BRAZING METHOD AND METAL FILM FORMING TOOL FOR BRAZING

In a film formation step of a brazing method, a metal brush formed by bundling a plurality of metal wires is brought into contact with a film formation target portion of a workpiece. Here, the film formation target portion is a portion that includes a joining target portion and a brazing-material-allowed portion but does not include an avoidance portion. In this state, the film formation target portion and the metal brush are relatively moved to each other. Thus, the metal film is formed on the film formation target portion. In a brazing step, the joining target portions are joined in a state where a brazing material is arranged on the joining target portion and the brazing-material-allowed portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2021-153797 filed on Sep. 22, 2021 and No. 2021-153804 filed on Sep. 22, 2021, the contents all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a brazing method and to a tool for forming a metal film for brazing.

Description of the Related Art

In a brazing method for brazing a pair of joining target portions (portions to be joined) included in a pair of workpieces, to each other, it is known to form a metal film on each of the joining target portions before brazing. One of the purposes of forming the metal film is to enhance the wettability of the joining target portions with respect to a brazing material. Thereby, for example, the joining quality of the joint such as joint strength and durability is improved. This type of metal film can be formed by performing electroplating (wet plating) on the joining target portion, as disclosed in, for example, JP H10-183363 A.

The workpiece may have a portion where the formation of a metal film is not allowed. Hereinafter, this portion is referred to as an avoidance portion. In the workpiece disclosed in JP H10-183363 A, a plurality of cooling holes are formed in the avoidance portion in order to allow cooling air to flow therethrough. For performing electroplating on such a workpiece, it is necessary to perform, as a pretreatment, a masking step of masking the avoidance portion with a masking material. In addition, it is necessary to perform a masking material removal step of removing the masking material from the avoidance portion, as a post-treatment after the electroplating has been performed.

SUMMARY OF THE INVENTION

For example, as the shape of the avoidance portion becomes more complicated and more delicate, it becomes more difficult to mask the avoidance portion with the masking material in the masking step. Further, as the shape of the avoidance portion becomes more complicated and more delicate, in the masking material removal step, it becomes more difficult to remove the masking material without the masking material being left on the avoidance portion. Therefore, in the brazing method requiring the masking step and the masking material removal step, for example, there are concerns about the following issues. It takes a long time to complete the brazing. The cost of brazing is high. The process for completing brazing is complicated. That is, when the metal film is provided on the joining target portion to thereby improve the joining quality of the joint, there is a concern that it becomes difficult to efficiently and easily perform brazing.

An object of the present invention is to solve the above-described problems.

According to an aspect of the present invention, there is provided a brazing method for forming a metal film on at least one of a pair of joining target portions included in a pair of workpieces and thereafter brazing the pair of joining target portions to each other, wherein, of the pair of workpieces, a workpiece on which the metal film is to be formed includes a brazing-material-allowed portion adjacent to one joining target portion of the pair of joining target portions, and an avoidance portion on which formation of the metal film is not allowed, the brazing method including: a film formation step of forming the metal film on a film formation target portion by moving a metal brush relative to the film formation target portion with the metal brush being in contact with the film formation target portion, wherein the film formation target portion includes the one joining target portion and the brazing-material-allowed portion but does not include the avoidance portion, and the metal brush is formed by bundling a plurality of metal wires including a material for the metal film; and a brazing step of applying a brazing material to at least one of the pair of joining target portions and performing heat treatment on the pair of joining target portions between which the brazing material is provided, thereby joining the pair of joining target portions in a state where the brazing material is disposed on the pair of joining target portions and the brazing-material-allowed portion.

In this brazing method, the metal brush brought into contact with the film formation target portion is relatively moved with respect to the film formation target portion. Thus, the metal film can be formed on the film formation target portion. Therefore, for example, unlike a case where a metal film is formed by electroplating, a step of masking the avoidance portion is not necessary. As a result, it is possible to improve the joining quality of the joint by providing the metal film on the joining target portion and also to efficiently and easily perform brazing.

According to another aspect of the present invention, there is provided a metal film forming tool for brazing, for forming a metal film on at least one of a pair of joining target portions included in a pair of workpieces, before brazing the joining target portions to each other, the metal film forming tool for brazing including: a metal brush configured to form the metal film on the joining target portion by moving relative to the joining target portion in a state of being in contact with the joining target portion; and a support portion configured to support the metal brush, wherein the metal brush has a brush shape formed by bundling a plurality of metal wires, and each of the plurality of metal wires has a diameter of 0.1 to 0.6 mm.

In the metal film forming tool for brazing, the metal brush brought into contact with the film formation target portion is relatively moved with respect to the film formation target portion. Thus, the metal film can be formed on the film formation target portion. Therefore, for example, unlike a case where a metal film is formed by electroplating, a step of masking the avoidance portion is not necessary. As a result, it is possible to improve the joining quality of the joint by providing the metal film on the joining target portion and also to efficiently and easily perform brazing.

DESCRIPTION OF THE INVENTION

In the following drawings, components having the same or similar functions and effects are denoted by the same reference numerals, and repeated description thereof may be omitted.

In the brazing method according to the present embodiment, after a metal film is formed on at least one of a pair of joining target portions included in a pair of workpieces, the pair of joining targets are brazed to each other. In this brazing method, a metal film forming tool for brazing214(which will be hereinbelow referred to as a brazing metal film forming tool) shown inFIG.10AandFIG.10Bis suitably used. That is, the brazing metal film forming tool214forms a metal film on at least one of the pair of joining target portions before brazing the pair of joining targets included in the pair of workpieces to each other. The above-described brazing method and the brazing metal film forming tool214can be more suitably applied to a workpiece having a joining target portion having a relatively small area.

An example of a joined body obtained by brazing workpieces of this type includes a heat exchanger10for a Stirling engine shown inFIGS.1and2. Another example of the joined body includes a diffuser14(FIG.5) included in a gas turbine engine12shown inFIG.4. Yet another example of the joined body includes a nozzle16(FIG.7) of the gas turbine engine12shown inFIG.4. However, the workpiece is not limited to the components of the above-described joined body. The brazing metal film forming tool214according to the present embodiment can be applied to various workpieces to be brazed, to form a metal film thereon.

Hereinafter, a case where the heat exchanger10shown inFIGS.1and2, the diffuser14shown inFIG.5, and the nozzle16shown inFIG.7are obtained by a brazing method using the brazing metal film forming tool214will be described as an example. First, the configuration of the heat exchanger10will be briefly described with reference toFIGS.1to3B. In the following description, an upper portion in the drawings ofFIGS.1to3Bis referred to as an “upper portion”, and a lower portion in the drawings ofFIGS.1to3Bis referred to as a “lower portion”. However, the actual orientation (posture) of the heat exchanger10is not limited to this, and can be variously set according to the usage mode.

The heat exchanger10is applied to, for example, a p-type Stirling engine. The heat exchanger10has a low-temperature-side portion18and a high-temperature-side portion20as a pair of workpieces W. As will be described later, the heat exchanger10is formed by joining the joining target portion22of the low-temperature-side portion18and the joining target portion22of the high-temperature-side portion20by applying a brazing method using the brazing metal film forming tool214.

The low-temperature-side portion18is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. However, the material for the low-temperature-side portion18is not particularly limited. The low-temperature-side portion18may be made of maraging steel, for example.

As shown inFIGS.1and2, the low-temperature-side portion18has a tubular shape with both axial ends opened. As shown inFIG.2, the low-temperature-side portion18has a double-tube structure formed by an inner wall24and an outer wall26. The low-temperature-side portion18contains a small inner-diameter portion28at a lower portion thereof. The low-temperature-side portion18further contains a large inner-diameter portion30above the small inner-diameter portion28. The inner diameter of the large inner-diameter portion30is larger than the inner diameter of the small inner-diameter portion28. Further, a step portion32is formed between the small inner-diameter portion28and the large inner-diameter portion30, due to a difference in inner diameter therebetween.

