JPH11320132A - Joining method for titanium-aluminum alloy member and constructive steel member, and joined part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability against a high temperature strength of a joining part by joining a turbine wheel composed of TiAl alloy and a steel shaft, using an alloy as an intermediate member whose thermal expansion coefficient is equivalent to that of the TiAl alloy. SOLUTION: When a steel made shaft 2 is joined with the TiAl alloy made turbine wheel being composed of and including, at an atomic ratio, 45-48% Al, 5-9% Nb, 1-2% Cr, 0.2-0.5% Si, 0.3-2% Ni, 0.01-0.05% Y and, Ti and an avoidable impurity as a balance, an intermediate material 3 composed of an incoloy 903, 907 or 909 is used. A concave part is formed on either one part of the joining faces between the turbine wheel 1 and the intermediate member 3, and a convex part is formed on the other face part. An abrasion welding is then carried out under the condition that the concaved and convexed parts are abutted. The joining face shape is made in a manner that the central part, which being equivalent to 20-70% of cross section diameter being orthogonal to the shaft, is vertical against the shaft and its outer surrounding is slanted by 20-40 deg., preferably 30 deg. from the face vertical against the shaft.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joining method for joining a TiAl alloy member and a structural steel material, and a joining part joined by the joining method.

[0002]

2. Description of the Related Art In small turbochargers for diesel engines and gasoline engines for passenger cars and trucks, the transient response characteristic is improved because the weight of the turbine wheel is reduced to reduce the moment of inertia at the start of rotation. As a result, it is possible to contribute to the improvement of the acceleration performance of the engine and the reduction of black smoke due to the improvement of the combustion efficiency. Therefore, it has been conventionally considered to apply a lightweight material to the turbine wheel. However, Al alloys and Ti alloys, which are ordinary lightweight metal materials, have insufficient heat resistance and are difficult to apply. In addition, although ceramics, a new lightweight material, have been partially commercialized, there is a problem that the blade tip is easily chipped because it is a brittle material, and the blade shape of the turbine wheel is aerodynamic due to manufacturing restrictions. The scope of application is not so widespread because there is a problem that it cannot be optimized. In addition to the turbine wheel of a small turbocharger, there is a similar problem in a gas turbine, a small turbine disk for a turbocharger, a small turbine rotor, and the like.

On the other hand, TiAl, which has been developed recently,
Alloys based on intermetallics (Ti and A in atomic%)
1 is almost equivalent: hereinafter, referred to as TiAl alloy) has a specific gravity of about 1 / of that of a conventional Ni-base heat-resistant alloy which is a turbine wheel material.
2 and lighter, have higher heat resistance than Al-based alloys and Ti-based alloys, and higher reliability than ceramics. Since it can be formed into an aerodynamically optimal wing shape by precision casting, it has recently been promising as a new material that can meet the above demand. TiAl
There is no problem in the manufacturing technology when incorporating an alloy turbine wheel into a small turbocharger because the turbine wheel itself can be manufactured by near net by precision casting, but there is no problem with the joining technology of joining this turbine wheel to a shaft made of structural steel. Development is required. Conventionally, vacuum brazing has been applied as this joining technique, but vacuum brazing is not suitable for mass-produced products such as this product due to the long time required for joining work and the large number of work steps. there were. Furthermore, the exhaust gas temperature has also increased with the increase in the output of the engine, and the temperature of the joints has also increased. This has raised concerns that the strength cannot be maintained by vacuum brazing. Accordingly, studies have been made on joining by friction welding that enables highly efficient joining and has a high high-temperature strength at a welded portion, and various methods have been proposed.

