METHOD FOR MANUFACTURING A PART MADE OF CARBON/CARBON COMPOSITE MATERIAL WITH IMPROVED MECHANICAL PROPERTIES

Abstract

Method for manufacturing a part made from carbon/carbon composite material, comprising: the formation of a carbonaceous preform, partial densification of the preform by a pyrocarbon matrix thus forming a partially densified blank, the impregnation of the partially densified blank with an impregnation solution including ceramic particles or ceramic precursors, and the drying of the impregnated blank.

Furthermore, the viscosity of the dispersion or impregnation solution is controlled in order to control the homogeneity of the distribution of the ceramic particles in the part of the impregnated composite material during drying.

Claims

1. Method for manufacturing a part made from carbon/carbon composite material, comprising: the formation of a fibrous carbonaceous preform; partial densification of the preform by a pyrocarbon matrix in order to obtain a partially densified blank, the impregnation of the partially densified blank with an impregnation solution including ceramic particles or ceramic precursors; and the drying of the impregnated blank, wherein a viscosity of the impregnation solution is controlled in order to control the homogeneity of the distribution of the ceramic particles in the part of the impregnated composite material during drying, the viscosity of the impregnation solution being controlled so as to maintain a dynamic viscosity value of between 12 and 700 mPa s.

2. Manufacturing method according to claim 1, wherein the impregnation solution comprises a sol-gel type solution including ceramic precursors.

3. Manufacturing method according to claim 2, further comprising control of the partial gelling of the sol-gel type solution by gelling the sol-gel to the required viscosity, the partial gelling being obtained either by controlling the given duration of change at ambient temperature and atmospheric pressure, or by accelerating the process by heating the sol-gel under inert atmosphere.

4. Manufacturing method according to claim 1, wherein the impregnation solution comprises a colloidal dispersion of ceramic particles.

5. Manufacturing method according to claim 1 wherein the impregnation solution comprises a mass fraction of zirconium, titanium, yttrium, hafnium or tantalum, or a mixture of several of these, between 3 and 15%.

6. Manufacturing method according to claim 1, wherein the impregnation solution includes macromolecules of ceramic precursors or ceramic particles with a mean size less than or equal to 1 m.

7. Manufacturing method according to claim 1, wherein at least one thickening additive is added to the impregnation solution.

8. Manufacturing method according to claim 1, further comprising the formulation of an impregnation solution of predetermined viscosity.

9. Manufacturing method according to claim 2, wherein the impregnation solution is a derivative of zirconium, titanium, yttrium, hafnium or tantalum, or a mixture of several of these derivatives.

10. Manufacturing method according to claim 4, wherein the impregnation solution comprises zirconium dioxide, titanium dioxide, yttrium(III) oxide, hafnium dioxide, tantalum dioxide, or a mixture of two or more of these.

11. Manufacturing method according to claim 7 wherein the at least one thickening additive is a polymer in the poloxamer family.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other aims, advantages and features will emerge from the following description, given purely by way of illustration and made with reference to the accompanying drawings, on which:

[0026] FIG. 1 illustrates a method for manufacturing a carbon/carbon composite material according to an embodiment in accordance with the invention.

[0027] FIG. 2 is a graph showing the filler gradient of a carbon/carbon composite material obtained according to three examples of compositions of an impregnation solution of the sol-gel type.

[0028] FIG. 3 is a graph showing the filler gradient of a carbon/carbon composite material obtained according to four examples of compositions of an impregnation solution of the colloidal dispersion type.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0029] Hereinafter, the bounds of a range of values are included within this range, in particular in the expression included between.

[0030] FIG. 1 illustrates a method for manufacturing a part made from carbon/carbon composite material according to an embodiment of the invention.

[0031] In a first step 100, a carbon preform is formed. In the example illustrated, the preform is fibrous. The form of the part to be produced, for example a brake disc, can advantageously be given to the preform.

[0032] In a second step 200, the carbonaceous preform is partially densified by a pyrocarbon matrix in order, only in part, to fill in the porosity of the preform, forming a partially densified carbonaceous blank. The desiccation is, for example, implemented by chemical vapour infiltration (CVI).

[0033] Advantageously, the degree of porosity of the partially densified carbonaceous blank can be between 47 and 72% by volume.

[0034] An impregnation of the composite material obtained by an impregnation solution comprising ceramic particles or ceramic precursors is next implemented in a following step 300. According to an example embodiment, the impregnation solution can be a solution of the sol-gel type including ceramic precursors.

[0035] The ceramic precursors can be selected from: a derivative of a ceramic compound such as zirconium, titanium, yttrium, hafnium or tantalum, or a mixture of several of these derivatives.

[0036] According to an alternative embodiment, the impregnation solution can be a colloidal dispersion.

[0037] The colloidal dispersion can advantageously comprise zirconium dioxide, titanium dioxide, yttrium(III) oxide, hafnium dioxide, tantalum pentoxide or a mixture of a plurality of these.

