Environmental barrier

Abstract

A powder formed of fused particles. More than 95% by number of the feed particles exhibiting a circularity of greater than or equal to 0.85. The powder contains more than 88% of a silicate of one or more elements chosen from Zr, Hf, Y, Ce, Sc, In, La, Gd, Nd, Sm, Dy, Er, Yb, Eu, Pr, Ho and Ta, less than 10% of a dopant, as percentage by weight based on the oxides. The powder has a median particle size D.sub.50 of less than 15 μm, a 90 percentile particle size, D.sub.90, of less than 30 μm, and a size dispersion index (D.sub.90-D.sub.10)/D.sub.10 of less than 2. The powder has a relative density of greater than 90%. The D.sub.n percentiles of the powder are the particle sizes corresponding to the percentages, by number, of n %, on the cumulative distribution curve of the size of the particles of the powder. The particle sizes are classified in increasing order.

Claims

1. A powder formed of fused particles, more than 95% by number of said feed particles exhibiting a circularity of greater than or equal to 0.85, said powder containing more than 88% of a silicate of one or more elements chosen from Zr, Hf, Y, Ce, Sc, In, La, Gd, Nd, Sm, Dy, Er, Yb, Eu, Pr, Ho and Ta, less than 10% of a dopant, as percentage by weight based on the oxides, and having: a median particle size D.sub.50 of less than 15 μm, a 90 percentile particle size, D.sub.90, of less than 30 μm, and a size dispersion index (D.sub.90-D.sub.10)/D.sub.10 of less than 2; a relative density of greater than 90%, the D.sub.n percentiles of the powder being the particle sizes corresponding to the percentages, by number, of n %, on the cumulative distribution curve of the size of the particles of the powder, the particle sizes being classified in increasing order.

2. The powder as claimed in claim 1, exhibiting: a percentage by number of particles having a size of less than or equal to 5 μm which is greater than 5%, and/or a median particle size D.sub.50 of less than 10 μm, and/or a 90 percentile particle size D.sub.90 of less than 25 μm, and/or a 99.5 percentile particle size D.sub.99.5 of less than 40 μm, and/or a size dispersion index (D.sub.90-D.sub.10)/D.sub.10 of less than 1.5.

3. The powder as claimed in claim 1, wherein the median particle size D.sub.50 is less than 8 μm.

4. The powder as claimed in claim 1, said element being Y and/or Yb and/or Sc and/or Er.

5. The powder as claimed in claim 1, said dopant being chosen from the group consisting of the oxides of an element chosen from aluminum, silicon, alkali or alkaline earth metals; iron oxides; LiYO.sub.2; mullite; barium and/or strontium aluminosilicate; and yttrium aluminum oxide composites.

6. A method for manufacturing a powder, said method comprising the following steps: a) granulation of a particulate feedstock so as to obtain a powder formed of granules having a median size D′.sub.50 of between 20 and 60 microns, the particulate feedstock comprising more than 98% of a silicate of one or more elements chosen from Y, Ce, Sc, In, La, Gd, Nd, Sm, Dy, Er, Yb, Eu, Pr, Ta, Zr, Ho and Hf, as percentage by weight based on the oxides; b) injection of said powder formed of granules, via a carrier gas, through at least one injection orifice up to a plasma jet generated by a plasma gun, under injection conditions which cause shattering of more than 50% by number of the injected granules, as percentage by number, so as to obtain molten droplets; c) cooling of said molten droplets so as to obtain said feed powder as claimed in claim 1; d) optionally, particle size selection of said feed powder.

7. The method as claimed in claim 6, wherein the injection conditions are predetermined so as to cause shattering of more than 70% of the injected granules, as percentage by number.

8. The method as claimed in claim 7, wherein the injection conditions are predetermined so as to cause shattering of more than 90% of the injected granules, as percentage by number.

