JP2012180549A - Method for partially repairing thermal barrier coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for partially repairing a thermal barrier coating, capable of forming a repair film having high peeling resistance.SOLUTION: The method for partially repairing a thermal barrier coating includes: a repair film forming step of thermally spraying a thermal spray material mainly composed of zirconia to a damage portion of a ceramic layer 3 mainly composed of zirconia of a member having a metal bond layer 2 and the ceramic layer 3 successively formed on a heat-resisting alloy base material 1 to form a repair film 9; and a vertical crack formation step of irradiating a surface of the repair film 9 with laser beam after coating the surface of the ceramic layer 3 that can be a passage of laser beam around the repair film 9 with a reflecting material having laser reflecting capability to form vertical cracks 11 in the repair film 9.

Description

  The present invention relates to a method for partially repairing a thermal barrier coating applied to a member used in a high temperature environment such as a moving blade and a stationary blade of a gas turbine or a combustor.

  A power generation device such as a gas turbine is used in a high temperature environment. 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. Further, a thermal barrier coating (TBC) is formed on the base material of the heat resistant member to protect the heat resistant member from high temperature.

The TBC has a structure in which a metal bonding layer (undercoat layer) and a ceramic layer (topcoat layer) are laminated from the substrate side.
The metal bonding layer mainly contains an MCrAlY alloy (M: represents at least one element of Co and Ni) excellent in oxidation resistance, and is sprayed on the substrate. The metal bonding layer has a corrosion resistance function to the substrate and a function as a binder that bonds the substrate and the ceramic layer.

The ceramic layer is sprayed onto the metal bonding layer using a zirconia (ZrO ₂ ) ceramic powder material. Examples of the ZrO ₂ ceramic powder material include partially stabilized zirconia stabilized with a rare earth element, and a mixed powder of a rare earth element having a pyrochlore structure and zirconia. Since the ceramic layer is required to have high heat shielding properties, the ceramic layer has a porous structure containing pores.

  When the ceramic layer of the TBC is partially damaged, the TBC is repaired. As a general repair method, the ceramic layer and the metal bonding layer are peeled over the entire surface of the member, and after the surface treatment of the member, a new metal bonding layer and a ceramic layer are sequentially formed. In this method, since it is necessary to repair the entire surface of the member, there is a problem that the construction period becomes long and the repair cost is high. Therefore, a method for partially repairing the TBC is required.

  As a method of partially repairing TBC, a method of spraying ceramic particles on the damaged part to form a repair film, or a paste material prepared by mixing ceramic particles and a binder material is applied to the damaged part to repair the TBC. There is a method of forming (Patent Document 1).

JP 2010-505 A (paragraphs [0009] and [0010])

  When the TBC is partially repaired, the interface between the repair film and the surrounding healthy ceramic layer (sound part) is discontinuous, and thus there is a problem that the repair film is easily peeled off.

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the partial repair method of the thermal barrier coating which forms a repair film with high peeling resistance.

  In order to solve the above problems, the present invention mainly includes zirconia in a damaged portion of the ceramic layer of a member in which a metal bonding layer and a ceramic layer mainly containing zirconia are sequentially formed on a heat-resistant alloy substrate. A coating process for forming a repair film by spraying a thermal spray material to be coated, and a surface of the ceramic layer that can serve as a laser beam passage around the repair film is coated with a reflective material having a laser reflectivity, There is provided a partial repair method for a thermal barrier coating comprising: a longitudinal crack forming step of irradiating a surface of a repair film with a laser beam under a predetermined condition to form a longitudinal crack in the repair film.

  When the repair film is irradiated with laser, a rapid temperature difference is generated in the repair film, and vertical cracks are formed. Since the repair film in which the vertical crack is formed has a gap, the stress during thermal expansion can be relaxed. Thereby, the thermal cycle durability of the repaired portion is increased, and the peel resistance is improved. A longitudinal crack means the crack extended in the thickness direction of a repair film.

  Since the damaged portion of the ceramic layer is a part of the structural member, in order to irradiate the repair coating with laser, the laser must pass over a healthy ceramic layer (sound portion) around the repair coating. According to the said invention, it can prevent that a healthy part is damaged by laser irradiation by masking on the healthy part around a repair film with a reflecting material.

  1 aspect of the said invention WHEREIN: The surface grinding | polishing process which grind | polishes the surface of the said ceramic layer which can become a passage of the thermal spraying construction of the circumference | surroundings of the said damage part before the said repair film formation process, and makes surface roughness below a predetermined value Preferably, after the surface polishing step, the repair coating is formed without covering the surface of the ceramic layer around the damaged portion with a masking material.

