JP2011117012A - Executing method of thermal barrier coating, heat-resistant member, and gas turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an executing method of a thermal barrier coating having high heat cycle durability and high thermal barrier property. <P>SOLUTION: The executing method includes a step of forming a bond coat layer 2 on a heat-resistant alloy base material 1, and a step of forming a top coat layer 3 on the bond coat layer 2. The step of forming the top coat layer 3 includes a step of forming a plurality of ceramic films 3a by the thermal spraying, and a step of executing the temperature control so that the surface temperature of the top coat layer 3 is ≤450°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thermal barrier coating construction method, a heat-resistant member, and a gas turbine, and more particularly to a thermal barrier coating component such as a gas turbine, a film-formed component, and a construction method thereof.

  For example, gas turbine components of power generation gas turbine plants are used in high temperature environments. Therefore, the stationary blades and moving blades constituting the gas turbine, the wall material of the combustor, and the like are made of heat resistant members. Furthermore, a thermal barrier coating in which a ceramic layer (topcoat layer) made of oxide ceramics is laminated on a base material of the heat-resistant member by a film forming method such as thermal spraying through a metal bonding layer (bond coat layer). , TBC) to protect the heat-resistant member from high temperatures.

  The formation conditions of the thermal barrier coating are usually optimized by an element test using a test piece. However, there is a difference in heat capacity between the test piece and the actual machine. Therefore, if a thermal barrier coating is formed on an actual part without considering the difference in heat capacity, the durability and thermal barrier properties of the thermal barrier coating are adversely affected. For example, when a thermal barrier coating is formed on a solid blade having a large heat capacity under the same conditions as in the element test, a layered defect may occur in the top coat layer of the thermal barrier coating. On the other hand, when a multilayer coating is continuously performed on a small, hollow blade having a small heat capacity and the blade is overheated, the coating portion is damaged. Such a coating layer has low thermal cycle durability.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the construction method of the thermal barrier coating which has high durability and high thermal-insulation property.

  In order to solve the above-mentioned problems, the present invention comprises a step of forming a bond coat layer on a heat-resistant alloy substrate and a step of forming a top coat layer on the bond coat layer, and forming the top coat layer There is provided a thermal barrier coating construction method comprising a step of forming a plurality of ceramic films by thermal spraying and a step of controlling the temperature so that the surface temperature of the topcoat layer is 450 ° C. or lower.

  Conventionally, the top coat layer is formed by laminating a plurality of ceramic films by repeatedly performing thermal spraying to have a desired film thickness. Therefore, in the production of an actual machine, if an attempt is made to apply a thermal barrier coating under the same conditions as in the element test, the temperature of the substrate will rise due to the difference in heat capacity. The substrate whose temperature has risen expands, and the expanded substrate shrinks when returning to room temperature. Since there is a difference in thermal expansion coefficient between the base material and the top coat layer, the shrinkage of the base material gives a compressive stress to the top coat layer, and cracks are likely to occur in the top coat layer. That is, the heat cycle durability of the topcoat layer is reduced. According to the construction method of the present invention, by controlling the surface temperature of the topcoat layer to be 450 ° C. or lower, the expansion of the base material is suppressed, so that the compressive stress applied to the topcoat layer can be suppressed. . Thereby, generation | occurrence | production of a crack is suppressed and a thermal barrier coating with high thermal cycle durability can be applied.

  The heat shielding property of the top coat layer is affected by the porosity. When the porosity is lowered, the thermal conductivity is increased, so that the heat shielding property is lowered. When the surface temperature of the topcoat layer is controlled to be 450 ° C. or lower, it is possible to suppress a decrease in the porosity of the topcoat layer due to a temperature rise during film formation. Thereby, a thermal barrier coating having a high thermal barrier property can be applied.

In the above invention, the temperature controlling step provides a predetermined time interval between the thermal spraying for forming one ceramic film and the thermal spraying for forming another ceramic film on the one ceramic film. It may be done by means.
When the thermal spraying is continuously performed, the temperature of the base material and the ceramic film increases. By providing a predetermined time interval between the thermal spraying, the temperature rise width of the base material and the ceramic film can be suppressed by atmospheric heat dissipation or the like.

