Method of fabricating a ceramic from a chemical reaction

Abstract

A method of fabricating a ceramic material, the method including forming a ceramic material by performing a first chemical reaction at least between a first powder of an intermetallic compound and a reactive gas phase, a liquid phase being present around the grains of the first powder during the first chemical reaction, the liquid gas phase being obtained from a second powder of a metallic compound by melting the second powder or as a result of a second chemical reaction between at least one element of the first powder and at least one metallic element of the second powder, a working temperature being imposed during the formation of the ceramic material, which temperature is low enough to avoid melting the first powder.

Claims

1. A method of fabricating a turbomachine element including a step of fabricating a ceramic material to form said turbomachine element, the ceramic material being fabricated by performing a method comprising forming the ceramic material by performing a first chemical reaction at least between a first powder of a metallic disilicide MSi.sub.2 where M is a transition metal and a reactive gas phase, the first chemical reaction being a nitriding reaction and the reactive gas phase comprising the element N or the first chemical reaction being a carburizing reaction and the reactive gas phase comprising the element C, a liquid phase obtained from a second powder being present around the grains of the first powder during the first chemical reaction, a working temperature being imposed during the formation of the ceramic material, which temperature is low enough to avoid melting the first powder, and one of the two following characteristics being true: the second powder is a powder of nickel and the liquid phase is obtained as a result of a second chemical reaction between at least one element of the first powder and the nickel of the second powder, and when M is Ti, the ceramic material comprises a Ni.sub.4Ti.sub.4Si.sub.7 phase, and is free of free silicon, TiSi.sub.2 orNiSi/NiSi.sub.2, or the second powder is a powder of an alloy of aluminum and of silicon AlSi13 comprising substantially 13% by weight silicon and the liquid phase is obtained by melting by said alloy of aluminum and of silicon.

2. A method according to claim 1, wherein the first powder is a powder of TiSi.sub.2, a powder of CrSi.sub.2, a powder of ZrSi.sub.2, or a powder of VSi.sub.2.

3. A method according to claim 2, wherein the first powder is a powder of TiSi.sub.2 and the second powder is a powder of nickel.

4. A method according to claim 2, wherein the first powder is a powder of ZrSi.sub.2 and the second powder is a powder of the alloy of aluminum and of silicon AlSi13.

5. A method according to claim 1, wherein, prior to beginning the first chemical reaction, the quantity of material of the first powder is greater than the quantity of material of the second powder.

6. A method according to claim 5, wherein, prior to starting the first chemical reaction, the following conditions are satisfied: the ratio of (the quantity of material of the first powder) divided by (the quantity of material of the first powder plus the quantity of material of the second powder) is greater than 0.825 and less than 0.925; and the ratio of (the quantity of material of the second powder) divided by (the quantity of material of the first powder plus the quantity of material of the second powder) is greater than 0.075 and less than 0.175.

7. A method according to claim 1, wherein the reactive gas phase comprises at least one of the following gases: NH.sub.3, N.sub.2, a gaseous hydrocarbon, or tetramethylsilane.

8. A method according to claim 1, wherein the working temperature is less than or equal to 1150 C. and/or the first chemical reaction is performed at a pressure lying in the range 3 mbar to 10 bar.

9. A method according to claim 1, wherein the turbomachine element is a ceramic matrix composite material part and wherein the ceramic material is formed in the pores of a fiber preform.

10. A method according to claim 1, wherein the turbomachine element is a ceramic material block.

11. A method according to claim 1, wherein the ceramic material forms a coating present on a surface of the turbomachine element.

12. A ceramic material essentially comprising TiN, Si.sub.3N.sub.4, and Ni.sub.4Ti.sub.4Si.sub.7, and presenting a weight content of residual free silicon less than or equal to 1% the ceramic material obtained by carrying out a method comprising: forming the ceramic material by performing a first chemical reaction at least between a first powder of a metallic disilicide MSi.sub.2 where M is a transition metal and a reactive gas phase, the first chemical reaction being a nitriding reaction and the reactive gas phase comprising the element N or the first chemical reaction being a carburizing reaction and the reactive gas phase comprising the element C, a liquid phase obtained from a second powder being present around the grains of the first powder during the first chemical reaction, a working temperature being imposed during the formation of the ceramic material, which temperature is low enough to avoid melting the first powder, the second powder being a powder of nickel and the liquid phase is obtained as a result of a second chemical reaction between at least one element of the first powder and the nickel of the second powder; and when M is Ti, the ceramic material comprises a Ni.sub.4Ti.sub.4Si.sub.7 phase, and is free of free silicon, TiSi.sub.2 or NiSi/NiSi.sub.2.

13. A ceramic matrix composite material part comprising: fiber reinforcement; and a matrix present in the pores of the fiber reinforcement, the matrix comprising a ceramic material according to claim 12.

