Sized yarn intended to undergo a textile operation

Abstract

A sized yarn for subjecting to a textile operation, the yarn including a plurality of ceramic and/or carbon fibers; an interphase coating covering the fibers; and a film covering the interphase coating and including a linear polysiloxane.

Claims

1. A sized yarn for subjecting to a textile operation, the yarn comprising: a plurality of ceramic and/or carbon fibers; an interphase coating covering the fibers; and a film covering the interphase coating and including a linear polysiloxane.

2. A yarn according to claim 1, wherein the interphase coating includes pyrolytic carbon, boron-doped carbon, or BN.

3. A yarn according to claim 1, wherein a ratio [weight of polysiloxane]/[weight of fibers+weight of interphase coating] is greater than or equal to 0.3%.

4. A yarn according to claim 1, wherein the polysiloxane is a linear poly(dimethylsiloxane).

5. A yarn according to claim 1, wherein the fibers include SiC fibers.

6. A method of preparing a yarn according to claim 1, including a step of treating a plurality of ceramic and/or carbon fibers covered in an interphase coating with a sizing composition, the sizing composition including a linear polysiloxane.

7. A method according to claim 6, wherein, prior to the treatment with the sizing composition, the fibers present an initial sizing coating, the initial sizing coating being eliminated in full or in part prior to the treatment with the sizing composition.

8. A method of fabricating a fiber structure wherein one or more textile operations are performed using at least one yarn according to claim 1.

9. A method according to claim 8, wherein the at least one yarn comprises a plurality of yarns and wherein a woven structure is fabricated by weaving said plurality of yarns.

10. A method according to claim 9, wherein the yarns are wrapped before weaving, at least one wrapping yarn being wound around each of the yarns during wrapping.

11. A method according to claim 8, wherein, after performing the one or more textile operations, the method includes a step of eliminating all or part of the film covering the interphase coating.

12. A method of fabricating a part including a step of forming a matrix in the pores of a fiber structure obtained after performing the method according to claim 8.

13. A fiber structure including a plurality of yarns according to claim 1.

14. The yarn according to claim 1, wherein the film completely covers the interphase coating.

15. The yarn according to claim 1, wherein the sized yarn is completely covered by the film.

16. The yarn according to claim 1, wherein the film entirely covers an outer surface of the sized yarn.

17. The yarn according to claim 1, wherein the film is present in each gap formed between the fibers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the invention appear from the following description of particular embodiments of the invention given as non-limiting examples and described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic section view of a first embodiment of a yarn of the invention;

(3) FIG. 2 is a diagrammatic section view of a second embodiment of a yarn of the invention;

(4) FIG. 3 is a diagrammatic section view of a third embodiment of a yarn of the invention;

(5) FIG. 4 is a flow chart showing an implementation of a yarn fabrication method of the invention;

(6) FIG. 4A shows one way of depositing the sizing composition on a set of fibers grouped together in a yarn suitable for use in the context of the present invention;

(7) FIG. 5 is a flow chart showing various steps that may be performed using yarns of the invention;

(8) FIG. 6A is a scanning electron microscope photograph of a yarn based on SiC fibers coated in an interphase coating;

(9) FIG. 6B is a scanning electron microscope photograph of a yarn of the invention; and

(10) FIG. 7 shows the result of thermogravimetric analysis of a sizing composition usable in the context of the invention.

(11) FIG. 8 shows a schematic representation of a wrapped yarn.

DETAILED DESCRIPTION OF EMBODIMENTS

(12) FIG. 1 shows a section of a yarn 1 of the invention. The yarn 1 presents a film 4 obtained by sizing treatment and is suitable for being subjected to a textile operation, e.g. weaving. The yarn 1 has a plurality of fibers 2 made of silicon carbide (SiC) and/or of carbon. By way of example, suitable SiC fibers are supplied under the names Nicalon, Hi-Nicalon, or Hi-Nicalon-S from the Japanese supplier NGS, or Tyranno SA3 from the supplier UBE. By way of example, suitable carbon fibers are supplied under the name Torayca T300 3K from the supplier Toray.

(13) In an embodiment, all of the fibers of the yarn may be SiC fibers. In a variant, all of the fibers of the yarn may be carbon fibers. In another variant, the yarn may comprise a mixture of SiC fibers and of carbon fibers.

(14) The diameter d.sub.1 of the fibers 2, defined as their greatest transverse dimension, may for example be less than or equal to 30 micrometers (m). For SiC fibers, the fiber diameter may lie in the range 8 m to 25 m, for example. For carbon fibers, the fiber diameter may lie in the range 7 m to 10 m, for example. The fibers 2 present in the yarn 1 may optionally all have the same diameter.

(15) The fibers 2 present on their outer surfaces S.sub.f an interphase coating 3. In the embodiment shown, the interphase coating 3 is in contact with the fibers 2.