For example, Japanese Patent Publication No. Hei.
In the joining of iAl alloy and structural steel, austenitic stainless steel or heat-resistant steel, or Ni
A joining method is disclosed in which a base alloy or a Co-based superalloy is used, and the joining of the TiAl alloy and the intermediate material and the joining of the intermediate material and the structural steel are performed by friction welding. FIG.
1 is a cross-sectional view showing a configuration of a hot wheel of a turbocharger joined by this method, where 1 is a turbine wheel,
2 is a shaft, 3 is an intermediate material. In this method,
Friction welding between an intermediate material and a shaft material is a welding method that has been used in the past and is not particularly problematic. However, friction welding between a TiAl alloy and an intermediate material has the following problems when applied to a small turbocharger. is there. 1) In a small turbocharger, a heat cycle of heating and cooling is applied to a turbine when a passenger car, a truck and the like are started and stopped. However, the intermediate materials listed in this publication all have a linear expansion coefficient compared to TiAl. Is large (intermediate material 13-20 × 10
⁻⁶ / ° C., TiAl alloy 9-11 × 10 ⁻⁶ / ° C.), and thermal stress due to the difference in the linear expansion coefficient is applied to the joint interface between the two materials. Since this thermal stress is applied every time heating and cooling, that is, every time a small turbocharger starts and stops, considering the usage of passenger cars and trucks, a very large number of cycles are required when using a small turbocharger. Thermal stress will be applied. Here, there is no problem if the joint has toughness, but in the first place, the TiAl itself is brittle compared to a normal metal material, and the joint with the intermediate material is more brittle. The multi-cycle loading of stress may eventually lead to fatigue failure of the joint.

[0005] 2) According to the configuration diagram of the joining component in this publication, the joining interface between the intermediate material and the TiAl alloy is linear and perpendicular to the axial direction. Therefore, in the case of a small turbocharger, when a bending moment is generated on the shaft, a stress in a direction in which the joint surface is opened is applied. In the case of a normal metal-to-metal friction joint, since the friction joint itself has toughness, no problem occurs even when the above stress is applied, but as described above, the friction joint between TiAl and the intermediate material is Since it is brittle and has very low resistance to crack propagation (K _IC ), when the direction of the joint surface coincides with the direction of the crack opening, there is a problem that the surface of the joint becomes sensitive to minute defects, scratches, and the like. In other words, when a bending moment is applied to the shaft, cracks easily propagate from the surface defects as a starting point to the joint interface, and eventually the joint may be broken.

[0006] On the other hand, Japanese Patent Application Laid-Open No. 2-157403 discloses that a TiAl alloy and a structural steel are bonded together.
The joining method is characterized in that the joining of the alloy and the intermediate material is performed by friction welding, and the joining of the intermediate material and the structural steel is performed by a welding method such as electron beam welding. The intermediate material is defined as a material having a good bonding property with the TiAl alloy, for example, Incoloy 903
And the shape is a hollow ring shape.
FIG. 6 is a cross-sectional view showing the structure of a joint part according to this method, wherein 1 is a turbine wheel, 2 is a shaft, 3 is an intermediate material, 4 is a hollow portion, and A is a joint between the TiAl alloy and the intermediate material. , B are joints between the intermediate member and the shaft.
Also in this method, the welding method of the intermediate material and the shaft material is a joining method that has been used in the past, and there is no particular problem. TiAl
Regarding the friction joining between the alloy and the intermediate material, when using a material such as Incoloy 903, which is a low thermal expansion material mainly composed of iron, nickel and cobalt, and having a coefficient of linear expansion substantially equal to that of the TiAl alloy, as the intermediate material, Fairness 18-1815
The problem 1) of the method disclosed in Japanese Patent Application Laid-Open Publication No. HEI 1 (1), that is, the load of thermal stress caused by the difference in the coefficient of linear expansion is avoided. However, since the joint surface is perpendicular to the axis, the joint surface is sensitive to minute defects and scratches on the joint surface, and the same applies to the problem 2) in which a crack is easily propagated by a bending moment.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances of the prior art, and has been used for joining a TiAl alloy member and an intermediate material when joining a TiAl alloy member and a structural steel material using an intermediate material. At the interface, a method of joining a TiAl alloy member to a structural steel material, in which the load of thermal stress due to the difference in the coefficient of thermal expansion is reduced, and the problem of being sensitive to surface defects at the joint and weak to the load of bending moment is solved. And a joint component obtained by the method.

[0008]

The present invention adopts the following aspects (1) to (5) as means for solving the above-mentioned problems. (1) In a method of joining a TiAl alloy member and a structural steel material using an intermediate material, an alloy having a thermal expansion coefficient equivalent to that of the TiAl alloy is used as the intermediate material, and TiA is used.
(1) A convex portion is formed on one surface of the joining surface between the alloy member and the intermediate member, and a concave portion is formed on the other surface. A method for joining a TiAl alloy member and a structural steel material, wherein the joining is performed by friction welding in a state where the formed surfaces are butted against each other.

