Protecting parts made of carbon-containing composite material from oxidation

Abstract

A method of protecting a part made of carbon-including composite material against oxidation, the method including a) applying a coating composition on at least a portion of the outside surface of the part, the coating composition being in the form of an aqueous suspension including: a metallic phosphate; a powder of a compound comprising titanium; and a B.sub.4C powder; and b) applying heat treatment to the coating composition applied during step a) with a treatment temperature lying in the range 330° C. to 730° C. being imposed during the heat treatment in order to obtain a coating on the outside surface of the part, the coating including a first phase in which the metallic phosphate is in crystalline form and a second phase in which the metallic phosphate is in amorphous form.

Claims

1. A method of protecting a part made of carbon-including composite material against oxidation, the method comprising: a) applying a coating composition on at least a portion of an outside surface of the part, the coating composition being in the form of an aqueous suspension comprising: a metallic phosphate; a powder of a compound comprising titanium; and a B.sub.4C powder; and b) applying heat treatment to the coating composition applied during step a) with a treatment temperature lying in the range 330° C. to 730° C. being imposed during the heat treatment in order to obtain a coating on the outside surface of the part, the coating comprising a first phase in which the metallic phosphate is in crystalline form and a second phase in which the metallic phosphate is in amorphous form.

2. The method according to claim 1, wherein the coating composition also comprises an organic dispersing agent.

3. The method according to claim 2, wherein the organic dispersing agent is an alkoxylated acetylenic polyol.

4. The method according to claim 1, wherein the titanium-comprising compound is selected from the group consisting of titanium metal, titanium diboride, titanium carbide, titanium dioxide, and mixtures thereof.

5. The method according to claim 4, wherein the coating composition includes a powder of titanium metal and/or a powder of titanium diboride.

6. The method according to claim 1, wherein the coating composition includes an aluminum phosphate.

7. The method according to claim 1, wherein the coating composition further includes a self-healing vitreous compound.

8. The method according to claim 1, wherein the coating composition comprises, before step a): the metallic phosphate at a content by weight lying in the range 27% to 36%; the B.sub.4C powder at a content by weight lying in the range 11.5% to 21%; and the powder of the titanium-comprising compound at a content by weight lying in the range 8% to 18%.

9. The method according to claim 8, wherein the coating composition comprises, before step a): aluminum phosphate at a content by weight lying in the range 27% to 36%; the B.sub.4C powder at a content by weight lying in the range 11.5% to 21%; the powder of the titanium-comprising compound at a content by weight lying in the range 8% to 18%; an alkoxylated acetylenic polyol at a content by weight lying in the range 0.1% to 1.5%; and water at a content by weight lying in the range 33% to 50%.

10. The method according to claim 1, wherein at least one internal protection layer is formed before step a) by impregnating at least a portion of the part made of composite material with an impregnation composition including a metallic phosphate.

11. The method according to claim 10, wherein the impregnation composition comprises aluminum phosphate.

12. The method according to claim 1, wherein the treatment temperature is imposed during the heat treatment for a duration greater than or equal to 1 hour.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and benefits of the method appear on reading the following description made by way of non-limiting indication and with reference to the accompanying drawings, in which:

(2) FIG. 1 shows successive steps of an example method of an embodiment of the invention;

(3) FIG. 2 plots curves illustrating mass variation as a function of oxidation duration for samples made of C/C composite material provided with protection against oxidation by a method of an embodiment of the invention;

(4) FIGS. 3A and 3B plot curves showing mass variation as a function of oxidation duration for samples made of C/C composite material protected against oxidation by performing methods of an embodiment of the invention and exposed to a carbon oxidation catalyst;

(5) FIG. 4 shows performance in terms of protection against oxidation for coating compositions incorporating various boron compounds;

(6) FIG. 5 shows performance in terms of protection against oxidation for coating compositions incorporating various compounds comprising titanium;

(7) FIG. 6 shows in particular performance in terms of protection against oxidation for a coating composition including a borosilicate type vitreous compound;

(8) FIG. 7 shows performance in terms of protection against oxidation imparted by various methods of embodiments of the invention; and

(9) FIG. 8 compares performance in terms of the protection imparted against oxidation firstly by a method of an embodiment of the invention and secondly by a known method of the prior art.

DETAILED DESCRIPTION

(10) In the description below, protection against oxidation is to be given to parts made of C/C composite material, and more particularly to brake disks. More generally, an embodiment of the invention is applicable to protecting any kind of part made of carbon-containing composite material against oxidation.