9. The method for manufacturing a powder as claimed in claim 6, wherein, in step b), the injection conditions are adapted to cause a rate of shattering of the granules identical to a plasma gun having a power of from 40 to 65 kW and generating a plasma jet in which the amount by weight of granules injected through each injection orifice, in g/min per mm.sup.2 of the surface area of said injection orifice, is greater than 10 g/min per mm.sup.2.

10. The method as claimed in claim 9, in which the amount by weight of granules injected through each injection orifice, in g/min per mm.sup.2 of the surface area of said injection orifice, is greater than 15 g/min per mm.sup.2.

11. The method for manufacturing a powder as claimed in claim 6, wherein said injection orifice defines an injection channel exhibiting a length at least one times greater than the equivalent diameter of said injection orifice.

12. The method as claimed in claim 11, in which said length is at least two times greater than said equivalent diameter.

13. The method for manufacturing a powder as claimed in claim 6, wherein, in step b), the flow rate of powder formed of granules is less than 3 g/min per kW of power of the plasma gun.

14. The method as claimed in claim 6, wherein the granulation comprises an atomization.

15. A thermal spraying method, comprising a step of thermal spraying of a powder as claimed in claim 1.

16. A method to manufacture a body comprising a substrate and an environmental barrier coating at least partially covering said substrate, said method comprising a plasma thermal spraying of a powder as claimed in claim 1 to obtain said environmental barrier coating.

17. A method according to claim 16, in which said body is placed in an environment having a temperature of greater than 1200° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other characteristics and advantages of the invention will become more clearly apparent on reading the following description and on examining the appended drawings, in which:

(2) FIG. 1 schematically represents step a) of a method of according to the invention;

(3) FIG. 2 schematically represents a plasma torch for the manufacture of a feed powder according to the invention;

(4) FIG. 3 schematically represents a method for manufacturing a feed powder according to the invention;

(5) FIG. 4 illustrates the method which is used to evaluate the circularity of a particle.

DETAILED DESCRIPTION

(6) Method for Manufacturing a Feed Powder

(7) FIG. 1 illustrates an embodiment of step a) of a method for manufacturing a feed powder according to the invention.

(8) Any known granulation method may be used. In particular, those skilled in the art know how to prepare a slip suitable for granulation.

(9) In one embodiment, a binder mixture is prepared by addition of PVA (polyvinyl alcohol) 2 to deionized water 4. This binder mixture 6 is then filtered through a 5 μm filter 8. A particulate feedstock, consisting of powdered silicate 10 (for example of 99.99% purity) and having a median size of 1 μm, is mixed into the filtered binder mixture to form a slip 12. The slip may contain, for example, 55% silicate and 0.55% PVA by weight, the remainder to 100% being made up of water. This slip is injected into an atomizer 14 to obtain a powder formed of granules 16. Those skilled in the art know how to adapt the atomizer to obtain the desired particle size distribution.

(10) The granules are preferably agglomerates of particles of an oxide material having a median size preferably of less than 3 μm, preferably less than 2 μm, preferably less than 1.5 μm.

(11) The powder formed of granules may be screened (5 mm screen 18, for example) in order to eliminate the presence of any residues which have fallen from the walls of the atomizer.

(12) The resulting powder 20 is a “spray-dried only”, or SDO, powder formed of granules.

(13) FIGS. 2 and 3 illustrate an embodiment of the melting step b) of a method for manufacturing a feed powder according to the invention.

(14) An SDO powder formed of granules 20, for example, such as manufactured according to the method illustrated in FIG. 1, is injected by an injector 21 into a plasma jet 22 produced by a plasma gun 24, for example a ProPlasma HP plasma torch. Conventional injection and plasma spraying devices may be used, so as to mix the SDO powder formed of granules with a carrier gas and to inject the resulting mixture into the core of the hot plasma.

(15) However, the injected powder formed of granules must not be consolidated (SDO), and the injection into the plasma jet should be done abruptly so as to promote breakage of granules. The violence of the impacts determines the intensity of shattering of the granules, and hence the median size of the powder produced.

