KR20190081792A - Method for manufacturing three-layer ceramic thermal barrier coatings having excellent thermal durability - Google Patents

Abstract

The present invention relates to a step (a) of preparing a first suspension in which first oxide particles are dispersed, a second suspension in which second oxide particles are dispersed, and a third suspension in which third oxide particles are dispersed; a step (b) of forming a first coating layer on a first coating layer on a base material with suspension plasma spraying (SPS) by using the first suspension; a step (c) of forming a second coating layer on the first coating layer; and a step (d) of forming a third coating layer on the second coating layer. According to the manufacturing method, a three-layered ceramic thermal barrier coating layer can be formed to enhance high-temperature durability during a thermal cycle.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a three-layer ceramic thermal barrier coating layer having excellent thermal durability,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a ceramic thermal barrier coating layer deposited on a surface of a high temperature superalloy part of a gas turbine engine.

 Thermal barrier coatings (TBCs) are heat-resistant ceramic coatings deposited on the surface of super high temperature superalloy parts of power and aviation gas turbine engines to increase the turbine inlet temperature (TIT) to improve the thermal efficiency of the gas turbine It plays a role.

Yttria-stabilized zirconia (YSZ), which is widely used in industry, is a metastable tetragonal prime phase with no phase change depending on the temperature when it is made into a thermal barrier coating by plasma spraying or electron beam physical vapor deposition '-phase). This t'-phase YSZ is separated into a thermodynamically stable tetragonal phase and a cubic phase when exposed to a high temperature of 1200 ° C. or more. During the cooling process, the tetragonal phase is transformed into a monosial phase having a large unit volume, As the deterioration occurs, the applicable temperature is limited.

A new generation of thermal barrier coating materials, recently studied extensively for applications in high efficiency gas turbine engines operating above the application temperature of conventional YSZ thermal barrier coatings, is lanthanide rare earth zirconate. Conventional yttria stabilized zirconia has a low thermal conductivity and a relatively high coefficient of thermal expansion for ceramics, and has high fracture toughness, which is superior to high temperature durability of thermal barrier coatings, but its application temperature is limited to 1200 ° C. On the other hand, the lanthanide-based rare earth zirconate has a low thermal conductivity compared to YSZ and a phase stability existing in the cubic state from the melting point to the melting point. However, when manufactured by thermal barrier coating with relatively low thermal expansion property and fracture toughness, .

In addition, the microstructure of thermal barrier coatings with low thermal conductivity and stable ceramics at high temperatures influences not only the mechanical and thermal properties of the coating but also the high temperature durability, especially the composition, pore volume, shape and distribution Is one of the main parameters affecting the mechanical properties such as the Young's modulus and hardness of the coating, which affects the thermal stress generated in the thermal cycling process of the gas turbine and the high temperature durability of the coating.

Therefore, it is possible to solve the respective problems caused by forming a thermal barrier coating with YSZ or lanthanide-based rare earth zirconate, and to improve not only the thermal stress between the base material and the coating layer of the thermal barrier coating layer but also the high temperature durability in the thermal cycle There is an increasing need for technology that can be used.

 D. R. Clarke, Surf. Coat. Technol., 163-164 (2003) 67.  C. G. Levi, Curr. Opi. in Sol. St. Mater. Sci., 8 (2004) 77.  R. Vaughan, M. O. Jarligo, T. Steinke, D. E. Mack, D. St ㆆ ver, Surf. Coat. Technol., 205 (2010) 938.  D. R. Clarke, M. Oechsner, N. P. Padture, MRS Bull., 37 (2012) 891.  W. Pan, S. R. Phillpot, C. Wan, A. Chernatynskiy, Z. Qu, MRS Bull., 37 (2012) 917.  X. Ren, W. Pan, Acta Mater., 69 (2014) 397.  N. P. Padture, M. Gell, E. H. Jordan, Science, 296 (2002) 280.  J. Wu, X. Z. Wei, N. P. Padture, P. G. Klemens, M. Gell, E. Garcia, P. Miranzo and M. Osendi, J. Am. Ceram. Soc., 85 (2002) 3031.  S. Sampath, U. Schulz, M.O. Jarligo and S. Kuroda, MRS Bull., 37 (2012) 903.  E. Bakan, D. E. Mack, G. Mauer, R. Muecke and R. Vassen, J. Am. Ceram. Soc., 98 (2015) 1.  V. Viswanathan, G. Dwivedi and S. Sampath, J. Am. Ceram. Soc., 98 (2015) 1769.

