阅读说明：本技术 用于制造cmc组件的方法 (Method for manufacturing CMC components ) 是由 阿尔贝托·奥尔托纳 阿尔贝特·马里亚·沃杰尔迈尔 乔瓦尼·比安希 马丁·扎科夫斯基 于 2019-02-11 设计创作，主要内容包括：提出了用于制造CMC组件(6)的方法,所述方法至少包括以下步骤：使由纤维(15)增强热塑性材料(14)制成的生坯(1、10)热解(2)；和通过液态碳化物形成物质(31)对经热解的生坯进行浸润(4)。生坯(1、10)的纤维(15)被布置成一条或数条股线(16),这些股线(16)各自具有主延伸方向。每条股线(16)的纤维(15)的长度大于生坯(1、10)沿该股线(16)的主延伸方向的总长度(L)。(A method for manufacturing a CMC component (6) is proposed, the method comprising at least the following steps: pyrolysing (2) a green body (1, 10) made of a fibre (15) -reinforced thermoplastic material (14); and infiltrating (4) the pyrolyzed green body with a liquid carbide-forming substance (31). The fibers (15) of the green body (1, 10) are arranged in one or several strands (16), the strands (16) each having a main direction of extension. The length of the fibres (15) of each strand (16) is greater than the total length (L) of the green body (1, 10) in the main extension direction of the strand (16).)

1. A method for manufacturing a CMC component (6) comprising at least the steps of:

-pyrolysing (2) a green body (1, 10) made of a fibre (15) reinforced thermoplastic material (14); and

-infiltrating (4) the pyrolysed green body with a liquid carbide-forming substance (31);

wherein the fibers (15) of the green body (1, 10) are arranged in one or several strands (16), which strands (16) each have a main direction of extension,

and wherein the length of the fibres (15) of each strand (16) is greater than the total length (L) of the green body (1, 10) along the main extension direction of that strand (16).

2. The method according to claim 1, wherein the length of all fibers (15) is greater than the maximum total length (L) of the green body (1, 10).

3. The method according to claim 1 or 2, wherein the pyrolysis (2) is performed in an inert atmosphere and with the green body (1, 10) positioned in a mould (20).

4. The method according to one of the preceding claims, wherein the fibers (15) are arranged in the green body (1, 10) such that the fibers (15) at least partially follow the three-dimensional shape of the green body (1, 10).

5. The method according to one of the preceding claims, wherein the fibers (15) of each strand (16) are at least partially entangled with each other.

6. The method according to one of the preceding claims, wherein the length of the fibers (15) is kept substantially constant before completing the CMC component (6).

7. Method according to one of the preceding claims, wherein the thermoplastic material (14) of the green body (1, 10) is Polyetheretherketone (PEEK).

8. Method according to one of the preceding claims, wherein the fibres (15) are made of carbon or silicon carbide.

9. The method according to one of the preceding claims, wherein the fibers (15) are coated.

10. The method according to one of the preceding claims, wherein the green body (1, 10) is manufactured by flow pressing, in particular by pushing and/or pultrusion, the fibre (15) reinforced thermoplastic material (14).

11. The method according to one of the preceding claims, wherein the content of the fibers (15) in the fiber (15) reinforced thermoplastic material (14) of the green body (1, 10) is in the range of 20 to 70 vol-%, in particular 40 to 60 vol-%.

12. Method according to one of the preceding claims, wherein boron nitride (32) is applied to at least a portion (13) of the pyrolysed green body prior to the infiltration (4) with the carbide-forming substance (31).

13. A CMC component (6) manufactured according to the method of one of the preceding claims.

14. The CMC component (6) of claim 13, wherein the CMC component (6) is a turbine blade, a nozzle, a gear or a fastening component, in particular a screw (10), a nut, a bolt, a pin or a rivet.

15. The CMC component of claim 13 or 14, wherein the CMC component (6) is adapted for use in medical technology, aerospace, nuclear power plants or fusion reactors.

Technical Field

The present invention relates to a method for manufacturing a Ceramic Matrix Composite (CMC) component and a CMC component manufactured according to such a method. CMC materials consist of fibers embedded in a ceramic matrix and can be used in various technical fields, in particular in medical technology, aerospace and power station development.

