system and with siliconisation are converted largely into SiC.

[0046] Celluloses, starches or sugars, preferably present in the form of a solution, may also be used, as binders. These binders only have to be dried, and the carbon residue created with the carbonisation and siliconization is largely converted into SiC.

[0047] The use of silicates, water glass or silicon-containing polymers as binder, preferably present in the form of a solution, also has the advantage that these binders also only have to be cured.

[0048] Preferred binders are phenolic resins, such as phenolic resin novalaks with e.g. hexamethylenetetramine as hardener. Another preferred binder are furan resins.

[0049] The amount of binder used in the printed SiC preform (green body) is 1 .0 to 30.0 Vol. %, preferably 5.0 to 25.0 Vol%, more preferably 10.0 to 20.0 Vol %, in relation to the total volume of the green body.

[0050] As mentioned above, due to the use of SiC particles with a specific roundness there is no need to apply an impregnation solution to the printed SiC preform before curing, i.e this specific impregnation step can be omitted.

[0051] As discussed above, the green body obtained after consolidation undergoes a curing step to obtain a cured green body.

[0052] The green body may be cured in a further step at room temperature or at an elevated temperature, such as 140-200°C. The temperature applied depends on the type of binder used, in particular if the binder is mixed with a curing agent. Typically higher curing temperatures upto 200°C are used.

[0053] The curing at room temperaturemay be of an advantage, since there is no need for the temperature application, thus constituting a more economical method step. Furthermore, the speed of the curing may be controlled in a targeted manner by the proportion of curing agent that is added to the binder. It is sought here to achieve a curing time in a range of from 10 minutes to 12 hours, preferably from 6 to 12 hours depending on the curing temperatures. This adjustable curing time is directed here towards the desired processing times

[0054] After the curing, the used resin is not meltable and therefore may be carbonised. A further advantage of the curing at room temperature lies in the fact that a temperature application leads to a temporary reduction of the resin viscosity and therefore to the discharge of the resin from the pores of the green body. Such a discharge on the one hand results in a local loss of resin, and on the other hand the green body may lose its form since parts of the resin adhere undesirably to the lower part of the green body.

[0055] The SiC preform (green body) obtained by printing and subsequent consolidation and curing (before carbonization and infiltration with Si) has a density of > 1.5 g / cm3, preferably of > 1 .53 g / cm3, more preferably of > 1.55 g / cm3, such as in a range between 1.5 and 3.0 g / cm3, preferably between 1.53 and 2.5 g / cm3, more preferably between 1.53 and 2.0 g / cm3, even more preferably between 1 .55 and 1 .8 g / cm3.

[0056] When using a bimodal composition as described above the cured SiC green body (or preform) has a density of > 1.6 g / cm3, preferably of > 1.65 g / cm3, more preferably of > 1.7 g / cm3, such as in a range between 1.6 and 3.0 g / cm3, preferably between 1.65 and 2.5 g / cm3, more preferably between 1 .65 and 2.0 g / cm3, even more preferably between 1 .65 and 1 .8 g / cm3

[0057] The density is measured by the Archimedes method using mercury as liquid according to DIN EN 623-2; ISO 18754.

[0058] Immediately after the curing or drying of the binder, the green body is still surrounded by a powder bulk formed of loose particles of the powdery composition. The green body must therefore be removed from the powder bulk or separated from the loose, non-solidified particles. This is also referred to in the literature relating to 3D printing as an "unpacking" of the printed component. The unpacking of the green body may be followed by a (precision) cleaning of the green body in order to remove adhering particle residues. The unpacking may be performed for example by sucking up the loose particles using a high-performance sucker. The way the unpacking is performed, however, is not particularly limited, and all known methods may be employed.

[0059] In an embodiment, the , the dried or cured SiC preform (green body) may be carbonized and densified. For this purpose, the cured green body may be subjected to a carbon black solution impregnation and subsequent densification treatment.

[0060] The term "carbonisation" is understood to mean the thermal conversion of the organic binder system, such as resin system, contained by the green body into carbon. The carbonisation may occur by heating to temperatures in a range of from 500°C.-1100° C., preferably from 800° C. to 1000° C., in an inert gas atmosphere (for example in an argon or nitrogen atmosphere) with subsequent hold time. In view of the solvent contained in the pores, it is advantageous if the heating to the carbonisation temperature is performed gently, since cracking products are expelled. If this expulsion is not performed slowly or gently, the green body may explode.