In the above invention, the step of controlling the temperature may be performed by means for cooling the heat-resistant alloy base material with a cooling medium from a surface opposite to the side on which the top coat layer of the heat-resistant alloy base material is formed. good.
By cooling from the back surface of the heat-resistant alloy substrate, the temperature distribution in the plate thickness direction of the substrate can be controlled such that the side on which the topcoat layer is formed is high and the back surface side is low. Since the cooled heat-resistant alloy base material acts to generate a tensile stress on the side on which the topcoat layer is formed, the compressive stress applied to the topcoat layer due to the thermal expansion of the base material is reduced. This reduces the occurrence of cracks in the topcoat layer, leading to improved durability of the thermal barrier coating. Further, since the surface on which the topcoat layer is formed is not directly cooled, there is no adverse effect on the flow of external cooling gas or the flattening behavior of the spray particles due to the temperature drop on the surface on which the topcoat layer is formed. Furthermore, since the temperature can be controlled simultaneously with the formation of the topcoat layer, the manufacturing time can be shortened and the manufacturing cost can be reduced.

  In the above invention, the step of forming the top coat layer includes a step of preheating the heat-resistant alloy substrate on which the bond coat layer is formed to 100 ° C. or higher before forming the first layer of the ceramic film. Is preferred.

When the first layer of the ceramic film is formed by thermal spraying on the substrate (heat-resistant alloy substrate / bond coat layer), the substrate temperature affects the flattening behavior of the spray particles. When the temperature rises, the flattening of the spray particles is promoted, and the structure of the ceramic film changes in the direction of densification.
In general, it seems to be good to use conditions that make the particles completely flat (pancake-like flat state), but in the case of ceramic thermal barrier coating, it is necessary to form appropriate pores in the film Therefore, it is not always optimal to make it too flat considering only adhesion.
This tendency varies depending on the material on the substrate side, the heat capacity, the roughened state, and the like. Also, if the preheating temperature is raised too much, it will lead to an increase in the overall temperature during film formation, which may lead to a decrease in heat shielding properties and durability, and preheating (deposition start temperature) as described later. In addition, it is necessary to control the entire temperature during film formation.
Therefore, preheating is preferably performed at 100 ° C. or higher and 200 ° C. or lower. As a result, the effect of improving the adhesion can be obtained with little influence on the densification and durability of the structure. Even if it is considered that the influence of the substrate temperature on the flattening behavior of the thermal spray particles is small, such as a film formation target with a small heat capacity (target with a small plate thickness), the film formation part The effect of removing adhering moisture and the like can be obtained, and adhesion and systematic improvement effects can be expected.

In the above invention, the thermal spraying is preferably plasma spraying, and the preheating is preferably performed by plasma without spraying the raw material particles.
Not spraying the raw material particles means a state in which the raw material particles are not supplied. The plasma can be generated by using a thermal spraying apparatus used for forming a ceramic film, and is used as a heat source for ceramic thermal spraying. That is, thermal spraying is performed by supplying ceramic powder into this plasma, but if the powder is not supplied, it can be used as a simple heating source. Similar to the thermal spraying construction, a uniform heating state can be obtained in the setting state before the thermal spraying construction by heating the plasma gun so that the surface of the object to be sprayed is covered evenly by the robot. Although the plasma itself has a high temperature of about 10000 ° C., the temperature of the sprayed object is heated by the radiant heat from the plasma by keeping the distance between the plasma gun and the sprayed object appropriate. Control can be performed relatively easily and accurately. Therefore, since heating can be performed in the setting state at the time of thermal spraying, by accurately controlling the time from the end of heating to the start of thermal spraying film formation, the accuracy of the preheating temperature can be increased, and the number of manufacturing processes and manufacturing costs are increased. In addition, there is no concern about contamination caused by movement of the base material.

  According to the present invention, when the ceramic film is formed, a thermal barrier coating having high thermal cycle durability and high thermal barrier properties can be applied by controlling the surface temperature of the topcoat layer. A heat-resistant member on which such a thermal barrier coating is applied and a gas turbine using the member have high thermal barrier properties and excellent durability.

It is explanatory drawing of the temperature profile of a base material and a ceramic film when forming a topcoat layer with the construction method which concerns on embodiment of this invention. It is a schematic cross section of a laser type thermal cycle testing apparatus. Fig.3 (a) is a graph which shows typically the temperature change of the sample with which the apparatus shown in FIG. 2 was used for the thermal cycle test. FIG. 3B is a schematic cross-sectional view of a sample used for the thermal cycle test. It is a graph which shows the result of a heat cycle durability test. About Example 11, it is a scanning electron micrograph at the time of one thermal spray particle colliding on the graph which shows the relationship between preheating temperature and an oblateness rate, and a base material. About Example 12, it is a scanning electron micrograph at the time of one thermal spray particle colliding on the graph which shows the relationship between preheating temperature and an oblateness rate, and a base material.