(11) In a particular implementation of the method as shown in FIG. 1, a first stage 10 consists in forming internal protection within the accessible pores of the part or within a portion of the part to be protected, which internal protection comprises at least one metallic phosphate suitable in particular for providing protection against catalytic oxidation of carbon.

(12) It is possible to proceed as described in Document U.S. Pat. No. 5,853,821. A first step 12 consists in depositing a wetting agent within the accessible pores of the composite material. For this purpose, use is made of an aqueous solution of a wetting agent, such as for example the substance sold by the German supplier Sasol GmbH under the name “Marlophen NP9”. After the composite material has been impregnated with this wetting solution and after drying (step 14), a first impregnation composition in the form of an aqueous solution containing a metallic phosphate is applied to the entire outside surface of the part, or selectively to a portion of the outside surface of the part, e.g. using a brush or by spraying (i.e. spray gun) (step 16). By way of example, use is made of an aqueous solution of aluminum hydrogen-phosphate Al(H.sub.2PO.sub.4).sub.3. The metallic phosphate may also be a zinc phosphate, e.g. having the following chemical formula: Zn.sub.3(PO.sub.4).sub.2.xH.sub.2O, a manganese phosphate, e.g. having the following chemical formula: Mn(H.sub.2PO.sub.4).sub.2.2H.sub.2O, or indeed a magnesium phosphate, e.g. having the following chemical formula: Mg.sub.3(PO.sub.4).sub.2.8H.sub.2O.

(13) The wetting agent present on the surface of the accessible pores of the composite material facilitates penetration of the impregnation composition within the accessible pores of the composite material. Drying followed by heat treatment (step 18) are then performed in order to limit the surface accessibility of the pores by virtue of metallic phosphate internal protection. The heat treatment is performed by raising the temperature up for a dwell of one or several hours at a temperature lying in the range 200° C. to 750° C., e.g. about 700° C. under a non-oxidizing atmosphere, e.g. under nitrogen (NO.

(14) A second stage 20 of the method consists in forming a covering and coating outer protective coating.

(15) For this purpose, it is possible to use a second composition (also referred to as a coating composition) that is constituted essentially (i.e. at least 90% by weight) by at least one metallic phosphate, a boron carbide B.sub.4C powder, a titanium powder, at least one dispersing agent, and water.

(16) The metallic phosphate may be aluminum hydrogen-phosphate Al(H.sub.2PO.sub.4).sub.3. Such a compound is commercially available in an aqueous solution at 48% to 50% by weight. In the same manner as above, it is possible to use a phosphate of zinc, of manganese, or of magnesium.

(17) The boron carbide B.sub.4C may be in the form of particles having a size less than or equal to 30 micrometers (μm), e.g. less than or equal to 7.5 μm. Unless mentioned to the contrary, the term “size” is used to mean the dimension given by statistical grain size distribution at half the population, referred to as D50.

(18) The powdered titanium used may be in the form of dry titanium particles (not in suspension in water) having a size that is preferably less than 150 μm. Refractory fillers other than B.sub.4C may be added in a proportion that is in an embodiment less than 10% by weight, e.g. one or more ceramic powders of oxide, nitride, or carbide type.

(19) The organic dispersing agent may be as mentioned above, and in particular it may be an alkoxylated acetylenic polyol sold under the name “Surfynol®”, and in particular “Surfynol® 440”, As mentioned above, this organic dispersing agent may be sufficiently wetting to provide very good cohesion between the coating and the underlying part. The organic dispersing agent may enable the metallic phosphate of the second composition to penetrate into the residual pores in order to create anchor points that are chemically and mechanically strong with the internal protection underlayer of metallic phosphate.

(20) The additional refractory fillers, e.g. one or more ceramics of oxide, nitride, or carbide type may be in the form of particles that in an embodiment have a size of less than 150 μm.

(21) By way of example, the second composition is applied with a brush or by spraying (step 22) on the outside surface of the part or on a portion of its outside surface, in an embodiment at the same locations as the first composition. For brake disks made of carbon-based composite material, application of the first composition and of the second composition may be limited to those outside surface portions that are not friction portions, the friction annular surface of an end disk in a set of stator and rotor disks, or the opposite friction surfaces of disks situated between the end disks then not being impregnated in order to avoid spoiling their tribological properties. Thereafter, final heat treatment is performed (step 24) raising temperature gradually up to a value lying in the range 330° C. to 730° C., with a dwell of one or several hours at that temperature. The relatively moderate temperature of the heat treatment serves to conserve the metallic phosphate phase in the amorphous state, thereby preserving its coating capacity. The heat treatment of step 24 is not necessarily performed under a non-oxidizing atmosphere. This heat treatment may be performed under air or under nitrogen. In particular, this heat treatment may be performed under air up to 350° C. or under nitrogen above 350° C.