[0061] In another variant, the impregnation can be omitted completely. If suitable binder components are used for the production process that form a sufficiently high carbon residue after coking, the silicon content in the SiSiC component can be significantly reduced, in particular to less than 40 vol%, preferably less than 35 vol% in relation to the total volume of the volume of the component. Such a suitable binder is for example a water based phenol resin as described above.

[0062] In a further preferred embodiment, the carbonised SiC preform (green body) is infiltrated with liquid silicon in a further step and a SiSiC material is formed.

[0063] In the event of siliconisation of such a green body, the pores of the green body are filled with silicon. The step of silconisation increases the density of the SiSiC material. In the present case using SiC particles with a specific roundness a final density of up to 2.75 g / cm3, preferably of up to 2.79 g / cm3or higher upto 3.1 g / cm3may be achieved.

[0064] The infiltration of the SiC preform (green body) with liquid for obtaining SiSiC material can be achieved in different ways. In one embodiment, the SiC preform (green body) is placed on silicon and / or a silicon alloy, such as a silicon bed, and is subsequently heated in a vacuum or inert atmosphere to a temperature above the melting temperature of Si and I or Si alloys, i.e. to temperatures of more than 1400°C, for example 1400 - 1800 °C, preferably 1600°C. The molten silicon is sucked into the green body by capillary forces and fills the pores of the green body with silicon.

[0065] The component obtained from a SiC preform (green body) in a 3D print method using the round particles shows good properties. In particular, the combination of roundness and distribution width of the particles still allows for good component quality.

[0066] This was surprising since a person skilled in the art would rather assume that particles with the surface structure of natural quartz sand with corners and edges are preferable, since such particles can interlock better and are less susceptible to mutual displacement.

[0067] The invention is now explained in more detail with reference to the examples and figures. It shows:

[0068] Figure 1 A a microscopic view of the SiC particles used according to the invention;

[0069] Figure 1 B a microscopic view of standard SiC particles;

[0070] Figure 2A a microscopic view of a green body obtained with the SiC particles used according to the invention;

[0071] Figure 2B a microscopic view of a green body obtained with standard SiC particles.

[0072] Example 1 : unimodal SiC particles

[0073] The SiC particles used according to the invention are illustrated in Fig 1A, a 200x enlarged transmitted light image. For comparison, Fig 1 B shows standard SiC particles (as described in “Silicon Carbide Ceramics: Structure, Properties and Manufacturing” by Andrew J. Ruys, 2023, Elsevier Series of Advanced Ceramic Materials, ; classified according to ISO 6344).

[0074] The roundness of the SiC particles was determined as follows: A spatula tip of powder is sprinkled onto a glass slide and viewed under a microscope using transmitted light. An area should be selected in which the grains have practically no contact with each other and a very strong black / white contrast is achieved. The resulting image is then analyzed using the Stream software (Olympus) with the “count and measure” function. The particles are recognized on the basis of an intensity threshold value and the desired property is then calculated.

[0075] The roundness can be defined as a measure of the sharpness of the corners and edges of the particle:

[0076] Roundness wherein n are the radii of the curvature of p corners of a section of the particle and R is the maximum inscribed radius of the particle. Roundness value range from 0 to 1 , wherein 1 stands for a round circle (see Singh and Ramakrishnan, Powder Characterization by Particle Shape Assessment, Kona, 1996, 16-30).

[0077] Elongation EL is defined as the ratio of length I breadth (L / B); see Singh and Ramakrishnan, Powder Characterization by Particle Shape Assessment, Kona, 1996, 16-30.

[0078] Bulk density was measured according to DIN EN 725-9, ISO 23145-2:

[0079] The powder flows freely through a funnel into a defined cylinder until the powder protrudes. The excess powder is then scraped off and the powder in the cylinder is weighed, from which the bulk density is calculated using the volume of the cylinder.