The present invention provides a three-layer ceramic thermal barrier coating layer formed by using a suspension plasma sprayer having a suspension supplier suitable for forming an inclined functional coating layer using a suspension in which pre-treated oxide particles are dispersed, And a method for manufacturing a three-layer ceramic thermal barrier coating layer capable of enhancing high temperature durability in a thermal cycle by controlling thermal stress between a base material and a coating layer by controlling porosity.

In order to accomplish the above object, the present invention provides a method for producing a thermal barrier coating comprising the steps of: (a) mixing a first suspension in which first oxide particles for thermal barrier coating are dispersed, ethanol and distilled water in a mixing medium at a weight ratio of 80:20 to 60:40, Preparing a second suspension in which second oxide particles for coating are dispersed and a third suspension in which third oxide particles for a thermal barrier coating are dispersed, respectively; (b) forming a first coating layer on the base material by suspension plasma spraying (SPS) using the first suspension; (c) forming a second coating layer on the first coating layer by suspension plasma spraying (SPS) using the second suspension; And (d) forming a third coating layer on the second coating layer by suspension plasma spraying using the third suspension. The present invention also provides a method for manufacturing a three-layer ceramic thermal barrier coating layer.

Wherein the first oxide and second oxide for thermal barrier coating are YSZ (Yttria-stabilized zirconia) and the third oxide for thermal barrier coating is rare-earth zirconates. A method for producing a pulmonary coating layer is proposed.

Also, the rare earth zirconate is La _1.89-x Gd _x Zr _2.12 O _7.06 (x is 0.24 to 1.65), and proposes a method of manufacturing a three-layer ceramic thermal barrier coating layer.

In addition, the step of preparing the first suspension in the step (a) includes the following steps:

(a-1) mechanically pulverizing oxide powder for thermal spray coating; And (a-2) forming a slurry comprising the pulverized oxide powder.

In addition, the step of preparing the second suspension in the step (a) includes the following steps:

(a-1) mechanically pulverizing oxide powder for thermal spray coating; And (a-2) dispersing the pulverized oxide powder in a mixing medium comprising ethanol and distilled water at a weight ratio of 80:20 to 60:40 to form a slurry.

In addition, the step of preparing the third suspension in the step (a) includes the following steps:

(a-1) mixing two or more oxide powders to perform mechanical alloying; And (a-2) forming a slurry containing the oxide powder for thermal spray coating obtained in the step (a-1).

Also, the two or more types of oxide powders preferably contain (i) at least one selected from Y ₂ O ₃ , Gd ₂ O ₃ and La ₂ O ₃ , and (ii) at least one oxide selected from ZrO ₂ and CeO ₂ Layer ceramic thermal barrier coating layer.

In the step (a-1), the mechanical pulverization or mechanical alloying of the oxide powder is performed by planetary ball milling, attrition milling or shaker milling. Layer ceramic thermal spray coating layer.

Further, the present invention further proposes a method for manufacturing a three-layer ceramic thermal barrier coating layer characterized by further comprising the step of calcining the oxide powder obtained in the step (a-1) before the step (a-2) .

In addition, after forming the second coating layer in the step (c), suspension plasma spraying is performed on the second coating layer using the mixed suspension of the second suspension and the third suspension, and the second oxide and the third Layer ceramic thermal barrier coating layer characterized in that a buffer layer in which the oxide content ratio continuously changes is formed.

The step (c) may further include: a first storage tank in which the second suspension is stored; A second storage tank in which the third suspension is stored; A first transfer pipe for supplying a second suspension from the first storage tank to a plasma spray gun; A first opening / closing valve provided in the first transfer pipe for controlling a supply amount of the second suspension to the plasma spray gun; A second transfer pipe connecting between the first storage tank and the second storage tank and transferring the third suspension to the first storage tank; A second opening / closing valve provided in the second transfer pipe for controlling a flow rate of the third suspension to the first storage tank; A third transfer pipe for supplying a third suspension from the second storage tank to a plasma spray gun; And a third opening / closing valve provided in the third transfer pipe for controlling an amount of supply of the third suspension to the plasma spray gun. The three-layer ceramic thermal spraying coating apparatus according to any one of the preceding claims, Of the present invention.