The member thermally coated by the construction method according to the present embodiment includes a heat-resistant alloy substrate 1, a bond coat layer 2 formed on the heat-resistant alloy substrate 1, and a top formed on the bond coat layer 2. It is comprised with the coating layer 3 (refer Fig.1 (a) V).
As the heat-resistant alloy substrate 1, a Ni-based heat-resistant alloy such as IN738LC is used.
The bond coat layer 2 is made of MCrAIY alloy (M is a metal element such as Ni, Co, Fe, or a combination of two or more of these), and is determined by the usage environment such as the usage temperature of the parts. However, it is generally formed with a thickness of 0.05 mm or more and 0.2 mm or less.
The top coat layer 3 is made of 8 mass% yttria partially stabilized zirconia or the like, and is determined by the usage environment such as the usage temperature of the parts. The ceramic film 3a is laminated (see FIG. 1 (a) III).

Below, the construction method of the thermal barrier coating in this embodiment is demonstrated.
The construction method in the present embodiment includes a step of forming the bond coat layer 2 and a step of forming the top coat layer 3.
In the step of forming the bond coat layer 2, the bond coat layer 2 is formed on the heat-resistant alloy substrate 1 using a known technique such as thermal spraying or vapor deposition. In this embodiment, a low pressure plasma spraying method is used.
In the step of forming the topcoat layer 3, the base material formed up to the bond coat layer 2 is preheated by plasma, and then the ceramic film 3a is formed by plasma spraying. At this time, thermal spraying is repeatedly performed until the top coat layer 3 has a desired film thickness.

  Preheating is performed by measuring the temperature of the substrate surface with a thermo viewer and heating the substrate surface temperature to 100 ° C. or higher. Note that this preheating step may be omitted.

  In forming the topcoat layer 3, the materials and thicknesses of the heat-resistant alloy substrate 1, the bondcoat layer 2 and the topcoat layer 3 and the operations during film formation are performed so that the surface temperature of the topcoat layer 3 is 450 ° C. or less. The surface temperature of the top coat layer 3 is controlled in consideration of the environment and the like. In the present embodiment, the surface temperature of the topcoat layer 3 is set at a predetermined time interval between the thermal spraying for forming an arbitrary ceramic film 3a and the thermal spraying for forming another ceramic film 3a on the ceramic film 3a. Is provided so that the surface temperature of the ceramic film 3a is 450 ° C. or lower.

  In addition, you may control the surface temperature of the topcoat layer 3 so that it may become 450 degrees C or less by cooling from the opposite side to the side in which the ceramic layer 3 of the heat-resistant alloy base material 1 is formed. Some gas turbine members such as blades include a passage for internal cooling. When a thermal barrier coating is applied to such a member, the substrate temperature can be controlled by performing thermal spraying while flowing a cooling gas whose flow rate is controlled through the passage.

  FIG. 1 shows an example of the surface temperature profile of the base material and the ceramic film 3a when the topcoat layer 3 is formed by the construction method according to this embodiment. 1A shows a case where the surface temperature of the topcoat layer 3 is controlled during the formation of the topcoat layer 3, and FIG. 1B shows a case where the surface temperature of the topcoat layer 3 is changed during the formation of the topcoat layer 3. It is a temperature profile when the temperature rise of a base material progresses without being controlled. As shown in FIG. 1, the temperature of the base material is increased by repeatedly performing thermal spraying (I to IV), and is decreased after film formation is completed (IV to V). Since the heat-resistant alloy substrate 1 and the bond coat layer 2 have a larger coefficient of thermal expansion than the top coat layer 3, the heat-resistant alloy substrate 1 and the bond coat layer 2 contract more greatly when the substrate temperature is lowered. A compressive stress is applied to the coat layer 3. The greater the substrate temperature drop, the greater the compressive stress. In FIG. 1B, since the temperature drop of the base material after the film formation is large, it becomes a factor for generating the crack 4 in the topcoat layer 3. On the other hand, in FIG. 1A, temperature control can suppress an increase in substrate temperature. Therefore, the temperature drop after film formation is reduced, and the compressive stress applied to the topcoat layer 3 can be reduced. Further, as can be seen from FIG. 1A, when the temperature is controlled, the temperature rise of the ceramic film 3a becomes saturated from the middle. Therefore, in this embodiment, it is considered that the temperature difference in the plate thickness direction between the base material during film formation and the top coat layer 3 is small.