[0080] The properties of SiC particles according to the invention and standard SiC particles are summarized in the following Table 1. The average particle size is according to F240, specifically d10 35-37 pm, d50 48-51 pm, d90 57-69pm (obtained by laser diffraction)

[0081] Table 1

[0082] Example 2: Green body using unimodal SiC particles

[0083] The green body obtained when using the SiC particles to the invention is shown in Fig 2A, a 200x enlarged light image. For comparison, Fig 2B shows a green body obtained when using standard SiC particles.

[0084] When comparing the green bodies of Fig. 2A and Fig. 2B it is apparent that the packaging density is increased in the green body according to the invention (Fig. 2A).

[0085] The green body based on silicon carbide may be produced as follows:

[0086] A silicon carbide with grain size F240 (d50 48-51 pm), roundness of 0.61 and bulk density of 1.77 g / cm3was used.

[0087] This was processed by means of a 3D printing powder bed machine. A doctor blade unit applied a silicon carbide powder layer (approximately 0.15 mm high) to a planar powder bed, and a kind of inkjet printing unit printed a water based phenol resin solution onto the silicon carbide powder bed in accordance with the desired component geometry. The printing table was then lowered by the layer thickness, and another layer of silicon carbide was applied, and phenol resin was again printed on locally. By repeating the procedure, cuboidal test specimens for example with dimensions of 60mm (length)x10 mm (width)x 10 mm (height) were constructed. As soon as the complete "component" was printed, the powder bed was introduced into a furnace preheated to 140° C and was held there for approximately 6 hours, the phenol resin having formed a fully cured and dimensionally stable green body. The excess silicon carbide powder was then sucked away after the cooling and removed from the green body. Density of the cured green body: 1.59 g / cm3

[0088] Measurement using the buoyancy principle (according to ISO 18754) but with mercury as the liquid. Measurement is carried out on the part that is removed directly from the printer after printing and consists only of SiC and the binder of the printing process.

[0089] Example 3 Siliconisation

[0090] The SiC preform (green body) is placed on silicon and / or a silicon alloy, such as a silicon bed, and is subsequently heated in a vacuum or inert atmosphere to a temperature above the melting temperature of Si and I or Si alloys, i.e. to temperatures of more than 1400°C. The molten silicon is sucked into the green body by capillary forces and fills the pores of the green body with silicon.

[0091] Example 4:

[0092] A silicon carbide with grain size F240 (d50 48-51 pm), roundness of 0.61 and bulk density of 1 .77 g / cm3was used. Tap density is 1 .98 g / cm3.

[0093] The powder composition was processed by means of a 3D printing powder bed machine. A doctor blade unit applied a silicon carbide powder layer (approximately 0.15 mm high) to a planar powder bed, and an inkjet printing unit printed a water based phenol resin solution onto the silicon carbide powder with a scanning speed of 0.3m / s and the layer thickness of the control printing is 0.15mm.

[0094] When printing the powder a frequency 4000Hz is simultaneously applied to obtain a silicon carbide powder layer with a density of 1 .80 g / cm3.

[0095] The printing table was then lowered by the layer thickness, and another layer of silicon carbide was applied, and phenol resin was again printed on locally. By repeating the procedure, cuboidal test specimens for example with dimensions of 60mm (length)x10 mm (width)x 10 mm (height) were constructed.

[0096] As soon as the complete "component” was printed, the powder bed was introduced into a furnace preheated to 200° C and was held there for approximately 12 hours to obtain the cured green body, whereby the phenol resin having formed a fully cured and dimensionally stable green body. The excess silicon carbide powder was then sucked away after the cooling and removed from the green body.

[0097] The density of the cured green body is 1.57 g / cm3.

[0098] The cured green body sample is subjected to carbon black solution impregnation and densification treatment.

[0099] The densely treated ceramic green is infiltrated with liquid silicon. The infiltration temperature above 1600°C to obtain silicon carbide composite ceramics with a density of 2.88g / cm3; Elastic modulus 280GPa.

[0100] Example 5 : bimodal SiC particle composition

[0101] A bimodal SiC particle mixture was composed of 74 wt% of the round grain (roundness 0.61) with a particle size d50 of 48-51 pm and 26 wt% of the small grain with a particle size d50 of 9 pm. The minor fraction of smaller particles has a narrow size distribution of (d3-d95 5pm).

[0102] The bulk density of the bimodal composition is 1.9 g / cm3and tap density is 2.22 g / cm3.