(2) In a method of joining a TiAl alloy member and a structural steel material using an intermediate material, an alloy having a thermal expansion coefficient equivalent to that of the TiAl alloy is used as a first intermediate material, and the TiAl alloy member is further used. A concave portion is provided at a central portion of at least one of opposing surfaces of the first intermediate member and
The TiAl alloy member and the first and second intermediate members are friction-welded with the second intermediate material made of a material having high toughness embedded in the recesses, and a second intermediate material is provided between the TiAl alloy member and the first intermediate material. A method for joining a TiAl alloy member and a structural steel material, wherein the joining is performed so as to form an intermediate material layer.

(3) A joined part of a TiAl alloy member and a structural steel material, wherein the TiAl alloy member and the structural steel material are joined by the method (1) or (2). (4) The joining component according to (3), wherein the TiAl alloy member is a turbine wheel, and the structural steel material is a steel shaft. (5) The TiAl alloy member has an atomic percentage of Al: 45-4.
8%, Nb: 5 to 9%, Cr: 1 to 2%, Si: 0.2
0.5%, Ni: 0.3-2%, Y: 0.01-0.
(3) characterized in that it is a TiAl alloy member containing 0.05%, with the balance being Ti and unavoidable impurities.
Or the joined component of (4).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an atomic% Ti: 50%,
Al: TiAl alloy member containing 50% as a basic component and SC
M435: a method for joining with structural steel such as SNCM439, for example, TiA in a small turbocharger
The present invention is applied to, for example, joining of a turbine wheel made of an alloy and a shaft made of structural steel. This method is also applicable to a small turbine disk such as a gas turbine or a supercharger, or a joint between a small turbine rotor and a shaft. For the sake of simplicity of description, the T
An example of joining a turbine wheel made of an iAl alloy to a shaft made of structural steel will be described.

[0012] Even if the TiAl alloy member and the structural steel material are directly joined by friction welding, cracks occur after the joining, and a joint cannot be formed. Therefore, in the case of such joining, an intermediate material having good joining properties with the TiAl alloy is used. In the method (1) of the present invention, the coefficient of thermal expansion is smaller than that of a normal metal material, and the TiAl alloy (coefficient of thermal expansion:
An alloy having a coefficient of thermal expansion (8 to 10 × 10 ⁻⁶ / ° C. at room temperature to 600 ° C.) equivalent to 9 to 11 × 10 ⁻⁶ / ° C. at room temperature to 600 ° C. is used. Examples of such alloys include Incoloy 909, Incoloy 903, Incoloy 907 (all trade names). Table 1 shows the compositions of these alloys. By using such a material as the intermediate material, it is possible to prevent the occurrence of thermal stress due to the difference in the coefficient of thermal expansion between the TiAl alloy member and the intermediate material, which is one of the problems in the prior art.

[0013]

[Table 1]

In the method (1) of the present invention, in addition to the selection of the material of the intermediate material, a convex portion is formed on one surface of the joining surface between the TiAl alloy member and the intermediate material, and a concave portion is formed on the other surface. Then, the joining of the TiAl alloy member and the intermediate material is performed by friction welding in a state where the surface on which the convex portions are formed and the surface on which the concave portions are formed abut against each other. By doing so, the shape of the joining interface between the TiAl alloy member and the intermediate material does not become a straight line perpendicular to the central axis when viewed in a cross-sectional view parallel to the central axis. Crack growth from the defect can be suppressed. In addition,
It is not always necessary to fit the convex portion and the concave portion formed on each joint surface in a state where there is no gap, and if friction welding is performed in a state where the surface where the convex portion is formed and the surface where the concave portion is formed are abutted. , And the TiAl alloy member and the intermediate material are plastically deformed to form a complete close contact surface. In this case, the joining interface can be joined so as to take various shapes. As a preferred example of the joining, as shown in an example in which the turbine wheel 1 and the shaft 2 are joined via the intermediate member 3 in FIG. The shape of the interface is 20 to 70 of the diameter of the cross section perpendicular to the axis.
%, Preferably a central portion corresponding to 30 to 50% is a straight line parallel to the plane perpendicular to the axis, and the outer part thereof is inclined at 20 to 40 °, preferably about 30 ° from the plane perpendicular to the axis. There is. Further, as another preferred shape, as shown in an example in which the turbine wheel 1 and the shaft 3 are joined via the intermediate member 3 in FIG. 2, the shape of the joining interface is a straight line parallel to a plane perpendicular to the axis. 20 to 7 of diameter of section perpendicular to axis
There is a step-like shape in which a step having a height of about 20 to 50% of the joint diameter is provided between a central part corresponding to 0%, preferably 30 to 50% and an outer part thereof.