(22) The quantity of the second composition to be applied may be selected so that during step b) a coating is obtained on the outside surface of the part that is of mean thickness (arithmetic mean) lying in the range 20 μm to 150 μm. An embodiment of the invention beneficially makes it possible to have very good protection against oxidation with a coating of thickness that is significantly thinner than the coatings known in the prior art.

(23) The thickness of the coating is measured perpendicularly to the outside surface of the coated part.

EXAMPLE 1

(24) Parts made of C/C composite material for airplane brake disks of density lying in the range 1.65 grams per cubic centimeter (g/cm.sup.3) to 1.9 g/cm.sup.3 approximately and with residual porosity in volume terms lying in the range 6% to 18% approximately were provided with anti-oxidation protection as follows: impregnating with a first composition formed by an aqueous solution of “Marlophen NP 9” and drying; robotically applying an aqueous solution of monoaluminum phosphate at 50% by weight of water by means of a brush or by spraying (e.g. a spray gun); applying heat treatment under a nitrogen atmosphere (N.sub.2) with temperature being raised progressively up to 700° C. and with this temperature being maintained for a minimum of 1 h; using a brush or spraying to apply the following second composition comprising by weight: 67% aqueous solution of monoaluminum phosphate at 50% by weight of water; 16.3% of B.sub.4C powder with no more than 2% impurities, the grains of the powder having a size of less than 7.5 μm; 11% dry titanium powder with grain size distribution up to 150 μm (grain size: approximately 90 μm) or smaller, up to 50 μm (grain size: 20 μm approximately); 4.7% water; and 1% “Surfynol® 440”; and applying heat treatment under air by raising temperature progressively up to 350° C. and maintaining this temperature for 10 h.

(25) Depending on the parts, the layer of coating composition (layer of second composition) prior to heat treatment presented a weight per unit area lying in the range 16 milligrams per square centimeter (mg/cm.sup.2) to 22 mg/cm.sup.2. Depending on the parts, the coating obtained after heat treatment presented thickness lying in the range 40 μm to 70 μm.

(26) Two similar additional tests were performed in which: the final heat treatment was performed under air by progressively raising the temperature up to 350° C. and maintaining this temperature for 5 h; and the final heat treatment was performed under air by raising the temperature progressively up to 450° C. and maintaining this temperature for 8 h.

(27) 1D/2D NMR spectroscopic analysis of the .sup.31P and .sup.27Al solid nuclei was used to quantify the proportions by weight of the crystalline and amorphous phases of the metallic phosphate in the resulting coating. The results obtained are given in Table 1 below.

(28) TABLE-US-00001 TABLE 1 Crystalline metallic Amorphous metallic Sample phosphate content phosphate content Example 1: 76% 24% 350° C., 5 h, air Example 1: 89% 11% 450° C., 8 h, air

(29) For this second composition example, the temperature from which a coating having both the amorphous monoaluminum phosphate and the crystalline monoaluminum phosphate begins to be obtained is about 330° C.

(30) Parts having the anti-oxidation protection have been subjected to the following oxidation protocols: P650: exposure at 650° C. to air for 4 h, repeated six times with return to ambient temperature after each exposure; P850: exposure at 850° C. to air for 30 minutes (min), repeated six times with return to ambient temperature after each exposure; P1200: exposure at 650° C. for 4 h, return to ambient temperature, followed by exposure to 1200° C. for 15 min, return to ambient temperature, then return twice to 650° C. for 4 h with intermediate return to ambient temperature; P1200 H.sub.2O: same protocol as P1200, but adding 24 h in water at ambient temperature after exposure to 1200° C. and before the two final exposures at 650° C.; P650AcK: exposure to air at 650° C. for 4 h, followed by pollution with potassium acetate at ambient temperature, then two exposures to air at 650° C. for 4 h with intermediate return to ambient temperature; and P1200AcK: same protocol as P650AcK, but adding exposure to air at 1200° C. for 15 min after the first exposure to air at 650° C., the pollution with AcK being performed after the exposure at 1200° C.