[0103] The powder composition was processed by means of a 3D printing powder bed machine. A doctor blade unit applied a silicon carbide powder layer (approximately 0.15 mm high) to a planar powder bed, and an inkjet printing unit printed a water based phenol resin solution onto the silicon carbide powder with a scanning speed of 0.3m / s and the layer thickness of the control printing is 0.15mm.

[0104] When printing the powder a frequency 4000Hz is simultaneously applied to obtain a silicon carbide powder layer with a density of 1 ,90g / cm3.

[0105] The printing table was then lowered by the layer thickness, and another layer of silicon carbide was applied, and phenol resin was again printed on locally. By repeating the procedure, cuboidal test specimens for example with dimensions of 60mm (length)x10 mm (width)x 10 mm (height) were constructed. As soon as the complete "component” was printed, the powder bed was introduced into a furnace preheated to 200° C and was held there for approximately 12 hours to obtain the cured green body, whereby the phenol resin having formed a fully cured and dimensionally stable green body. The excess silicon carbide powder was then sucked away after the cooling and removed from the green body

[0106] The density of the cured green body is 1.66-1.71 g / cm3.

[0107] The cured green body sample is subjected to carbon black solution impregnation and densification treatment.

[0108] The densely treated ceramic green is infiltrated with liquid silicon. The infiltration temperature above 1600°C to obtain silicon carbide composite ceramics with a density of 2.95 g / cm3; Elastic modulus 280GPa.

Claims

Claims1 . Method for obtaining a SiC preform (green body) by powder bed print comprising the steps of:Providing a composition, in particular a powdery composition, comprising at least 80 wt%, preferably at least 85wt%, more preferably at least 90wt% (based on the overall weight of the composition) of SiC particles having o an average grain size (dso) of 2 to 70 pm, preferably 3 to 65 pm, more preferably 5 to 50 pm, such as 25 to 60 pm, preferably 40 to 55 pm, o a roundness of > 0.55, preferably > 0.58, more preferably > 0.6 (as described in experimental section), o bulk density of > 1.6 g / cm3, preferably > 1.65 g / cm3, more preferably > 1.7 g / cm3, even more preferably > 1.75 g / cm3(according to DIN EN 725-9 ISO 23145-2), spreading or printing the SiC particle composition to form at least one first layer while being simultaneously vibrated, applying at least one binder to the at least one first layer of the SiC particles containing composition and thermal and / or light induced consolidating the at least one first layer, and curing the silicon carbide ceramic material green body to obtain a cured green body.

2. Method according to claim 1 , characterized in that the composition comprises 80-100 wt%, preferably 80 - 100 wt%, more preferably 85- 100 wt%, even more preferably 90- 100 wt% of SiC particles.

3. Method according to one of the preceding claims, characterized in that the at least one first composition layer (and preferably each subsequent composition layer) has a layer thickness between 10 and 250 pm, preferably between 50 and 200 pm, more preferably between 80 and 150 pm.

4. Method according to one of the preceding claims, characterized in that the at least one binder is selected from one of acrylates, epoxies, enol ethers, vinyls, phenolic resins, furan resins, epoxy resins, graphite resins, starch, sugar or cellulose solutions.

5. Method according to one of the preceding claims, characterized in that the amount of binder in the printed SiC preform (green body) is 1.0 to 30.0 Vol %, preferably 5.0 to 25.0 Vol %, more preferably 10.0 to 20.0 Vol %, in relation to the total volume of the green body.

6. Method according to one of the preceding claims, characterized in that the SiC preform (green body) is dried or cured.

7. Method according to one of the preceding claims, characterized in that at least one of the SiC preforms (green body) obtained by printing (after drying or curing) has a density > 1.5 g / cm3, preferably > 1.53 g / cm3, more preferably > 1.55 g / cm3, such as in a range between 1.5 and 3.0 g / cm3, preferably between 1.53 and 2.5 g / cm3, more preferably between 1.53 and 2.0 g / cm3, even more preferably between 1.55 and 1.8 g / cm3.

8. Method according to one of the claims 6-7, characterized in that the dried or cured SiC preform (green body) is carbonized.

9. Method according to claim 8, characterized in that the carbonized SiC preform (green body) is infiltrated with liquid silicon.

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