As described above, by not making the joining interface with the TiAl alloy straight, but making it inclined, for example, at an angle of about 30 °, or stepped, it is possible to be sensitive to surface defects, which is one of the problems of the prior art. Can be avoided. That is, even if there is a defect on the surface of the joint and a bending moment is generated on the axis, in the case of FIG. 1, the crack propagation direction due to this stress is different from the direction of the brittle joint interface. It has the advantage that cracks are less likely to propagate compared to technology joints. In addition, in the case of FIG. 2, the initial crack growth starting from the surface defect is the same as that of the conventional technique, but since the crack growth is stopped at the step portion,
There is an advantage that it does not lead to breakage. In any case, the joining of the intermediate member 3 and the structural steel material constituting the shaft 2 may be performed by a normal joining method such as electron beam welding.

In the method (2) of the present invention, the first intermediate material, which is the main intermediate material, has a smaller thermal expansion coefficient than that of the ordinary metal material, and is at least about 600 ° C. as in the case of the method (1). Up to a TiAl alloy (coefficient of thermal expansion: 9 to 11 × 10 ⁻⁶ / ° C. at room temperature to 600 ° C.) (8 to 10 × 10 ⁻⁶ / ° C. at room temperature to 600 ° C.) use. The TiAl alloy member and the first and second intermediate materials are further embedded in a state where a recess is provided at the center of the surface of the first intermediate material on the side in contact with the TiAl alloy and the second intermediate material made of a material having high toughness is embedded. Are joined by friction welding to form a second intermediate material layer between the TiAl alloy member and the first intermediate material. As the second intermediate material, a material having toughness such as Ti, Ni, and Cu and having a high-temperature strength up to about 500 ° C. can be used.
Ti or Ni which does not form an embrittlement phase at the interface with the Al alloy is preferable.

FIGS. 3 and 4 show specific examples of the joining method according to this method. In this example, as shown in FIG. 3, a concave portion is provided at the center of the surface of the first intermediate member 4 which is in contact with the turbine wheel 1, and friction welding is performed with the second intermediate member 5 embedded.
During the friction welding, the second intermediate member 5 is extruded to the joint interface,
As shown in FIG. 4, a thin layer of the second intermediate member 5 is formed at the bonding interface. The thickness of the layer of the second intermediate material 5 is about 20 to 50% of the diameter of the joint before joining. In addition, the concave portion in which the second intermediate member 5 is embedded may be formed on the surface of the turbine wheel 1, but is preferably provided in the first intermediate member from the viewpoint of ease of processing and the like. Also in this example, the first intermediate material 4
The joint between the shaft and the structural steel material constituting the shaft 2 may be made by a normal joining method such as electron beam welding.

By using the above-mentioned material as the first intermediate material, the thermal expansion coefficient between the TiAl alloy member and the intermediate material, which is one of the problems in the prior art, as in the above method (1), Can be prevented from being generated due to the difference in the thermal stress. Since the second intermediate material after joining becomes thin, the thermal stress generated between the second intermediate material and the TiAl alloy and between the second intermediate material and the first intermediate material is small enough to cause no problem. Also, the shape of the bonding interface in this example is a straight line perpendicular to the central axis as in the prior art. However, since the bonding portion is filled with the tough second intermediate material, Even when there is a defect on the surface, the crack growth is suppressed because the resistance to crack growth (K _IC ) is large. Although the high-temperature strength of the second intermediate material is lower than that of the TiAl alloy, the temperature of the joining portion is as low as 500 ° C. or less in a small turbocharger.
There is no problem if it has a high-temperature strength up to about 0 ° C.