A cooling portion34, which will be described later, is provided between the inner wall24and the outer wall26of the small inner-diameter portion28. A plurality of slit-shaped low-temperature-side ports36penetrating the inner wall24are provided at a lower part of the inner wall24of the small inner-diameter portion28. Although not shown, the plurality of low-temperature-side ports36are disposed at intervals in the circumferential direction of the small inner-diameter portion28. Each low-temperature-side port36allows the inside of the inner wall24of the small inner-diameter portion28to communicate with the cooling portion34.

A chamber38is formed between the inner wall24and the outer wall26of the large inner-diameter portion30. The inner wall24of the large inner-diameter portion30is provided with a plurality of slit-shaped heat source gas outlet ports40penetrating the inner wall24. As shown inFIG.1, the plurality of heat source gas outlet ports40are arranged at intervals in the circumferential direction of the large inner-diameter portion30. As shown inFIG.2, each heat source gas outlet port40provides communication between the chamber38and a heat source gas discharge port42, described below, of the high-temperature-side portion20.

The high-temperature-side portion20is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. However, the material for the high-temperature-side portion20is not particularly limited. The high-temperature-side portion20may be made of maraging steel, for example.

The high-temperature-side portion20has a bottomed tubular shape with a closed upper end and an open lower end. The high-temperature-side portion20has a single-tube portion44provided at a lower part of the high-temperature-side portion20and a double-tube portion46provided above the single-tube portion44. A lower end portion of the single-tube portion44is inserted into an upper end portion of the small inner-diameter portion28of the low-temperature-side portion18. Each of an outer peripheral surface of the lower end portion of the single-tube portion44and an inner peripheral surface of the upper end portion of the small inner-diameter portion28has a joining target portion22. These joining target portions22are joined to each other by brazing after the metal films92have been formed by the brazing metal film forming tool214, thereby forming a first joint48. Details of the first joint48will be described later.

The outer diameter of the single-tube portion44is smaller than the inner diameter of the large inner-diameter portion30of the low-temperature-side portion18. An outer peripheral surface of the single-tube portion44and an inner peripheral surface of the large inner-diameter portion30face each other with a gap therebetween, and a regeneration portion50, which will be described later, is provided therebetween. The double-tube portion46has a double-tube structure formed by an inner wall52and an outer wall54. The inner wall52of the double-tube portion46extends integrally with the single-tube portion44in the axial direction of the single-tube portion44. The inner side of the inner wall52of the double-tube portion46, the inner side of the single-tube portion44, and the inner side of the small inner-diameter portion28of the low-temperature-side portion18integrally form a cylinder chamber56.

A heating portion58described later is provided between the inner wall52and the outer wall54of the double-tube portion46. A bottom wall60extending between the inner wall52and the outer wall54is provided at a lower end of the double-tube portion46(heating portion58). The regeneration portion50is provided between the bottom wall60of the high-temperature-side portion20and the step portion32of the low-temperature-side portion18. A plurality of heat source gas discharge ports42are provided on a portion of the outer wall54of the double-tube portion46that lies in the vicinity of the bottom wall60. As shown inFIG.1, the plurality of heat source gas discharge ports42are arranged at intervals in the circumferential direction of the double-tube portion46. As shown inFIG.2, the heat source gas discharge ports42face the respective heat source gas outlet ports40of the low-temperature-side portion18. On the outer wall54of the double-tube portion46, a portion reserved for joining62is provided below the heat source gas discharge port42.

The outer peripheral surface of the double-tube portion46has a joining target portion22around each heat source gas discharge port42. The inner peripheral surface of the large inner-diameter portion30has a joining target portion22around each heat source gas outlet port40. These joining target portions22are joined to each other by brazing after the metal films92have been formed, thereby forming a second joint64. Details of the second joint64will be described later.

The inner wall52contains, near an upper part of the double-tube portion46, a plurality of slit-shaped high-temperature-side ports66penetrating the inner wall52. Although not shown, the plurality of high-temperature-side ports66are disposed at intervals in the circumferential direction of the double-tube portion46. Each high-temperature-side port66allows the cylinder chamber56and the heating portion58to communicate with each other.

A working gas such as nitrogen gas, helium gas, or the like is sealed inside the cylinder chamber56. The cylinder chamber56contains thereinside a displacer piston68and a power piston70. Each of the displacer piston68and the power piston70is disposed so as to be capable of reciprocating in the axial direction of the cylinder chamber56. The displacer piston68is disposed above the power piston70.

Although not shown in the drawings, the displacer piston68and the power piston70are connected to a crank shaft via different connecting rods. Accordingly, the displacer piston68and the power piston70can reciprocate while maintaining a phase difference of 90 degrees. The power piston70outputs a rotational force to the crankshaft via the connecting rod. The crankshaft is coupled to, for example, a rotating shaft of a generator (not shown).

In the cylinder chamber56, a low-temperature chamber72is formed between the displacer piston68and the power piston70. In the cylinder chamber56, a high-temperature chamber74is formed between the displacer piston68and an upper end portion of the cylinder chamber56. The volumes of the low-temperature chamber72and the high-temperature chamber74change according to the reciprocating movement of the displacer piston68and the power piston70. When the volume of the high-temperature chamber74increases, the volume of the low-temperature chamber72decreases.

In the cooling portion34, a cooling flow path76through which a cooling fluid flows and a low-temperature-side working gas flow path78through which a working gas flows are provided so as to be able to exchange heat with each other. A cooling fluid is supplied to the cooling flow path76from a cooling fluid supply portion (not illustrated). The cooling fluid flowing through the cooling flow path76is discharged to a cooling fluid discharge portion (not shown).

One end of the low-temperature-side working gas flow path78communicates with the low-temperature chamber72via the low-temperature-side ports36. The other end of the low-temperature-side working gas flow path78communicates with the regeneration portion50via a first port80provided in the step portion32. The working gas in the low-temperature-side working gas flow path78is cooled by heat exchange with the cooling fluid in the cooling flow path76.

As will be described later, the flow direction of the working gas flowing through the low-temperature-side working gas flow path78changes according to changes in the volumes of the low-temperature chamber72and the high-temperature chamber74. When the flow direction of the working gas is a direction from the low-temperature chamber72toward the high-temperature chamber74via the cooling portion34, the regeneration portion50, and the heating portion58, the working gas in the low-temperature chamber72can flow into the low-temperature-side working gas flow path78via the low-temperature-side ports36. The working gas flowing from the low-temperature chamber72into the low-temperature-side working gas flow path78can flow into the regeneration portion50via the first port80of the step portion32.

Conversely, when the flow direction of the working gas is a direction from the high-temperature chamber74toward the low-temperature chamber72via the heating portion58, the regeneration portion50, and the cooling portion34, the working gas in the regeneration portion50can flow into the low-temperature-side working gas flow path78via the first port80of the step portion32. The working gas flowing into the low-temperature-side working gas flow path78from the regeneration portion50can flow into the low-temperature chamber72via the low-temperature-side ports36.

In the heating portion58, a heating flow path82through which a heat source gas flows and a high-temperature-side working gas flow path84through which the working gas flows are provided so as to be able to exchange heat with each other. The heat source gas is supplied to the heating flow path82from a heat source gas supply portion (not illustrated). The heat source gas flowing through the heating flow path82is discharged to a heat source gas discharge portion (not shown) via the heat source gas discharge port42of the high-temperature-side portion20, the heat source gas outlet port40of the low-temperature-side portion18, and the chamber38.

One end of the high-temperature-side working gas flow path84communicates with the high-temperature chamber74via the high-temperature-side ports66. The other end of the high-temperature-side working gas flow path84communicates with the regeneration portion50via a second port86provided in the bottom wall60of the high-temperature-side portion20. The working gas in the high-temperature-side working gas flow path84is heated by heat exchange with the heat source gas in the heating flow path82.

When the flow direction of the working gas is a direction from the high-temperature chamber74toward the low-temperature chamber72via the heating portion58, the regeneration portion50, and the cooling portion34, the working gas in the high-temperature chamber74can flow into the high-temperature-side working gas flow path84via the high-temperature-side ports66. The working gas flowing from the high-temperature chamber74into the high-temperature-side working gas flow path84can flow into the regeneration portion50via the second port86of the bottom wall60.