Hereinafter, the grounds for setting the surface temperature of the topcoat layer 3 to 450 ° C. or less will be described.
(Porosity)
Example 1
A thermal barrier coating member having the following constitution was produced and used as a test piece of Example 1.
Heat-resistant alloy substrate 1: IN738LC
Bond coat layer 2: CoNiCrAIY alloy, film thickness 0.1 mm
Topcoat layer 3: 8% by weight yttria partially stabilized zirconia, film thickness 0.5 mm
Ceramic film 3a is an atmospheric plasma spraying method, spraying current 600 (A), spray distance 0.99 (mm), a powder supply amount 60 (g / min), Ar / H 2 volume; 35 / 7.4 (l / min ) Was formed so as to include pores. The time interval between the layers of thermal spraying was 20 seconds.

Example 2
The same process as in Example 1 except that the heat-resistant alloy substrate 1 / bond coat layer 2 was preheated to 100 ° C. by plasma without supplying the raw material particles before forming the first layer of the ceramic film 3a. A test piece was prepared.

Example 3
A test piece was prepared in the same process as in Example 1 except that the preheating temperature in Example 2 was changed to 200 ° C.

Example 4
A test piece was prepared in the same process as in Example 1 except that the preheating temperature in Example 2 was changed to 300 ° C.

Table 1 shows the surface temperature and porosity at the end of the construction of the topcoat layer 3 of the test pieces of Examples 1 to 4. The surface temperature at the end of the construction of the topcoat layer 3 was measured with an infrared radiation thermometer from the uppermost layer surface side of the ceramic film 3a immediately after the topcoat layer 3 was formed. The porosity was calculated from the tissue image processing result.

  It was confirmed that when the surface temperature at the end of the construction of the topcoat layer 3 exceeds 450 ° C., the porosity starts to decrease and a denser structure is obtained.

(Thermal cycle durability)
Examples 5 to 10 and Comparative Example 1
A test piece was prepared in the same process as in Example 1 except that the preheating temperature of Example 1 and the time interval between the layers of thermal spraying and thermal spraying were changed. Table 2 shows the preheating temperature, the time interval, and the surface temperature at the end of the construction of the topcoat layer 3 in each example.
Here, Comparative Example 1 corresponds to the state as shown in FIG. 1B in the case where the construction is continuously performed without considering the increase in the substrate temperature.

  The thermal cycle durability of Examples 5 to 10 and Comparative Example 1 was measured. FIG. 2 is a schematic cross-sectional view of a laser thermal cycle test apparatus used for evaluation of thermal cycle durability. In the laser thermal cycle testing apparatus shown in this figure, a top coat layer 131B is formed on a base material (heat-resistant alloy base material 1 / bond coat layer 2) 131A on a sample holder 132 disposed on a main body 133. The sample 131 is arranged so that the top coat layer 131B is on the outside, and the sample 131 is heated from the top coat layer 131B side by irradiating the sample 131 with the laser light L from the carbon dioxide laser device 130. It has become. In addition, the sample 131 is caused by the gas flow F discharged from the tip of the cooling gas nozzle 134 that passes through the main body 133 simultaneously with the heating by the laser device 130 and faces the back side of the sample 131 inside the main body 133. Is cooled from the back side.

According to this laser type thermal cycle test apparatus, a temperature gradient can be easily formed inside the sample 131, and evaluation according to the use environment when applied to a high temperature part such as a gas turbine member can be performed. . Fig.3 (a) is a graph which shows typically the temperature change of the sample with which the apparatus shown in FIG. 2 was used for the thermal cycle test. Curves A to C shown in this figure correspond to temperature measurement points A to C in the sample 131 shown in FIG. As shown in FIG. 3 (b), according to the apparatus shown in FIG. 2, the top coat layer 131B surface (A) of the sample 131, the interface (B) between the top coat layer 131B and the base material 131A, and the back surface of the base material 131A. It can heat so that temperature may become low in order of the side (C).
For example, by setting the surface of the topcoat layer 131B to a high temperature of 1200 ° C. or higher and setting the temperature at the interface between the topcoat layer 131B and the base material 131A to 800 to 1000 ° C., the temperature conditions are the same as those of an actual gas turbine. Can do. It should be noted that the heating temperature and temperature gradient by the test apparatus can be easily set to desired temperature conditions by adjusting the output of the laser apparatus 130 and the gas flow rate F.

  Using the laser thermal cycle test apparatus shown in FIG. 2, the maximum surface temperature (the maximum temperature of the top coat layer surface) is set to 1750 ° C., and the maximum interface temperature (the top coat layer and the heat resistant alloy substrate 1 / bond coat layer 2 Repeated heating was performed at a maximum interface temperature of 900 ° C. In order to clarify the effect of this condition, a considerably severe condition (temperature acceleration condition) is used in terms of temperature. In this thermal cycle test, the number of cycles at the time when peeling occurred in the topcoat layer 131B was used as an evaluation value for thermal cycle durability.