Background

Fiber reinforced ceramic materials, also known as Ceramic Matrix Composite (CMC) materials, are used in a variety of applications and technical fields. CMC materials combine the advantages of ceramic materials with the resistance of fibers to mechanical or thermomechanical loads, creating materials with new and superior properties. The primary purpose of reinforcing ceramic materials by fibers is to provide structural robustness (robustness) to otherwise brittle ceramic materials. CMC materials have unique characteristics such as high temperature stability, high thermal shock resistance, high hardness, high corrosion resistance, lightweight, and versatility, providing unique engineering solutions. The combination of these characteristics makes ceramic matrix composites an attractive alternative to traditional process industry materials such as superalloys and refractory metals.

There are several different methods to make CMC materials. One common method is to pyrolyze the fiber-containing polymer. And then infiltrating the high-porosity matrix obtained after pyrolysis with liquid silicon to react to generate silicon carbide.

In DE 19957906, the manufacture of fiber-reinforced composite articles is disclosed, in which a fiber-reinforced plastic material is pyrolyzed.

DE 102014200510 discloses a method for manufacturing ceramic composites, wherein a fiber reinforced thermoplastic material is injection molded in pellet form to form a green body, which is subsequently pyrolyzed and converted into the final CMC component. Due to the particulate form of the fibre-reinforced thermoplastic material, only limited structural robustness of the final product can be achieved using this method.

DE 10164231 proposes the manufacture of brake disks and clutch plates from ceramic materials reinforced by short fibers. Conductive fiber reinforced mass (mass) is filled into a compression mold and subsequently hardened under pressure into a green body. The green body is then carbonized and infiltrated with liquid metal.

EP 1340733 discloses a method for manufacturing a ceramic composite material with unidirectionally arranged reinforcing fibers. In this method, the reinforcing fibers are first wrapped with a sacrificial polymer and then treated by adding a binder resin before carbonizing them. Due to the use of sacrificial polymers, shrinkage of the parallel fibers to each other can be avoided. The pores of the carbonized assembly were then infiltrated with liquid silicon. Due to the unidirectional arrangement of the fibers, a high structural robustness can be achieved with this method only for components having a relatively simple three-dimensional structure with flat surfaces.

An article entitled carbonization of the carboxylic acid on the mechanical properties of thermoplastic polymer derived C/C-SiC composites in Journal of the European Ceramic Society,2017.37(2), page 523 and 529, Reichert, F., A.M.P. rez-Mas, D.Barreda, C.blanco, R.Santamaria, C.Kuttner, A.Fery, N.Langhef and W.Krenkel, investigated the effect of carbonization temperature on the mechanical properties of thermoplastic polymer derived C/C-SiC composites. It further discloses infiltrating the composite with liquid silicon after carbonization.

Disclosure of Invention

It is an object of the present invention to provide a method for manufacturing a CMC component which may have a relatively complex three-dimensional structure and/or surface, but which still has a high structural robustness.

This object is solved by a method as claimed in claim 1. Further embodiments of the method are provided in the dependent claims 2 to 12. Claimed in claim 13 is a CMC component manufactured according to this method, and further embodiments of the CMC component are provided in dependent claims 14 and 15.

Accordingly, the present invention provides a method for manufacturing a CMC component, the method comprising at least the steps of:

-pyrolysing a green body made of a fibre-reinforced thermoplastic material; and

infiltration of the pyrolyzed green body by liquid carbide-forming substances, in particular by liquid silicon or by liquid silicon alloys.

The fibers of the green body are arranged in one or several strands, each having a main direction of extension. The length of the fibres of each strand is greater than the total length of the green body in the main extension direction of the strand.