According to the method for manufacturing a three-layer ceramic thermal barrier coating layer using a suspension plasma spray having a connected suspension supplier suitable for forming a multilayer thermal barrier coating layer according to the present invention, particles of oxide (YSZ or the like) pulverized through high energy milling or alloyed composite The suspension plasma spray with a suspension supply connected with three kinds of suspensions in which oxide (rare earth zirconate or the like) particles are dispersed in a mixed medium containing ethanol or ethanol and distilled water at a weight ratio of 80:20 to 60:40, By forming a ceramic thermal barrier coating layer, the coating layer has a mixture phase of pyrochlore or fluorite, or pyrochlore and fluorite, which has a low thermal conductivity and excellent high-temperature stability in the upper layer, m-ZrO ₂ causes the degradation of the rare earth zirconates is not present, the low In the lower layer, a three-layer ceramic thermal barrier coating layer is formed by depositing YSZ having a thermal expansion coefficient close to the substrate and excellent in high temperature mechanical properties, particularly two layers having different porosity, and controlling composition and porosity in the microstructure, Layer ceramic thermal barrier coating layer which can be used at a higher temperature than the YSZ single layer coating and can improve the high temperature durability in the thermal cycle by adjusting the thermal stress between the base material and the coating layer.

1 is a flow chart of a method of manufacturing a thermal barrier coating layer using a suspension plasma spray according to the present invention.
FIG. 2 (a) is a diagram showing the results of a previous study (Non-Patent Document 0011) V. Viswanathan, G. Dwivedi and S. Sampath, J. Am. Ceram. Soc., 98 (2015) 1769) and the microstructure of the actual thermal barrier coating layer.
FIG. 2 (b) is a diagram showing the results of a previous study (Non-Patent Document 0011) V. Viswanathan, G. Dwivedi and S. Sampath, J. Am. Ceram. Soc., 98 (2015) 1769).
3 is a view showing a suspension supply device for a suspension plasma spraying apparatus according to the present invention.
4 is an optical microscope photograph showing the cross-sectional microstructure and coating thickness of the three-layer ceramic thermal barrier coating specimen prepared in Example 1 of the present application.
5 is a scanning electron microscope (SEM) photograph and pore image showing the cross-sectional microstructure for measuring the porosity of each layer of the three-layer ceramic thermal barrier coating specimen manufactured in Example 1 of the present application.
6 is a scanning electron microscope (SEM) image showing the cross-sectional microstructure and coating thickness of the two-layer ceramic thermal barrier coating specimen prepared in Comparative Example 1 of the present invention.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises ", or" having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

FIG. 1 is a flow chart showing a method for manufacturing a three-layer ceramic thermal barrier coating layer using suspension plasma spraying according to the present invention. As shown in FIG. 1, the method for manufacturing a three- ) A second suspension in which second oxide particles for thermal spray coating are dispersed in a mixed medium comprising a first suspension in which first oxide particles for thermal spray coating are dispersed, ethanol and distilled water at a weight ratio of 80:20 to 60:40, Preparing a third suspension in which third particles for pulverous coating are dispersed, respectively; (b) forming a first coating layer on the base material by suspension plasma spraying (SPS) using the first suspension; (c) forming a second coating layer on the first coating layer by suspension plasma spraying (SPS) using the second suspension; And (d) forming a third coating layer on the second coating layer by suspension plasma spraying using the third suspension. Hereinafter, each step will be described in detail.

The first oxide and the second oxide for the thermal barrier coating have a low thermal conductivity and a relatively high thermal expansion coefficient as ceramics, and an oxide excellent in high temperature durability of the thermal barrier coating, for example, Yttria-stabilized zirconia ), And the third oxide for thermal barrier coating is preferably an oxide excellent in phase stability from low thermal conductivity and melting point, for example rare-earth zirconates. As the rare earth zirconate, La _1.89-x Gd _x Zr _2.12 O _7.06 (x is 0.24 to 1.65), for example, but not limited thereto.