14. A turbomachine including a ceramic material according to claim 12.

15. A turbomachine including a part according to claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages appear from the following description given with reference to the accompanying drawings, in which:

(2) FIG. 1 is the binary phase diagram of the NiSi system;

(3) FIG. 2 is the ternary phase diagram at 1100 C. of the NiSiTi system;

(4) FIGS. 3A to 3C are photographs of a ceramic material obtained after performing a method of the invention;

(5) FIG. 4 is a XRD diagram of a ceramic material obtained after performing a method of the invention;

(6) FIGS. 5A to 5C are photographs showing the fibers of a fiber preform, the interphase, and the matrix formed after performing a method of the invention for forming a ceramic matrix;

(7) FIGS. 6A and 6B are photographs of a ceramic material obtained after performing a method of the invention;

(8) FIGS. 7A and 7B are photographs of a ceramic material obtained after performing a non-invention method; and

(9) FIG. 8 shows thermogravimetric analysis measurements comparing the results obtained between methods of the invention and methods not of the invention.

EXAMPLES

Example 1 (Invention)

(10) FIGS. 3A to 3C are photographs showing the material obtained after converting a sample having an initial composition of 90 at % TiSi.sub.2+10 at % Ni by treatment under normal pressure with N.sub.2 at 1100 C. for 40 hours (h). The phases present at the end of the treatment were TiN, Si.sub.3N.sub.4, and Ni.sub.4Ti.sub.4Si.sub.7 (see FIG. 4). It should be observed that at the end of the treatment, free silicon and residual TiSi.sub.2 were absent. This reaction was accompanied by an increase in volume of about 50%.

(11) FIGS. 5B and 5C are photographs showing in particular a matrix obtained by converting an infiltrated powder (d.sub.50=300 nanometers (nm)) having an initial composition of 90 at % TiSi.sub.2+10 at % Ni treated under normal pressure with N.sub.2 at 1100 C. for 40 h within a fiber preform. The phases formed were identical to those described above (TiN, Si.sub.3N.sub.4, and Ni.sub.4Ti.sub.4Si.sub.7). No reaction was observable between the powder and the Nicalon fibers coated in a PyC/SiC interphase.

(12) Likewise, FIG. 5A also shows the absence of reaction between the powder and the interphase coated fibers when a preform of carbon fibers coated in a PyC interphase was treated under the same operating conditions.

(13) The absence of reactivity, in particular of the liquid phase, can be attributed to the nitrogen atmosphere that tends to encourage nitriding. A part is thus obtained in which neither the fibers nor the interphase are degraded by the nitriding, together with a matrix that is dense and rigid with a microstructure that is uniform. It should also be observed that there is good adhesion between the interphase and the matrix.

(14) FIGS. 6A and 6B are photographs of ceramic matrices obtained after performing another example of a method of the invention using an initial atomic content of nickel in the mixture of 12.5%. A material was obtained that was hard, dense, and uniform, containing only TiN, Si.sub.3N.sub.4, and Ni.sub.4Ti.sub.4Si.sub.7. In this example, the Ni.sub.4Ti.sub.4Si.sub.7 was present at a molar content equal to 2%, a weight content equal to 14%, and a volume content equal to 10%.

(15) Table 1 below lists the results obtained by using a TiSi.sub.2+Ni system at 1100 C. for 40 h with N.sub.2 in association with various concentrations of nickel.

(16) TABLE-US-00001 TABLE 1 Weight Nitrogen Nickel Theoretical gain (%) content (%) content volume Exp. Exp. Free NiSi/ (% mol) gain (%) (2) Th. (5) Th. Ni.sub.4Ti.sub.4Si.sub.7 TiN Si.sub.3N.sub.4 Si TiSi.sub.2 NiSi.sub.2 10 50.8 37.7 41.8 48 51.5 X X X 12.5 48.6 38.1 39.7 50 50.4 X X X 15 46.4 36.3 37.7 50 49.2 X X X

(17) These implementations lead to a reaction that is complete, forming TiN+Si.sub.3N.sub.4+Ni.sub.4Ti.sub.4Si.sub.7. It should also be observed that impurities such as free silicon, TiSi.sub.2, or NiSi/NiSi.sub.2 were absent.

Example 2 (Comparative)

(18) The results obtained by a method of the invention were compared with those obtained by a method not of the invention in which the second powder was not used. The non-invention method of obtaining the composite material and used in this comparative example is described below: impregnating TiSi.sub.2 powder within a fiber preform; heat treatment under dinitrogen: nitriding reaction in order to form TiN and Si.sub.3N.sub.4.

(19) In order to avoid degrading the SiC (Nicalon) fibers of the preform, the treatment temperature was limited to 1100 C. The results obtained for the non-invention test at a reaction temperature of 1100 C. are given in FIGS. 7A and 7B. At that temperature, the inventors have observed that the nitriding reaction was slow and incomplete because the formation of Si.sub.3N.sub.4 can be relatively difficult at temperatures less than or equal to 1100 C. The volume gain obtained was smaller and the presence of mechanically and chemically undesirable metallic silicon was observed.

