JP3534633B2 - Joint member and turbine member - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotating member for a turbine wheel of a small supercharger for passenger cars and trucks, a large supercharger for ships, a jet engine, an industrial gas turbine blade, etc. The present invention relates to a member in which a compound base alloy and another material are joined.

[0002]

2. Description of the Related Art Due to the increasing interest in environmental problems in recent years,
It is required to improve the performance of superchargers used in transportation machines such as passenger cars, trucks and ships, and to improve the efficiency of jet engines and industrial gas turbines. One of the important components that control the performance and efficiency of the above products is a turbine, and in recent years, it has been required for the turbine to have improved transient response characteristics, a higher turbine inlet temperature, and a higher rotation speed. In order to meet these three demands, it has been desired to improve the materials that make up rotating members such as turbine wheels, turbine disks, and turbine blades. However, regarding the high turbine inlet temperature and high-speed rotation, the rotating members are currently used. When the used Ni-based superalloy is used as a base, further improvement in high temperature strength including creep strength is required. However, from the viewpoint of composition, the current Ni
It is almost difficult to improve the high-temperature strength of the base superalloy, and studies are underway to improve the high-temperature strength by a special process such as single crystallization. The adoption of this special process
The above measures are also effective for high-priced small-volume products such as jet engine blades, but it is difficult to apply costly to mass-produced products with complicated shapes such as small superchargers for passenger cars. Further, the transient response characteristics cannot be improved because the specific gravity of the Ni-base superalloy is about 8 to 9 regardless of its composition.

As an alternative to the Ni-base superalloy, an alloy containing TiAl as the main phase (herein referred to as TiAl-based intermetallic compound-base alloy) has attracted attention as a promising material for the above three performance improvements. ing. This alloy has a specific gravity of about 4 and is lightweight, so the moment of inertia is small,
Improvement of transient response characteristics can be expected. Further, in the rotating member, since the stress applied may be taken into consideration by dividing the specific strength by the specific gravity, the specific gravity of the TiAl-based intermetallic compound-based alloy is about 1/2 that of the Ni-based superalloy, so that the high temperature strength is If it is 1/2 or more of that of Ni-based superalloy, the turbine inlet temperature will rise
High-speed rotation is possible.

When a turbine wheel made of a TiAl-based intermetallic compound-based alloy is incorporated in a small supercharger, the turbine wheel itself can be produced by near-net by precision casting such as the lost wax method, but there is no problem. The joining technique for joining to a shaft made of is important.

Regarding this joining technique, Japanese Patent Publication No. 8-181
No. 51 or Japanese Patent Laid-Open No. 2-157403 makes a new proposal. In other words, Japanese Patent Publication No. 8-18151
In joining TiAl-based intermetallic compound-based alloy and structural steel, an intermediate material made of austenitic stainless steel, heat-resistant steel, Ni-based or Co-based superalloy is arranged between the turbine wheel and the shaft, and each joining is performed. We propose a joining method by friction welding. FIG. 5 is a sectional view showing the structure of a hot wheel of a turbocharger joined by this method, in which 1 is a turbine wheel, 2 is a shaft, and 3 is an intermediate material.

Further, Japanese Patent Laid-Open No. 2-157403 discloses Ti
A joining method is proposed in which the Al-based intermetallic compound-based alloy and the intermediate material are joined by friction welding, and the intermediate material and the shaft are joined by electron beam welding. Then, as the intermediate material, it is recommended to use Incoloy 903 (trade name), which has good bondability with the TiAl-based intermetallic compound-based alloy. FIG. 6 is a cross-sectional view showing the structure of a hot wheel of a turbocharger joined by this method. 1 is a turbine wheel, 2 is a shaft, 3 is an intermediate material, 4 is an intermediate portion, and A is a TiAl-based intermetallic material. The joint between the compound-based alloy and the intermediate material, and B is the joint between the intermediate material and the shaft.

[0007]

SUMMARY OF THE INVENTION The Japanese Patent Publication No. 8-181
In the proposal of No. 51, the friction joining between the intermediate material and the shaft is a joining method that has been proven in the past and there is no problem, but the friction joining between the TiAl-based intermetallic compound-based alloy and the intermediate material is as follows. There's a problem. That is, all of the intermediate materials adopted in Japanese Patent Publication No. 8-18151 are T
The linear expansion coefficient is larger than that of the iAl-based intermetallic compound-based alloy (intermediate material: 13 to 20 × 10 ⁻⁶ / ° C., TiAl-based intermetallic compound-based alloy: 9 to 11 × 10 ⁻⁶ / ° C.). Assuming that a small turbocharger for a truck is assumed, the turbine is made to start and stop, and a thermal cycle of heating and cooling is applied to the turbine. Therefore, a turbine wheel made of a TiAl-based intermetallic compound-based alloy and an intermediate material are Thermal stress due to the difference in linear expansion coefficient between the two is applied to the bonding interface. This thermal stress is applied to heating and cooling, that is, every time the small supercharger starts and stops. Therefore, in view of the actual use situation of passenger cars, trucks, etc., it is extremely large when the small supercharger is used. The thermal stress of the cycle will be loaded. If the toughness of the friction joint is good, it can withstand the load of this thermal stress.
The Al-based intermetallic compound-based alloy itself has poor toughness, and
Since the friction-bonded portion with the intermediate material is further brittle, multicycle loading of thermal stress due to the difference in linear expansion coefficient may cause fatigue fracture in the friction-bonded portion.
In Japanese Patent Laid-Open No. 2-157403, since Incoloy 903 (trade name) constituting the intermediate material has a linear expansion coefficient equivalent to that of a TiAl-based intermetallic compound-based alloy, it is disclosed in Japanese Patent Publication No. 8-181151. The problem of thermal stress loading due to the difference in linear expansion coefficient is avoided. However, as shown in FIG. 6, the joining interface between the turbine wheel 1 and the intermediate member 2 is
Since it is a plane perpendicular to the axial direction, when a bending moment acts on the shaft 3 during the manufacturing process and use of the product, a stress in the direction of opening the joint interface is applied.