The green body forms the original component for carrying out the method of the invention and may in particular be manufactured according to the method as disclosed in DE 4445305, the entire content of which is incorporated herein by reference. Thus, the green body may be considered an intermediate product in the manufacture of CMC components. However, the green body may also be represented by components that are originally intended to form by themselves the final assembly for various applications. Preferably, the green body is produced by flow-pressing, in particular push-extruding and/or pultrusion, of a fibre-reinforced thermoplastic material. In this case, the molten fibre-reinforced thermoplastic material is pressed into a mould in order to adopt the desired green shape. During the flow compaction, the fibers embedded in the thermoplastic material preferably exit the extruder in a unidirectional manner, thereby self-aligning within the die to at least partially follow the profile of the die and thus the profile of the green body. Alternatively, the green compact may be manufactured by, for example, a pultrusion process (pultrusion process). The green body is preferably made using continuous fibers.

Being longer than the total length of the green body in the main extension direction of the respective fiber strand, the individual fibers necessarily comprise one or several bends and are usually also entangled with each other. As a result, the fibers improve the structural stability of the green body, and thus the final CMC component, not only in the main extension direction of their respective strands, but also in other directions. Furthermore, by this arrangement of the fibers, components having a relatively complex three-dimensional structure can be easily manufactured. Fine surface features such as threads may be provided and may be enhanced by the strands.

To achieve good results in terms of structural stability of the CMC component, preferably the fibers are 1.2 to 4 times, more preferably 1.2 to 2.5 times, most preferably 1.2 to 1.8 times as long as the green body in the main extension direction of the respective strands. Of course, additional fibers may be present in the green body, which are shorter than the strands and/or which are not even part of the strands. Such additional fibers may be advantageous, for example, in order to improve the strength of the CMC component in a direction perpendicular to the main extension direction of the strands.

The method for manufacturing the CMC component is preferably a near net shape manufacturing method, which means that the final CMC component has substantially the same form as the green body, both in shape and size. The arrangement of fibers within the component is preferably also substantially the same for both the green and final CMC components. During manufacture, the length of the fibers preferably remains substantially unchanged prior to completion of the CMC component. Thus, the fibers are present in the CMC component in the same manner as in the green body and function to reinforce the CMC component in the same manner as for the green body.

A strand is understood to mean a bundle of fibers all having the same main direction of extension. Fiber strands are often used to reinforce a certain part of or the entire assembly, in particular along the main extension direction of the strand, but also in other directions. The individual fibers of a strand are generally longer than the total length of the strand in its main extension direction.

In a particularly preferred embodiment, the length of all fibres is greater than the maximum total length of the green body. To simplify the manufacturing process of the green body, no additional fibers are present in the green body which are shorter than the maximum total length of the green body.

During pyrolysis, the thermoplastic material of the green body is carbonized to at least partially react to form carbides during subsequent wetting with a liquid carbide-forming substance. The pyrolysis is preferably carried out in an inert atmosphere, for example in the presence of argon or nitrogen. In order to hinder the thermal expansion of the thermoplastic material and thus maintain the shape of the green body, the green body is preferably positioned in a mould during pyrolysis.

For wetting, liquid silicon (Si) is preferably used as the liquid carbide-forming substance to react at least partially to silicon carbide. Infiltration may also be performed using a liquid silicon alloy to at least partially react to form silicon carbide and possibly other carbides. In the case of liquid silicon alloys, it is preferable to alloy silicon with metals, such as in particular with elements from the group of titanium (Ti), zirconium (Zr), molybdenum (Mo) and hafnium (Hf) or mixtures thereof.

Alternatively, elements from the group of titanium (Ti), zirconium (Zr), molybdenum (Mo) and hafnium (Hf) may also be used as liquid carbide-forming substances. In this regard, one of these elements of Ti, Zr, Mo and Hf may be used alone, or a mixture thereof may be used. The elements Ti, Zr, Mo and Hf, or mixtures thereof, may be alloyed with silicon.

The carbide formed as a result of infiltration with the carbide-forming substance preferably has a hardness suitable for the component to be used as a (mechanical) fastening component, turbine blade, nozzle or gear. The carbide may in particular be silicon carbide and/or a metal carbide.

Advantageously, the fibres are arranged in the green body such that the fibres at least partially follow the three-dimensional shape of the green body. Thus, preferably at least some of the fibres follow the three-dimensional profile of the green body along at least a portion of their overall extension. Thus, the extension and arrangement of the fibers therethrough advantageously reflects the three-dimensional shape of the green body. By following the contour of the green body, the fibers reinforce the green body in an optimal manner in the surface region and thus reinforce the final CMC component.