  In a normal spraying process, when a repair coating is partially formed, the periphery of a region where the spray coating is to be formed is covered with a masking material, and the spray frame is scanned thereon. According to one aspect of the present invention, the surface of the region that can be a passage for thermal spraying that should normally be covered with a masking material is polished. Since a sprayed coating cannot be fixed on a substrate having such a surface, a repair coating can be partially formed without using a masking material.

  When a masking material is used, the masking material is removed after the repair coating is formed. As a result, a step is generated at the boundary between the repair coating and the surrounding healthy part, and a post-processing step for removing this step is required. According to one aspect of the invention, a step is unlikely to occur at the boundary between the repair coating and the surrounding healthy part, and thus the post-processing process can be simplified.

  In one aspect of the invention, it is preferable that the surface of the damaged portion is blasted before the repair coating forming step so that the surface roughness of the damaged portion is a predetermined value or more.

  By setting the surface roughness of the damaged portion to a predetermined value or more, the repair coating sprayed on the damaged portion can be firmly fixed on the base.

  In one aspect of the invention, before the surface polishing step, a thermal spray coating forming step of forming a thermal spray coating with a predetermined thickness on the surface of the ceramic layer that can be a thermal spraying passage located around the damaged portion. It is preferable to further provide.

  By forming the thermal spray coating in advance, the sound part of the ceramic layer can maintain a desired film thickness even after being polished in the surface polishing step. The predetermined film thickness is preferably equivalent to a film thickness that decreases when the surface roughness is set to a predetermined value or less in the surface polishing step.

  According to the present invention, the thermal cycle durability of the repaired part can be improved by forming vertical cracks in the repaired film. In addition, by polishing the surface of the ceramic layer that can serve as a passage for thermal spraying in advance, it is possible to simplify the processing steps before and after the formation of the repair coating and improve workability.

It is a fragmentary sectional view of the member to be repaired in a 1st embodiment. It is a figure which shows the channel | path of the thermal spray flame | frame assumed in 1st Embodiment. It is the figure which planarly viewed the to-be-repaired member coat | covered with the masking material from the upper surface. It is a figure which shows the passage route of the laser beam which concerns on 1st Embodiment. It is the figure which planarly viewed the to-be-repaired member coat | covered with the reflecting material from the upper surface. It is a fragmentary sectional view of the to-be-repaired member repaired in 1st Embodiment.

Hereinafter, an embodiment of a partial repair method for a thermal barrier coating according to the present invention will be described with reference to the drawings.
(First embodiment)
In FIG. 1, the fragmentary sectional view of the to-be-repaired member in this embodiment is shown. The repaired member 10 has a structure in which a TBC composed of a metal bonding layer 2 and a ceramic layer 3 is laminated on a base material 1, and a part of the ceramic layer 3 is damaged. In the present embodiment, the damaged portion 4 having a radius of about 20 mm or less is a main repair target.

The base material 1 is a Ni-based heat-resistant alloy such as IN738LC.
The metal bonding layer 2 is formed on the base material 1 by a low pressure plasma spraying method or the like. The metal bonding layer 2 is an MCrAlY alloy (M represents at least one element of Ni and Co) and the like, and generally has a thickness of 0.05 mm or more and 0.2 mm or less.

The ceramic layer 3 is formed on the metal bonding layer 2 by an atmospheric plasma spraying method (APS). The ceramic layer 3 is made of a ceramic mainly composed of zirconia (ZrO ₂ ). Examples of the ceramic layer 3 include YSZ (yttria stabilized zirconia), YbSZ (ytterbia stabilized zirconia), DySZ (dysprosia stabilized zirconia), ErSZ (erbia stabilized zirconia), SmYbZr ₂ O _{7 and the} like. The ceramic layer 3 generally has a thickness of 0.1 mm to 1 mm and a porosity of 1 volume% to 30 volume%.

The partial repair method according to the present embodiment includes a repair film forming step and a vertical crack forming step.
First, the surface of the ceramic layer 3 that can be a passage for thermal spraying around the damaged portion 4 is covered with a masking material. FIG. 2 shows a passage of the thermal spray frame 5 assumed in the present embodiment. FIG. 2 is a plan view of the repaired member 10 as viewed from the upper surface (ceramic layer side). FIG. 3 shows a plan view of the repaired member 10 covered with the masking material 6 from above.