In the case of friction welding of ordinary metal materials,
Since the friction-bonded part itself has toughness, no problem will occur even if the above stress is applied, but as described above, TiAl
The friction joint between the intermetallic compound base alloy and the intermediate material is brittle,
Since the resistance to crack growth (KIC) is very small, when the joint surface and the crack opening direction coincide with each other, it becomes sensitive to surface defects such as minute defects and scratches on the joint surface. That is, when a bending moment is applied to the shaft, a crack may easily propagate along the joint interface starting from a minute surface defect, and eventually the joint may be broken.

Therefore, the present invention provides a joining member having a joining structure which prevents fatigue failure of a joint due to a difference in linear expansion coefficient and which is unlikely to cause crack propagation even when a bending moment is applied to the shaft. Is an issue. Another object of the present invention is to provide a turbine member having such a joint structure.

[0010]

Means for Solving the Problems The present inventor has conducted a study for solving the above problems on the premise of brazing as a joining means. Then, not only the surface perpendicular to the axial direction but also the bonding surface not only in the circumferential direction but also in the circumferential direction, the growth of cracks is suppressed. As a specific structure for realizing this joining, a concave joining portion is formed on one member forming the joining portion and a convex joining portion is formed on the other member, and the concave joining portion and the convex joining portion are fitted together. It is effective to braze in this state.

At this time, as the brazing material to be used, it is possible to use the same brazing material for both the surface perpendicular to the axial direction and the bonding surface in the circumferential direction, but a brazing material having high strength is used for the bonding surface in the circumferential direction. Then, the stress generated by the contraction during solidification is applied to the TiAl-based intermetallic compound-based alloy without being relaxed by the plastic deformation of the brazing material. However, since the TiAl-based intermetallic compound-based alloy has insufficient toughness, there is a concern that cracks may occur due to this applied stress. Therefore, it was decided to use a low-strength brazing material for the joint surface in the circumferential direction to alleviate the stress generated during solidification due to plastic deformation of the brazing material itself. Since this stress is not applied to the joint surface perpendicular to the axial direction, in consideration of the specification of the main joint that the joint surface is exposed to high temperature for a long time, a high-strength brazing material is used to maintain durability.

When the convex joint is formed on a member made of a TiAl-based intermetallic compound-based alloy and the concave joint is formed on the other member, the operating temperature of the joint is less than the brazing temperature. The other member has an average linear expansion coefficient between room temperature and a brazing temperature which is larger than that of the brazing temperature of the TiAl-based intermetallic compound-based alloy, but is between room temperature and a temperature at which the joining member is used. Is composed of a material smaller than that of the TiAl-based intermetallic compound-based alloy, defects can be prevented, brazing strength can be increased, and sufficient bonding strength during use can be secured. That is, considering the brazing process, first, at room temperature, a brazing material is inserted between both members, and the brazing material is heated to a brazing temperature above the melting point of the brazing material. At the brazing temperature, the inserted brazing material melts, so that the void between the member made of the TiAl-based intermetallic compound base alloy having the convex joint shape and the other member having the concave joint shape becomes the brazing material. Will be satisfied. Next, during the cooling process from the brazing temperature to room temperature, the brazing material once melted will solidify again, but at this time, both these members will contract. Here, due to the difference in the average linear expansion coefficient between the room temperature and the brazing temperature of both members, the amount of shrinkage of the concave joint becomes larger than that of the convex joint. Due to this action, the gap between both members at room temperature becomes smaller than the gap amount at the brazing temperature. Therefore, since the amount of voids is reduced during the cooling process, defects in the brazing portion are less likely to occur, and a so-called shrink fit effect is also produced, so that the brazing strength can be increased.
On the other hand, considering the usage status of the joining member, both members expand when the temperature is raised from room temperature at the usage temperature. Here, due to the difference in average linear expansion coefficient from room temperature to operating temperature of both members, the expansion amount of the convex joint becomes larger than the expansion amount of the concave joint, and the gap between the two filled with the brazing material is Decrease. Therefore, the shrink fitting effect is similarly generated in the brazing portion, and the brazing strength can be increased. Incoloy 909 (trade name) is listed as a material that satisfies the condition of the linear expansion coefficient in relation to the TiAl-based intermetallic compound-based alloy. A typical composition of Incoloy 909 is% by weight, Ni: 38%, C
o: 13%, Fe: 42%, Nb: 4.7%, Ti:
1.5%, Si: 0.4%, Al: 0.03%, C:
It is 0.01%.

The present invention is based on the above findings and ideas, and includes a base made of a TiAl-based intermetallic compound-based alloy,
In a joining member including a shaft portion joined to the base portion, a convex portion is formed on one of the joint surfaces of the base portion and the shaft portion, and a concave portion is formed on the other, and the convex portion and the concave portion are fitted together. In this state, the first brazing material having a high strength is used for the joining surface in the axial direction between the base portion and the shaft portion, and the joining surface in the circumferential direction is stronger than the first brazing material. The joining member is characterized by using a small second brazing material.