To further improve the structural robustness of the CMC component, the fibers of each strand are advantageously at least partially entangled with each other.

The green thermoplastic material is preferably Polyetheretherketone (PEEK). The fibers are preferably made of carbon and/or silicon carbide for higher temperature resistance. The fibers may be coated fibers. In certain preferred embodiments, no additional materials, in particular no binder resins or the like, are present or added to the green body before and/or during pyrolysis. In other, also preferred, embodiments, a first pyrolysis is performed, then the pyrolyzed green body is infiltrated with a polymer, such as a phenolic resin, followed by a second pyrolysis, and then any number of further cycles of polymer infiltration and subsequent re-pyrolysis may be performed.

The green body is preferably made in one piece as a whole. Advantageously, the green body is manufactured directly as a whole, which means that there are no separate parts that are manufactured separately and then joined together to form the green body, for example. In the case of a green body which is manufactured directly as a whole, there is no abrupt transition in the green body with respect to the properties and/or fibers of the thermoplastic material.

The content of fibers in the green fiber-reinforced thermoplastic material is advantageously in the range from 20 to 70% by volume, in particular in the range from 40 to 60% by volume. The fibres are advantageously regularly distributed in the green body, which means that the fibre content is approximately the same in all regions of the green body.

In order to reduce the wettability of the pyrolysed component and thus reduce the formation of residual molten carbide-forming species (e.g. silicon) on the surface of the component, particularly on surface portions of the component comprising fine features (e.g. threads), boron nitride may be applied to at least a portion of the pyrolysed component prior to infiltration with the liquid carbide-forming species.

The invention also relates to a CMC component manufactured according to the above method. The CMC component may be a turbine blade, a nozzle, a gear or a fastening component, in particular a screw, a nut, a bolt, a pin or a rivet. The CMC component manufactured according to the method may be particularly suitable for use in medical technology, aerospace, nuclear power plants or fusion reactors.

Drawings

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which are for illustrative purposes only and are not limiting. Shown in the drawings are:

FIG. 1: a flow chart of a preferred embodiment of a method for manufacturing a CMC component in accordance with the present invention;

FIG. 2: a schematic cross-sectional view of a green body for use in the method according to the invention, wherein the arrangement of fibers within the green body is visualized;

FIG. 3: a perspective exploded view of a mold with a green body inserted during the pyrolysis process; and

FIG. 4: schematic cross-sectional view of an infiltration apparatus with pyrolyzed green bodies inserted during liquid silicon infiltration.

Detailed Description

FIG. 1 shows a flow chart illustrating a preferred embodiment of the method of the present invention for fabricating CMC components.

To carry out the method of the invention for manufacturing the CMC component 6, the green body 1 is used as a raw component. The green body 1 is made of a fiber-reinforced thermoplastic material and can be produced in particular according to the method disclosed in DE 4445305.

Fig. 2 illustrates an exemplary embodiment of such a green body 1 in the form of a screw 10. The screw 10 has a head 11 and a shank 12. The shaft 12 includes threads 13, the threads 13 defining a majority of the exterior surface of the shaft 12. Due to the thread 13, the outer surface of the shank 12 comprises local elevations and depressions which are essential for the function of the screw. High structural robustness is particularly critical in these locally raised and recessed regions of the thread 13.

The green body 10 is made of a thermoplastic material 14, preferably Polyetheretherketone (PEEK) 14. In a specific embodiment, the material Victrex^TMPEEK 150 is used as thermoplastic material 14. The thermoplastic material 14 may also be another material, in particular a Polyaryletherketone (PAEK) from the family of polymers, such as Polyetherketone (PEK), Polyetherketoneketone (PEKK), etc.; or other so-called high performance thermoplastics such as Polyetherimide (PEI), Polyethersulfone (PESU), Polysulfone (PSU), Thermoplastic Polyimide (TPI), and the like.

Fibers 15 are embedded in the thermoplastic material 14. The fibers 15 may in particular be carbon fibers or silicon carbide fibers. In a particular embodiment of the process of the present invention,product(s)Continuous carbon fiber IM7 was used for the fibers 15. As an alternative, for example, the product TyrannoThe same may be used for the fibers 15.

