JPS6242706B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for joining heat-resistant superalloys using a brazing filler metal.

[Prior Art] In general, heat-resistant superalloys such as iron-based, Ni-based, or Co-based superalloys contain reinforcing elements that are easily oxidized in their components in order to obtain high high-temperature strength. For example, Ni-based strong precipitation type alloys obtain high high-temperature strength through precipitation hardening of the γ' phase (mainly composed of the intermetallic compound Ni ₃ (Al, Ti)), and therefore have extremely poor bondability.

A common joining method is fusion welding, but cracks tend to occur during welding work or the subsequent heat treatment process, making it difficult to achieve sound welding. Additionally, there are many cases where fusion welding cannot be performed due to structural reasons.

Vacuum brazing, diffusion bonding, etc. have traditionally been used as bonding methods other than fusion welding. In the case of vacuum brazing, the common method is to use Ni or Pd brazing filler metal as specified by JIS or ASTM, which has many advantages such as being simpler than fusion welding. Used in some parts. However, it has a fundamental drawback of low high-temperature strength, which limits its range of use considerably. On the other hand, as a bonding method with excellent high-temperature strength, there is, for example, a diffusion bonding method. This method involves directly pressurizing and heating the base materials to join them in a solid state, or by inserting a thin metal foil into the gap between the base materials and diffusing it into the base material to homogenize the structure. There are various methods such as the TLP method, but for any method, it is essential that the interface between the base materials to be joined be sufficiently clean and that the finishing accuracy be strict. Furthermore, a long time is required for the diffusion treatment of the bonded portion.

Another method for obtaining excellent high-temperature strength is to improve the high-temperature strength of the brazing filler metal itself. this is
This method uses a brazing filler metal containing age-hardening elements such as Ti and Al, and is said to provide excellent high-temperature properties close to the strength of the base material. On the other hand, however, the brazing filler metal is extremely susceptible to oxidation during the brazing process, making the joining work more difficult than when using a brazing filler metal that does not contain elements that are easily oxidized, such as Ti and Al.

[Problems to be Solved by the Invention] As described above, several joining methods have been devised that provide excellent high-temperature strength, but all of them require extremely sophisticated joining techniques. Furthermore, if oxidation of the base metal interface or the brazing material cannot be sufficiently prevented during the joining process, a sound joint cannot be obtained and the strength will naturally decrease. Therefore, it is not easy to obtain a highly reliable joint.

[Means for Solving the Problems] In the present invention, when joining base materials of Ni-based heat-resistant superalloys, the initial gap is set to 0.1 mm to 0.9 mm, and 3 to
A Ni-based brazing filler metal containing 9% B is interposed between the base materials, and the base metal is heated to a temperature higher than that at which the surface of the base metal melts when it comes into contact with the molten brazing filler metal, thereby melting the brazing filler metal and joining the base materials. The planned surface is eroded by 0.015 mm or more, and the base metal and filler metal are fused together, and the joint where the strengthening elements contained in the base metal are distributed remains even after the temperature has cooled down. It is characterized in that it is formed between the two base materials so that the base materials are joined to each other through this joint portion.

Further, in the present invention, a strengthening heat treatment is further performed as necessary.

[Function] In the present invention, a Ni-based brazing material containing B is interposed between the Ni-based heat-resistant superalloy (base material) to join the two base materials, but the brazing material is melted by heating. , it also melts the bonding interface of the base metal. With this melting, the melt composition of the brazing filler metal approaches the composition of the heat-resistant superalloy. In this way, in the present invention,
The following series of reactions: melting of the brazing filler metal, penetration of the base metal interface to a predetermined depth or higher, liquid-phase diffusion of melted components, rapid shift of the melt composition to the base metal composition, solidification of the melt, and so on. Through the process, the bonding between the base materials is completed through a joint formed by distributing the reinforcing elements contained in the base materials. The bonded portion remains between the base materials even after bonding is completed (temperature decrease). This joint does not disappear even when subjected to strengthening heat treatment.

As described above, in the present invention, a new joint (joint layer) is basically created and left between base materials by liquid phase diffusion using a specific brazing material. Therefore, (a) This joint contains reinforcing elements distributed from the base material, and unlike the conventional soldering layer,
High temperature strength.

(b) Since the surface of the base material is melted, even if there is an oxide film on the surface of the base material, it will be melted and removed.