Since the joined body of the present invention is joined in a state in which the convex portion and the concave portion are fitted to each other, the joint surface is formed not only in the plane perpendicular to the axial direction but also in the circumferential direction. Therefore,
Even when a bending moment is applied to the shaft during manufacturing or use, crack propagation from surface defects in the joint is suppressed compared to the conventional joint structure in which the joint surface is formed only on the plane perpendicular to the axial direction. be able to.

Further, a brazing material having high strength is used for the joint surface perpendicular to the axial direction of the base portion and the shaft portion to secure sufficient joint strength, while the joint surface in the circumferential direction is relatively strong. By using a brazing filler metal having a small size, the stress load due to the contraction of the brazing filler metal on the rotating member made of the TiAl-based intermetallic compound-based alloy is reduced while ensuring a predetermined bonding strength. The present invention is not limited to the case where the second brazing material is used on the entire bonding surface in the circumferential direction, but the first brazing material is used for the bonding surface in the circumferential direction as long as the stress load does not occur. Good. Further, as the first brazing material having high strength, a gold brazing material represented by JIS BAu-12,
JIS BAg-8 is used as the second brazing material having low strength.
It is desirable to use a silver wax represented by.

In the present invention, the composition of the TiAl-based intermetallic compound-based alloy is not limited, but in atomic%, Al: 4
4.5-48.5%, Nb: 5-9.5%, Cr: 0.
5-2%, Si: 0.1-0.4%, Ni: 0.2-
It is desirable to use a TiAl-based intermetallic compound-based alloy having a composition of 0.4 % , the balance unavoidable impurities, and Ti. An alloy having this composition can be produced by specifying the production method to obtain a γ-TiAl phase (hereinafter, γ phase) and α ₂
-Ti ₃ Al having a lamellar structure composed of a phase (hereinafter, α ₂ phase) and a γ phase, or a lamellar structure, and a three phase structure having a γ phase and a β phase (hereinafter, β phase), Excellent oxidation resistance, high temperature strength, and toughness / ductility can be obtained.

Further, according to the present invention, it comprises a base portion having a convex connecting portion made of a TiAl-based intermetallic compound base alloy, and a shaft portion having a concave connecting portion fitted to the convex connecting portion of the base portion. In the joining member, the base portion and the shaft portion are joined by a brazing material, the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the operating temperature of the joining member is α1, and the material forming the shaft portion. Is β1, the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the brazing temperature is α2, and the average linear expansion coefficient of the material forming the shaft portion is β2, α1>
Provided is a joining member characterized by satisfying the conditions of β1, α2 <β2.

In this joint member, since the convex connecting portion of the base made of the TiAl-based intermetallic compound base alloy and the concave connecting portion of the shaft portion are joined together, the joint surface is axially oriented. Since it is formed not only on the vertical surface but also in the circumferential direction, it suppresses crack propagation from surface defects in the joint part compared to the conventional joint structure in which the joint surface is formed only on the plane perpendicular to the axial direction. You can

The average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the operating temperature of the joining member is α1, the average linear expansion coefficient of the shaft portion is β1, and the TiAl-based alloy at room temperature to brazing temperature. When the average linear expansion coefficient of the intermetallic compound-based alloy is α2 and the average linear expansion coefficient of the shaft portion is β2, the shaft portion is made of a material that satisfies the conditions of α1> β1 and α2 <β2. At the time of brazing, for example, a brazing temperature of BAu-12 of a gold wax is 9
In the cooling process from 40 ° C. to room temperature, since the linear expansion of the shaft portion is large, the voids with the base portion made of the TiAl-based intermetallic compound-based alloy are reduced, so that the brazing defect is prevented and the shrink-fit effect is obtained. Can increase the bonding strength. On the other hand, the temperature during actual use, for example, the temperature near the junction in the case of a turbine of a small turbocharger, about 450 ° C.
In the above, since the linear expansion of the shaft portion is small, stress is generated in the direction of compressing the brazed portion, which is useful for ensuring the joint strength.

As described above, there is Incoloy 909 (trade name) as a material satisfying such conditions and having a predetermined heat resistance. Incoloy 909 and Ti
The linear expansion coefficient of the Al-based intermetallic compound-based alloy is shown in FIG.
As shown in FIG. 3, the TiAl-based intermetallic compound-based alloy has a large average linear expansion coefficient from room temperature up to about 700 ° C.
Above this temperature, Incoloy 909 has a larger linear expansion coefficient from room temperature.

In the present invention, a shaft body made of structural steel may be connected to the shaft portion. In this case, the shaft portion corresponds to the intermediate member of the conventional joint structure shown in FIGS. Of course, the shaft portion may be integrally formed with the shaft body. In this case, since the average linear expansion coefficient from the room temperature of the structural steel is larger than that of the TiAl-based intermetallic compound-based alloy regardless of the temperature, the effect of preventing defects and improving the joint strength during the cooling process during brazing is not affected by incoloy. Although it is similar to 909, the effect of improving the bonding strength at the time of use cannot be expected. In addition, the effect of using a brazing material having a high strength on the joint surface in the axial direction between the base portion and the shaft portion described above and using a brazing material having a relatively low strength on the joint surface in the circumferential direction is structural. The same is true when steel is used.

The TiAl-based intermetallic compound-based alloy, in atomic%, Al: 44.5 to 48.5%, Nb:
5 to 9.5%, Cr: 0.5 to 2%, Si: 0.1
As described above, it is desirable to use a TiAl-based intermetallic compound-based alloy having a composition of 0.4%, Ni: 0.2 to 0.4 % , the balance unavoidable impurities, and Ti.