Conversely, when the flow direction of the working gas is a direction from the low-temperature chamber72toward the high-temperature chamber74via the cooling portion34, the regeneration portion50, and the heating portion58, the working gas in the regeneration portion50can flow into the high-temperature-side working gas flow path84via the second port86of the bottom wall60. The working gas flowing into the high-temperature-side working gas flow path84from the regeneration portion50can flow into the high-temperature chamber74via the high-temperature-side ports66.

Although not shown, the regeneration portion50is provided with a heat storage material formed by compression-forming metal fibers having thermal conductivity. The heat storage material has voids therein. The working gas can flow through the heat storage material via the voids. The working gas flowing from the cooling portion34into the regeneration portion50through the first port80of the step portion32moves upward in the regeneration portion50and flows into the heating portion58through the second port86of the bottom wall60. Conversely, the working gas flowing from the heating portion58into the regeneration portion50through the second port86of the bottom wall60moves downward in the regeneration portion50and flows into the cooling portion34through the first port80of the step portion32.

When the working gas moves from the high-temperature chamber74to the low-temperature chamber72, the regeneration portion50performs the same function as the cooling portion34that cools the high-temperature working gas by storing heat in the heat storage material. Conversely, when the working gas moves from the low-temperature chamber72to the high-temperature chamber74, the regeneration portion50performs the same function as the heating portion58by providing the thermal energy stored in the heat storage material to the working gas. As a result, the fuel efficiency of the Stirling engine can be improved.

In the Stirling engine configured as described above, when the displacer piston68is at the top dead center position, the volume of the low-temperature chamber72is maximized. At this time, the working gas in the cylinder chamber56is mainly in the low-temperature chamber72and is cooled by heat exchange with the cooling portion34. As a result, the working gas in the cylinder chamber56contracts and a negative pressure acts on the power piston70, so that the power piston70receives a driving force in the upward direction. When the power piston70moves upward, the crank shaft connected to the power piston70via the connecting rod rotates. When the crank shaft rotates, the displacer piston68connected to the crank shaft via the connecting rod descends.

When the displacer piston68descends, the volume of the high-temperature chamber74increases, the volume of the low-temperature chamber72decreases, and the working gas flows from the low-temperature chamber72to the high-temperature chamber74through the cooling portion34, the regeneration portion50, and the heating portion58. In this case, the working gas is heated by passing through the regeneration portion50and the heating portion58.

When the power piston70is positioned at the top dead center, the working gas in the cylinder chamber56is mainly in the high-temperature chamber74and is heated by heat exchange with the heating portion58of the heat exchanger10. As a result, the working gas in the cylinder chamber56expands and a positive pressure acts on the power piston70, and the power piston70receives a driving force in the descending direction. When the power piston70descends, the crank shaft coupled to the power piston70via the connecting rod rotates.

The displacer piston68reaches the bottom dead center point, and the displacer piston68then starts rising. As a result, the volume of the high-temperature chamber74decreases and the volume of the low-temperature chamber72increases, and the working gas flows from the high-temperature chamber74to the low-temperature chamber72through the heating portion58, the regeneration portion50, and the cooling portion34. The working gas is cooled by passing through the regeneration portion50and the heating portion58.

When the power piston70is positioned at the bottom dead center, the working gas in the cylinder chamber56is mainly in the low-temperature chamber72, and is cooled by heat exchange with the cooling portion34of the heat exchanger10. As a result, the working gas in the cylinder chamber56contracts and a negative pressure acts on the power piston70, so that the power piston70receives a driving force in the upward direction. When the power piston70moves upward, the crank shaft connected to the power piston70via the connecting rod rotates. The above-described process is repeatedly performed, and the crank shaft rotates, whereby electricity is generated by the generator.

As described above, in the heat exchanger10, the first joint48and the second joint64are provided as joint portions between the low-temperature-side portion18and the high-temperature-side portion20. As shown inFIG.3B, in the first joint48, the low-temperature-side portion18(workpiece W) has, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to a lower portion of the joining target portion22, and an avoidance portion90in which formation of the metal film92is not allowed. The brazing-material-allowed portion88of the low-temperature-side portion18is provided below a portion of the inner peripheral surface of the small inner-diameter portion28that overlaps the single-tube portion44of the high-temperature-side portion20. The avoidance portion90of the low-temperature-side portion18is a first port80for the working gas, formed in the step portion32. In other words, the avoidance portion90is a portion in which an opening through which the working gas (fluid) can flow is formed.

It is preferable that a coating layer for improving the heat resistance of the low-temperature-side portion18is provided on a surface of the low-temperature-side portion18excluding the joining target portion22and the brazing-material-allowed portion88. Examples of the material for the coating layer include ceramics such as alumina and silica, but are not particularly limited thereto. In a case where such a coating layer is provided on the surface of the low-temperature-side portion18, the avoidance portion90also includes a region where the coating layer is formed.

As shown inFIG.3B, in the first joint48, the high-temperature-side portion20(workpiece W) has, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to an upper portion of the joining target portion22. The brazing-material-allowed portion88of the high-temperature-side portion20is provided above a portion of the outer peripheral surface of the single-tube portion44that overlaps the small inner-diameter portion28of the low-temperature-side portion18.

It is preferable that a coating layer for improving the heat resistance of the high-temperature-side portion20is provided on a surface of the high-temperature-side portion20excluding the joining target portion22and the brazing-material-allowed portion88. An example of the material for the coating layer is the same as that for the coating layer of the low-temperature-side portion18. When such a coating layer is provided on the surface of the high-temperature-side portion20, the high-temperature-side portion20further includes an avoidance portion90which is a portion where the coating layer is formed.

In the first joint48, the metal film92is formed on a film formation target portion that includes the joining target portion22and the brazing-material-allowed portion88but does not include the avoidance portion90. A brazing material94for joining the joining target portion22of the low-temperature-side portion18and the joining target portion22of the high-temperature-side portion20is disposed on the metal film92. Therefore, a fillet96made of the solidified brazing material94is formed on the brazing-material-allowed portion88.

As shown inFIG.3A, in the second joint64, the low-temperature-side portion18(workpiece W) includes, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to a lower portion of the joining target portion22, and an avoidance portion90in which formation of the metal film92is not allowed. The brazing-material-allowed portion88of the low-temperature-side portion18is provided below a portion of the inner peripheral surface of the large inner-diameter portion30that overlaps with the portion reserved for joining62of the high-temperature-side portion20. The avoidance portion90of the second joint64is the heat source gas outlet port40. In other words, the avoidance portion90is a portion in which an opening through which the heat source gas (fluid) can flow is formed. In a case where the coating layer is provided on the surface of the low-temperature-side portion18, the avoidance portion90also includes a portion where the coating layer is formed.

In the second joint64, the high-temperature-side portion20(workpiece W) includes, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to an upper portion of the joining target portion22, and an avoidance portion90in which formation of the metal film92is not allowed. The brazing-material-allowed portion88of the high-temperature-side portion20is provided above a portion of the outer wall54of the double-tube portion46that overlaps the large inner-diameter portion30of the low-temperature-side portion18. The avoidance portion90of the high-temperature-side portion20includes the heat source gas discharge port42and the second port86. In other words, the avoidance portion90is a portion in which an opening through which the heat source gas or the working gas (fluid) can flow is formed. In addition, when the coating layer is provided on the surface of the high-temperature-side portion20, the avoidance portion90also includes a region where the coating layer is formed.

In the second joint64, the metal film92is formed on a film formation target portion that includes the joining target portion22and the brazing-material-allowed portion88but does not include the avoidance portion90. In other words, in the second joint64, the metal film92is formed on each of an upper portion above the avoidance portion90(the heat source gas outlet port40and the heat source gas discharge port42) and a lower portion below the avoidance portion90. A brazing material94for joining the joining target portion22of the low-temperature-side portion18and the joining target portion22of the high-temperature-side portion20is disposed on the metal film92. Therefore, a fillet96made of the solidified brazing material94is formed on the brazing-material-allowed portion88.