(31) FIG. 2 shows the relative loss of weight in percentage for the various parts as measured during the oxidation protocols without potassium acetate pollution, the protection being implemented with a second composition containing titanium powder having grain size distribution less than or equal to 150 μm.

(32) Very good ability to withstand oxidation can be seen including at high temperature and in the presence of water, since loss of weight is less than 5%. By way of comparison, for an oxidation protocol similar to the above P1200H.sub.2O protocol, the loss of weight observed for parts protected using the method of Document US 2007/0026153 is about 7%.

(33) FIG. 3A shows the relative loss of weight in percentage measured during oxidation protocols with potassium acetate pollution, the protection being implemented with a second composition containing titanium powder with grain size distribution less than 50 μm.

(34) FIG. 3B also shows the performance obtained after performing a method similar to that described above and treatment with a second composition having the following composition by weight: 27.7% monoaluminum phosphate; 13.5% B.sub.4C powder; 9% titanium powder; 0.8% Surfynol®; and 49% water.

(35) As shown in FIG. 3B, such a composition, after performing a P1200 AcK protocol, provides excellent protection against catalytic oxidation.

EXAMPLE 2

Technical Effect Produced by Using a B4C Powder

(36) In this example, three compositions have been compared for performance in terms of ability to withstand oxidation. The three compositions under test differed in the chemical nature of the boron compound present.

(37) More precisely, parts made out of C/C composite material for airplane brake disks with density lying in the range 1.6 g/cm.sup.3 to 1.9 g/cm.sup.3 approximately and with residual porosity by volume lying in the range 6% to 18% approximately were provided with anti-oxidation protection as follows: impregnating with a first composition formed by an aqueous solution of “Marlophen NP 9” and drying; using a brush to apply an aqueous solution of monoaluminum phosphate at 50% by weight of water; applying heat treatment under an atmosphere of nitrogen (N.sub.2) with temperature being raised progressively up to 700° C. and maintained at this temperature for a minimum of 1 h; using a brush to apply the following second composition comprising by weight: 34% monoaluminum phosphate; 16% boron compound (B, ZrB.sub.2, or B.sub.4C depending on the composition under test); 11.2% titanium powder; and 38.8% water; and applying heat treatment under air with temperature being raised progressively up to 350° C. and maintained at this temperature for 10 h.

(38) FIG. 4 shows the performance of the various compositions in terms of protection against oxidation depending on the nature of the boron compound present (protocol used: P1200 AcK).

(39) Incorporating B.sub.4C powder in the coating compositions of the invention procures results that are significantly better in terms of protection against oxidation compared with using other powders based on boron, such as powders of boron or of ZrB.sub.2.

EXAMPLE 3

Tests Varying the Chemical Nature of the Compound Comprising Titanium

(40) In this test, various coating compositions of the invention were evaluated for performance in terms of the resistance they imparted to oxidation. Each of the coating compositions incorporated a different titanium-comprising compound.

(41) Parts made of C/C composite material for airplane brake disks having density lying in the range 1.65 g/cm.sup.3 to 1.9 g/cm.sup.3 approximately and residual porosity by volume lying in the range 6% to 18% approximately were provided with anti-oxidation protection as follows: impregnating with a first composition formed by an aqueous solution of “Marlophen NP 9” and drying; using a brush to apply an aqueous solution of monoaluminum phosphate at 50% by weight of water; applying heat treatment under an atmosphere of nitrogen (N.sub.2) by raising temperature progressively up to 700° C. and maintaining this temperature for 1 h minimum; using a brush to apply the second composition; and applying heat treatment under air by progressively raising temperature to 350° C. and maintaining this temperature for 10 h.

(42) The formulations by weight of the second composition sued are given below: “Ti” composition (the corresponding curve is labeled “Ti” in the drawings): 34% monoaluminum phosphate; 16% B.sub.4C powder; 11.2% titanium powder; and 38.3% water. “TiB.sub.2” composition (the corresponding curve is labeled “TiB.sub.2” in the drawings): 34.4% monoaluminum phosphate; 14.2% B.sub.4C powder; 16% TiB.sub.2 powder; 1% Surfynol®; and 34.4% water. “TiC” composition (the corresponding curve is labeled “TiC” in the drawings): 36% monoaluminum phosphate; 12.2% B.sub.4C powder; 14.7% TiC powder; 1% Surfynol®; and 36% water. “TiO.sub.2” composition (the corresponding curve is labeled “TiO.sub.2” in the drawings): 34.75% monoaluminum phosphate; 11.8% B.sub.4C powder; 17.8% TiO.sub.2 powder; 1% Surfynol®; and 34.75% water.