(16) Those skilled in the art know how to adapt the injection parameters for an abrupt injection of the granules, such that the feed powder obtained at the end of steps c) or d) has a particle size distribution according to the invention.

(17) In particular, those skilled in the art know that: an approximation of the injection angle θ between the injection axis of the granules Y and the axis X of the plasma jet to 90°, an increase in the powder flow rate per mm.sup.2 of surface area of the injection orifice, a reduction in the powder flow rate, in g/min, per kW of power of the gun, and an increase in the flow rate of the plasmagen gas,

(18) are factors which promote breakage of the granules.

(19) In particular, WO2014/083544 does not disclose injection parameters allowing the breakage of more than 50% by number of the granules, as described in the examples hereinbelow.

(20) It is preferable to rapidly inject the particles so as to disperse them in a very viscous plasma jet which flows at a very high speed.

(21) When the injected granules come into contact with the plasma jet, they are thus subjected to violent impacts which can break them into pieces. In order to penetrate into the plasma jet, the unconsolidated, and in particular unsintered, granules to be dispersed are injected at a sufficiently high speed to benefit from a high kinetic energy which is however limited in order to ensure a good shattering efficiency. The absence of consolidation of the granules reduces their mechanical strength, and hence their resistance to these impacts.

(22) Those skilled in the art know that the speed of the granules is determined by the flow rate of the carrier gas and the diameter of the injection orifice.

(23) The speed of the plasma jet is also high. Preferably, the flow rate of plasmagen gas is greater than the median value recommended by the manufacturer of the torch for the anode diameter chosen. Preferably, the flow rate of plasmagen gas is greater than 50 l/min, preferably greater than 55 l/min.

(24) Those skilled in the art know that the speed of the plasma jet may be increased by using a small-diameter anode and/or by increasing the flow rate of the primary gas.

(25) Preferably, the flow rate of the primary gas is greater than 40 l/min, preferably greater than 45 l/min.

(26) Preferably, the ratio of the flow rate of secondary gas, preferably molecular hydrogen (H.sub.2), to the flow rate of plasmagen gas (composed of the primary and secondary gases) is between 20% and 25%.

(27) Of course, the energy of the plasma jet, influenced in particular by the flow rate of the secondary gas, must be sufficiently high to melt the granules.

(28) The powder formed of granules is injected with a carrier gas, preferably without any liquid.

(29) In the plasma jet 22, the granules are melted into droplets 25. The plasma gun is preferably adjusted so that the melting is substantially total.

(30) The melting advantageously makes it possible to reduce the content of impurities.

(31) On leaving the hot zone of the plasma jet, the droplets are rapidly cooled by the cold surrounding air, but also by a forced circulation 26 of a cooling gas, preferably air. The air advantageously limits the reducing effect of the hydrogen.

(32) Preferably, the plasma torch comprises at least one nozzle arranged so as to inject a cooling fluid, preferably air, so as to cool the droplets resulting form the heating of the powder formed of granules that has been injected into the plasma jet. The cooling fluid is preferably injected toward the downstream direction of the plasma jet (as represented in FIG. 2) and the angle γ between the path of said droplets and the path of the cooling fluid is preferably less than or equal to 80°, preferably less than or equal to 60° and/or greater than or equal to 10°, preferably greater than or equal to 20°, preferably greater than or equal to 30°. Preferably, the injection axis Y of any nozzle and the axis X of the plasma jet are secant.

(33) Preferably, the injection angle θ between the injection axis Y and the axis X of the plasma jet is greater than 85°, preferably approximately 90°.

(34) Preferably, the forced cooling is generated by a set of nozzles 28 arranged around the axis X of the plasma jet 22 so as to create a substantially conical or annular flow of cooling gas.

(35) The plasma gun 24 is oriented vertically toward the ground. Preferably, the angle α between the vertical and the axis X of the plasma jet is less than 30°, less than 20°, less than 10°, preferably less than 5°, preferably essentially zero. Advantageously, the flow of cooling gas is therefore perfectly centered with respect to the axis X of the plasma jet.