(16) In the embodiment shown, the interphase coating 3 is a discontinuous interphase coating in which there is no continuity of material between the interphase coatings 3.sub.1, 3.sub.2, . . . , 3.sub.n covering each of the fibers 2. In this embodiment, the fibers are initially coated in an interphase coating and then the coated fibers are grouped together in a yarn. In the embodiment shown, the interphase coatings 3.sub.1, 3.sub.2, . . . , 3.sub.n are single-layer interphase coatings, but it would not go beyond the ambit of the invention for the interphase coatings to be multilayer interphase coatings.

(17) The thickness e.sub.1 of the interphase coating 3 may be greater than or equal to 50 nanometers (nm), and preferably greater than 200 nm.

(18) The thickness e.sub.1 of the interphase coating 3 may be less than or equal to 1 m, preferably less than 600 nm. In particular, the thickness e.sub.1 of the interphase coating 3 may lie in the range 50 nm to 1 m, and preferably in the range 200 nm to 600 nm.

(19) The thickness e.sub.1 of the interphase coating 3 corresponds to the greatest dimension of the interphase coating 3 measured perpendicularly to the surfaces S.sub.f of the fibers 2.

(20) A film 4 including linear polysiloxane covers the interphase coating 3. The film 4 in the embodiment shown is in contact with the interphase coating 3.

(21) The film 4 provides cohesion and bridging between the fibers 2. The film 4 forms a continuous coating at the surface S of the yarn 1. As shown, the film 4 is also present inside the yarn 1 in its internal pores (i.e. in the gaps 5 between the fibers of the yarn 1). In the embodiment of FIG. 1, a sufficient quantity of polysiloxane has been deposited to ensure that the film 4 is present in each gap 5 between fibers of the yarn 1. The yarn 1 may be such that over at least 50% of its length, and possibly over substantially its entire length, the film 4 is present in each of the gaps 5 between fibers of the yarn 1. Such a film 4 may be obtained by using a ratio (deposited weight of polysiloxane)/(weight of treated fibers coated in the interphase coating) that is greater than about 5%.

(22) FIG. 2 shows a variant yarn 1 of the invention. In this embodiment, the fibers 2 are initially grouped together into a yarn and the interphase coating 3 is formed thereafter. Once the interphase coating 3 has been formed, the sizing film 4 is deposited. In the embodiment of FIG. 1, a sufficient quantity of polysiloxane is deposited to ensure that the film 4 is present in each of the gaps 5 between the fibers of the yarn 1.

(23) FIG. 3 shows a variant yarn 1 of the invention. Unlike the embodiment of FIGS. 1 and 2, the polysiloxane is deposited in the example of FIG. 3 with a quantity that is insufficient to be present in each of the gaps 5 between the fibers of the yarn 1.

(24) By modifying the quantity of polysiloxane deposited on the fibers, it is advantageously possible to modify the properties of the resulting yarn. Thus, a yarn obtained after depositing a relatively small quantity of polysiloxane presents greater flexibility resulting from the relatively dispersed bridging between the fibers. A yarn obtained after depositing a relatively large quantity of polysiloxane presents great cohesion because of the strong binding between the fibers provided by the film.

(25) In an implementation shown in FIG. 8, the yarns 1 may be wrapped before weaving, at least one wrapping yarn being wound around each of the yarns during wrapping. Wrapping serves advantageously to further increase the protection of the yarn during weaving operations.

(26) FIG. 4 is a flow chart showing a succession of steps enabling a yarn of the invention to be fabricated.

(27) In a first step (step 10), an interphase coating is formed on a plurality of ceramic and/or carbon fibers. The interphase coating may be formed using any known method. As mentioned above, the interphase coating may be formed on the fibers while they are already grouped together as a yarn. In a variant, an interphase coating is initially formed on each of the fibers, and the fibers are then grouped together to form a yarn.

(28) The fibers covered by the interphase coating are then treated by a sizing composition (step 20). The sizing composition includes a linear polysiloxane. During step 20, the sizing composition is put into contact with the fibers covered in the interphase coating. As mentioned above, the sizing composition may be deposited by any known method such as impregnation, dip rolling, or spraying. The sizing composition is preferably deposited by impregnation or by dip rolling. Such methods serve advantageously to obtain a deposit that is uniform.

(29) A drying step may then be performed, serving to eliminate some or all of the solvent or water initially present in the sizing composition.

(30) The sizing composition used may be as described above and it may be deposited in the proportions specified above. By way of example, the sizing composition may be deposited as a temperature of 20 C.

(31) FIG. 4A shows one way of depositing a sizing composition on fibers that is suitable for use in the context of the present invention. In this implementation, fibers covered in an interphase coating and grouped together to form a yarn F are caused to travel through a nozzle 22. The sizing composition 21 is deposited on the yarn F by being injected through the nozzle 22. Once deposition has been achieved, a drying step may be performed in order to obtain a yarn of the invention.

(32) FIG. 5 shows an example of a succession of steps performed using a plurality of yarns of the invention. Initially, one or more textile operations are performed involving a plurality of yarns of the invention in order to form a fiber structure (step 30). During step 30, a plurality of yarns of the invention may for example be woven together in order to form a woven structure. More generally, the yarns of the invention may be used in any textile technique for making any textile surface.