As can be seen in fig. 2, all fibers 15 are longer than the maximum overall length L of the screw 10. In the present case of the screw, the maximum overall length L of the screw 10 is measured along a central longitudinal axis extending in the longitudinal extension of the shaft 12. The length of the fibers 15 is greater than the maximum total length L of the screw 10, since the extensions of the individual fibers 15 are not straight and are not parallel to each other. Instead, each fiber 15 is bent several times along its main extension direction. The fibers 15 are also at least partially entangled/intermingled with each other. At the same time, all the fibres 15 extend along substantially the same main direction oriented parallel to the central longitudinal axis of the screw 10 (and in particular of the shank 12 thereof). Due to this bent and tangled arrangement of the fibers 15, a particularly high structural robustness of the screw 10 (and ultimately of the CMC component 6) may be achieved not only along the common main direction of the fibers 15, but also in all other directions, although still extending along the same main direction.

It can also be seen in fig. 2 that in the region of the thread 13, i.e. close to the outer side of the shaft 12, the fibres 15 follow the bulges and depressions formed by the thread 13. In a particularly preferred embodiment, the fibers 15 form a helix even in the region of the thread 13, in particular in the raised region of the thread 13, to follow the shape of the continuous raised helix formed by the thread 13. Since the respective fiber 15 extends through the sectional view plane of fig. 2, the respective fiber 15 is visualized in fig. 2 by a point in the region of the thread 13. In the region of the screw head 11, the fibres 15, in particular the fibres 15 arranged near the sides of the screw 10, follow the contour of the head 11, which greatly enhances the structural stability of the head 11.

The fibres 15 together form a strand 16, the main direction of the strand 16 extending along the central longitudinal axis of the screw 10. Unlike in the present embodiment of the screw, in other embodiments there may be several fiber strands, wherein each strand extends along a different main direction. The fibers 15 of each strand 16 extend substantially along the same main direction, but are bent several times and at least partially entangled with each other. Thus, each strand 16 improves the structural stability of the screw 10 (and ultimately of the CMC component 6) mainly in its main extension direction and also in all other directions.

To manufacture the CMC component, the green bodies 1, 10 are pyrolyzed as shown in step 2 of fig. 1. Pyrolysis is carried out in a mould 20 as shown in figure 3 to retard thermal expansion of the thermoplastic material 14 and maintain the shape of the green body 1, 10. The mould 20 is thus used for maintaining the original shape of the green body 1, 10, in particular for preserving functionally critical surface structures, such as the threads 13 of the screws 10.

The mold 20 used in fig. 3 includes a first mold body 21 and a second mold body 22. In the present embodiment, the mold 20 further includes a head insert 23 and a threaded insert 24, the head insert 23 and the threaded insert 24 having inner surfaces that form the negative (negative) surfaces of the head 11 and the threads 13 of the screw 10, respectively. The head insert 23 and the threaded insert 24 each have an upper portion and a lower portion. By using inserts 23, 24, the design of the head 11 and the thread 13 can be easily changed by simply replacing the inserts 23, 24 with respective different inserts. Towards the side, the mold 20 may be closed and held together by a first front plate 25 and a second front plate 26. In the closed state of the mold 20, the first mold body 21 and the second mold body 22 form, together with the respective upper and lower portions of the head insert 23 and the threaded insert 24 and with the first front plate 25 and the second front plate 26, an inner cavity for accommodating the screw 10. This cavity forms an almost exact negative of the screw 10 and therefore limits the profile of the screw 10 during pyrolysis.

The mold 20 is designed to ensure certain manufacturing tolerances (productiontollence) with respect to the final CMC component 6. For example, the die 20 may have a maximum over-dimension (maximum-sizing) of 0.02mm to 0.05mm with respect to the nominal dimensions of the external features (e.g., the protrusions formed by the threads 13) of the final CMC component 6. Accordingly, with respect to the internal features of the final CMC component 6 (e.g., the depressions formed by the threads 13), for example, a maximum undersize (maximum under-sizing) of 0.02mm to 0.05mm may be provided.

