Process for coating a substrate with an abradable ceramic material, and coating thus obtained

Abstract

The invention relates to the field of the coating of substrates with an abradable material. More specifically it relates to a method for coating at least one surface of a substrate with at least one ceramic compound, as well as to a thereby obtained coating. It also relates to a substrate having at least one surface coated with such a coating. It further relates to a device for applying the coating method. Applications: fields of mechanical engineering and aeronautical design.

1 . A method for coating at least one surface of a substrate with at least one layer comprising at least one ceramic compound, the method comprising:
 a) simultaneously injecting:
 solid particles of n ceramic compounds S 1 , . . . , S n  through a first injection means, n being an integer greater than or equal to 1, and at least 90 percent (%) by a number of the solid particles of the n ceramic compounds S 1 , . . . , S n  having a greatest dimension of more than 5 micrometers (μm); and 
 a liquid phase through a second injection means, the liquid phase comprising a solvent, solid particles of p ceramic compounds L 1 , . . . , L p  and/or at least one precursor of the solid particles of the p ceramic compounds L 1 , . . . , L p , p being an integer greater than or equal to 1, and at least 90% by number of the solid particles of the p ceramic compounds L 1 , . . . , L p  having a greatest dimension of less than or equal to 5 μm, 
   into a thermal jet, whereby a mixture of the solid particles of the n ceramic compounds S 1 , . . . , S n  and of the liquid phase is obtained in the thermal jet ( 35 ); and then   b) projecting the thermal jet, which contains the mixture of the solid particles of the n ceramic compounds S 1 , . . . , S n  and of the liquid phase, on said surface of the substrate, whereby the layer comprising at least one ceramic compound is formed on said surface.   
     
     
         2 . The method according to  claim 1 , wherein each of the n ceramic compounds S 1 , . . . , S n  and of the p ceramic compounds L 1 , . . . , L p  includes at least one element selected from the Periodic Classification of the Elements from among transition elements, metalloids and lanthanides. 
     
     
         3 . The method according to  claim 2 , wherein each of the n ceramic compounds S 1 , . . . , S n  and of the p ceramic compounds L 1 , . . . , L p  is selected from oxides, silicates and zirconates of at least one element selected from the Periodic Classification of the Elements from among transition elements, metalloids and lanthanides. 
     
     
         4 . The method according to  claim 3 , wherein each of the n ceramic compounds S 1 , . . . , S n  and of the p ceramic compounds L 1 , . . . , L p  is selected from simple oxides, silicates and zirconates of at least one element selected from among aluminum, silicon, titanium, strontium, zirconium, barium, hafnium, scandium, yttrium and lanthanides. 
     
     
         5 . The method according to  claim 4 , wherein each of the n ceramic compounds S 1 , . . . , S n  and of the p ceramic compounds L 1 , . . . , L p  is selected from the following ceramic compounds:
 a simple oxide of an element selected from zirconium, hafnium, scandium, yttrium and lanthanides, simple oxides of zirconium and hafnium which may be stabilized by an yttrium oxide;   a silicate of at least one element selected from among aluminum, yttrium, scandium and lanthanides, the silicate may be doped with at least one oxide of at least one element of the second column of the Periodic Classification of the Elements;   a zirconate of at least one element selected from among yttrium, scandium and lanthanides, the zirconate being selected from among those which crystallize according to a pyrochlore or perovskite structure;   and mixtures of these ceramic compounds.   
     
     
         6 . The method according to  claim 1 , wherein at least 90% by number of the solid particles of the n ceramic compounds S 1 , . . . , S n  have a greatest dimension of more than 5 μm and less than 100 μm. 
     
     
         7 . The method according to  claim 1 , wherein the liquid phase is a colloidal aqueous solution of the solid particles of the p ceramic compounds L 1 , . . . , L p  and/or of at least one precursor of the solid particles of the p ceramic compounds L 1 , . . . , L p . 
     
     
         8 . The method according to  claim 1 , wherein the n ceramic compounds S 1 , . . . , S n  are all identical with the p ceramic compounds L 1 , . . . , L p . 
     
     
         9 . The method according to  claim 1 , wherein n and p are both equal to 1, and the ceramic compounds S 1  and L 1  are both mullite. 
     
     
         10 . The method according to  claim 1 , wherein:
 the injecting of the solid particles of the n ceramic compounds S 1 , . . . , S n  is carried out with an angle α S  formed by the directions of the tilt axis of the means for injecting the solid particles of the n ceramic compounds S 1 , . . . , S n  and of the longitudinal axis of the thermal jet, comprised between 75 and 105 degrees (°); and   the injecting of the liquid phase is carried out with an angle α L  formed by the directions of the tilt axis of the means for injecting the liquid phase and of the longitudinal axis of the thermal jet, comprised between 75° and 105°.   
     
     
         11 . The method according to  claim 1 , wherein the liquid phase is injected into the thermal jet at a distance from the substrate which is less than or equal to the distance from the substrate at which the solid particles of the n ceramic compounds S 1 , . . . , S n  are injected into the thermal jet. 
     
     
         12 . The method according to  claim 1 , wherein deposition of the layer is achieved with a blown arc plasma projection method by means of a plasma-forming gas. 
     