The reason for setting the above composition range will be described below. Al: Al is a main constituent element of the present alloy and forms an intermetallic compound phase together with Ti. Al concentration is 44.
If it is less than 5%, the ductility at room temperature decreases. On the other hand, 4
If it exceeds 8.5%, the high temperature strength will decrease. Therefore, it is 44.5 to 48.5%.

Nb: Nb has the function of improving the oxidation resistance and further improving the high temperature strength. In the case of a small turbocharger turbine, the temperature at the joint is about 450 ° C, but the temperature at the tip of the turbine wheel is at least 800 ° C. 5
If it is less than%, there is no effect in improving the oxidation resistance and the high temperature strength. On the other hand, if it exceeds 9.5%, the room temperature ductility decreases. Therefore, it is set to 5 to 9.5%. If it is less than 6%, the oxidation resistance in the temperature range of about 850 ° C., which is the environment of use of a general small turbocharger, is insufficient, and if it exceeds 8.5%, the acid resistance corresponding to the amount added is required. Since it is not possible to obtain the chemical conversion property and the specific gravity increases, it is desirable to set the content to 6 to 8.5%.

Cr: Cr is added for the purpose of improving toughness and ductility at room temperature. If it is less than 0.5%, the toughness and ductility at room temperature are insufficiently improved, while if it exceeds 2%, the high temperature strength is reduced. Therefore, in the present invention,
0.5 to 2%. The desirable amount of Cr is 0.7 to
It is 1.3%.

Si: Si has the function of improving the oxidation resistance and the creep strength. If the addition amount is less than 0.1%, the effect of addition is not sufficient, while if it exceeds 0.4%, the toughness / ductility at room temperature decreases. Therefore, 0.1
~ 0.4%. A desirable amount of Si is 0.15 to 0.
35%.

Ni: Ni is added for the purpose of improving oxidation resistance and high temperature strength. If the amount added is less than 0.2%, the effect of addition is insufficient, while if it exceeds 0.4%, the toughness / ductility at room temperature decreases. Therefore, 0.2-
0.4%. A desirable amount of Ni is 0.25 to 0.
35%.

Others: Other than the above-mentioned constituent elements, it consists of unavoidable impurities and Ti. Of the impurity elements, O (oxygen)
Is contained in the alloy in excess of 1000 ppm, the toughness is lowered. Therefore, it is recommended to regulate O to 1000 ppm or less.

When the alloy having the above composition is produced by the method described later, a lamellar structure consisting of γ phase and α ₂ phase and a _two- phase structure of γ phase, or a lamellar structure, γ phase and β phase
It becomes a three-phase organization of phases. With such a two-phase structure or a three-phase structure, the γ phase and β phase exhibit an effect of preventing coarsening of the lamellar structure. Next, the above-mentioned TiAl
A preferred method for producing the joining member of the present invention will be described by taking a system-based intermetallic compound-based alloy as an example. First, in atomic%, Al: 4
4.5-48.5%, Nb: 5-9.5%, Cr: 0.
5-2%, Si: 0.1-0.4%, Ni: 0.2-
An alloy of 0.4 or less and the balance unavoidable impurities and Ti is melted and cast. A conventionally known method can be applied to the melting method and the casting method. For example, when a turbine wheel of a small supercharger is targeted, a high frequency melting method can be applied as a melting method, and a lost wax method can be applied as a casting method.

Next, the obtained casting is subjected to hot isostatic pressing. This hot isostatic pressing treatment is performed for the purpose of eliminating casting defects such as cavities that may exist in the casting when the casting is relatively large. Therefore, it may be omitted when targeting small-sized products in which casting defects are less likely to occur.

Conditions for the hot isostatic pressing treatment are as follows: heating temperature: 1200 to 1300 ° C., pressure: 1100 to 1300.
Atm, processing time: 0.5 to 3 hours is desirable. This is because if the temperature is less than 1200 ° C., it is insufficient to eliminate the casting defects, and if it exceeds 1300 ° C., the contamination due to surface oxidation cannot be ignored. Of course, the hot isostatic pressing process is performed in a non-oxidizing atmosphere such as argon. However, since pressure is applied, the partial pressure of oxygen existing as an impurity in the gas increases, and when the temperature rises, some oxidation occurs on the surface. At this time, there is no problem as long as the target product can remove the surface, but if the surface of the casting such as a turbine wheel of a small supercharger is used as it is and the blade is very thin, this oxidation is not desirable. Pressure is 1100at
This is because if it is less than m, it is not sufficient to eliminate casting defects, and if it exceeds 1300 atm, the effect is saturated, but there are restrictions such as limited hot isostatic pressing equipment that can do this. This is because if the treatment time is less than 0.5 hours, it is insufficient to eliminate the casting defects, and if it exceeds 3 hours, the effect is saturated but the treatment cost is high.

After hot isostatic pressing, heat treatment is carried out in an inert atmosphere by heating and holding at 1300 to 1400 ° C. for 10 to 100 minutes and then rapidly cooling. The non-oxidizing atmosphere is used as the heat treatment atmosphere in order to prevent oxidation of the casting. Here, the non-oxidizing atmosphere means a vacuum or an inert gas such as Ar. Further, the heating temperature is set to 1300 to 1400 ° C. because the structure of the present invention, that is, the lamellar structure, the three-phase structure of the γ phase and the β phase can be stably obtained in this temperature range. If the temperature is lower than 1300 ° C, a low-strength structure composed of a fine two-phase structure of γ phase and β phase, and if the temperature exceeds 1400 ° C, a low ductility structure composed of a coarse lamellar single-phase structure tends to be formed. Therefore, the heating temperature is 1340 to 138.
It is desirable to set it to 0 ° C. Furthermore, the heating hold time is 1
If it is less than 0 minutes, a desired tissue cannot be obtained even if the heating temperature is within the range of the present invention, and holding for about 100 minutes is sufficient to obtain the desired tissue, and if it exceeds that, Since the energy is wasted, the heating and holding time is 10
~ 100 minutes is good. More desirable heat holding time is 15 ~
70 minutes.

