Method for manufacturing shaped si-sic articles, shaped articles and uses

Abstract

The invention relates to a method for producing a shaped body and a shaped body, a green body is formed from a silicon carbide-based ceramic material using an additive manufacturing process, the green body is subsequently subjected to a high-temperature treatment, and the silicon carbide is recrystallized as a result of the high-temperature treatment.

Description

[0001] The invention relates to a method for producing a shaped body and a shaped body of recrystallized silicon carbide. The invention also relates to the use of reactively bonded silicon-infiltrated silicon carbide for producing recrystallized silicon carbide.

[0002] Shaped bodies of silicon carbide (SiC) are known in the prior art and are used in particular for high-temperature applications.

[0003] There are several variations of materials having silicon carbide, including, in particular, recrystallized silicon carbide (RSiC) and reaction-bonded silicon-infiltrated silicon carbide (SiSiC).

[0004] Due to their relatively high temperature resistance, shaped bodies made of recrystallized silicon carbide are often used in high-temperature applications with application temperatures exceeding 1400°C. For example, in a slip casting process, a mixture of silicon carbide grains containing a coarse-grained fraction and a fine-grained fraction is typically used to produce a green compact for this type of shaped body. This green compact is then fired at a relatively high temperature of 2300°C to 2500°C. As a result of diffusion processes, the relatively small grains dissolve, while relatively larger grains form or grow. As a result, a relatively coarse-grained and porous ceramic shaped body is obtained, which no longer exhibits any material changes, even at high temperatures. However, a disadvantage is that the forming of this type of shaped body is limited to ceramic forming methods such as casting, pressing, and injection molding. In particular, this type of shaped body cannot yet be produced using additive manufacturing or 3D printing processes. As a result, there are limited forming options and geometries, and therefore, limited areas of application for this type of shaped body.

[0005] Shaped bodies formed from reaction-bound silicon infiltrated with silicon carbide, also for high-temperature applications, are obtained, for example, by initially forming a matrix of silicon carbide, subsequently saturating it with a carbon black suspension, and then infiltrating it with (metallic) silicon. The matrix can be produced using additive manufacturing processes, as described, for example, in DE 10 2013 017 193 A1. Advantageously, such shaped bodies can also be produced with complex geometries. However, a disadvantage here is that such shaped bodies always have a certain proportion of free (metallic) silicon. Due to the melting point of free (metallic) silicon, the application areas of such shaped bodies are therefore limited to application temperatures of <1400°C.

[0006] It is therefore an object of the present invention to propose a method for producing shaped bodies, shaped bodies and the use of shaped bodies to expand their field of application.

[0007] This object is achieved by a method having the features of claim 1 , a shaped body having the features of claim 19 and a use having the features of claim 23 .

[0008] In the method according to the invention for producing a shaped body, a green body is formed from a ceramic material based on silicon carbide using an additive manufacturing process, which green body is subsequently subjected to a high-temperature treatment as a result of which the silicon carbide is recrystallized.

[0009] According to the present invention, a green body is formed from a suitable silicon carbide-based ceramic material or silicon carbide material or silicon carbide using an additive manufacturing process or a 3D printing process, resulting in a green body formed from a silicon carbide-based ceramic material or silicon carbide material or silicon carbide. Multiple process steps can be provided for forming the green body, with the use of an additive manufacturing process also being able to constitute only one process step. The use of an additive manufacturing process allows the formation of green bodies or shaped bodies with a high degree of design freedom or a wide variety of shapes, allowing the shaped bodies to have complex geometries and thus be more widely usable.

[0010] According to the invention, it is further provided that the green body is subsequently subjected to a high-temperature treatment or annealing treatment or high-temperature annealing, in such a way that the material or silicon carbide material or silicon carbide recrystallizes as a result of the high-temperature treatment. In other words, the silicon carbide is converted into recrystallized silicon carbide, so that a recrystallized silicon carbide shaped body is obtained that can be used at application temperatures >1400°C.