  FIG. 4 shows the results of the thermal cycle durability test. In the figure, the horizontal axis represents the sample name, and the vertical axis represents the thermal cycle relative life when the case of Example 5 is 100%. Examples 5 to 10 had variations in durability, but all had a lifetime of about 100% as in Example 5. On the other hand, the thermal cycle relative life of Comparative Example 1 was about 10%, and a clear decrease in durability was observed. From the above results, the heat cycle durability can be improved by setting the surface temperature at the end of the construction of the top coat layer 3 to 450 ° C. or less.

(Preheating the base material)
Example 11 and Example 12
IN738LC (Example 11) or 8 mass% yttria partially stabilized zirconia (Example 12) was used as a base material on which the raw material particles were sprayed. As raw material particles of the ceramic film 3a, 8 mass% yttria partially stabilized zirconia (Example 12) was used. The raw material particles of the ceramic film 3a were sprayed on the base material whose preheating temperature was changed by plasma spraying, and the flat state of the particles was observed. FIG. 5 (Example 11) and FIG. 6 (Example 12) are graphs showing a relationship between a scanning electron micrograph and a preheating temperature and a flattening rate when one sprayed particle collides with a substrate. Photographs I to III in FIG. 5 and photographs II to III in FIG. 6 correspond to the numbers (I to III) in the graph. The flatness was calculated as a ratio obtained by dividing the number of flat particles in the scanning electron microscope observation field by the total number of particles. Here, the flat particles are particles generally flat like pancakes as shown in Photo III of FIG. 5 and flattened so as to spread in a circular shape on the substrate surface.

  5 and 6, it can be seen that the particles are less likely to flatten when the temperature of the substrate is low, and flattened easily when the temperature rises. In Example 11, the preheating temperature was 200 ° C. or higher, and in Example 12, the preheating temperature was 100 ° C. or higher. The temperature of the spray particles is estimated to be near the melting point (2700 ° C. or higher) of yttria partially stabilized zirconia. For this reason, when the sprayed particles collide with the base material, if the base material temperature is low, the particles are rapidly cooled and the temperature of the particles becomes lower than the melting point, so that it is considered that the particles are hardly deformed. In Example 12, since the base material is ceramic, the thermal conductivity is lower than that of the metal base material of Example 11. Therefore, it is considered that the flat form is changed even at a temperature lower than that of Example 11 because the heat of the particles is not easily taken.

Example 13
A thermal barrier coating was applied to the moving blade of a gas turbine with an inlet temperature of 1500 ° C. The construction method will be described below. The bond coat layer 2 was formed on the rotor blade by low pressure plasma spraying. Then, it heated until the base-material surface became 100 degreeC using the plasma spray gun. Next, the raw material particles were sprayed from a plasma spray gun to form a multilayer ceramic film 3a.

  As a result of using the rotor blade constructed above in the gas turbine verification test device, troubles such as peeling off the topcoat layer 3 even if the usage time is 2500 hours or more and the start / stop is 150 times or more. And could be used well.

DESCRIPTION OF SYMBOLS 1 Heat-resistant alloy base material 2 Bond coat layer 3 Top coat layer 3a Ceramic film 4 Crack 130 Laser apparatus 131 Sample 132 Sample holder 133 Main-body part 134 Cooling gas nozzle

Claims (7)

A step of forming a bond coat layer on the heat-resistant alloy substrate, and a step of forming a top coat layer on the bond coat layer,
A method for applying a thermal barrier coating, wherein the step of forming the topcoat layer comprises a step of forming a plurality of ceramic films by thermal spraying and a step of controlling the temperature so that the surface temperature of the topcoat layer is 450 ° C. or lower.   The temperature controlling step provides a predetermined time interval between thermal spraying for forming one ceramic film and thermal spraying for forming another ceramic film on the one ceramic film. The thermal barrier coating construction method described.   2. The thermal barrier coating according to claim 1, wherein the temperature controlling step cools the heat-resistant alloy base material with a cooling medium from a surface opposite to a side of the heat-resistant alloy base material on which the topcoat layer is formed. Construction method.   The step of forming the topcoat layer includes a step of preheating the heat-resistant alloy base material on which the bond coat layer is formed to 100 ° C. or higher before forming the first layer of the ceramic film. The construction method of the thermal barrier coating in any one of claim | item 3.   The thermal spray coating method according to claim 4, wherein the thermal spraying is plasma thermal spraying, and the preheating is performed by plasma without spraying raw material particles.   A heat-resistant member that has been heat-shielded by the construction method according to claim 1.   A gas turbine using the heat-resistant member according to claim 6.

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