(c) Therefore, as in the TLP method, it is not necessary to clean the interface of the base materials to be joined or to maintain the surface with high finishing accuracy. Furthermore, since the joint (interlayer between base materials) itself has high strength, it is not necessary to perform a long diffusion treatment (solid phase diffusion treatment) to eliminate the interlayer between base materials as in the TLP method.

(d) The brazing material itself does not contain easily oxidizable elements such as Ti and Al, and is extremely easy to process during the brazing process.

The following effects are achieved.

[Supplementary explanation of means] The heat-resistant superalloy joined by the present invention is a known
It is Ni-based. Strengthening elements contained in this Ni-based heat-resistant superalloy include Al, Ti, Mo, W, Nb,
Examples include Ta.

In other words, the strengthening mechanism of heat-resistant superalloys is as follows:
Broadly speaking, there are two types:

One is through a precipitation hardening mechanism.
This creates intermetallic compounds such as Ni ₃ Al and Ni ₃ Ti in the material to strengthen it at high temperatures, and the strengthening elements include Al and Ti. Another strengthening mechanism is through a solid solution strengthening mechanism. This strengthens the entire matrix by dissolving elements in the matrix, and examples of strengthening elements include Mo, W, Nb, and Ta.

The brazing filler metal used in the present invention should be an alloy of the same base as the base metal to be joined, and it should also contain B, an interstitial element with an extremely large diffusion constant, as the main melting point-depressing element. Yes, but
There is no problem even if it additionally contains substituted melting point lowering elements such as C, P, Si, and Mn.
Any brazing filler metal may be used as long as it satisfies these conditions, and there are no restrictions on other alloy components. Therefore, certain types of known brazing materials can be used as they are in the present invention. For example, in joining Ni-based heat-resistant superalloy members, brazing filler metals BNi-2, BNi-7, etc. specified by JIS can be used. As mentioned above, these brazing fillers are made of Ti, Al
It is easy to handle because it does not contain reinforcing elements that are easily oxidized.

In addition, in the present invention, in order to make the melting amount of the base metal appropriate, the B content of the brazing filler metal is 3 to 9.
% (weight).

In order to reliably and uniformly melt all the interfaces of the base metals to be joined, the penetration depth of the base metal interface layer should be at least 0.015 mm or more. Experimental studies have shown that the base metal interface tends to melt selectively along grain boundaries, so if the penetration depth is less than 0.015 mm, unmelted parts may remain. It became clear. The penetration depth of the base metals is controlled by the initial gap between the two base metals to be joined, the B element content in the brazing filler metal, the heating temperature, and the heating time. That is, as the initial gap increases, the penetration depth also increases. In order to ensure a penetration depth of 0.015 mm or more, in addition to adjusting the combination of base metal and filler metal, the initial gap must be adjusted appropriately, that is, the initial gap is larger than that of conventional joining methods. It is important to do so.

This is because a large amount of brazing filler metal is required to melt the bonding interface of the base metal sufficiently deeply. General vacuum brazing requires a narrow gap of 0.1 mm or less, but the joining method of the present invention requires an initial gap of 0.1 mm or more, and even if the initial gap is widened to 0.9 mm, it will still work well. Shear strength is obtained.

As mentioned above, the appropriate B content in the brazing filler metal is 3 to 9%. Further, the bonding temperature is preferably 1100° C. or higher, and a holding time of about several minutes at that temperature is sufficient. In addition, in the present invention, it is essential to uniformly melt the interface layer of the base material, so it is desirable to bond at the highest possible temperature range without damaging the base material. For example, the soldering temperature of BNi-2 used in the examples below is 1010 to 1175.
℃, but in the case of Example 1, bonding was performed at 1150°C (held for 5 minutes), which is close to the upper limit.

As mentioned above, the joining method of the present invention has the major feature that good joining performance can be obtained even when the initial gap is wide (0.9 mm or less), and therefore high finishing accuracy is not required. . Therefore, in addition to simply joining two planes facing each other, we can also join curved parts,
It is also possible to easily join the fitting members. FIG. 4 shows an example of such a joint, which is a double-layer blade for a turbomachine. In Figure 4, 1 is the blade root body, 2
is a core, and the part 3 to be joined has a crushed cylindrical shape.

