Method for forming a protective coating against high-temperature oxidation on a refractory composite material based on silicon and niobium

Abstract

The invention relates to a method for forming a protective coating against high-temperature oxidation on a surface of a refractory composite material based on silicon and niobium, wherein chromium present on the surface to be protected is reacted with a reactive gas which contains silicon and oxygen in order to produce a composite coating having two phases, a first phase of which is an oxide phase based on silica which has viscoplastic properties and a second phase of which is based on silicon, chromium and oxygen, and wherein the first phase and second phase are coalesced at high temperature, which allows a protective coating to be formed in which the second phase acts as a reservoir to reform, during operation, the first phase by means of reaction with an oxidising gas. The invention is preferably used in the field of aeronautical engines.

1 . A composite coating comprising a first phase and a second phase, the first phase being an oxide phase and comprising silicon, the second phase comprising silicon, chromium and oxygen, wherein the first phase and the second phase are configured to coalesce at an operating temperature in the presence of an oxidizing gas. 
     
     
         2 . The composite coating according to  claim 1 , wherein the operating temperature is 700° C. or more. 
     
     
         3 . The composite coating according to  claim 1 , wherein the first phase further comprises at least one melting element selected from a boron type melting element and a germanium type melting element. 
     
     
         4 . The composite coating according to  claim 1 , wherein the second phase further comprises at least one element selected from boron, aluminum, and iron. 
     
     
         5 . The composite coating according to  claim 1 , wherein the second phase is configured to reform the first phase by filling cracks formed in the first phase, during operation. 
     
     
         6 . A composite material comprising the composite coating according to  claim 1 , coated thereon. 
     
     
         7 . The composite material according to  claim 6 , wherein the composite material comprises Nb and Si. 
     
     
         8 . The composite material according to  claim 7 , further comprising chromium. 
     
     
         9 . A protective coating against high-temperature oxidation on a surface of a composite material comprising silicon and niobium, the protective coating obtainable by reacting chromium present on the surface of the composite material with a reactive gas containing silicon and oxygen, to produce a composite coating having two phases, wherein:
 the first phase is an oxide phase and comprises silicon,   the second phase comprises silicon, chromium, and oxygen, and   the first phase and second phase are configured to coalesce at a set temperature in the presence of an oxidizing gas.   
     
     
         10 . The protective coating according to  claim 9 , wherein the reactive gas comprises silicon monoxide (SiO) and is produced in situ from a donor cement which comprises silica (SiO 2 ) and is subjected to a temperature greater than or equal to 1450° C. 
     
     
         11 . The protective coating according to  claim 10 , wherein the donor cement comprises silica (SiO 2 ) and silicon carbide (SiC) in a powder form. 
     
     
         12 . The protective coating according to  claim 9 , wherein the first phase further comprises at least one melting element selected from a boron type melting element and a germanium type melting element. 
     
     
         13 . The protective coating according to  claim 12 , wherein the first phase further comprises boron and wherein the reactive gas comprises silicon monoxide (SiO) and boron monoxide (BO). 
     
     
         14 . The protective coating according to  claim 9 , wherein the reacting of chromium present on the surface of the composite material with a reactive gas containing silicon and oxygen, comprises:
 reacting a first reactive gas, the first reactive gas comprising silicon monoxide (SiO) and being produced from a donor cement which comprises silica (SiO 2 ) and silicon carbide (SiC) in powder form, and   reacting a second reactive gas comprising silicon monoxide (SiO) and boron monoxide (BO) produced from a second donor cement which contains silica (SiO 2 ) and boron carbide (B 4 C) in powder form.   
     
     
         15 . The protective coating according to  claim 9 , wherein all or part of the chromium present on the surface of the composite material is obtained by predepositing the chromium on the surface of the composite material, the predepositing of the chromium comprising forming a layer of chromium. 
     
     
         16 . The protective coating according to  claim 15 , wherein the predepositing comprises using an electrolytic depositing technique or using cathode spraying, and wherein a thickness of the layer of chromium is between 5 and 20 μM. 
     
     
         17 . The protective coating according to  claim 16 , wherein the thickness of the layer of chromium is 15 μM. 
     
     
         18 . The protective coating according to  claim 15 , further comprising one selected from:
 depositing tin on the surface of the composite material before the predepositing of the chromium;   depositing a precious metal selected from platinum, palladium and gold, on the surface of the composite material before the predepositing of the chromium; and   depositing titanium nitride on the surface of the composite material before the predepositing of the chromium.   
     
     
         19 . The protective coating according to  claim 18 , wherein the depositing of tin is followed by performing a thermal processing operation at reduced pressure, and wherein the depositing of the precious metal is followed by performing an interdiffusion annealing operation. 
     
     
         20 . A composite material comprising the protective coating according to  claim 9 .