The step (a) is a step of forming a suspension in which oxide particles are dispersed as a feed stock used for suspension plasma spraying. In this step, one or two or more kinds of oxides as a raw material for forming a thermal barrier coating layer The powder is subjected to high-energy milling to obtain an oxide powder for thermal spray coating, which is then dispersed in a solvent to produce a first suspension or a second suspension separately.

For example, when one type of oxide powder such as YSZO (Yttria-stabilized zirconia) is used as a raw material, (a-1) mechanically pulverizing oxide powder for thermal spray coating; And (a-2) forming a slurry containing the pulverized oxide powder to form a suspension.

Also, when one type of oxide powder such as YSZO (Yttria-stabilized zirconia) is used as a raw material, (a-1) mechanically pulverizing oxide powder for thermal spray coating; And (a-2) dispersing the pulverized oxide powder in a mixing medium containing ethanol and distilled water at a weight ratio of 80:20 to 60:40 to form a slurry, thereby forming a suspension.

At this time, it is preferable that a mechanical milling method capable of applying high energy is used in step (a-1). Specific means for this purpose include planetary ball milling, attrition milling or shaker Milling (shaker milling) and the like.

In the step (a-2), the oxide powder of the pulverized size is uniformly dispersed in a solvent such as ethanol or a mixed medium of ethanol and distilled water through ball milling or the like.

Further, in the case where the oxide for thermal barrier coating such as rare-earth zirconates is prepared by using two or more kinds of commercially available oxide powders as raw materials in the step (a), (a-1) 2 Mixing at least two kinds of oxide powders for thermal spray coating to perform mechanical pulverization or mechanical alloying; And (a-2) a step of forming a slurry containing the oxide powder obtained in the step (a-1).

In the step (a-1), the at least two oxides include (i) at least one selected from Y ₂ O ₃ , Gd ₂ O ₃ and La ₂ O ₃ and (ii) at least one oxide selected from the group consisting of ZrO ₂ and CeO ₂ And at least two kinds of oxide powders may be mixed and then mixed with at least one selected from the group consisting of planetary ball milling, attrition milling or shaker milling, Or mechanical alloying through high energy milling, such as, for example,

In the step (a-2), the composite oxide powder is homogeneously dispersed in a solvent such as ethanol or a mixed medium of ethanol and distilled water through ball milling or the like.

In carrying out the present step (a), the oxide particles are pulverized or mechanically alloyed in the step (a-1), the impurities such as organic substances are degreased before the step (a-2) A step of calcining in an oxidizing atmosphere may be additionally performed as necessary. At this time, it is preferable that the calcination is carried out at a temperature and a time such that the compound can be synthesized while the impurities are completely removed.

Next, in the step (b), a first coating layer is formed on the base material by suspension plasma spraying (SPS) using the first suspension.

For reference, a suspension plasma spray is a spraying method in which a suspension in a liquid state is directly supplied to a plasma jet instead of a powder material. Suspensions injected into a plasma jet are atomized in a plasma jet to evaporate the solvent by heating, dissolve the material, And a collision of the two layers.

Next, in the step (c), a second coating layer is formed on the first coating layer by suspension plasma spraying using the second suspension.

If necessary, in order to form a cushioning layer in which the content ratio of the second oxide and the third oxide continuously changes in the thickness direction of the coating layer in the step (c), the second coating layer is formed and then the second suspension and the third suspension The buffer layer may be formed on the second coating layer by using a mixed suspension of the first coating layer and the second coating layer.

Finally, in the step (d), a third coating layer is formed on the second coating layer by suspension plasma spraying using the third suspension.

2, as a result of the structure and thermal durability of the multi-layer coatings disclosed in the Sampath group, there is a train which is applied at a temperature of 1,200 ° C or more, which can stably use t'-YSZ, Studies on additives that can increase the stabilization temperature of conventional t'-YSZ for pulmonary coatings and approaches to multilayer coatings such as those reported in the literature are available. In the literature shown in FIG. 2, the porosity of each layer is adjusted based on the two-layer coating concept of GZ (gadolinium zirconate) / YSZ to minimize thermal stress during thermal cycling and to enhance thermal durability The high temperature durability of the thermal barrier coating is improved when the structure of the lower YSZ coating is made into dense / porous structure.