The mold 20 should preferably be made of hot work tool steel (hot work tool) suitable for periodic exposure to harsh thermal conditions. In a particular embodiment, AISI 1.2343 is used as the steel for die 20.

The roughness Ra of all surfaces of the mold 20 in direct contact with the green bodies 1, 10 to be pyrolyzed is preferably 0.4 μm or less. The configuration of the mold 20 should ensure that after pyrolysis, no significant mechanical stress acts on the screw 10 when the screw 10 is removed from the mold 20. The design of the mould 20 should ensure that the mould parts 21 to 26 are tightly connected during the entire pyrolysis process 2. The mold design and mold material should ensure that the mold 20 maintains its shape throughout the pyrolysis process 2, in accordance with the shape tolerances of the final CMC component 6. It is generally not necessary that the mould 20 is airtight, but it should preferably be ensured that no solids or liquids can leach out of the mould 20 during pyrolysis 2.

Pyrolysis 2 is carried out under an inert atmosphere, such as a flow of argon or nitrogen (100 nl/min). Good results are achieved when the heating rate is increased from room temperature up to e.g. 1000 ℃ with a heating rate in the range of 10 to 60 ℃/hour. The temperature may then be further raised, for example, up to 1600 ℃ to 1800 ℃.

During pyrolysis 2, gases resulting from the decomposition of the thermoplastic material 14 (e.g., the PEEK matrix) are preferably allowed to escape from the screw 10 and pass through the mold 20, e.g., through the interface between the various mold components 21-26.

After the pyrolysis 2 is carried out, a boron nitride coating 3 (see fig. 1) is optionally but preferably applied before the step of liquid silicon impregnation 4. The step of boron nitride coating serves to reduce the wettability of functionally critical parts of the surface of e.g. the pyrolysed green body 1, 10 with respect to the molten silicon. Such a vital surface part may for example be the region of the thread 13 of the screw 12. The boron nitride coating 3 greatly reduces the need for post-treatment and finishing operations on the various surface portions. By reducing the wettability of the respective surface portions, the formation of residual molten silicon on the component due to the step of wetting 4 with liquid silicon can be significantly reduced. For this purpose, for example, in the region of the thread 13, the shank 12 of the pyrolyzed screw 10 may be dip-coated in a water-based boron nitride suspension. After appropriate drying, the assembly may then be wetted with liquid silicon as shown in step 4 of fig. 1.

The liquid silicon impregnation 4 is carried out to at least partially, preferably substantially completely, convert the pyrolysed thermoplastic material 14 of the screw 10 into silicon carbide. For this purpose, liquid silicon or a liquid silicon alloy is introduced into the component through the hole of the screw 10 left after the pyrolysis 2. Within the pyrolysed green body 1, 10, silicon reacts at least partially with carbon produced during pyrolysis 2 to form silicon carbide and possibly other carbides if infiltrated with a silicon alloy.

For liquid silicon infiltration 4, the pyrolyzed screws 10 are placed in a graphite crucible 33 of an infiltration apparatus 30 (fig. 4). To avoid silicon wetting the crucible 33, a boron nitride coating is preferably applied to the inner surface of the crucible 33. The wafer may then be placed on the bottom of crucible 33. In this case, a sufficient amount of silicon is selected to achieve the desired degree of wetting.

Instead of infiltrating the pyrolyzed green body with silicon in step 4, essentially any other carbide-forming substance may be used, such as a silicon alloy or a single element of the group Ti, Zr, Mo and Hf, or a mixture thereof, which may be alloyed with silicon. Thus, the use of silicon for the wetting should be considered as only one example of performing step 4 of the method. The example of using silicon is a preferred but certainly not exclusive example of how infiltration of a pyrolysed green body may be carried out to produce a carbide or carbides.