After the above heating and holding, a rapid cooling process is performed. By this rapid cooling treatment, the structure of the cast product after cooling becomes the above-mentioned two-layer structure or three-phase structure. In this rapid cooling process, heating and holding are performed in a vacuum or in an inert gas atmosphere, but when the heating is released after a predetermined heating time elapses, and when the heating and holding is performed in a vacuum, the heating is not performed in the heating furnace. Introduce active gas and stir the gas, or stir the inert gas in the heating furnace if heated and held in an inert gas atmosphere, or newly introduce the inert gas into the heating furnace. Then, the gas may be stirred. As a heat treatment furnace capable of performing such heat treatment, there is a vacuum gas fan cooling heat treatment furnace (hereinafter referred to as GFC). However, the quenching process is not limited to these modes,
After holding for a predetermined amount of heat, remove from the heat treatment furnace and air cool,
Alternatively, it may be a means such as introducing and spraying an inert gas into this chamber after moving it into another chamber.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION <Experimental example> An experiment conducted for setting an optimum brazing condition will be described. Using test pieces as shown in (a) and (b) of FIG. 4, the quality of the brazing part, that is, the presence or absence of a brazing defect, the room temperature of the brazing part, and
The joint strength at 50 ° C was evaluated. The shape of the joint part to be brazed is the same for all test pieces.
Brazing materials A, B, and C were arranged between the convex test piece 11 made of the intermetallic compound-based alloy and the concave test piece 12 made of Incoloy 909 as shown in the drawing. Here, the brazing material A is a brazing material used for joining a joining surface perpendicular to the axial direction, and the brazing material B is a brazing material used for a joining surface in the circumferential direction. Also,
The brazing material C is for preventing a brazing defect particularly on the joint surface in the circumferential direction, and corresponds to a riser for preventing a casting defect. Brazing is 940 ° C under vacuum,
It was carried out under the condition of holding for 10 minutes.

First, the quality evaluation result of the brazing part examined by using the test piece of FIG. 4A will be described. In this test, the brazing materials A and B were made of BA having a thickness of 100 μm.
A sheet-shaped brazing material made of u-12, the brazing material C being powdered BAg-8, narrow band-shaped BAg-8 (thickness 100 μm
m) and wire-like BAg-8 (0.8 mmφ). The composition of each brazing material is as follows. Also,
Brazing was also carried out on the products without the brazing material C. The gap (one side) between the convex test piece 11 and the concave test piece 12 at room temperature was 140 μm. That is, 100
A further gap was provided in consideration of inserting a brazing material of μm. After brazing, it was cut vertically and examined for brazing defects, that is, the presence or absence of voids. The results are also shown in Table 1. BAu-12 Au-12.5 wt% Ag-12.5 wt% Cu BAg-8 Ag-28 wt% Cu

[0036]

[Table 1]

From the results shown in Table 1, the following can be said. If the brazing material C is not provided, defects (voids) are generated in the brazing portion, whereas the use of the brazing material C suppresses the occurrence of defects in the brazing portion. The brazing material C is preferably in the form of wire or narrow band rather than powder. The reason for this is as follows. First, in order to insert the brazing material B at room temperature, a gap larger than that of the brazing material is necessary. In this experiment, this is 140 μm (one side).
And The thickness of the brazing material is at least +20 μm for practical use.
Gaps are required. Therefore, the volume of this gap becomes larger than the volume of the brazing material, and when there is no additional brazing material C,
Brazing defects will inevitably occur. Next, when powder is used as the brazing material C, since the specific surface area of the powder is very large, even a small amount of oxygen as an impurity causes oxidation even under vacuum, and light sintering causes a phenomenon in which not all melt. Therefore, it is considered that a defect occurred because it stayed at the position where it was placed and the amount of inflow to the lower part decreased. On the other hand, when a wire-shaped or narrow band material is used as the brazing material C, the specific surface area is significantly smaller than that of the powder, so even if the surface is slightly oxidized, melting occurs and inflow to the lower part occurs. It is considered that the defects that occur only with the brazing material B can be filled.