Next, the structure of the gas turbine engine12including the diffuser14and the nozzle16will be briefly described mainly with reference toFIG.4. In the following description, an upper portion inFIG.4is referred to as an “upper portion”, and a lower portion inFIG.4is referred to as a “lower portion”. Further, a left portion inFIG.4will be described as a “left portion”, and a right portion inFIG.4will be described as a “right portion”. However, the actual orientation (posture) of the gas turbine engine12is not limited to these, and can be set in various ways depending on the mode of use.

The gas turbine engine12is integrated with, for example, a rotary electric machine98to constitute a combined power system100. The combined power system100can be used as, for example, a power source for propulsion in a flying object such as a drone, a ship, an automobile, or the like, or a power source for an auxiliary power supply in an aircraft, a ship, a building, or the like. The gas turbine engine12and the rotary electric machine98are arranged side by side on the same axis. The gas turbine engine12is disposed to the right of the rotary electric machine98. InFIG.4, only the portion of the rotary electric machine98connected to the gas turbine engine12and its vicinity are shown, and the other portions are not shown.

The rotary electric machine98includes a rotor102and a stator104surrounding an outer peripheral side of the rotor102. The rotary electric machine98is housed in a rotary electric machine housing106. The rotor102is provided on the outer periphery of a rotary shaft108. An output shaft114of the gas turbine engine12is coupled to a right end portion of the rotary shaft108.

The gas turbine engine12includes an engine housing116. The engine housing116includes an inner housing118coupled to the rotary electric machine housing106and an outer housing120coupled to the inner housing118. In addition to the engine housing116, the gas turbine engine12includes a flow directing member122, a shroud case124, a compressor wheel126, a turbine wheel128, a ring member130, an intermediate plate132, a diffuser14, a combustor136, and a nozzle16. These components are housed inside the engine housing116.

The flow directing member122is fixed to the rotary electric machine housing106in a state in which the rotary shaft108is inserted into the flow directing member122. The shroud case124is a hollow body. A right end portion of the flow directing member122and a left end portion of the shroud case124are disposed side by side at an interval in the axial direction of the rotary shaft108. The left end portion of the shroud case124is disposed in an intake space140that communicates with the outside of the inner housing118.

The compressor wheel126is rotatably accommodated in the shroud case124. As will be described later, when the compressor wheel126is rotationally driven, air is taken in between the inner wall surface of the shroud case124and the compressor wheel126via the intake space140. Each of the compressor wheel126and the turbine wheel128is supported on the output shaft114. As described above, the output shaft114and the rotary shaft108of the rotary electric machine98are coupled to each other. Therefore, the compressor wheel126and the turbine wheel128can rotate integrally with the rotary shaft108.

A shaft hole142extending along the left-right direction is formed so as to penetrate through the center of the compressor wheel126in the radial direction. In a state where the output shaft114is inserted into the shaft hole142, the compressor wheel126and the output shaft114are, for example, spline-coupled to each other. Further, inside the shaft hole142, the rotary shaft108is coupled to a left end portion of the output shaft114, and a left end portion of the turbine wheel128is coupled to a right end portion of the output shaft114.

A ring member130is interposed between the compressor wheel126and the turbine wheel128. The outer periphery of the ring member130is surrounded by a tubular portion144of the intermediate plate132. The intermediate plate132includes an annular extending portion146extending from the right end portion of the tubular portion144toward the outer side in the radial direction of the tubular portion144. A portion of the extending portion146other than an outer edge portion thereof is disposed between the compressor wheel126and the turbine wheel128. The outer edge portion of the extending portion146is disposed between the combustor136and the diffuser14.

An annular combustion air flow passage148through which combustion air flows is formed between an outer peripheral surface of the combustor136and an inner peripheral surface of the outer housing120. The diffuser14is provided at a beginning part of the combustion air flow passage148. As will be described later, the diffuser14converts kinetic energy (velocity energy) of compressed air taken in and compressed between the shroud case124and the compressor wheel126, into pressure energy. As a result, combustion air obtained by converting the kinetic energy of the compressed air into pressure energy is supplied to the combustion air flow passage148. Details of the structure of the diffuser14will be described later.

A relay hole150for communicating the inside of the combustor136with the combustion air flow passage148is formed in the combustor136. The combustor136is also formed with fine holes (not shown) for forming an air curtain for cooling the inside of the combustor136. The combustion air in the combustion air flow passage148reaches the inside of the combustor136via the relay hole150. A fuel supply nozzle138for supplying fuel to the combustor136is positioned and fixed to a right end surface of the outer housing120. Therefore, a combustion reaction between the combustion air and the fuel can be caused inside the combustor136.

The combustor136has a discharge port152for discharging burned fuel (synonymous with “combustion gas” and “exhaust gas after combustion”) generated by the above combustion reaction. The burned fuel discharged from the discharge port152of the combustor136flows toward a delivery hole156formed in the peripheral wall of a large-diameter portion154of the nozzle16. The turbine wheel128is rotatably disposed inside the nozzle16. The nozzle16converts pressure energy of the burned fuel into kinetic energy (velocity energy) and transmits the kinetic energy to the turbine wheel128. Therefore, the burned fuel introduced into the nozzle16through the delivery hole156rotates the turbine wheel128.

A plurality of small holes158(FIG.7) are formed in portions of the peripheral wall of the large-diameter portion154of the nozzle16, other than the delivery hole156. A part of the compressed air taken in and compressed between the shroud case124and the compressor wheel126via the intake space140(hereinafter, also referred to as “split air”) is sent to the small holes158from the outside in the radial direction of the nozzle16via a branch path (not illustrated). The small holes158allow the split air to pass from the outer side toward the inner side in the radial direction of the nozzle16. Thus, the split air introduced into the nozzle16forms an air curtain that cools the interior of the nozzle16. Details of the configuration of the nozzle16will be described later.

After transmitting the kinetic energy to the turbine wheel128, the burned fuel is discharged from an opening of a fixed tubular portion160provided at a right end portion of the nozzle16. An opening of the fixed tubular portion160of the nozzle16communicates with a burned fuel discharge port162formed at a right end portion of the outer housing120. The fixed tubular portion160of the nozzle16is fixed to a peripheral edge of the burned fuel discharge port162of the outer housing120. The burned fuel discharge port162is provided with a discharge pipe (not shown) for discharging the burned fuel. Therefore, the burned fuel is blown to the outside of the outer housing120through the burned fuel discharge port162by the action of the rotating turbine wheel128.

The operation of the gas turbine engine12configured as described above will be briefly described. In the gas turbine engine12, the rotary shaft108is rotated by, for example, a known starter. The rotational torque of the rotary shaft108is transmitted to the output shaft114. Therefore, the compressor wheel126and the turbine wheel128supported by the output shaft114rotate integrally with the output shaft114. As a result, atmospheric air is sucked from the intake space140into the shroud case124. The sucked air is directed, by the flow directing member122, so as to flow toward the shroud case124.

The air sucked into the shroud case124flows between the compressor wheel126and the shroud case124, and is compressed. This produces compressed air. The compressed air flows into the diffuser14and becomes combustion air. The combustion air discharged from the diffuser14flows into the combustion air flow passage148. The combustion air enters the inside (combustion chamber) of the combustor136via, for example, the relay hole150and the fine holes formed in the combustor136and the clearance between the combustor136and the fuel supply nozzle138.

The combustor136is heated in advance. Further, fuel is supplied into the combustor136from a fuel supply nozzle138. The fuel becomes a high-temperature burned fuel by a combustion reaction with the combustion air. The burned fuel is supplied from the delivery hole156into the nozzle16, and expands in the nozzle16, whereby the turbine wheel128rotates at a high speed. Accordingly, the output shaft114and the compressor wheel126integrally rotate at a high speed. The burned fuel is discharged to the outside of the outer housing120through a discharge pipe provided in the burned fuel discharge port162.

When the output shaft114starts to rotate at a high speed, the rotary shaft108integrally rotates at a high speed. Accordingly, since the rotor102provided on the outer periphery of the rotary shaft108rotates relative to the stator104, it is possible to obtain electric power by the combined power system100.