3 is a suspension supply device 1 provided in a suspension plasma spraying apparatus for implementing the method for manufacturing a three-layer ceramic thermal spraying coating layer according to the present invention. In particular, the three- Is a conceptual diagram of a connected suspension supply suitable for forming the same multilayer coating layer.

The suspension supply device (1) for a suspension plasma spraying apparatus basically comprises: a plurality of storage tanks for storing suspensions in which components constituting a material of a coating layer are dispersed; A transfer pipe connected to the storage tanks to enable movement of suspensions or to supply suspensions to the plasma spray gun; And an on-off valve provided on the transfer tube for opening and closing the flow of the suspension.

More specifically, the suspension supply device (1) for the suspension plasma spraying apparatus includes a first storage tank (11) in which a first suspension or a second suspension is stored; A second storage tank (12) in which the third suspension is stored; A first transfer pipe (21) for supplying a first suspension or a second suspension from the first storage tank to a plasma spray gun; A first opening / closing valve (22) provided in the first transfer pipe for controlling a supply amount of the first suspension or the second suspension to the plasma spray gun; A second transfer pipe (31) connecting between the first storage tank and the second storage tank and transferring the third suspension to the first suspension storage tank; A second opening / closing valve (32) provided in the second transfer pipe for controlling the flow rate of the third suspension to the first storage tank; A third transfer pipe (41) for supplying a third suspension from the second storage tank to a plasma spray gun; And a third open / close valve (42) provided in the third transfer pipe for controlling the supply amount of the third suspension to the plasma spray gun.

For reference, the first suspension tank is filled with the first suspension tank 11 and the second suspension is filled with the first coating layer formed through suspension plasma spraying or after the first coating layer is formed.

According to the method for manufacturing a three-layer ceramic thermal barrier coating layer using a suspension plasma spray having a connected suspension supply suitable for forming a multilayer thermal spray coating layer as described above, oxide particles such as YSZ pulverized through high energy milling or alloyed rare earth zirconia Layer or the like is dispersed in a mixed medium containing ethanol or ethanol and distilled water in a mixing ratio of 80:20 to 60:40 by weight, the suspension is coated with a suspension plasma feeder having a suspension feeder connected to three layers of a ceramic thermal barrier coating layer , There is no m-ZrO ₂ in the upper layer of the coating layer, which has a low thermal conductivity and a high temperature stability and has a mixed phase of pyrochlore or fluorite or two phases, which causes deterioration of the thermal barrier coating A rare earth zirconate, and a lower layer which is a low temperature portion, Layer ceramic thermal barrier coating layer formed by depositing YSZ excellent in high temperature mechanical properties, especially two layers having different porosity, to control the composition and porosity in the microstructure, so that the YSZ single layer coating has a higher Layer ceramic thermal barrier coating layer capable of improving the durability of the thermal cycle in the thermal cycle by adjusting the thermal stress between the base material and the coating layer.

Hereinafter, the present invention will be described in detail by way of examples with reference to the drawings. However, the embodiments according to the present disclosure can be modified in various other forms, and the scope of the present specification is not construed as being limited to the embodiments described below. Embodiments of the present disclosure are provided to more fully describe the present disclosure to those of ordinary skill in the art.

≪ Example 1 >

1. Suspension for Suspension Plasma Spraying

A commercially available YSZ (7.5 wt% Y ₂ O ₃ -ZrO ₂ , 271-4, Praxair surface technologies, USA) was used and ball milled with a 3 mm diameter zirconia ball for 24 hours using ethanol as a solvent Powder having a size of several μm was prepared, heated at the same time as stirring, and then dried at 80 ° C. In order to manufacture a suspension, YSZ powder having a reduced particle size was dispersed in a solvent of suspension at a ratio of 1: 9 to the weight of each powder mixed in ethanol and distilled water in the ratio shown in Table 1 below and ball milled for 1 hour 1 and a second suspension.

In addition, _{La 2 O 3 (High purity chemicals} , Japan, 99.99%, 10 μm), Gd 2 O 3 (High purity chemicals, Japan, 99.99%, 2 ~ 3 μm), ZrO 2 (High purity chemicals, Japan, 98% , 5 μm) Using the raw material powder, La _0.24 Gd _1.65 Zr _2.12 O _7.06 powder was synthesized as shown in the composition of Table 2, and a third suspension was prepared.