Next, using the test piece of FIG. 4 (b), the strength evaluation result of the brazed portion evaluated by performing a tensile test on the test piece after brazing at room temperature and 450 ° C. will be described.
In this test piece, the brazing materials A and B have a thickness of 100 μm
The sheet-like brazing material was used, the brazing material C was a wire-shaped brazing material having a diameter of 0.8 mm, and the best combination was examined by changing the material of each brazing material. For reference, a tensile test was also performed on the TiAl-based intermetallic compound-based alloy itself having the same shape without brazing. The convex test piece 1
The gap (one side) between the test piece 1 and the concave test piece 12 at room temperature is 140 μm, which is the same as the test piece for the quality evaluation result of the brazing part. The results are shown in Table 2. Test condition 1 is brazing material A, B, C
Both are made of BAu-12, which is a brazing filler metal, but at room temperature, it fractures in a TiAl-based intermetallic compound-based alloy with a very low strength of about 1/2 that of the base metal. On the other hand, at 450 ° C., it fractures from the brazed portion with strength almost equal to that of the base metal. Test condition 2 is that the brazing materials A and B are BAu-12, and the brazing material C is silver brazing BAg-8. Although it is better than the test condition 1 at room temperature, it also fractures in the TiAl-based intermetallic compound-based alloy with considerably lower strength than the base metal. On the other hand, at 450 ° C., it is equivalent to the test condition 1. Test condition 3 is brazing material A with BAu-1
No. 2 and the brazing materials B and C are silver brazing BAg-8. Although fractured at the TiAl-based intermetallic compound-based alloy at room temperature, it is significantly better than the test conditions 1 and 2. On the other hand, at 450 ° C., the brazed part was broken, but it was good, not much different from the test conditions 1 and 2. Test condition 4 is that all of the brazing materials A, B, and C are BAg-8.
The strength at room temperature is the best, but the strength at 450 ° C is low.

Considering the above results, they are as follows. First, regarding the result of 450 ° C., at this temperature all fractures occurred in the brazed portion, and it is considered that the strength of the brazing material simply limited the tensile strength. Further, the difference in strength under each test condition can be simply explained by the blending ratio of the brazing material. That is, the higher the blending ratio of BAu-12 having higher high temperature strength, the higher the high temperature strength. Next, regarding the results at room temperature, all of the fractures were caused by the TiAl-based intermetallic compound-based alloys, but it is characteristic that the strengths are completely different. Generally, if a normal ductile metal material is used, such a difference in rupture strength of the base material cannot occur, but since TiAl-based intermetallic compound-based alloy is extremely brittle at room temperature, such a specific phenomenon occurs. Is thought to have occurred. That is, BAu-12, which has a high strength, is used for the brazing materials B and C which are the circumferential joints.
When the alloy is used, residual stress occurs due to shrinkage in the cooling process after brazing, but this cannot be relaxed by the plastic deformation of the brazing material itself. Therefore, the TiAl-based intermetallic compound-based alloy of the convex test piece 11 cannot be relaxed. Will be stressed. However, since the TiAl-based intermetallic compound-based alloy is extremely brittle, it is considered that the TiAl-based intermetallic compound-based alloy cannot withstand this stress and fine cracks occur. Further, since the crack propagation speed of the TiAl-based intermetallic compound-based alloy at room temperature is very high, it is considered that this crack easily propagated in the tensile test at room temperature and ruptured under a low load under the test conditions 1 and 2. . At 450 ° C., the crack propagation rate becomes slower, and it is considered that the brazing material showed good strength even under the test conditions 1 and 2. Room temperature strength and 4
It was the test condition 3 in which BAu-12 was used as the brazing material A and BAg-8 was used as the brazing materials B and C.
Since a soft brazing material BAg-8 was used for this, stress was relaxed by plastic deformation of this brazing material during contraction after brazing, and no cracks occurred in the TiAl-based intermetallic compound-based alloy. It is considered that the strength has improved. Further, since BAu-12, which has high strength at high temperature, was used as the brazing material A on the bottom surface which is the joint surface in the axial direction, it is considered that sufficient strength was maintained even at 450 ° C. In addition, this point is that all test conditions 4 using low strength BAg-8.
Is the difference.

[0040]

[Table 2]

The present invention will be described below based on specific embodiments. <First Embodiment> A turbine for a passenger car small turbocharger having a structure shown in Fig. 1 was produced. In FIG. 1, 1 is a turbine wheel (base), and 2 is a shaft (shaft). The turbine wheel 1 is in atomic%, Al: 45.8%, Nb:
8.6%, Cr: 1.2%, Si: 0.25%, Ni:
It is composed of a TiAl-based intermetallic compound-based alloy having a composition of 0.35%, O2: 700 ppm, the balance unavoidable impurities, and Ti. The turbine wheel 1 is obtained by the lost wax method. The shaft 2 is made of a material equivalent to JIS SCM435. Observation of the microstructure of the turbine wheel 1 revealed that a lamellar structure composed of γ phase and α ₂ phase, γ
It was confirmed to have a three-phase structure of a phase and a β phase.

As shown in FIG. 1, the turbine wheel 1 is formed with a convex joint portion 1a and the shaft 2 is formed with a concave joint portion 2a. The convex joint portion 1a and the concave joint portion 2a are formed.
Are fitted and the turbine wheel 1 and the shaft 2 are joined.

At the time of brazing, the same method as the test condition 3 in Table 2 was used between the convex joint portion 1a and the concave joint portion 2a.
That is, brazing materials A (BAu-12), B (BAu-8) and C (wire-shaped BAu-8) were arranged as shown in FIG. 4 (C). Here, the brazing material A is a brazing material used for joining a joining surface perpendicular to the axial direction, and the brazing material B is a brazing material used for a joining surface in the circumferential direction. Soldering is under vacuum at 940 ° C, 10
It was carried out under the condition of holding the minute.

In the above turbine, BAu-12, which is a high-strength brazing material, is used for the joint surface of the turbine wheel 1 and the shaft 2 in the axial direction, and a low-strength brazing material is used for the joint surface in the circumferential direction. Since a certain BAg-8 is used, the stress load on the convex joint 1a of the turbine wheel 1 is relieved by brazing, and at the time of high temperature of about 450 ° C. which is the temperature of the joint when the turbine is used. Bonding strength can also be secured.