  Next, the surface (bottom surface) of the damaged portion 4 is appropriately blasted as necessary, and the surface roughness of the damaged portion 4 is set to a predetermined value or more. The predetermined value is larger than 7 Ra, preferably about 9 Ra to 15 Ra. By doing so, when the thermal spraying is applied in the next process, the repair film is caught by the unevenness of the base by the anchor effect, and is firmly bonded to the base.

  Next, a repair coating 9 is formed on the damaged portion 4 by thermal spraying using a thermal spray material mainly composed of zirconia (repair coating formation step). The thermal spray material has the same composition as the sound ceramic layer 3 (sound part) around the damaged part 4, but may have a different composition. In the present embodiment, as shown in FIG. 2, after scanning the sprayed frame 5 so as to pass over the damaged part 4 from the one end side to the other end side of the member to be repaired, the above-described scanning direction is obtained at the other end part. Then, the position is shifted in the vertical direction and then folded and scanned so as to pass over the damaged portion 4 toward one end. By repeating this appropriately, a repair coating is formed on the damaged portion 4.

The repair coating is, for example, a spray gun (for example, F4 gun) manufactured by Sulzer Metco Co., Ltd. It is possible to form a film under typical conditions of Ar / H ₂ amount: 35 / 7.4 (l / min).

  Next, the masking material 6 is removed, and the level difference generated at the interface between the healthy part and the repair film is removed.

  Next, the surface of the ceramic layer 3 that can serve as a laser beam path around the repair coating is coated with a reflective material having laser reflectivity, and then the laser beam is irradiated to the surface of the repair coating under predetermined conditions (formation of vertical cracks). Process). FIG. 4 shows a path through which the laser beam 7 passes. In FIG. 5, the figure which planarly viewed the to-be-repaired member 10 coat | covered with the reflector 8 from the upper surface is shown.

  The reflector 8 is preferably a powder or a thin plate, and is preferably composed of a heat resistant resin containing an organic light absorber. In detail, the reflecting material 8 has a sum of the absorptance and the reflectance with respect to the laser light of the heat-absorbing agent-containing heat-resistant resin processed into a thin plate having a thickness of 3 mm, preferably 60% or more and 90% or less, preferably It is good that it is 65% or more and 85% or less. The mixing ratio with the organic light absorber is adjusted so as to achieve the above optical characteristics.

  The heat-resistant resin is a thermoplastic resin having a melting point of 200 ° C. or higher, preferably 250 ° C. or higher. Examples thereof include polyphenylene sulfide, polyamide 66, polyamide 46, polyethylene terephthalate, polycyclohexanedimethylene terephthalate, polyethylene naphthalate, polytetrafluoroethylene, perfluoroalkoxyalkane, and ethylene-tetrafluoroethylene copolymer.

  The organic light absorber has absorption near the wavelength of the laser beam used. For example, when an Nd: YAG laser is used, it is preferable that the organic light absorber has absorption in the vicinity of a wavelength of 1064 nm. As the organic light absorber, an azine dye that does not contain a metal as a constituent element is suitable. The azine dye has absorption in the vicinity of the above wavelength region and is excellent in heat resistance and light resistance. For example, LTW-8170C, LTW-8400C, LTW-8950H, LTW-8000C, LWT-8901H and LAW-4801 manufactured by Orient Chemical Industries, Ltd. are used.

  The organic light absorber is dispersed and contained in the heat resistant resin. The organic light absorber may be applied alone to the surface of the heat resistant resin. Alternatively, the organic light absorber may be dispersed in the heat resistant resin and applied to the surface of the healthy part around the repair film 9 together with the heat resistant resin.

  As shown in FIG. 4, the laser beam is scanned so that the laser beam passes over the repair film 9 from one end of the member to be repaired 10 toward the other end, and then in the scanning direction at the other end. On the other hand, the position is shifted in the vertical direction, and then folded and scanned to pass through the repair film 9 toward one end. This process is repeated to irradiate the entire surface of the repair film 9 with a laser beam. As a result, a vertical crack 11 extending in the thickness direction of the repair film 9 as shown in FIG. 6 is formed in the vicinity of the laser beam irradiation portion.

The laser beam power density 40~200W / mm ^2, the range of the energy density 2~5J / mm ^2, it is preferable to irradiate and the product of both density conditions to be ^{180W / mm 2 · J / mm} 2 or more . By doing so, it is possible to make the repair coating 9 capable of relaxing thermal stress while maintaining soundness.