[0011] As a result, the method according to the invention makes it possible to produce shaped bodies having an expanded field of application.

[0012] Advantageously, reactively bonded silicon infiltrated silicon carbide (SiSiC) can be used as the silicon carbide or material to form the green body, so that the green body can be formed from reactively bonded silicon infiltrated silicon carbide. This is generally suitable for processing in the context of additive manufacturing. The green body can be produced according to the method described in DE 10 2013 017 193 A1.

[0013] Advantageously, when forming a green body, the matrix can be formed from granules comprising silicon carbide or primary silicon carbide using an additive manufacturing process. The matrix can be integrally constructed layer by layer from the amorphous granules using a physical or chemical hardening or melting process. The granules can have a content of at least 95% silicon carbide or primary silicon carbide. For example, the average grain size can be 70 μm to 200 μm. A binder, such as a resin, can be used for hardening.

[0014] In one embodiment of the method, the granules or silicon carbide of the granules can have a coarse-grained portion and a fine-grained portion. Accordingly, it can be arranged to use granules with a bimodal grain size distribution in the additive manufacturing process. For example, additive manufacturing can then be carried out using fused filament fabrication (FFF). As a result of the high-temperature treatment or diffusion process, the fine grains of the fine-grained portion can then be dissolved, and the coarse grains of the coarse-grained portion can grow or form. The binder can form the fine-grained portion together, or the silicon carbide precursor can be processed as a binder, whereby the fine-grained portion can be produced.

[0015] Advantageously, the substrate can be impregnated with a carbon suspension, in particular a carbon black suspension or a graphite suspension.The substrate can then be saturated at least once with the carbon suspension.

[0016] Alternatively, the carbon may be introduced into the matrix by vapor deposition.

[0017] Alternatively, the substrate may be impregnated with a resin which can subsequently be converted into carbon. The conversion of the resin into carbon may be performed by a temperature treatment, in particular by a high temperature treatment.

[0018] Advantageously, the matrix can be infiltrated with (metallic) silicon. Contact of the carbon with liquid or gaseous (metallic) silicon can then form secondary silicon carbide in a subsequent reaction firing, which can solidify the resulting bonded composite material. This can produce a green compact. Preferably, the infiltration of the matrix with (metallic) silicon occurs after impregnation of the matrix with a carbon suspension or with a resin, or after the carbon has been introduced into the matrix.

[0019] Advantageously, the green silicon carbide can then have at least primary silicon carbide that together form or form a coarse grain portion and at least secondary silicon carbide that together form or form a fine grain portion, the fine grains of the fine grain portion being dissolved, and the coarse grains of the coarse grain portion being able to grow or form as a result of the high temperature treatment or diffusion process. In other words, the secondary silicon carbide, which is finer in grain size than the primary silicon carbide, can form a kind of "sacrificial phase" for the subsequent recrystallization process. If the primary silicon carbide of the granular material already has a coarse grain portion and a fine grain portion, the fine grain portion of the primary silicon carbide of the granular material can together form the fine grain portion of the green body. The coarse grain portion of the green body can then be formed from the coarse grain portion of the primary silicon carbide of the granular material.

[0020] Advantageously, free (metal) silicon can be removed as a result of a (chemical) etching process or as a result of a high-temperature treatment, in particular by evaporation, in such a way that the shaped body can be essentially free of free (metal) silicon. If the free (metal) silicon remaining in the green body or the shaped body as a result of the infiltration with (metal) silicon is removed from the green body or the shaped body in a high-temperature treatment, the shaped body obtained thereby can then be used at application temperatures >1400° C. Preferably, the free (metal) silicon can be removed by evaporation, preferably vacuum evaporation. By removing the free (metal) silicon, the shaped body is essentially or largely free of free (metal) silicon. Trapped silicon residues can remain in the shaped body. The mass fraction of free (metal) silicon remaining in the shaped body should be well below 5%.