The joining method is as follows. The gap between the blade base body made of Ni-based superalloy IN738 and the core made of Halosteroy X is approximately 0.3 mm.
BNi-2 was added as a brazing material, bonding conditions were 1150℃
It was held for 5 minutes. Once cooled, a strengthening heat treatment was performed at 1130°C for 2 hours to further strengthen the material. This core has fine cooling holes in its front surface, which serve as passages for cooling air flowing in from the lower part of the blades. Due to the presence of this core, the inside of the blade is efficiently cooled, the temperature of the entire blade is prevented from increasing, and the performance of the blade can be maintained.

The high temperature of the turbine blades etc. shown in this example,
For rotating equipment, reliability of joints is extremely important. That is, one turbine has several hundred blades, and if one of these blades is poorly connected, the turbine will be destroyed. Therefore, the reliability of the joint is extremely important. Incidentally, when conventional bonding methods are used, unless extremely sophisticated surface cleaning treatment is applied, a thick oxide film layer remains at the bonding interface of the base materials, and this area becomes an unbonded area and fails to bond. This may cause damage to the parts and decrease in strength. This unattached layer is the main cause of variations in strength and reduces reliability.

On the other hand, when the method of the present invention is adopted,
Since the interface between the base materials is melted, there is no oxide film, and the bonding strength and reliability are greatly improved.

In the present invention, when a precipitation hardening type base material is joined, the high temperature strength can be further improved by performing a heat treatment similar to the strengthening heat treatment of the base material as necessary. When the strengthening heat treatment is performed, among the elemental components, the diffusion of component B, which is already contained in a large amount in the brazing filler metal and whose purpose is to melt the base material, into the base material is promoted. For this reason, strengthening occurs as the melting point of the joint increases, but since the diffusion rate of substances other than B in the joint metal part itself is extremely slow,
It does not disappear through this strengthening heat treatment. Further, the shear strength can be significantly improved by performing solution treatment and aging treatment in accordance with the heat treatment conditions of the base material after bonding.

[Example] The present invention will be explained in further detail by showing examples below.

JIS BNi-2 was used as a brazing material to join Ni-based superalloy IN738 specimens. Figure 1 shows the results of investigating the relationship between the initial gap at the bonding interface and the penetration depth of the base metal interface layer. In addition, the bonding conditions are
The temperature was maintained at 1150° C. for 5 minutes in a vacuum of 10 ⁻⁴ torr. Further, the temperature increase rate was 300°C/min, and the temperature decrease rate was also the same.

From Figure 1, if the initial gap is set to 0.1 mm or more,
The penetration depth of the base metal is 0.015 mm or more, which indicates that a good bonding interface can be obtained.

Example 2 An IN738 test piece and a Hastelloy X test piece were bonded under the same bonding conditions as in Example 1. The measurement results of the room temperature shear strength in this case are shown in FIG. 2 (white circles in FIG. 2).

As shown in the figure, when the initial gap becomes 0.1 mm or more,
It was observed that the room temperature shear strength increased significantly, especially at an initial gap of 0.2 to 0.4 mm. (As mentioned above, this is because the base metal penetration depth has become sufficiently large.) Example 3 In Example 2, after completion of bonding, solution heat treatment was performed at 1130°C for 2 hours, which was the same as the heat treatment conditions for the base metal. and
Aging heat treatment was performed at 843°C for 24 hours. Second result
Indicated by black circles in the figure.

As a result, it was found that even higher room temperature shear strength than in Example 2 was exhibited. Further, as in Example 2, it was also observed that the room temperature shear strength increases when the initial gap is 0.1 mm or more, and particularly, the strength is extremely high at an initial gap of 0.2 to 0.4 mm.

In addition, in both Examples 2 and 3, the initial gap was 0.3 mm.
The highest intensity was obtained before and after.

In addition, in Examples 2 and 3, the initial gap was set to 0.3
High-temperature shear strength was measured when the mm was constant. The results are shown in FIG. Figure 3 shows that the shear strength gradually decreases as the test temperature increases, but the test specimens subjected to solution treatment and aging treatment
It is recognized that even at 800°C, a high value of 30 Kg/mm ² or more can be obtained. Furthermore, although FIG. 3 shows the high-temperature strength of Hastelloy X, which is one of the base materials, as a comparison material, it is recognized that all the materials of the present invention have higher strength than Hastelloy X. Incidentally, there have been no examples of heat-resistant brazing using such a brazing filler metal in which high bonding strength as described above has been achieved.