[0038] Preferably, the impregnation solution of the sol-gel or colloidal dispersion type comprises a mass fraction of zirconium, titanium, yttrium, hafnium or tantalum or a mixture of a plurality of these of between 3 and 15%.

[0039] In addition, the impregnation solution will preferably include macromolecules of ceramic precursors or ceramic particles with a mean size less than or equal to 1 m.

[0040] As is the case in the example illustrated, the impregnation can be implemented under vacuum, advantageously at a pressure of between 0.1 and 0.5 mbar, at ambient temperature for a period of 30 minutes to 1 hr.

[0041] According to the invention, the viscosity of the impregnation solution is controlled. In other words, the partially densified carbonaceous blank is impregnated with an impregnation solution of predetermined viscosity, selected so that it allows a homogeneous distribution in the material of the ceramic particles contained in the impregnation solution.

[0042] Preferably, the value of the dynamic viscosity of the impregnation solution is between 12 and 700 mPa s, considered at ambient temperature, around 23 C.

[0043] Preferably, the value of the viscosity of the impregnation solution is controlled over time, for example at various instants, so as to be maintained in this range of values, i.e. between 12 and 700 mPa s, in order to guarantee during drying a homogeneous distribution of the ceramic particles contained in the impregnation solution.

[0044] The lower bound of the above range of dynamic viscosity values is fixed by obtaining a heterogeneous material with a lower-viscosity solution. In addition, the upper bound is fixed by the impossibility of impregnating the material with a higher-viscosity solution.

[0045] The viscosity of the impregnation solution can be controlled by directly adjusting the formulation of an impregnation solution so that it has a predetermined viscosity.

[0046] According to another example, at least one thickening additive can be added to the impregnation solution. Preferably a polymer in the poloxamer family, preferably again tri-block polymers of general formula poly(ethylene oxide) x-poly (propylene oxide).sub.n-poly(ethylene oxide).sub.m, m and n are fixed by the synthesis method of the manufacturer. For example, Pluronic L44 or Tergitol L64 can be used.

[0047] As an alternative, in the case of an impregnation solution of the sol-gel type, the manufacturing method may comprise control of the partial gelling of the sol-gel solution.

[0048] The manufacturing method next comprises a step 400 of drying the impregnated material.

[0049] In the example illustrated, the drying is preferably implemented at atmospheric pressure, at a temperature of between 60 and 100 C., for 48 hr to 72 hr and, advantageously, under inert atmosphere, for example under nitrogen.

[0050] The material can next be subjected to heat treatment, according to a following step 500, to allow conversion of the ceramic precursor or precursors into oxide or oxides.

[0051] The heat treatment can also be implemented to achieve the pyrolysis of any additives such as a thickener or a surfactant.

[0052] In the example illustrated, the heat treatment is advantageously implemented at a temperature of between 600 and 1700 C., preferably under a flow of nitrogen and under vacuum, at a pressure below atmospheric pressure.

[0053] Furthermore, the manufacturing method may comprise a following step 600 of densification of the carbon/carbon composite material thus filled with ceramic particles, advantageously by chemical gas infiltration, by the pyrocarbon matrix, in order to fill in the residual porosity.

[0054] Preferably, the final density of the carbon/carbon composite material is greater than 1700 g/cm.sup.3.

[0055] Advantageously, the final mass fraction of derivative of zirconium, titanium, yttrium, hafnium or tantalum of the carbon/carbon composite material obtained can be between 1 and 10%.

[0056] The composition of the particles is preferentially, in a dominant manner, ZrO.sub.xC.sub.y, TiO.sub.xC.sub.y, HfO.sub.xC.sub.y, with x between 0 and 2 and y between 0 and 1, or Y.sub.wO.sub.xC.sub.y with w between 1 and 2, x between 0 and 3 and y between 0 and 1, or Ta.sub.wO.sub.xC.sub.y with w between 1 and 2, x between 0 and 5 and y between 0 and 1.

Examples a, B and C: Impregnation Solutions of the Sol-Gel Type

[0057] Three pieces made from carbon/carbon composite material were manufactured according to the manufacturing method illustrated above. Three impregnation-solution formulations were tested.

[0058] The matrix is made from pyrocarbon and the degree of open porosity of the blank partially densified by the matrix is between 62% and 72% by volume.

[0059] The composition of three examples of impregnation solution and the viscosity values of these measured compositions are presented in Table 1 below.

TABLE-US-00001 TABLE 1 Example A Example B Example C Composition Zirconium sol-gel Zirconium sol-gel + Partially gelled 25% by mass zirconium sol-gel Pluronic L44 Dynamic 4 19.2 667 viscosity (mPa s)

[0060] The composition of the sol-gel impregnation solution of each example A, B and C comprises zirconium butoxide diluted in a butanol/ethanol mixture in the presence of water, hydrochloric acid and acetyl acetone.

[0061] In the examples illustrated, the viscosity of the impregnation solution is measured by means of a rotary viscometer. The sample of carbon/carbon composite material obtained according to each formulation is thermostatically controlled by means of a double-jacket assembly wherein the temperature of the heat-transfer fluid is regulated at 23 C. Three measurements were made on each sample. The speed of the rotor is fixed at 30 revolutions/min. The final viscosity value indicated in table 1 corresponds to the mean of the three measurements.