The configuration of the diffuser14will be described in detail with reference toFIGS.4to6. As shown inFIGS.5and6, the diffuser14includes an inlet member164and a plurality of outlet members166. The inlet member164and each of the plurality of outlet members166are joined by brazing to form the diffuser14. Hereinafter, a joint portion between the inlet member164and each outlet member166is also referred to as a third joint168. Details of the third joint168will be described later.

The diffuser14defines a plurality of diffuser flow passages170. Compressed air flows in from a flow passage inlet172of each diffuser flow passage170. Each diffuser flow passage170changes the flow direction of the compressed air from the radial direction of the compressor wheel126inFIG.4to the axial direction thereof, and makes the compressed air into combustion air. Then, the combustion air is discharged from the flow passage outlet174of each diffuser flow passage170.

The inlet member164is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. As shown inFIG.5, the inlet member164has a plurality of flow passage inlets172and a plurality of connection ports176equal in number to the flow passage inlets172. The inlet member164has a substantially disk shape (annular shape) having a hole178at the center in the radial direction of the inlet member164. The compressor wheel126ofFIG.4is rotatably disposed inside the hole178.

Each of the flow passage inlets172is opened in the inner wall of the inlet member164on the radial center side. The plurality of flow passage inlets172are arranged at intervals in the circumferential direction of the inlet member164. Each of the connection ports176is opened in the outer wall of the inlet member164on the radial outer side. The plurality of connection ports176are arranged at intervals in the circumferential direction of the inlet member164. The inlet member164is formed with through passages180that connect the flow passage inlets172and the connection ports176on a one-to-one basis. A part of the diffuser flow passage170is formed inside the through passage180.

As shown inFIG.6, an insertion port182is provided in the vicinity of the flow passage inlet172of the through passage180. The flow passage cross-sectional area of the insertion port182is larger than the flow passage cross-sectional area of a portion of the through passage180adjacent to the insertion port182. Therefore, a stepped surface184is provided between the insertion port182and the portion of the through passage180adjacent to the insertion port182. In the inlet member164, the joining target portions22are provided on the inner wall surface of the insertion port182and on the stepped surface184.

The inlet member164includes through holes186passing through the inlet member164in the axial direction. When viewed in the axial direction of the inlet member164, each through hole186is formed between the connection ports176adjacent to each other in the circumferential direction of the inlet member164. The inlet member164, the outer edge portion of the extending portion146of the intermediate plate132, and the combustor136are fastened together, for example, by bolt fixation via the through holes186.

Each outlet member166is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. As shown inFIGS.5and6, each outlet member166has a pipe shape, and contains therein the diffuser flow passage170. As shown inFIG.6, one end portion of each outlet member166in the extending direction has an insertion portion188to be inserted into the insertion port182of the inlet member164. In each outlet member166, the joining target portions22are provided on the outer peripheral surface of the insertion portion188and on the end surface of the insertion portion188. After the metal films92are formed on the joining target portions22of the outlet member166, the joining target portions22of the outlet member166and the joining target portions22of the inlet member164are joined together by brazing, thereby forming the third joint168.

A flow passage outlet174is provided at the other end portion of each outlet member166in the extending direction. As shown inFIG.5, each outlet member166has a portion curved with respect to the radial direction of the inlet member164and a portion curved in a direction rising up along the axial direction of the inlet member164, on the way of extending from the insertion portion188toward the flow passage outlet174.

By joining the joining target portions22of the inlet member164and the joining target portions22of the outlet member166as described above, the inside of the through passage180of the inlet member164and the inside of the outlet member166communicate with each other. Accordingly, the inlet member164and the outlet member166integrally form the diffuser flow passage170.

In the third joint168, the inlet member164(workpiece W) has an avoidance portion90(FIG.5) in which formation of the metal film92is not allowed, in addition to the joining target portions22(FIG.6). The avoidance portion90of the inlet member164is a flow passage inlet172. In other words, the avoidance portion90of the inlet member164is a portion in which an opening through which compressed air (fluid) can flow is formed. The flow passage inlet172is required to have high dimensional accuracy. Therefore, it is required to avoid a situation where a change in the dimension of the flow passage inlet172is caused by the formation of the metal film92on the inner wall surface of the flow passage inlet172and on the wall surface in the vicinity of the flow passage inlet172.

As shown inFIG.6, in the third joint168, the outlet member166(workpiece W) has a brazing-material-allowed portion88adjacent to the joining target portion22, in addition to the joining target portion22. The brazing-material-allowed portion88is disposed on the outer peripheral surface of each outlet member166, more specifically adjacent to the insertion portion188and outside the insertion port182.

In the third joint168, the metal film92is formed on a film formation target portion that includes the joining target portions22and the brazing-material-allowed portion88but does not include the avoidance portion90. A brazing material94for joining the joining target portion22of the inlet member164and the joining target portion22of the outlet member166is disposed on the metal film92. Therefore, a fillet96made of the solidified brazing material94is formed on the brazing-material-allowed portion88.

The configuration of the nozzle16will be described in detail with reference toFIGS.4,7,8, and9. As shown inFIGS.7and8, the nozzle16is configured by joining an inflow-side member190and a discharge-side member192by brazing. Hereinafter, a joint portion between the inflow-side member190and the discharge-side member192is also referred to as a fourth joint194. Details of the fourth joint194will be described later.

The inflow-side member190is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. The inflow-side member190has a hollow shape, and the turbine wheel128ofFIG.4is rotatably disposed inside the inflow-side member190.

Specifically, as shown inFIGS.7and8, the inflow-side member190includes a large-diameter portion154and an intermediate shaft portion196having an inner diameter smaller than that of the large-diameter portion154. The large-diameter portion154is provided with a plurality of fins198arranged at intervals in the circumferential direction of the large-diameter portion154. The delivery holes156are provided between the fins198adjacent to each other in the circumferential direction of the large diameter portion154in order to establish communication between the inside and the outside of the large-diameter portion154. The delivery hole156faces the discharge port152of the combustor136ofFIG.4, and allows the burned fuel discharged from the discharge port152to flow toward the inside of the large-diameter portion154.

A plurality of small holes158are formed in each fin198constituting a peripheral wall of the large-diameter portion154. As described above, these small holes158form an air curtain that cools the inside of the nozzle16by allowing the split air to flow from the outer side to the inner side in the radial direction of the large-diameter portion154(nozzle16).

The intermediate shaft portion196extends in the axial direction of the nozzle16. As shown inFIG.8, one end portion of the intermediate shaft portion196in the extending direction is integrally connected to the large-diameter portion154. A small outer diameter portion200is provided at the other end portion of the intermediate shaft portion196in the extending direction. The outer diameter of the small outer diameter portion200is smaller than the outer diameter of a portion of the intermediate shaft portion196adjacent to the small outer diameter portion200. Therefore, a stepped surface202is provided between the small outer diameter portion200and the portion of the intermediate shaft portion196adjacent to the small outer diameter portion200. In the inflow-side member190, the joining target portions22are provided on the outer peripheral surface of the small outer diameter portion200and on the stepped surface202.

The discharge-side member192is preferably made of a heat-resistant alloy. Preferable examples of the heat-resistant alloy include a nickel-based alloy containing one or both of titanium and aluminum, and an iron-based alloy containing one or both of titanium and aluminum. The discharge-side member192includes an external fitting tubular portion204, a fixed tubular portion160, and a bellows portion208. The external fitting tubular portion204has an external fitting end portion210that is externally fitted onto the small outer diameter portion200of the inflow-side member190. The fixed tubular portion160is fixed to the peripheral edge of the burned fuel discharge port162of the outer housing120ofFIG.4. The bellows portion208is provided between the external fitting tubular portion204and the fixed tubular portion160.

An inner diameter of the external fitting end portion210is slightly larger than an outer diameter of the small outer diameter portion200of the inflow-side member190. The small outer diameter portion200is inserted into the external fitting end portion210. In the discharge-side member192, the joining target portions22are provided on the inner peripheral surface of the external fitting end portion210and on the end surface of the external fitting end portion210. After the metal film92is formed on each of the joining target portions22of the inflow-side member190and the joining target portions22of the discharge-side member192, the joining target portions22of the inflow-side member190and the joining target portions22of the discharge-side member192are joined by brazing to form the fourth joint194.