Example 4 Brazing filler metal with B content of 3.0%, 4.4%, and 8.7%
Using a Ni-6%Cr-6%Si-B alloy, welded the base material (IN 738 alloy) with an initial gap of 0.1mm at a joining temperature of 1110 to 1250°C. The penetration depth of the base metal was measured (other conditions were the same as in Example 1, and the joining temperature was 300℃/
Increase the temperature for 5 minutes, hold each bonding temperature for 5 minutes,
Thereafter, the temperature was lowered at a rate of 300°C/min. ). The results are shown in Figure 5.

As mentioned above, in the present invention, it is essential to melt the interface layer of the base material above a certain limit, so it is necessary to control this amount. It is recognized that the weld depth of the base metal can be easily adjusted by using or changing the bonding temperature.

Furthermore, as shown in Fig. 5, the lower the B content, the smaller the penetration depth of the base metal, and when the B content is less than 3%, sufficient bonding cannot be achieved at a temperature of 1100°C or higher. It is also recognized that high-temperature bonding may become necessary.

[Effect] Conventionally, localized melting of the interface layer of the base metal was called corrosion and was considered a type of soldering defect, but in the present invention, by uniformly melting the interface layer above a certain limit, the following effects can be achieved: Four remarkable effects have been obtained.

The first effect is that the oxide film and impurities present on the surface of the base material are removed, and the wettability between the base material and the brazing metal is significantly improved, resulting in a highly reliable joint. The second effect is that as the molten base metal surface layer and brazing metal fuse, the reinforcing elements contained in the base metal are distributed to the joint, and as a result, the joint is significantly strengthened. It is. Furthermore, as a third effect, an improvement in high-temperature strength is expected due to an increase in the melting point of the joint due to fusion with the surface layer of the base material. (As the base material surface layer fuses, the proportion of melting point lowering elements in the brazing filler metal decreases, and as a result, the melting point of the newly formed joint increases.
High temperature strength is proportional to the melting point of the material, and the higher the melting point, the higher the strength. ) The fourth major advantage of using the joining method of the present invention is that the initial gap between the two base materials to be joined can be made larger than that required in conventional vacuum soldering or diffusion joining. . In other words, joints that generally have a curved surface other than a flat or cylindrical surface are
It is extremely difficult to perform finishing processing to maintain a gap of 0.1 mm or less, but with the present invention, the gap is 0.1 mm or less.
Finishing of the joint is extremely easy as wide gaps such as 0.9 mm are allowed. As described above, the present invention has the great advantage of being suitable for joining members having complicated joints.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the initial gap at the base metal interface and the penetration depth of the base metal in joining according to the present invention, Figure 2 also shows the relationship between the initial gap and shear strength, and Figure 3 shows the temperature versus shear strength at the same joint location. Show the impact of Figure 4 shows an application example of this joining method, where a is a longitudinal cross-sectional view and b is a vertical cross-sectional view.
is the X,X cross section of a, 1 is the turbine blade body, 2
is the core, and 3 is the joint part. Figure 5 shows the initial gap of 0.1mm.
A curve showing the relationship between welding temperature and base metal penetration depth in the case of .

Claims (1)

[Claims] 1. When joining base materials of Ni-based heat-resistant superalloys, the initial gap is 0.1 mm to 0.9 mm, and 3 to 9% B
A Ni-based brazing filler metal containing Ni is interposed between the base metals and heated to a temperature higher than that at which the surface of the base metal melts upon contact with the molten brazing filler metal, melting the brazing filler metal and reducing the surface of the base metals to be joined by 0.015 mm or more, and as a result, the base metal and brazing metal are fused, and the joint where the reinforcing elements contained in the base metal are distributed remains in the joint even after the temperature cools down. 1. A method for joining Ni-based heat-resistant superalloys, characterized in that a bond is formed between both base materials, and the two base materials are joined via this joint. 2 When joining base materials of Ni-based heat-resistant superalloys, the initial gap is set to 0.1 mm to 0.9 mm, and 3 to 9% B
A Ni-based brazing filler metal containing Ni is interposed between the base metals and heated to a temperature higher than that at which the surface of the base metal melts upon contact with the molten brazing filler metal, melting the brazing filler metal and reducing the surface of the base metals to be joined by 0.015 By eroding more than mm,
A base metal and a brazing metal are fused, and a joint is formed between the two members so that the joint remains even after the temperature is lowered, and the reinforcing elements contained in the base metal are distributed.
A method for joining Ni-based heat-resistant superalloys, characterized in that after the two base materials are joined through this joint, a strengthening heat treatment is performed.