Each oxide composition was mixed with zirconia balls, IPA (isopropyl alcohol) and 0.5 wt.% Dispersant (Dibutyl phosphate, Sigma-Aldrich, USA, 96%) for 24 hours in a ball mill. The mixture was heated with stirring using an agitator to evaporate the solvent and then dried in a dryer at 80 ° C. The dried powders were calcined at 1550 ℃ for 2 hours and granulated and sieved using induction to produce La _0.24 Gd _1.65 Zr _2.12 O _7.06 synthetic powder. The prepared La _0.24 Gd _1.65 Zr _2.12 O _7.06 (x = 0.24, 0.71, 1.18, 1.65) The powder was dispersed in a ratio of 1: 9 with YSZ ball and ethanol as a mixing medium and made into a suspension by ball milling for 1 hour.

2. Formation of thermal barrier coating layer using suspension plasma spray

The prepared slurry was deposited on a substrate of Amri 386-2 (Sulzer metco, Switzerland) bond coat composition deposited on a nickel-base superalloy substrate by high-speed oxy-fuel spraying (HVOF) to a thickness of about 200 μm. Suspension plasma spraying (Axial III plasma spray system, Northwest Mettech Corp., Canada). The mixing ratio of Ar, H ₂ and N ₂ was controlled to 7.5: 1.5: 1 as the coating condition. The distance between the coated substrate and the plasma torch was 75 mm, the rotation rate of the coated substrate was 1500 rpm, the suspension supply rate was 45 mL / min, The current was applied at 150V and 220A. FIG. 2 is a schematic view of a slurry supply apparatus for manufacturing a three-layer ceramic thermal spray coating by the suspension plasma spraying method. First, the slurry supplied at a feed rate of 45 ml per minute is calculated in accordance with time, and then the slurry is further supplied to the first storage tank in the second storage tank immediately before the completion of the slurry supply in the first storage tank Was repeated to produce a three-layer ceramic thermal barrier coating as shown in Table 2.

4 is an optical microscope photograph showing the cross-sectional microstructure and coating thickness of the three-layer ceramic thermal barrier coating specimen prepared in Example 1 of the present application. Layer ceramic thermal barrier coating layer having the structure of a first layer (dense-YSZ) of ~ 50 μm each, a second layer (porous-YSZ) of ~200 μm, and La _0.24 Gd _1.65 Zr _2.12 O _7.06 of ~270 μm Deposited.

5 is a scanning electron microscope (SEM) photograph and pore image showing the cross-sectional microstructure for measuring the porosity of each layer of the three-layer ceramic thermal barrier coating specimen manufactured in Example 1 of the present application. In particular, the porosity of the first layer (dense-YSZ) and the second layer (porous-YSZ) are different and it is expected that the high temperature durability will be improved by relaxing the thermal stress between the layers when the thermal barrier coating is applied at high temperature.

≪ Comparative Example 1 &

_{La 2 O 3 (Kojundo Chemical Lab} . Co., LTD, 99.9%, 11㎛), ZrO 2 , using an oxide powder (Kojundo Chemical Lab. Co., LTD , 98%, 40nm) La 2 Zr 2 O 7 Complex oxides were synthesized.

Specifically, each of the above powders was weighed to the composition shown in Table 4 below, and 1 mm zirconia balls and IPA (Isopropyl alcohol) were used as a mixing medium, and a dispersant of 0.5 Wt.% Relative to the powder content was added thereto. After the wet mixing, the mixed slurry was dried by stirring using a magnetic bar so that the slurry could not be precipitated. After that, the slurry was dried in an oven at 80 ° C for 24 hours and then pulverized using alumina induction to prepare mixed powder. The prepared powders were diluted at a ratio of 1: 9 with respect to ethanol and ball milled for 24 hours to prepare a liquid mixed slurry. The prepared slurry was sieved using a 10 μm sieve to prepare a granulated slurry.

Next, the assembled slurry was supplied to the plasma torch through the supply pipe, rotated at a speed of 1200 rpm while the jig equipped with the heat-resistant metal substrate was rotated at an interval of 75 mm between the substrate and the torch, , A 150 pass preheating process was performed under a coating condition of 220 A and 111.65 kW, and 1000 pass coating was carried out while supplying the slurry in the same manner.