After the infiltration apparatus 30 is prepared, the crucible 33, in which the pyrolyzed screws 10 are positioned, is placed in a furnace for performing the liquid silicon infiltration 4. As already mentioned, during the liquid silicon impregnation 4, the threads 13 of the screw 10 are preferably coated with boron nitride 32. Due to the boron nitride 32, the surface structure of the screw 10 in the region of the thread 13 is preserved, while still being able toComplete infiltration is achieved. To obtain a C-Si-SiC ceramic, at a temperature higher than the melting point of silicon (preferably in the range 1450 ℃ to 1600 ℃), in a vacuum (residual pressure advantageously 10)^-2Millibar or less) to infiltrate the screw 10 with molten Si. The crucible 33 is heated to these temperatures by an electric furnace with advantageously fast heating rates (e.g., 50 ℃ to 100 ℃ per minute). Once the desired temperature is reached, it is maintained for a sufficient amount of time (minutes up to hours for large parts) to allow the molten liquid silicon 31 to fully wet the screw 10. At these temperatures, the molten Si first wets the porous carbon body of the screw 10 by capillary action to react with it to form SiC. The skilled person will also refer to this process alone as Melt Infiltration (MI) or Liquid Silicon Infiltration (LSI) or Reactive Melt Infiltration (RMI). A carbon core, typically made of a rigid carbon felt or of pyrolized wood, may be placed between the pyrolized assembly and the crucible 33 to drain excess molten silicon 31.

After the liquid silicon infiltration 4, a post-treatment 5 is performed to obtain the final CMC component 6 (fig. 1). A post-treatment 5 is usually required due to the excess silicon left on the component surface after wetting 4 with liquid silicon. To achieve the final shape of the CMC component within the required manufacturing tolerances, different procedures may be applied, either alone or in combination with each other. Examples of such post-treatment processes are grinding, chemical etching, barrel finishing (tumbling) and liquid silicon desorption. Each of these procedures is well known to the skilled person.

In the case of chemical etching, in particular, etching of silicon according to the following reaction can be applied: 3Si +12HF +4HNO₃＝8H₂O+4NO+3SiF₄. Such chemical etching may be applied in particular to functionally critical parts of the assembly, for example in the region of the thread 13 of the screw 10. For example, a mixture of hydrofluoric acid and nitric acid at a ratio of about 3:1 may be applied at 100 ℃ for 24 hours with continuous stirring.

In the case of roller finishing, to remove excess silicon, the assembly may be placed, for example, in a High Density Polyethylene (HDPE) jar half-filled with silicon carbide coarse powder (grit FEPA 36-100) as the grinding mediumInside and inShaking in the mixer for 8 hours, wherein the mixer speed was set to 100 minutes^-1。

For liquid silicon desorption, excess silicon can be removed by remelting the silicon and draining it from the module. For this purpose, the assembly may be placed in a bed of graphite powder and heated to the silicon melting temperature. The molten silicon then flows into the bed of graphite powder driven by capillary action.

The final CMC component 6 (fig. 1) is obtained after completion of the post-treatment 5. The final CMC component 6 has the same outer shape as the green body 1. In addition, the arrangement of the fibers 15 within the component remains unchanged throughout the manufacturing of the CMC component 6 from the green body 1. Thus, the process of the present invention is a near net shape manufacturing process. In the manufacturing example of the screw 10 as listed above, after each of the steps 2 to 5 is performed, the shape and fiber arrangement of the screw finally obtained correspond to those of the screw 10 as shown in fig. 2.

The resulting CMC component 6 has advantageous properties such as, inter alia, high temperature stability, high thermal shock resistance, high hardness, high corrosion resistance, and light weight. At the same time, it may have a more complex three-dimensional shape and/or include small surface features, such as threads 13. Due to these characteristics and their radiation resistance, the resulting CMC component 6 is particularly suitable for use in aerospace, medical technology, nuclear power plants or fusion reactors. The final CMC component 6 may be, for example, a foil, a blade, a nut, a bolt, a rivet, or a formed connecting plate.

Reference numerals

1 green compact 20 mould

2 pyrolysis 21 first mould body

3 boron nitride coating 22 second mold body

4 liquid silicon impregnated 23 head insert

5 post-processing 24 threaded insert

6 Final CMC component 25 first front plate

26 second front plate

10 screw

11 head 30 soaks device

12 shaft 31 liquid silicon

13 thread 32 boron nitride

14 thermoplastic 33 crucible

15 fiber

Length of 16 strands L