Further, the turbine according to the present embodiment is
Since the convex connecting portion 1a of the turbine wheel 1 made of a TiAl-based intermetallic compound-based alloy and the concave connecting portion 2a of the shaft 2 are joined together in a fitted state, the joint surface is only a surface perpendicular to the axial direction. However, since it is also formed in the circumferential direction, compared to the conventional joint structure in which the joint surface is formed only on the surface perpendicular to the axial direction, the joint portion can be made even when a bending moment is applied during manufacture and use. It is possible to suppress the crack development from the surface defect.

In the above embodiment, the joint surface in the circumferential direction may be tapered, or the turbine wheel 1 may be provided with a concave connecting portion and the shaft 2 may be provided with a convex connecting portion.

<Second Embodiment> A small turbocharger turbine for a passenger car having a structure shown in FIG. 2 was produced. In FIG. 2, 1 is a turbine wheel, 2 is a shaft, and 3 is an intermediate material.
Turbine wheel 1 is in atomic%, Al: 45.8%,
Nb: 8.6%, Cr: 1.2%, Si: 0.25%,
It is composed of a TiAl-based intermetallic compound-based alloy having a composition of Ni: 0.35%, O2: 740 ppm, the balance unavoidable impurities, and Ti. Also, shaft 2
Is made of a material equivalent to JIS SCM435.
Further, the intermediate material 3 is, by weight%, Ni: 37.8%, C
o: 13.2%, Nb: 4.7%, Ti: 1.4%, S
i: 0.4%, Al: 0.03%, C: 0.01%,
The balance is composed of a Fe-based superalloy (trade name: Incoloy 909) containing Fe and unavoidable impurities. When the microstructure of the turbine wheel 1 was observed, it was confirmed that the turbine wheel 1 had a lamellar structure composed of γ phase and α ₂ phase, and a three-phase structure of γ phase and β phase.

As shown in FIG. 2, the turbine wheel 1 has a convex joint 1a, and the intermediate member 3 has a cup-like shape. The convex joint 1a of the turbine wheel 1 has an intermediate member 3a. The concave portion of the turbine wheel 1 and the intermediate material 2 are joined to each other through the brazing material. The intermediate member 3 and the shaft 2 are joined by electron beam welding.

In brazing, the same method as the test condition 3 in Table 2, that is, the brazing materials A, B and C between the convex joint portion 1a and the concave joint portion 2a are shown in FIG. 4 (C). I placed it in. Here, the brazing material A is BAu-12 used for joining the joining surface perpendicular to the axial direction, the brazing material B is BAg-8 used for the joining surface in the circumferential direction, and the brazing material C is especially for the joining surface in the circumferential direction. It is a wire-like BAg-8 arranged to prevent a brazing defect. Brazing conditions are 940 ° C
× 10 minutes. Regarding the bonding surface in the circumferential direction, BAg-8 is arranged on the entire surface in the present embodiment, but BAu-12 may be arranged up to a height of about ½, for example.

In the turbine according to the present embodiment, the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy forming the turbine wheel 1 at room temperature to 500 ° C. is about 11.
× 10 ⁻⁶ / ° C., the average linear expansion coefficient at room temperature to 900 ° C. (near the brazing temperature) is about 12 × 10 ⁻⁶ / ° C., and room temperature to 500 of Incoloy 909 constituting the intermediate material 3.
The average linear expansion coefficient is about 8.5 × 10 ⁻⁶ / ° C. at room temperature, and the average linear expansion coefficient is about 13.5 × 10 ⁻⁶ / ° C. at room temperature to 900 ° C. (near brazing temperature). That is,
The average linear expansion coefficient at room temperature to 500 ° C (temperature near the joint during use) is smaller for the intermediate material 3 than for the turbine wheel 1, but at room temperature to 900 ° C (near the brazing temperature) the average linear expansion coefficient is The intermediate material 3 is larger than the turbine wheel 1. Therefore, as described in detail so far, a force for tightening the brazing portion is generated during the cooling process after brazing and during use, so that a brazing defect is less likely to occur during brazing, and the pseudo baking is not performed. The fitting state is established and the joining strength between the two becomes strong.

Further, the turbine according to the present embodiment is
The joint surface of the turbine wheel 1 and the shaft 2 in the axial direction is made of a brazing material having a high temperature strength, BAu-1.
No. 2 is used and BAg-8, which is a brazing material having a low room temperature strength, is used for the joint surface in the circumferential direction, so that the convex joint portion 1a of the turbine wheel 1 is not broken at room temperature by brazing, and It is also possible to secure the bonding strength in a high temperature state of about 450 ° C. which is the temperature in the vicinity of the bonding portion when used in a passenger car compact turbocharger.

Further, the turbine according to the present embodiment is
Since the convex connecting portion 1a of the turbine wheel 1 made of a TiAl-based intermetallic compound-based alloy and the concave connecting portion 2a of the shaft 2 are joined together in a fitted state, the joint surface is only a surface perpendicular to the axial direction. However, since it is also formed in the circumferential direction, compared with the conventional joining structure in which the joining surface is formed only on the surface perpendicular to the axial direction, the joining is performed even when a bending moment is applied during manufacturing and use. It is possible to suppress the crack growth from the surface defect of the part.

[0053]

As described above, the convex portion and the concave portion are fitted in the joining member including the base portion made of the TiAl-based intermetallic compound base alloy of the present invention and the shaft portion joined to the base portion. Since they are joined in a state, the joining surface is formed not only in the plane perpendicular to the axial direction but also in the circumferential direction. Therefore,
Even when a bending moment is applied, it is possible to suppress crack propagation from the surface defect of the joint portion as compared with the conventional joint structure in which the joint surface is formed only on the surface perpendicular to the axial direction. Further, a brazing material having high strength is used for a joint surface perpendicular to the axial direction of the base portion and the shaft portion to secure sufficient joint strength, while a brazing material having relatively low strength is formed on the joint surface in the circumferential direction. By using the material, the stress load on the TiAl-based intermetallic compound-based alloy is reduced while ensuring a predetermined bonding strength.