(43) As shown in FIG. 5, the use of various compounds comprising titanium makes it possible to obtain very good resistance to oxidation, including at high temperature and in the presence of water, since weight loss was less than 5%.

EXAMPLE 4

Composition Including a Self-Healing Vitreous Compound

(44) A part made of C/C composite material for an airplane brake disk having density lying in the range 1.65 g/cm.sup.3 to 1.9 g/cm.sup.3 approximately and residual porosity by volume lying in the range 6% to 18% approximately was provided with anti-oxidation protection as follows: impregnating with a first composition formed by an aqueous solution of “Marlophen NP 9” and drying; using a brush to apply an aqueous solution of monoaluminum phosphate at 50% by weight of water; applying heat treatment under an atmosphere of nitrogen (N.sub.2) by progressively raising temperature up to 700° C. and maintaining this temperature for 1 h minimum; using a brush to apply the following second composition comprising by weight: 30% monoaluminum phosphate; 14.5% B.sub.4C powder; 9.8% titanium powder; 1% Surfynol®; 34% water; and 10.7% “Pyrex®” glass powder; and applying heat treatment under air by raising temperature progressively up to 350° C. and maintaining this temperature for 10 h.

(45) The corresponding curve is labeled “Pyrex®” in the drawings.

(46) The composition of Pyrex is substantially as follows (percentages by weight): SiO.sub.2: 80.60%; B.sub.2O.sub.3: 12.60%; Na.sub.2O.sub.3: 4.2%; Al.sub.2O.sub.3: 2.25%; Cl: 0.1%; CaO: 0.1%; MgOP: 0.05%; and Fe.sub.2O.sub.3: 0.05%.

(47) It can be seen that such a coating composition provides excellent protection against oxidation (see FIG. 6). For reference, the “TiC” and “TiO.sub.2” curves described above are also shown in FIG. 6.

EXAMPLE 5

Influence of the Temperature of the Heat Treatment Performed During Step b

(48) In this example, a part made of C/C composite material for an airplane brake disk having density lying in the range 1.65 g/cm.sup.3 to 1.9 g/cm.sup.3 approximately and residual porosity by volume lying in the range 6% to 18% approximately was provided with anti-oxidation protection as follows: impregnating with a first composition formed by an aqueous solution of “Marlophen NP 9” and drying; using a brush to apply an aqueous solution of monoaluminum phosphate at 50% by weight of water; applying heat treatment under an atmosphere of nitrogen (N.sub.2) by progressively raising temperature up to 700° C. and maintaining this temperature for 1 h minimum; using a brush to apply the following second composition comprising by weight: 33.5% monoaluminum phosphate; 16.3% B.sub.4C powder; 11% titanium powder; 1% Surfynol®; and 38.2% water; and applying heat treatment under air by raising temperature progressively up to 650° C. and maintaining this temperature for 1 h minimum.

(49) The corresponding curve is labeled “Example 5” in the drawings.

(50) FIG. 7 shows that after heat treatment at 650° C., good oxidation resistance properties are obtained. FIG. 7 also shows the “Ti” and “Pyrex” curves described above.

(51) 1D/2D NMR spectroscopic analysis of the .sup.31P and .sup.27Al solid nuclei served to quantify the proportions by weight of the crystalline and amorphous phases of the metallic phosphate in the resulting coating. The results obtained are given in Table 2 below.

(52) TABLE-US-00002 TABLE 2 Crystalline metallic Amorphous metallic Sample phosphate content phosphate content Example 5: 59% 41% 650° C., 1 h, N.sub.2

(53) FIG. 8 compares the performance in terms of protection against oxidation (P1200 H.sub.2O protocol) of a Coating constituted by a metallic phosphate composition entirely in crystalline form (labeled in FIG. 8 as “entirely crystalline metallic phosphate”) with the performance of a coating obtained after treatment in accordance with Example 5 of an embodiment of the invention. FIG. 8 shows that the protective coating obtained after performing a method of an embodiment of the invention provides very good resistance to oxidation in comparison with methods known in the prior art.

(54) The term “comprising/containing/including a” should be understood as “comprising/containing/including at least one”.

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