(33) Once the textile operation(s) is/are completed, the film including polysiloxane may be eliminated (step 40) by heat treatment or by treatment with a solvent, as explained above. In order to eliminate the film with a solvent, it is possible initially to immerse all or part of the fiber structure in a bath of solvent, e.g. for one hour at ambient temperature or while hot, and then to perform one or more rinsing operations at ambient temperature with the same solvent. The solvent may then be air evaporated and the fiber structure can then be dried.

(34) By way of example, the fiber structure as obtained in this way may then be subjected to consolidation and/or densification treatment with a matrix in a manner known to the person skilled in the art (step 50). The treatment may result in a part being formed in which the fiber structure is present within a matrix, e.g. a ceramic or carbon matrix, where it performs a mechanical reinforcement function.

(35) By way of example, the part formed in this way may constitute an after-body element of an airplane engine, e.g. an exhaust casing, an exhaust cone or plug, or a secondary nozzle. The part formed in this way may also constitute an element of an aeroengine, e.g. a ring, a nozzle, or a vane.

EXAMPLES

Example 1 (Invention)

(36) This element relates to the sizing treatment performed in the context of the invention.

(37) SiC fibers supplied under the name Hi Nicalon type S by the supplier NGS were used. The fibers were covered in an interphase coating having a thickness of 500 nm. A photograph of a yarn including these coated fibers is given in FIG. 6A.

(38) The yarn formed by the SiC fibers coated in this way was then treated with a sizing composition. A sizing composition was used that is in the form of an emulsion presenting an oil phase dispersed in water. The oil phase was constituted by a Bluesil 47 V1000 oil having viscosity of 1000 square millimeters per second (mm.sup.2/s), the oil including linear poly(dimethylsiloxane).

(39) Several tests were undertaken while varying the quantity of PDMS deposited on the yarn, as set out in Table 1 below. Whatever the quantity deposited, good flexibility and good weaveability were obtained.

(40) TABLE-US-00001 TABLE 1 Wt % of PDMS deposited on yarn Yarn appearance 8.0 flexible bridging between fibers 6.0 flexible bridging between fibers 3.0 flexible bridging between fibers 2.0 flexible bridging between fibers 1.0 flexible no bridging 0.7 flexible no bridging 0.5 flexible no bridging 0.3 flexible no bridging

(41) In those tests, the sizing composition was applied at 20 C. using the immersion method or the recto/verso dip rolling method (i.e. two successive dip rolling operations for depositing size on both sides of the yarn). The contact time of the yarn with the emulsion did not exceed 3 seconds in the immersion method and did not exceed about 2 seconds in the dip rolling method (i.e. a maximum of 4 seconds for this method).

(42) The yarns as treated in this way were dried by passing through a drying oven with a length of about 1 meter (m) that imposed a temperature lying in the range 120 C. to 250 C.

(43) Furthermore, FIG. 6B shows a photograph of a yarn of the invention in which the deposited weight of PDMS relative to the weight of treated fibers is 1%. The sizing deposit is uniform and the interphase coating is protected.

(44) Furthermore, the sizing composition used to form the protective film can be eliminated almost completely (>99.5%) by applying heat (see FIG. 7 showing thermal elimination of the sizing composition used for forming the sizing coating: the result of thermogravimetric analysis up to 900 C. under an atmosphere that is inert relative to a PDMS emulsion having a concentration of 20% by weight).

Example 2 (Comparative)

(45) The performance of a yarn of the invention obtained as in Example 1 (yarn 1) was compared in particular with the performance of a yarn (yarn 2) obtained after sizing treatment but with a composition including polyvinyl alcohol (PVA) instead of linear poly(dimethylsiloxane).

(46) The yarn 2 was fabricated in the same manner as the yarn 1 except for the sizing treatment which was performed using a PVA based composition instead of the PDMS based emulsion.

(47) The results obtained are given in Table 2 below. The yarn 2 does not give full satisfaction insofar as it presents a rigid nature and weaveability that is not very satisfactory.

(48) As shown in Table 2 below, other sizing compositions were tested, namely a composition having the trade name Avirol KW79 supplied by the supplier Pulcra Chemicals and the composition having the trade name Hydrolube 763 (written HL763) supplied by the supplier Michelman. Those compositions do not enable yarns to be obtained that present good weaveability or a protected interphase coating.

(49) TABLE-US-00002 TABLE 2 Type of Quantity Yarn Yarn sizing on yarn appearance cohesion Weaveability Deposit KW79 0.8 wt % good good not non- satisfactory uniform HL763 0.6 wt % good good not non- satisfactory uniform Yarn 2 1.2 wt % rigid good not adequate satisfactory Yarn 1 1 wt % flexible very good satisfactory uniform

(50) The term comprising/containing a should be understood as comprising/containing at least one.

(51) The term lying in the range . . . to . . . should be understood as including the limits.