[0062] Example A corresponds to an impregnation solution without the precaution of controlling the viscosity.

[0063] Example B a corresponds to an impregnation solution incorporating a thickening additive, Pluronic L44, aimed at increasing the viscosity of the solution.

[0064] Finally, example C corresponds to an impregnation solution the sol-gel of which is partially gelled.

[0065] The sol-gel mixture changes over time because of the polymerisation of the zirconium butoxide. This change results in an increase in the viscosity over time as far as total gelling of the mixture.

[0066] Partial gelling means gelling of the sol-gel to the desired viscosity. This control of the gelling can be obtained either by controlling the given duration of change at ambient temperature and atmospheric pressure, or by accelerating the process by heating the sol-gel under inert atmosphere. In the example illustrated, the change in the viscosity of the sol-gel was followed until the desired target value was obtained.

[0067] The distribution of the ceramic fillers of carbon/carbon composite materials obtained by impregnation of partially densified blanks by the compositions of examples A, B and C is controlled after heat treatment by measuring the filler gradient from the core to the edges of the material.

[0068] The filler gradient was measured for each example and the results are presented on the graph in FIG. 2.

[0069] A value of 1 is associated with a homogeneous material. A value of less than 1 represents an excess of ceramic fillers at the core of the carbon/carbon composite material, and a value greater than 1 represents an excess of ceramic fillers at the edge of the material, in this example on the faces of the brake disc.

[0070] The measurement of the filler gradient can be measured by measuring the proportion of ash at the core and on the faces of the sample. This technique consists in evaluating the mass of ash remaining after calcination of the material.

[0071] Calibrated test pieces of the material to be evaluated are oxidised in air at 1000 C. for 15 hr in order to eliminate the carbon and to keep only the ceramic compound. The gradient is next calculated by taking the ratio of the proportions of ash on each face to that of the core.

[0072] In the examples illustrated, the filler gradient was measured by measuring the amount of ash.

[0073] According to one alternative, the filler gradient can be measured by inductive coupling plasma spectrometry (ICP), and calculating the ratio of the amount of fillers on each face of the material to that of the core.

[0074] As can be seen on FIG. 3, example A, the viscosity of which is not controlled, has a filler gradient of approximately 2.5, i.e. much greater than 1. The material having high heterogeneity of distribution of the ceramic fillers, the ceramic fillers being mainly present at the edges of the material.

[0075] On the other hand, the materials obtained from the impregnation by an impregnation solution according to the compositions of examples B and C the viscosity of which is controlled have a filler gradient respectively of 1.1 and 1, representing homogeneous distribution.

[0076] When the viscosity of the impregnation solution is sufficient, i.e. in the predetermined range of values, advantageously between 12 and 700 mPa s, the material obtained has a homogeneous filler distribution.

Examples D, E, F and G: Impregnation Solutions of the Colloidal Dispersion Type

[0077] Four impregnation solution compositions were prepared, corresponding to examples D, E, F and G, the formulations being presented in table 2 below.

[0078] The experimental protocol is similar to examples A, B and C, however the sol-gel solution is replaced by a colloidal dispersion.

TABLE-US-00002 TABLE 2 Example D Example E Example F Example G Composition Colloidal Colloidal Colloidal Colloidal dispersion dispersion dispersion dispersion 20% by 20% by 20% by 15% by mass ZrO.sub.2 mass ZrO.sub.2 + mass ZrO.sub.2 mass ZrO.sub.2 low viscosity 10% by mass averagely averagely Tergitol L64 viscous viscous Dynamic 5.4 16.14 29.74 14.14 viscosity (mPa s)

[0079] Example D corresponds to an impregnation solution without the precaution of controlling the viscosity, with a low viscosity, i.e., in the example illustrated, with a viscosity of less than 12 mPa s.

[0080] Example E a corresponds to an impregnation solution comprising a thickening additive, Tergitol L64, aimed at increasing the viscosity of the solution.

[0081] Finally, examples F and G correspond to impregnation solutions directly formulated to have a predetermined viscosity, averagely viscous, respectively 29.74 mPa s and 14.14 mPa s.

[0082] The filler gradient was measured for each example and the results are presented on the graph in FIG. 3.

[0083] As can be seen on FIG. 3, the composition of example D with a viscosity less than the predetermined range of values leads to a filler gradient much greater than 1, i.e. a heterogeneous distribution of ceramic particles in the material.

[0084] On the other hand, the compositions of examples E, F and G lead to a particularly homogeneous distribution.

[0085] As has also been demonstrated in the sol-gel impregnation solution examples, when the viscosity of the impregnation solution is controlled, i.e. in the predetermined range of values, advantageously between 12 and 700 mPa s, the material obtained has a homogeneous filler distribution.

[0086] The result is a carbon/carbon composite material with homogeneous properties throughout its life. This material can therefore be renovated, this process making it possible to extend its service life.