(36) Preferably, the minimum distance d between the outer surface of the anode and the cooling zone (where the droplets come into contact with the injected cooling fluid) is between 50 mm and 400 mm, preferably between 100 mm and 300 mm.

(37) Advantageously, the forced cooling limits the generation of secondaries, resulting from the contact between very large hot particles and small suspended particles in the densification chamber 32. In addition, such a cooling operation makes it possible to reduce the overall size of the processing equipment, in particular the size of the collection chamber.

(38) The cooling of the droplets 25 makes it possible to obtain feed particles 30, which can be removed in the lower portion of the densification chamber 32.

(39) The densification chamber may be connected to a cyclone 34, the exhaust gases of which are directed toward a dust collector 36 so as to separate very fine particles 40. Depending on the configuration, certain feed particles in accordance with the invention may also be collected in the cyclone. Preferably, these feed particles can be separated, in particular with an air separator.

(40) Optionally, the collected feed particles 38 may be filtered such that the median size D.sub.50 is less than 15 microns.

(41) Table 1 below provides the preferred parameters for manufacturing a feed powder according to the invention. The characteristics of a column are preferably, but not necessarily, combined. The characteristics of both columns may also be combined.

(42) TABLE-US-00001 TABLE 1 Preferred Even more preferred characteristics characteristics Step b) Gun High-performance gun ProPlasma HP gun with low wear (to treat the powder without contaminating it) Anode Diameter >7 mm HP8 anode (8 mm diameter) Cathode Doped tungsten cathode ProPlasma cathode Gas injector Partially radial ProPlasma HP setup injection (“swirling gas injection”) Current 500-700 A 650 A Power >40 kW >50 kW, preferably approximately 54 kW Nature of the primary gas Ar or N.sub.2 Ar Flow rate of the primary gas >40 l/min, 50 l/min preferably >45 l/min Nature of the secondary gas H.sub.2 H.sub.2 Flow rate of the secondary gas >20 vol % of the 25 vol % of the plasmagen gas plasmagen gas mixture mixture Injection of the powder formed of granules Total flow rate of injected powder <180 g/min (preferably <100 g/min (g/min) (3 injection orifices) <60 g/min per injector) Flow rate in g/min per kW of power <5 <2 Diameter of the injection orifices <2 mm ≤1.5 mm (mm) preferably <1.8 mm Flow rate in g/min per mm.sup.2 of >10 >15 and <20 injection orifice surface area Nature of the carrier gas Ar or N.sub.2 Ar Flow rate of the carrier gas per >6.0 l/min, ≥7.0 l/min injection orifice preferably >6.5 l/min Injection angle with respect to the >85° 90° axis X of the plasma jet (angle θ in FIG. 2) Distance between an injection >10 mm ≥12 mm orifice and the axis X of the plasma jet Cooling of the droplets Cooling parameters Conical or annular air curtain, oriented toward the downstream direction of the plasma jet Angle γ between the direction of Toward the downstream Toward the downstream injection of the cooling fluid, from direction of the plasma jet, direction of the plasma jet, a nozzle, and the axis X of the ≥10° ≥30° and <60° plasma jet Total flow rate of the forced cooling 10-70 Nm.sup.3/h 35-50 Nm.sup.3/h fluid Flow rate of the exhaust gas 100-700 Nm.sup.3/h 250-500 Nm.sup.3/h

(43) The “ProPlasma HP” plasma torch is sold by Saint-Gobain Coating Solutions. This torch corresponds to the torch T1 described in WO2010/103497.

(44) The tests have shown that a feed powder according to the invention exhibits a relative density of greater than 90%, indeed even of greater than 95%.

(45) The invention thus provides a feed powder exhibiting a size distribution and a relative density which confer a very high density upon the environmental barrier coating. Furthermore, this feed powder may be efficiently plasma sprayed with good productivity.

(46) Of course, the invention is not limited to the embodiments described and represented.