(20) FIG. 8 shows thermogravimetric analysis (TGA) measurements obtained after treatment at 1100 C. with N.sub.2: of a mixture (100x) at % TiSi.sub.2+x at % Ni with x=10, 12.5, and 15 of nickel (invention); or of TiSi.sub.2 alone: without using a second powder and without forming a liquid phase (non-invention).

(21) It can be seen that the examples of the invention promote nitriding of silicon at a relatively low temperature of 1100 C. The nitriding of silicon is facilitated by the presence of the second powder of nickel that makes it possible to obtain a liquid phase that is rich in silicon around the grains. Adding nickel modifies and greatly increases transformation compared with systems not having nickel.

Example 3 (Comparative)

(22) The non-invention method used in this comparative example corresponded to a method of nitriding in which the nickel powder usable in the context of the invention was replaced by an Ni.sub.3Al powder. More precisely, the present comparative test evaluated the influence of adding 1% by volume of Ni.sub.3Al as taught in the publication by Zhang et al. (Influence of 1 vol % Ni.sub.3Al addition on sintering and mechanical properties of reaction-bonded Si.sub.3N.sub.4, Journal of the European Ceramic Society 15 (1995) pp. 1065-1070) on the nitriding reaction of silicon.

(23) A pellet comprising a mixture of a powder of silicon and of Ni.sub.3Al at a content of 1% by volume was obtained. The pellet presented a diameter of 10 millimeters (mm) and a thickness of 3 mm. The pellet was treated with N.sub.2 while imposing a temperature of 1100 C. as in Examples 1 and 2 above. The following results were obtained after 30 h of treatment: weight content of residual silicon: about 86.8%; weight content of Si.sub.3N.sub.4: 11.6%; and weight content of Si.sub.3N.sub.4: 1.6%.

(24) The weight contents were determined by X-ray diffraction.

(25) It can be seen that by using Ni.sub.3Al in proportions as taught in the above-cited publication by Zhang et al., while imposing a relatively low working temperature of 1100 C., gave rise to a degree of advance in the nitriding reaction that was significantly smaller than that obtained by adding a powder of nickel in accordance with Example 1 of the invention.

Example 4

(26) Pellets of ZrSi.sub.2 were nitrided for 40 h under normal pressure of dinitrogen at a temperature of 1100 C.

(27) When 10 at % of nickel were added to the mixture, and after 40 h of nitriding, the majority phases were ZrN and Si.sub.3N.sub.4. The presence of ZrSi.sub.2, ZrSi.sub.2Si, and NiZr was observed in the minority. The presence of free silicon was not observed.

(28) Without adding nickel (not the invention), the majority phases were ZrN and ZrSi.sub.2 after 40 h of nitriding. Si.sub.3N.sub.4 was detected, but it constituted a minority phase. Free silicon was also detected.

(29) Adding nickel thus facilitated nitriding of the metallic disilicide ZrSi.sub.2 even at a relatively low working temperature of 1100 C.

Example 5

(30) Pellets of ZrSi.sub.2 were nitrided for 40 h under normal pressure of dinitrogen at a temperature of 1100 C.

(31) When a powder of AS13 alloy was added at 10 at %, and after 40 h of nitriding, the majority phases were ZrN, Si.sub.3N.sub.4, and ZrSi.sub.2. The presence of a minimum quantity of free silicon was observed.

(32) Without adding the AS13 powder, and after 40 h of nitriding, the majority phases were ZrN and ZrSi.sub.2, with Si.sub.3N.sub.4, being observed in the minority. Free silicon was also detected.

(33) Adding an aluminum alloy to the silicon thus facilitated nitriding the metallic disilicide ZrSi.sub.2 even at a relatively low working temperature of 1100 C.

Example 6

(34) Pellets of VSi.sub.2 were nitrided for 40 h under normal pressure of dinitrogen at a temperature of 1100C.

(35) When an AS13 alloy powder was added at 10 at %, and after 40 h of nitriding, the majority phases were VSi.sub.2, VN, and Si.sub.3N.sub.4. The presence of V.sub.4.75Si.sub.3N.sub.0.58 was also observed in minimal quantity.

(36) Without adding the AS13 powder, and after 40 h of nitriding, the majority phase was VSi.sub.2, VN, Si.sub.3N.sub.4, and V.sub.4.75Si.sub.3N.sub.0.58 were in the minority.

(37) Adding an alloy of aluminum and of silicon thus facilitated nitriding the metallic disilicide VSi.sub.2 even at a relatively low working temperature of 1100 C.

Example 7

(38) The possibility of carburizing a mixture of TiSi.sub.2+10 at % Ni at 1100 C. under normal pressure with methane was evaluated by simulation using ThermoCalc software. The results of the simulation revealed the formation of SiC, Ti.sub.3SiC.sub.2, and Ni.sub.4Ti.sub.4Si.sub.7, and the absence of residual silicon or of TiSi.sub.2.

(39) The term lying in the range . . . to . . . should be understood as including the bounds.