 6 shows the microstructure of the coating layer of the specimen prepared in Comparative Example 1. As a result of observation of the microstructure, the coating itself has a very dense structure, and in particular, in the case of the composition of Lanthanum zirconate prepared in Comparative Example 1, a vertical crack was observed.

1: Suspension feeder for suspension plasma spraying machine
11: First storage tank
12: Second storage tank
21: First conveying pipe
22: first opening / closing valve
31: Second conveyance pipe
32: Third open / close valve
41: Third conveying pipe
42: Third open / close valve

Claims (11)

(a) a second suspension in which second oxide particles for thermal spray coating are dispersed in a mixed medium comprising a first suspension in which first oxide particles for thermal barrier coating are dispersed, ethanol and distilled water at a weight ratio of 80:20 to 60:40 And a third suspension in which third oxide particles for thermal barrier coating are dispersed, respectively;
(b) forming a first coating layer on the base material by suspension plasma spraying (SPS) using the first suspension;
(c) forming a second coating layer on the first coating layer by suspension plasma spraying (SPS) using the second suspension; And
(d) forming a third coating layer on the second coating layer with a suspension plasma spray using the third suspension. The method according to claim 1,
Wherein the first oxide and second oxide for thermal barrier coating are YSZ (Yttria-stabilized zirconia) and the third oxide for thermal barrier coating is rare-earth zirconates. ≪ / RTI > 3. The method of claim 2,
Wherein the rare earth zirconate is La _1.89-x Gd _x Zr _2.12 O _7.06 (x is 0.24 to 1.65). The method according to claim 1,
Wherein the step of preparing the first suspension in the step (a) comprises the following steps:
(a-1) mechanically pulverizing oxide powder for thermal spray coating; And
(a-2) forming a slurry containing the pulverized oxide powder. The method according to claim 1,
Wherein the step of preparing the second suspension in the step (a) comprises the following steps:
(a-1) mechanically pulverizing oxide powder for thermal spray coating; And
(a-2) dispersing the pulverized oxide powder in a mixing medium comprising ethanol and distilled water at a weight ratio of 80:20 to 60:40 to form a slurry. The method according to claim 1,
Wherein the step of preparing the third suspension in the step (a) comprises the following steps:
(a-1) mixing two or more oxide powders to perform mechanical alloying; And
(a-2) forming a slurry containing the oxide powder for thermal spray coating obtained in the step (a-1). The method according to claim 6,
(Ii) at least one oxide selected from the group consisting of Y ₂ O ₃ , Gd ₂ O _3, and La ₂ O ₃ , and (ii) at least one oxide selected from ZrO ₂ and CeO ₂ . Layer ceramic thermal barrier coating layer. 7. The method according to any one of claims 4 to 6,
The mechanical pulverization or mechanical alloying of the oxide powder in the step (a-1) is carried out by planetary ball milling, attrition milling or shaker milling. Layer ceramic thermal barrier coating layer. 7. The method according to any one of claims 4 to 6,
Further comprising the step of calcining the oxide powder obtained in the step (a-1) prior to the step (a-2). The method according to claim 1,
Wherein the second coating layer is formed on the second coating layer by suspension plasma spraying using the mixed suspension of the second suspension and the third suspension in the step (c), and the second and third oxides Wherein a cushioning layer in which the content ratio continuously changes is formed on the surface of the three-layer ceramic thermal barrier coating layer. 11. The method of claim 10,
The step (c)
A first storage tank in which the second suspension is stored;
A second storage tank in which the third suspension is stored;
A first transfer pipe for supplying a second suspension from the first storage tank to a plasma spray gun;
A first opening / closing valve provided in the first transfer pipe for controlling a supply amount of the second suspension to the plasma spray gun;
A second transfer pipe connecting between the first storage tank and the second storage tank and transferring the third suspension to the first storage tank;
A second opening / closing valve provided in the second transfer pipe for controlling a flow rate of the third suspension to the first storage tank;
A third transfer pipe for supplying a third suspension from the second storage tank to a plasma spray gun; And
And a third opening / closing valve provided in the third transfer pipe for controlling a supply amount of the third suspension to the plasma spray gun. The three-layer ceramic thermal spraying coating apparatus according to claim 1, Gt;

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