     
         13 . The method according to  claim 12 , wherein the plasma-forming gas is selected from argon, helium, dinitrogen, dihydrogen, binary mixtures of the latter, and the ternary mixtures of the latter. 
     
     
         14 . The method according to  claim 13 , wherein the plasma-forming gas is an argon-helium-dihydrogen ternary mixture. 
     
     
         15 . The method according to  claim 1 , wherein said layer or each of the layers comprising at least one ceramic compound has a thickness ranging from 10 μm to 2 mm. 
     
     
         16 . The method according to  claim 1 , wherein the volume proportion of solid particles of the p ceramic compounds L 1 , . . . , L p  and/or of precursors of said ceramic compounds in the liquid phase is comprised between 2% and 20%. 
     
     
         17 . The method according to  claim 1 , wherein the ratio of the volume of the solid particles of the n ceramic compounds S 1 , . . . , S n  to the volume of the solid particles of the p ceramic compounds L 1 , . . . , L p  is comprised in an interval ranging from 0.4 to 3. 
     
     
         18 . The method according to  claim 1 , wherein the flow rate with which the liquid phase is injected into the thermal jet, is (0.05±0.03) liters per minute (L/min). 
     
     
         19 . The method according to  claim 1 , wherein the sequence of the steps a) and b) is repeated once or several times. 
     
     
         20 . The method according to  claim 1 , wherein said layer or each of the layers comprising at least one ceramic compound has a porosity at least equal to 20%. 
     
     
         21 . An abradable coating (R m ) comprising at least one layer of at least one ceramic compound, said layer or each of said layers having a porosity at least equal to 20%, said layer comprising:
 a plurality of solid particles of n ceramic compounds S 1 , . . . , S n , n being an integer greater than or equal to 1, and at least 90% by number of the solid particles of the n ceramic compounds S 1 , . . . , S n  having a greatest dimension of more than 5 μm; and   a plurality of solid particles of p ceramic compounds L 1 , . . . , L p , p being an integer greater than or equal to 1, and at least 90% by number of the solid particles of the p ceramic compounds L 1 , . . . , L p  having a greatest dimension of less than or equal to 5 μm.   
     
     
         22 . The coating according to  claim 21 , wherein each of the n ceramic compounds S 1 , . . . , S n  and of the p ceramic compounds L 1 , . . . , L p  is selected from among simple oxides, silicates and zirconates of at least one element selected from among aluminum, silicon, titanium, strontium, zirconium, barium, hafnium, scandium, yttrium and lanthanides. 
     
     
         23 . The coating according to  claim 21 , wherein n and p are both equal to 1, and the ceramic compounds S 1  and L 1  are both mullite. 
     
     
         24 . The coating according to  claim 21 , wherein said layer or each of the layers comprising at least one ceramic compound has a thickness ranging from 10 μm to 2 mm. 
     
     
         25 . The coating according to  claim 21 , wherein said layer or each of the layers comprising at least one ceramic compound has a plurality of pores having a size comprised between 0.001 and 50 μm, the plurality of pores comprising:
 a network of micropores having a size comprised between 0.001 and 1 μm, which network of micropores is defined by the solid particles of the p ceramic compounds L 1 , . . . , L p  for which at least 90% by number have a greatest dimension of less than or equal to 5 μm, 
 wherein said network of micropores is included within a network of macropores having a size comprised between 1 and 50 μm, which network of macropores is defined by the solid particles of the n ceramic compounds S 1 , . . . , S n , for which at least 90% by number have a greatest dimension of more than 5 μm. 
 
     
     
         26 . The coating according to  claim 21 , wherein said layer or each of said layers of the coating always has a porosity at least equal to 20% after submitting the latter to a temperature above 1,000° C. 
     
     
         27 . A substrate having at least one surface on which was carried out the deposition of a coating (R m ) as defined in  claim 21 . 
     
     
         28 . A device for applying the method as defined in  claim 1 , the device comprising:
 a torch capable of producing a thermal jet;   a projection gas reservoir;   a first reservoir, which contains the solid particles of the n ceramic compounds S 1 , . . . , S n ;   a second reservoir, which contains the liquid phase;   a means for fixing and positioning the substrate with respect to the torch;   an injection system independently connecting
 the first reservoir and a first injection means provided at its end with a nozzle for injecting the solid particles of the n ceramic compounds S 1 , . . . , S n ; and 
 the second reservoir and a second injection means provided at its end with a nozzle for injecting the liquid phase, 
   wherein the injection system allows simultaneous injection of the solid particles of the n ceramic compounds S 1 , . . . , S n  and of the liquid phase into the thermal jet generated by the torch; and
 a pressure reducer, which allows adjustment of the pressure inside the second reservoir. 
   
     
     
         29 . The method according to  claim 13 , wherein the plasma-forming gas is an argon-helium mixture or an argon-dihydrogen mixture. 
     
     
         30 . The method according to  claim 20 , wherein said layer or each of the layers comprising at least one ceramic compound has a porosity at most equal to 40%. 
     
     
         31 . The coating according to  claim 21 , wherein said layer or each of the layers comprising at least one ceramic compound has a porosity at most equal to 40%.