The average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the operating temperature of the joining member is α1, the average linear expansion coefficient of the shaft portion is β1, and the TiAl-based alloy at room temperature to brazing temperature is Assuming that the average linear expansion coefficient of the intermetallic compound-based alloy is α2 and the average linear expansion coefficient of the shaft portion is β2, when the brazing temperature> the junction temperature during use, the shaft portion has α1> β1 and α2 <β2. If the material is made of materials that satisfy the conditions, a force that tightens the brazing part is generated both during the cooling process after brazing and during use. It will be in a state of shrink fitting, and the joint strength of both will be strong.

[Brief description of drawings]

FIG. 1 is a diagram showing a turbine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a turbine according to another embodiment of the present invention.

FIG. 3 is a graph showing the coefficient of linear expansion of Incoloy 909 and a TiAl-based intermetallic compound-based alloy.

FIG. 4 is a view showing an arrangement of test pieces and a brazing material used in a brazing test.

FIG. 5 is a diagram showing an example of a conventional turbine.

FIG. 6 is a diagram showing an example of a conventional turbine.

[Explanation of symbols]

1 turbine wheel (base) 2 shaft (shaft part) 3 Intermediate material (shaft)

Continuation of front page (56) Reference JP-A-11-320132 (JP, A) JP-A-10-220236 (JP, A) JP-A-10-118764 (JP, A) JP-A-5-78769 (JP , A) Actual development Sho 62-61901 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 35/00-35/30 B23K 1/00-1/20 B23K 31/00 -33/00 F02B 39/00

Claims (10)

(57) [Claims] 1. A joining member comprising a base portion made of a TiAl-based intermetallic compound base alloy and a shaft portion joined to the base portion, wherein a convex portion is provided on one of the joint surfaces of the base portion and the shaft portion, and the other is provided. A concave portion is formed in the concave portion, and the convex portion and the concave portion are fitted to each other by a brazing material, and a first brazing material having high strength is used for a joint surface in the axial direction between the base portion and the shaft portion. A second brazing material having a strength lower than that of the first brazing material is used for the bonding surface in the circumferential direction. 2. The joining member according to claim 1, wherein the first brazing material is a gold brazing material and the second brazing material is a silver brazing material. 3. The TiAl-based intermetallic compound-based alloy,
Atomic%, Al: 44.5-48.5%, Nb: 5-
9.5%, Cr: 0.5-2%, Si: 0.1-0.4
%, Ni: 0.2-0.4 % , the balance unavoidable impurities, and Ti. The joining member according to claim 1 or 2. 4. A joining member comprising a base portion having a convex connecting portion made of a TiAl-based intermetallic compound base alloy and a shaft portion having a concave connecting portion that fits into the convex connecting portion of the base portion. And the shaft portion are joined by a brazing material, and the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the operating temperature of the joining member is α1, and the average linear expansion coefficient of the material forming the shaft portion is When β1, the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the brazing temperature is α2, and the average linear expansion coefficient of the material forming the shaft portion is β2, the operating temperature is less than the brazing temperature. , Α1> β1 and α2 <β2 are satisfied. 5. The joining member according to claim 4, wherein a shaft body made of structural steel is joined to the shaft portion. 6. A first brazing material having high strength is used for a joint surface of the base portion and the shaft portion in an axial direction, and a second brazing material having a strength lower than that of the first brazing material is used for a joint surface in a circumferential direction. The joining member according to claim 4 or 5, wherein the brazing material is used. 7. The joining member according to claim 6, wherein the first brazing material is a gold brazing material, and the second brazing material is a silver brazing material. 8. The TiAl-based intermetallic compound-based alloy,
Atomic%, Al: 44.5-48.5%, Nb: 5-
9.5%, Cr: 0.5-2%, Si: 0.1-0.4
%, Ni: 0.2-0.4 % , the balance unavoidable impurities, and Ti. The joining member according to claim 4 . 9. A turbine member comprising a turbine wheel made of a TiAl-based intermetallic compound-based alloy and a shaft joined to the turbine wheel, wherein a convex portion is provided on one of the joining surfaces of the turbine wheel and the front shaft.
A concave portion is formed on the other side, and the convex portion and the concave portion are joined by a brazing material in a fitted state, and a first brazing material having high strength is formed on a joint surface in the axial direction between the turbine wheel and the shaft. A second brazing material having a strength lower than that of the first brazing material is used for the joint surface in the circumferential direction. 10. A turbine wheel having a convex connecting portion made of a TiAl-based intermetallic compound-based alloy, an intermediate material having a concave connecting portion fitted to the convex connecting portion of the turbine wheel, and connected to the intermediate material. In the turbine member including a shaft, the turbine wheel and the intermediate member are joined by a brazing material, and the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the operating temperature of the turbine member is α.
1. Let β be the average coefficient of linear expansion of the material that constitutes the intermediate material.
1. When the average linear expansion coefficient of the TiAl-based intermetallic compound-based alloy at room temperature to the brazing temperature is α2, and the average linear expansion coefficient of the material forming the intermediate product is β2, when the operating temperature <the brazing temperature, , Α1> β1 and α2 <β2 are satisfied.