The present invention can be applied to any TiAl alloy containing various additive components based on the TiAl phase. However, when the present invention is applied to a small turbocharger, the present invention is applied to a small turbocharger turbine wheel. The temperature at the tip of the blade is much higher than that at the joint, and reaches up to about 850 ° C for diesel engines and up to about 950 ° C for gasoline engines. It is desirable that the material has excellent high-temperature strength. As a TiAl alloy having such excellent characteristics, Al: 45 to 48% in atomic%, Nb: 5 to 9%, C
r: 1-2%, Si: 0.2-0.5%, Ni: 0.3
~ 2%, Y: 0.01-0.05%, the balance being T
There is a TiAl alloy consisting of i and unavoidable impurities. The joining part which is joined to the steel shaft by the method of the present invention using this TiAl alloy turbine wheel is lightweight, has high joining strength, and has excellent performance as a joining part to be incorporated in a small turbocharger.

[0020]

According to the method of the present invention, a TiAl alloy member and a structural steel material can be joined with high strength and high reliability. Such a method of the present invention comprises:
It is particularly suitable for joining a turbine shaft made of TiAl alloy and a steel shaft used for a small turbocharger. The joining part of the TiAl alloy member and the structural steel material obtained by the method of the present invention is characterized in that at the joining interface between the TiAl alloy member and the intermediate material, the fatigue fracture or joining of the joint due to the thermal stress load due to the difference in the coefficient of thermal expansion. It has excellent reliability without the risk of breakage of the joint due to crack propagation starting from the defect of the part. In particular, a joint part for a small turbocharger in which a turbine wheel made of a TiAl alloy having a specific composition and a steel shaft are joined by the method of the present invention has a lightweight, high-temperature strength, high reliability, and excellent characteristics. ing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the shape of a bonding interface in one embodiment of the method (1) of the present invention.

FIG. 2 is a sectional view showing the shape of a bonding interface in another embodiment of the method of the present invention (1).

FIG. 3 is a sectional view showing a state before joining in one embodiment of the method of the present invention (2).

FIG. 4 is a sectional view showing the shape of a joining interface after friction welding in the state of FIG. 3;

FIG. 5 is a cross-sectional view showing a configuration example of a wheel of a turbocharger joined by a conventional method.

FIG. 6 is a cross-sectional view showing another configuration example of a turbocharger wheel joined by a conventional method.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02B 39/00 F02B 39/00 U // B23K 103: 24

Claims (5)

[Claims] 1. A method for joining a TiAl alloy member and a structural steel material using an intermediate material, wherein Ti is used as the intermediate material.
An alloy having a coefficient of thermal expansion equivalent to that of an Al alloy is used, and a convex portion is formed on one surface and a concave portion is formed on the other surface of the joining surface between the TiAl alloy member and the intermediate material. A method of joining a structural steel material to a TiAl alloy member, wherein the joining with the material is performed by friction welding in a state where the surface on which the convex portion is formed and the surface with the concave portion are abutted. 2. A method of joining a TiAl alloy member and a structural steel material using an intermediate material, wherein an alloy having a thermal expansion coefficient equivalent to that of the TiAl alloy is used as a first intermediate material.
Further, a concave portion is provided at the center of at least one of the opposing surfaces of the TiAl alloy member and the first intermediate material, and the second intermediate material made of a high toughness material is embedded in the concave portion. The first and second intermediate members are friction-welded to form a second intermediate member between the TiAl alloy member and the first intermediate member.
A method for joining a TiAl alloy member and a structural steel material, wherein the joining is performed so as to form an intermediate material layer. 3. The method according to claim 1, wherein
A joined part of a TiAl alloy member and a structural steel material, which is formed by joining an Al alloy member and a structural steel material. 4. The joint component according to claim 3, wherein the TiAl alloy member is a turbine wheel, and the structural steel material is a steel shaft. 5. The method according to claim 1, wherein the TiAl alloy member is Al:
45 to 48%, Nb: 5 to 9%, Cr: 1 to 2%, S
i: 0.2-0.5%, Ni: 0.3-2%, Y: 0.
5. The joint component according to claim 3, wherein the component is a TiAl alloy member containing 0.01 to 0.05%, with the balance being Ti and unavoidable impurities. 6.