(Second Embodiment)
The present embodiment is characterized by including a surface polishing step before the repair film forming step.
First, the periphery of the damaged portion 4 is covered with a blasting masking material. Since it is masking only for blasting, the coating area is small compared to masking for thermal spraying. Next, as in the first embodiment, the surface (bottom surface) of the damaged portion 4 is appropriately blasted as necessary.

  After removing the masking material for blasting, the surface of the ceramic layer 3 that can be a passage for thermal spraying located around the damaged portion 4 is polished to reduce the surface roughness to a predetermined value or less (surface polishing step). The region to be polished is equivalent to the region covered with the masking material 6 in the first embodiment. Further, the whole surface of the healthy ceramic layer 3 on the repaired member 10 may be polished. The predetermined value is 7 Ra or less, preferably 5 Ra or less, and more preferably 3 Ra or less. By setting the surface roughness to a predetermined value or less, the sprayed film sprayed thereon cannot be firmly bonded to the base.

  Next, the surface roughness of the region (or the entire surface of the healthy ceramic layer on the repair member), the surface of the repair coating, and the interface between the healthy part and the repair coating are appropriately treated to obtain the surface roughness. Is 7 Ra or less. Even when a step due to the film thickness is generated at the interface between the healthy part and the repair coating, the step is considerably smaller than the step generated in the first embodiment. Therefore, it is possible to shorten the work time for removing the step and making the surface of the repair film have a desired roughness.

  According to this embodiment, since the thermal spraying is performed without using the masking material after the region to be covered with the masking material 6 is polished, not only the masking process for thermal spraying can be omitted, but also the aerodynamic characteristics of the repaired member are improved. be able to. When the member to be repaired is a member that rotates at a high speed, such as a moving blade of a gas turbine, smoothing the surface roughness leads to an improvement in the efficiency of the gas turbine.

  Next, as in the first embodiment, the repair coating is irradiated with a laser beam to form vertical cracks.

(Third embodiment)
This embodiment is characterized by including a thermal spray coating forming step before the surface polishing step.
First, similarly to the second embodiment, the surface of the damaged portion 4 is blasted. Next, a thermal spray coating having a predetermined film thickness is formed on the surface of the ceramic layer that can serve as a thermal spraying passage located around the damaged portion and the damaged portion. The thermal spraying conditions are preferably the same as those in the repair film forming step. The predetermined film thickness is preferably equivalent to a film thickness that decreases when the surface roughness is set to a predetermined value or less in the surface polishing step. For example, the predetermined film thickness is about 50 μm.
Next, similarly to the second embodiment, a surface polishing process, a repair film forming process, and a vertical crack forming process are performed.

  The present embodiment may be applied when the thickness of the sound ceramic layer on the member to be repaired is thin. According to the present embodiment, by forming a thermal spray coating in advance, it becomes possible for the ceramic layer of the sound part to maintain a desired film thickness even after being polished in the surface polishing step.

1 Base material (heat-resistant alloy base material)
2 Metal bonding layer 3 Ceramics layer (sound part)
4 Damaged part 5 Thermal spray frame 6 Masking material 7 Laser beam 8 Reflective material 9 Repair coating 10 Repair member 11 Vertical crack

Claims (4)

A repair coating is formed by spraying a thermal spray material mainly composed of zirconia on a damaged portion of the ceramic layer of a member in which a metal bonding layer and a ceramic layer mainly composed of zirconia are sequentially formed on a heat-resistant alloy substrate. Repair film formation process,
After the surface of the ceramic layer that can be a laser beam path around the repair coating is coated with a reflective material having laser reflectivity, the surface of the repair coating is irradiated with a laser beam under predetermined conditions, and the repair coating is applied to the repair coating. A vertical crack forming process for forming vertical cracks;
A partial repair method for a thermal barrier coating. Before the repair coating forming step, at least a surface polishing step of polishing the surface of the ceramic layer that can be a passage for thermal spraying around the damaged portion to reduce the surface roughness to a predetermined value or less,
The method for partially repairing a thermal barrier coating according to claim 1, wherein after the surface polishing step, the repair coating is formed without covering the surface of the ceramic layer around the damaged portion with a masking material.   The method for partially repairing a thermal barrier coating according to claim 1 or 2, wherein the surface of the damaged portion is blasted before the repair coating forming step so that the surface roughness of the damaged portion is a predetermined value or more.   The thermal spray coating forming step of forming a thermal spray coating with a predetermined film thickness on the surface of the ceramic layer, which can be a spray coating passage located around the damaged portion, before the surface polishing step. The partial repair method of the thermal barrier coating in any one of claim | item 3.

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