The outer diameter of the fixed tubular portion160is larger than the outer diameter of the external fitting tubular portion204. The fixed tubular portion160includes a flange212at an end thereof opposite to an end where the bellows portion208is disposed. The flange212protrudes from the inner peripheral surface of the fixed tubular portion160toward the center in the radial direction of the fixed tubular portion160. For example, the fixed tubular portion160is fixed to the peripheral edge portion of the burned fuel discharge port162of the outer housing120ofFIG.4by bolting via the flange212.

As shown inFIG.8, the wall portion constituting the bellows portion208has a concavo-convex shape (bellows structure) which meanders in the axial direction of the nozzle16. The bellows portion208can expand and contract in the axial direction of the nozzle16. Further, the bellows portion208can be bent and deformed in the radial direction of the nozzle16. The nozzle16and the components of the gas turbine engine12(FIG.4), such as the outer housing120to which the nozzle16is secured, may undergo dimensional change at different ratios due to, for example, temperature difference and difference in the thermal expansion coefficient of material that occur therebetween. Even in this case, since the bellows portion208is deformable as described above, it is possible to suppress the occurrence of stress between the nozzle16and the other components. As a result, the durability of the gas turbine engine12can be improved.

In the fourth joint194, the inflow-side member190(workpiece W) includes, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to the joining target portion22, and an avoidance portion90in which formation of the metal film92is not allowed. As shown inFIG.9, the brazing-material-allowed portion88of the inflow-side member190is provided on the stepped surface202. Specifically, the brazing-material-allowed portion88is provided on a portion of the stepped surface202that lies more outward in the radial direction of the inflow-side member190, than a portion thereof that faces the end surface of the external fitting end portion210. The avoidance portion90of the inflow-side member190includes the delivery holes156through which the burned fuel flows, and the small holes158through which the split air passes. In other words, the avoidance portion90is a portion in which an opening through which the burned fuel or the split air (fluid) can flow is formed. It is preferable that a coating layer for improving heat resistance and oxidation resistance of the inflow-side member190be provided on the surface of the inflow-side member190except for the joining target portions22. An example of the material for the coating layer may include the same material as that for the coating layer of the low-temperature-side portion18. When such a coating layer is provided on the surface of the inflow-side member190, the avoidance portion90also includes a region on which the coating layer is formed.

In the fourth joint194, the discharge-side member192(workpiece W) includes, in addition to the joining target portion22, a brazing-material-allowed portion88adjacent to the joining target portion22, and an avoidance portion90in which formation of the metal film92is not allowed. As shown inFIG.9, the brazing-material-allowed portion88of the discharge-side member192is provided at a portion of the inner peripheral surface of the external fitting tubular portion204that lies adjacent to the small outer diameter portion200of the inflow-side member190. As shown inFIG.8, the avoidance portion90of the discharge-side member192is a bellows portion208. In other words, the avoidance portion90is a portion where an uneven portion (concavo-convex portion) is formed. A coating layer for improving heat resistance and oxidation resistance of the discharge-side member192may be or may not be provided on the surface of the discharge-side member192excluding the joining target portions22and the brazing-material-allowed portion88. When such a coating layer is provided, examples of the material for the coating layer include the same materials as those for the coating layer of the low-temperature-side portion18. When the coating layer is provided on the surface of the discharge-side member192, the avoidance portion90also includes a portion on which the coating layer is formed.

In the fourth joint194, as shown inFIG.9, the metal film92is formed on a film formation target portion that includes the joining target portions22and the brazing-material-allowed portion88but does not include the avoidance portion90. A brazing material94for joining the joining target portions22of the inflow-side member190and the joining target portions22of the discharge-side member192is disposed on the metal film92. Therefore, a fillet96made of the solidified brazing material94is formed on the brazing-material-allowed portion88.

Hereinafter, an example in which the fourth joint194is formed by applying the brazing method using the brazing metal film forming tool214will be described, but it is also possible to form the first joint48, the second joint64, and the third joint168in the same manner as in the case of forming the fourth joint194.

The brazing method includes a film formation step (brazing pretreatment step) of forming the metal film92on the film formation target portion of the fourth joint194. In the film formation step, the metal film92is formed on the film formation target portion shown inFIG.9, using, for example, a metal film forming tool for brazing (brazing metal film forming tool)214shown inFIG.10AandFIG.10B.

The brazing metal film forming tool214includes a metal brush216and a support portion218. The metal brush216has a brush shape formed by bundling a plurality of metal wires220. The diameter of each metal wire220is set within a range of 0.1 to 0.6 mm. A particularly suitable diameter for the metal wires220is 0.15 mm. Each of the metal wires220includes the material for the metal film92. A preferable example of the material for the metal film92is nickel. That is, each of the metal wires220is preferably made of nickel. However, there is no particular limitation thereto. Another example of the material for the metal film92is gold. In this case, each of the metal wires220is made of gold.

The support portion218supports the metal brush216. In the present embodiment, the support portion218includes a pair of holding portions222and a shaft portion224fixed to the metal brush216via the pair of holding portions222. The plurality of metal wires220are radially arranged about a portion supported by the support portion218, i.e., with the portion supported by the support portion as the center. Thus, the appearance of the metal brush216is substantially cylindrical.

Each holding portion222has a disk shape in which an insertion hole is formed at the center. Each holding portion222is preferably formed from an elastically deformable material such as, for example, a thermoset elastomer (rubber) or a thermoplastic elastomer. The pair of holding portions222are disposed so as to sandwich the metal brush216from both sides in the axial direction thereof.

As shown inFIG.10A, in the metal brush216, it is preferable that the length of the metal wires220(hereinafter, also referred to as length L1of the metal wires220) protruding outward from the support portion218(holding portion222) is 40.0 mm or less. In the present embodiment, the length L1of the metal wires220is a length between the outer peripheral end surface of the holding portion222and the outer peripheral end surface of the metal brush216in the radial direction of the metal brush216. The length L1of the metal wires220is preferably 1.0 to 40.0 mm, and more preferably 3.0 to 9.0 mm.

In the metal brush216, the thickness of a bundle of the plurality of metal wires220(hereinafter also referred to as thickness L2of the metal brush216) is preferably 3.0 to 15.0 mm. In the present embodiment, the thickness L2of the metal brush216is a distance between the pair of holding portions222that sandwich the metal brush216. The thickness L2of the metal brush216is not particularly limited to the above-described ranges, and can be set in accordance with, for example, the size and shape of the film formation target portion and the size and shape of the workpiece W.

One end portion of the shaft portion224in the extending direction penetrates the metal brush216in an axial direction thereof via the insertion holes of the pair of holding portions222. A locking screw226having a head portion with a larger diameter than the insertion hole of the holding portion222is fixed to the tip of the shaft portion224penetrating the pair of holding portions222and the metal brush216. The head portion of the locking screw226abuts against the periphery of the insertion hole of one holding portion222. At this time, a flange portion228provided on the shaft portion224comes into contact with the periphery of the insertion hole of the other holding portion222. That is, the pair of holding portions222sandwiching the metal brush216is sandwiched between the head portion of the locking screw226and the flange portion228. As a result, the metal brush216, the pair of holding portions222, and the shaft portion224are integrated.

The other end portion of the shaft portion224opposite to the one end portion provided with the metal brush216is fixed to, for example, the rotary main shaft230. Thus, the metal brush216can be rotationally driven via the shaft portion224.

In the film formation step using the brazing metal film forming tool214configured as described above, as shown inFIG.11, the film formation target portion (the joining target portions22and the brazing-material-allowed portions88) and the metal brush216are relatively moved to each other in a state in which the metal brush216is brought into contact with the film formation target portion. Specifically, the peripheral surface of the metal brush216rotationally driven via the shaft portion224is brought into contact with the joining target portion22. Thus, as shown inFIGS.12A and12B, the metal film92is formed on the film formation target portion.