[0021] Advantageously, free (metallic) silicon can be initially removed and subsequently the silicon carbide can be recrystallized. This can thus involve two separate process steps. However, both processes can also occur simultaneously in a combined process step.

[0022] Advantageously, the removal of free (metallic) silicon can be performed under first process parameters and the recrystallization can be performed under second process parameters at least partially different from the first process parameters. In the present case, the term "process parameters" refers in particular to temperature and / or pressure.

[0023] Advantageously, the silicon carbide can be sintered as a result of the high temperature treatment.As a result, the silicon carbide grains can be sintered together.

[0024] Advantageously, the high temperature treatment can be carried out at a temperature of ≥ 2000° C., preferably 2100° C. to 2500° C. The high temperature treatment can be carried out in an oven or a treatment chamber. The residence time in the oven or treatment chamber can be several hours.

[0025] Advantageously, the high temperature treatment can be carried out at reduced atmospheric pressure, preferably under vacuum. For example, the high temperature treatment can be carried out at a pressure of 1 mbar to 300 mbar.

[0026] Advantageously, binder jetting can be used as an additive manufacturing process. However, other additive manufacturing processes are also conceivable or can be appropriately selected.

[0027] Advantageously, as a result of the high temperature treatment, silicon carbide can be converted into recrystallized silicon carbide (RSiC). In this way, shaped bodies can be produced from recrystallized silicon carbide that have high temperature resistance, creep resistance, and chemical resistance.

[0028] Advantageously, after the high-temperature treatment, the shaped body can be coated with silicon carbide (SiC) by chemical vapor deposition (CVD). Advantageously, particularly due to its corresponding purity, the shaped body can then also be used in the semiconductor sector. The fact that the shaped body is made of recrystallized silicon carbide provides a relatively high degree of flexibility in the selection of downstream coating processes.

[0029] The shaped body according to the invention relates to a green body formed from a ceramic material based on silicon carbide using an additive manufacturing process, said green body subsequently being subjected to a high-temperature treatment as a result of which the silicon carbide is recrystallized.

[0030] The shaped bodies according to the invention are therefore produced by the method according to the invention.

[0031] With regard to the advantageous effects of the shaped body according to the invention, reference is made to the description of the advantages of the method according to the invention.

[0032] Advantageously, the shaped body may be substantially free of free (metallic) silicon.

[0033] Advantageously, the shaped bodies can be used for high-temperature applications with application temperatures >1400° C., preferably >1500° C.

[0034] The shaped body may be a component, in particular a high-temperature component, such as a furnace component, or a component which can be used in the semiconductor industry or which can be formed in such a way.

[0035] Further advantageous embodiments of the shaped body result from the description of the features of the dependent claims which refer back to method claim 1 .

[0036] According to the invention, reaction-bonded silicon-infiltrated silicon carbide (SiSiC) is used to produce recrystallized silicon carbide (RSiC) for forming a shaped body, or when forming a shaped body, the reaction-bonded silicon-infiltrated silicon carbide is subjected to a high-temperature treatment in such a way that the reaction-bonded silicon-infiltrated silicon carbide is converted into recrystallized silicon carbide.

[0037] In other words, according to the present invention, reactively bonded silicon-infiltrated silicon carbide, which is then converted into recrystallized silicon carbide, is used as the starting point for forming the shaped body, rather than recrystallized silicon carbide. This "detour" through reactively bonded silicon-infiltrated silicon carbide on the "path" to forming the shaped body to be formed from recrystallized silicon carbide allows for flexible determination of the shape of the shaped body by the additive manufacturing process, since reactively bonded silicon-infiltrated silicon carbide can be processed more flexibly by additive manufacturing than recrystallized silicon carbide. This processing can be performed before the conversion.

[0038] During high temperature processing, free (metallic) silicon may be removed or evaporated.

[0039] With regard to the advantageous effects of the use according to the invention, reference is supplementarily made to the description of the advantages of the method according to the invention.