In the film formation step, when the metal brush216brought into contact with the film formation target portion is rotationally driven, as described above, the metal brush216is held by the holding portions222formed of an elastically deformable material. As a result, each metal wire220of the metal brush216is protected, and thus, for example, the metal wires220can be prevented from breaking or bending. Consequently, the metal film92can be favorably formed on the film formation target portion. Further, the durability of the metal brush216can be improved.

Here, as shown inFIG.14A, it is found that there is a correlation between the diameter of the metal wires220and the degree of surface roughness (surface roughness) of the metal film92obtained in the film formation step. Further, as shown inFIG.15A, it is found that there is a correlation between the length L1of the metal wires220of the metal brush216and the degree of roughness (surface roughness) of the metal film92obtained in the film formation step.

As described above, by setting the diameter of the metal wires220within the range of 0.1 to 0.6 mm, the surface roughness of the obtained metal film92can be adjusted to a level suitable for brazing. To be specific, if the diameter of the metal wires220is smaller than 0.1 mm, when the metal wires220are brought into contact with the film formation target portion and relatively moved in the film formation step, the metal wires220are likely to be deformed more than necessary in a direction in which the metal wires220fall over. Therefore, the metal film92is formed while the peripheral surface (side surface) of the metal wires220is brought into contact mainly with the film formation target portion. As a result, it is considered that the surface roughness tends to be small.

In addition, when the diameter of the metal wires220exceeds 0.6 mm, the increase rate of the surface roughness with respect to the diameter is smaller than in a case where the diameter of the metal wires220is equal to or less than 0.6 mm. Therefore, by setting the diameter of the metal wires220within the range of 0.1 to 0.6 mm, it is possible to favorably form the metal film92having a surface roughness suitable for brazing.

Further, as described above, by setting the length L1of the metal wires220of the metal brush216to 40.0 mm or less, it is possible to set the surface roughness of the obtained metal film92to a level suitable for brazing. To be more specific, if the length L1of the metal wires220exceeds 40.0 mm, when the metal wires220are brought into contact with the film formation target portion and relatively moved in the film formation step, the metal wires220are likely to be deformed more than necessary in a direction in which the metal wires220fall over. Therefore, the metal film92is formed while the peripheral surface (side surface) of the metal wires220is brought into contact mainly with the film formation target portion. As a result, it is considered that the surface roughness tends to be small.

Therefore, by setting the length L1of the metal wires220to 40.0 mm or less, it is possible to favorably form the metal film92having a surface roughness suitable for brazing. For example, the metal film92having an uneven surface (stepped surface) with a height difference of 1 to 15 μm can be obtained by the film formation step. Accordingly, the capillary action is promoted, and the wettability of the film formation target portion with respect to the brazing material94can be favorably enhanced.

In the metal brush216, since formation of the metal film92on the film formation target portion causes consumption of the metal wires220, the length L1of the metal wires220is shortened. In the brazing metal film forming tool214, it is preferable that, when the length L1reaches 1 mm (more preferably 3.0 mm) as a result of consumption of the metal wires220, the metal brush216should be replaced with a new metal brush216having metal wires220whose length L1is 40.0 mm or less.

As shown inFIG.14B, it is found that there is a correlation between the diameter of the metal wires220and the thickness (film thickness) of the metal film92obtained in the film formation step. Further, as shown inFIG.15B, it is found that there is a correlation between the length L1of the metal wires220of the metal brush216and the thickness (film thickness) of the metal film92obtained in the film formation step.

The thickness of the metal film92can also be adjusted, for example, by adjusting the pressure, processing time, and the like when the metal brush216is brought into contact with the film formation target portion. At this time, as described above, by setting the diameter of the metal wires220within the range of 0.1 to 0.6 mm, the obtained metal film92can easily have a thickness suitable for brazing. In addition, as described above, by setting the length L1of the metal wires220of the metal brush216to 40.0 mm or less, the obtained metal film92can easily have a thickness suitable for brazing.

In a case where the diameter of the metal wires220exceeds 0.6 mm, when the metal wires220are brought into contact with the film formation target portion and relatively moved in the film formation step, the amount of deformation in the direction in which the metal wires220fall over tends to be insufficient. For this reason, it is considered that the contact area between the metal wires220and the film formation target portion is small, and the thickness of the metal film92is likely to be thin.

In a case where the diameter of the metal wires220is less than 0.1 mm, when the metal wires220are brought into contact with the film formation target portion and relatively moved in the film formation step, the metal wires220are likely to be deformed more than necessary in a direction in which the metal wires220fall over. In this case, it is considered that it is difficult to press the metal wires220against the film formation target portion and that the metal wires220are likely to be broken. As a result, it is considered that the thickness of the metal film92tends to be thin. Therefore, by setting the diameter of the metal wires220within the range of 0.1 to 0.6 mm, it is possible to favorably form the metal film92having a thickness suitable for brazing.

If the length L1of the metal wires220exceeds 40.0 mm, when the metal wires220are brought into contact with the film formation target portion and relatively moved in the film formation step, the metal wires220are likely to be deformed more than necessary in a direction in which the metal wires220fall over. Therefore, as described above, it is considered that the thickness of the metal film92is likely to be thin. Therefore, by setting the length L1of the metal wires220to 40.0 mm or less, it is possible to favorably form the metal film92having a thickness suitable for brazing.

The thickness of the metal film92suitable for brazing is preferably 1 to 30 μm, for example. It is more preferably 2.5 to 25 μm. Brazing can be suitably performed with the metal film92having such a thickness, but a more suitable thickness of the metal film92is 17 to 19 μm. By setting the thickness of the metal film92within a range of 17 to 19 μm, it is possible to satisfactorily spread the melted brazing material94over the entire joining target portion22and the brazing-material-allowed portion88.

As shown inFIG.14C, it is found that there is a correlation between the diameter of the metal wires220and the durability of the metal brush216. Further, as shown inFIG.15C, it is found that there is a correlation between the length L1of the metal wires220of the metal brush216and the durability of the metal brush216. Here, the durability of the metal brush216refers to, for example, resistance to breaking or bending (difficulty in breaking or bending).

As the diameter of each metal wire220is larger, the metal wires220are less likely to be broken or bent, and the durability of the metal brush216can be increased. Therefore, as described above, it is preferable to increase the diameter of the metal wires220within a range in which the surface roughness and the thickness of the metal film92can be set to values suitable for brazing.

In addition, as described above, by setting the length L1of the metal wires220of the metal brush216to 40.0 mm or less, it is possible to prevent the metal wires220from being deformed more than necessary in the falling direction in the film formation step as described above. As a result, the durability of the metal brush216can be enhanced.

In the brazing method using the brazing metal film forming tool214, the brazing step is performed after the pretreatment for forming the metal film92is performed in the film formation step as described above. The brazing step includes a brazing preparation step of applying the brazing material94to the joining target portions22, and a heat treatment step of melting the brazing material94. As shown inFIGS.13A and13B, after the above-described pretreatment, the brazing material94is applied to at least one of the pair of joining target portions22, thereby completing the brazing preparation step. In the present embodiment, the brazing material94is applied to both of the pair of joining target portions22. At this time, the brazing material94may not be applied to the brazing-material-allowed portion88, or the brazing material94may also be applied to the brazing-material-allowed portion88, in addition to the joining target portions22. Examples of the material for the brazing material94include, but are not limited to, nickel, gold, silver, copper, and cobalt.

Then, as shown inFIGS.8and9, the pair of joining target portions22between which the brazing material94is provided are subjected to heat treatment in a heat treatment furnace. Thus, the pair of joining target portions22are joined together in a state in which the brazing material94is disposed on the joining target portions22and the brazing-material-allowed portions88, and the heat treatment step is completed. The brazing material94disposed in the brazing-material-allowed portion88is melted in the heat treatment furnace and then solidified, whereby the fillet96is formed on the brazing-material-allowed portion88. As a result, at the fourth joint194, the inflow-side member190and the discharge-side member192are integrated by brazing to obtain the nozzle16.

As described above, in the metal film forming tool for brazing214according to the present embodiment, the metal film92can be formed on the film formation target portion by relatively moving the metal brush216relative to the film formation target portion while being in contact with the film formation target portion. Therefore, for example, unlike a case where a metal film is formed by electroplating, a step of masking the avoidance portion90is not necessary. As a result, it is possible to improve the joining quality of the joint by providing the metal film on the joining target portion22and also to efficiently and easily perform brazing.

In a case where the metal film92is formed using the brazing metal film forming tool214, for example, compared to a case where a metal film is formed by electroplating, a metal film can be easily formed even on a film formation target portion having a small area. Therefore, even in the case of the workpiece W having a complicated shape, the formation of the metal film92on the avoidance portion90can be avoided with high accuracy, and the metal film92can be formed on both the joining target portion22and the brazing-material-allowed portion88in a pinpoint manner.

As a result, it is possible to effectively prevent the avoidance portion90from being affected by the metal film92. In addition, the pair of joining target portions22can be joined to each other with the metal films92being formed highly precisely on the joining target portions22and the brazing-material-allowed portions88, and the brazing material94being disposed thereon. Thus, it is possible to further improve the joining quality of brazing. Furthermore, the metal films92are not formed on portions other than the joining target portions22or the brazing-material-allowed portions88, and accordingly wasteful use of the metal films92can be reduced. As a result, the cost required for brazing can be effectively reduced.

The metal film92formed using the brazing metal film forming tool214has an uneven surface (stepped surface) as described above, and has a larger surface roughness (degree of surface roughness) than the metal film92formed by electroplating, for example. Therefore, by forming the metal film92on the film formation target portion using the brazing metal film forming tool214, it is possible to cause a capillary action between the concavity and the convexity of the metal film92. In this case, it is possible to promote melting and flowing of the brazing material94continuously occurring on the surface of the metal film92. Therefore, also owing to this, it is possible to satisfactorily spread the brazing material94on the metal film92and to improve the joining quality between the joining target portions22. In addition, since the fillet96can be favorably formed on the brazing-material-allowed portion88, it is possible to easily check whether brazing has been favorably performed.

In the brazing method according to the above-described embodiment, the avoidance portion90has at least one selected from: a portion where an opening through which a fluid can flow is formed; a portion, of the surface of the workpiece W, that is coated with a coating layer; and a portion where an uneven portion is formed.

In a case where the avoidance portion90is a portion in which an opening is formed, masking on the avoidance portion90is not necessary, and thus, for example, a masking material does not remain in the opening. In addition, it is possible to avoid formation of the metal film92on the avoidance portion90. Accordingly, it is possible to effectively prevent the flow of the fluid from being blocked by the masking material and the metal film92.

When the avoidance portion90is a portion coated with a coating layer, the formation of the masking material and the metal film92on the coating layer can be avoided. Therefore, for example, the masking material and the metal film92can be prevented from being peeled off and falling off the coating layer.

When the avoidance portion90is a portion where an uneven portion is formed, it is possible to prevent the masking material from remaining in the uneven portion. In addition, it is possible to prevent the metal film92from being formed on the uneven portion. For this reason, it is possible to prevent the concavity of the uneven portion from being occluded by the masking material and the metal film92, and to prevent the masking material and the metal film92from peeling off and falling off from the surface of the uneven portion.

Therefore, when the avoidance portion90has at least one selected from a group of a portion in which an opening through which a fluid can flow is formed, a portion of the surface of the workpiece W that is coated with a coating layer, and a portion in which an uneven portion is formed, the brazing method according to the present embodiment can be more suitably applied.

In the brazing method according to the above-described embodiment, the material for the metal film92is nickel, and the workpiece W is made of a heat-resistant alloy. The heat-resistant alloy generally tends to have low wettability with respect to the brazing material94. Therefore, by applying the brazing method to form the metal film92made of nickel on the workpiece W that is a heat-resistant alloy, it is possible to effectively improve the wettability of the joining target portions22and the brazing-material-allowed portions88with respect to the brazing material94. As a result, it is possible to satisfactorily spread the brazing material94over the joining target portions22and the brazing-material-allowed portions88, and to effectively improve the joining quality of the joint.

In the brazing method according to the above embodiment, the heat-resistant alloy is selected from a nickel-based alloy containing either titanium or aluminum, an iron-based alloy containing either titanium or aluminum, a nickel-based alloy containing both titanium and aluminum, and an iron-based alloy containing both titanium and aluminum. In a case where either titanium or aluminum is included in the heat-resistant alloy forming the workpiece W, there is a concern that at least one of titanium and aluminum diffuses to the brazing surface and brazing is inhibited. As such, by applying the brazing method according to the present embodiment to form the metal film92, it is possible to suppress diffusion of at least one of titanium and aluminum to the brazing surface. This makes it possible to effectively improve the joining quality of the joint.

Examples of the nickel-based alloys containing one or both of titanium and aluminum include Inconel 625, Inconel 718 (both of which are trade names of Inco Limited), and MAR-M247. Examples of the iron-based alloys containing one or both of titanium and aluminum include maraging steel and A286.

In the metal brush216of the metal film forming tool for brazing214according to the above-described embodiment, the length L1of portions of the metal wires220that protrude outward from the support portion218is 40.0 mm or less. In this case, as described above, it is possible to easily form the metal film92having a surface roughness and a thickness suitable for brazing. Further, the durability of the metal brush216can be improved.

In the metal brush216of the metal film forming tool for brazing214according to the above-described embodiment, the thickness L2of the bundle of the metal wires220is 3.0 to 15.0 mm. In this case, for example, even in the case of a film formation target portion having a relatively small area or a film formation target portion having a complicated shape, the metal brush216can be brought into good contact with the film formation target portion and can be relatively moved. As a result, the metal film92can be favorably formed.

In the metal film forming tool for brazing214according to the above-described embodiment, the metal wires220are made of nickel. In this case, the metal film92made of nickel can be formed by the metal film forming tool for brazing214. As a result, it is possible to effectively improve the wettability of the joining target portion22and the brazing-material-allowed portion88with respect to the brazing material94. As a result, it is possible to satisfactorily spread the brazing material94over the joining target portions22and the brazing-material-allowed portions88, and to effectively improve the joining quality of the joint. In addition, by forming the metal wires220from nickel, it is possible to reduce the cost for forming the metal film92, compared to a case of forming the metal film92from gold by using the metal wires220made of gold, for example.

On the other hand, the material for the metal wires220is not limited to nickel or gold. The material for the metal wires220can also be appropriately selected in accordance with the material for the brazing material94. For example, when at least one selected from nickel, silver, and copper is used as the material for the brazing material94, nickel can be used as the material for the metal wires220. When gold is used as the material for the brazing material94, nickel or gold can be used as the material for the metal wires220.

In the metal film forming tool for brazing214according to the above-described embodiment, the plurality of metal wires220are radially arranged with the portion supported by the support portion218as the center, so that the metal brush216has a cylindrical shape, the support portion218includes the shaft portion224passing through the center and extending in the axial direction of the metal brush216, and the metal brush216is rotationally driven via the shaft portion224, so that the peripheral surface of the rotating metal brush216can come into contact with the joining target portion22. In this case, with a simple configuration in which the peripheral surface of the metal brush216is brought into contact with the joining target portion22while the metal brush216is being rotated, it is possible to favorably form the metal film92on the film formation target portion.

The present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the essence and gist of the present invention.

For example, in the above-described embodiment, the external shape of the metal brush216is a cylindrical shape, but the external shape is not particularly limited thereto. The metal brush216may be formed by bundling a plurality of metal wires220such that the axial directions thereof are substantially parallel to each other.

In the above-described embodiment, the peripheral surface of the metal brush216rotationally driven via the shaft portion224is brought into contact with the film formation target portion. However, it is sufficient to relatively move the metal brush216relative to the film formation target portion with the metal brush216being in contact with the film formation target portion, and the present invention is not limited to rotating the metal brush216. For example, the metal brush216may be moved linearly relative to the film formation target portion.