[0040] Further advantageous embodiments of the use result from the description of the features of the dependent claims which refer back to method claim 1 .

Claims

1. A method for producing a shaped body, wherein a green body is formed from a ceramic material based on silicon carbide using an additive manufacturing process, the green body being subsequently subjected to a high-temperature treatment which causes the silicon carbide to recrystallize.

2. The method according to claim 1, It is characterized by: Reaction-bonded silicon-infiltrated silicon carbide (SiSiC) was used as the silicon carbide.

3. The method according to claim 1 or 2, It is characterized by: When forming the green body, a base body is formed from the pellets having silicon carbide using the additive manufacturing process.

4. The method according to claim 3, It is characterized by: The silicon carbide of the granules has a coarse-grained portion and a fine-grained portion.

5. The method according to claim 3 or 4, It is characterized by: The substrate is impregnated with a carbon suspension, in particular a carbon black suspension or a graphite suspension.

6. The method according to claim 3 or 4, It is characterized by: The carbon is introduced into the matrix by vapor deposition.

7. The method according to claim 3 or 4, It is characterized by: The substrate is impregnated with a resin which is subsequently converted into carbon.

8. The method according to any one of claims 5 to 7, It is characterized by: The matrix is ​​infiltrated with silicon.

9. The method according to claim 8, It is characterized by: The silicon carbide of the green body has primary silicon carbide that together form at least a coarse-grained portion and secondary silicon carbide that together form at least a fine-grained portion, and as a result of the high-temperature treatment, fine grains of the fine-grained portion are dissolved and coarse grains of the coarse-grained portion grow.

10. The method according to claim 8 or 9, It is characterized by: Free silicon is removed as a result of the etching process or is removed as a result of the high-temperature treatment, in particular vaporized, in such a way that the shaped body is essentially free of said free silicon.

11. The method according to claim 10, It is characterized by: The free silicon is initially removed and the silicon carbide is subsequently recrystallized.

12. The method according to claim 11, It is characterized by: The removal of free silicon is performed under first process parameters, and the recrystallization is performed under second process parameters that are at least partially different from the first process parameters.

13. The method according to one of the preceding claims, It is characterized by: The silicon carbide is sintered as a result of the high temperature treatment.

14. The method according to one of the preceding claims, It is characterized by: The high temperature treatment is performed at a temperature of ≥2000°C, preferably 2100°C to 2500°C.

15. The method according to one of the preceding claims, It is characterized by: The high temperature treatment is carried out under reduced atmospheric pressure, preferably under vacuum.

16. The method according to one of the preceding claims, It is characterized by: Use binder jetting as the additive manufacturing process.

17. The method according to one of the preceding claims, It is characterized by: As a result of the high temperature treatment, the silicon carbide is converted into recrystallized silicon carbide (RSiC).

18. The method according to one of the preceding claims, It is characterized by: After the high-temperature treatment, the shaped body is coated with silicon carbide (SiC) by chemical vapor deposition (CVD).

19. A shaped body formed from a silicon carbide based ceramic material using an additive manufacturing process to form a green body, the green body subsequently being subjected to a high temperature treatment as a result of which the silicon carbide is recrystallized.

20. The formed body according to claim 19, It is characterized by: The shaped body is formed in such a manner that the shaped body is substantially free of free silicon.

21. The shaped body according to claim 19 or 20, It is characterized by: The shaped bodies can be used for high-temperature applications with application temperatures >1400°C, preferably >1500°C.

22. The shaped body according to claim 19, It is characterized by: The shaped body is a component, in particular a high-temperature component or a component which can be used in the semiconductor industry.

23. Use of reaction-bonded silicon-infiltrated silicon carbide (SiSiC) for producing recrystallized silicon carbide (RSiC) for forming shaped bodies, said reaction-bonded silicon-infiltrated silicon carbide being subjected to a high-temperature treatment in such a way that said reaction-bonded silicon-infiltrated silicon carbide is converted into said recrystallized silicon carbide.