JPH0329516B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a diffusion bonding method using a metal or alloy insert material between bonding members, and particularly to a diffusion bonding method suitable for stabilizing diffusion bonding and increasing bonding strength. Diffusion bonding of metals is generally a bonding method that is performed under vacuum or an inert atmosphere by applying a pressure that does not cause deformation of the material at a temperature below the solidus line. The biggest feature of this diffusion bonding method, compared to the conventionally widely used fusion welding and brazing methods, is that there is little thermal or phase change in the bonded area and its vicinity, and properties comparable to those of the base metal can be obtained. be. Since the purpose of joining two metals is to create a metallic bond between them, the joining surfaces must be clean and flat. Further, even if excellent cleaning is used, organic substances, gases, oxides, etc. are adsorbed and not only hinder diffusion, but also remain at the bonding interface, which tends to cause a decrease in bonding strength. Therefore, various countermeasures have been taken against these harmful effects. One method is to interpose an insert material between the joining members, melt the insert material to bring the joining surfaces into close contact, and then use a diffusion process to average out the mutual components of the base material and the insert material. The so-called liquid phase diffusion bonding method is known (Japanese Patent Application Laid-Open No. 47-33850,
Special Publication No. 49-6470). These methods have been applied to heat-resistant superalloys, particularly Ni-based, Co-based, Fe-based superalloys, etc., which are formed by precipitating the γ″ phase, which is the root of the strengthening mechanism, and have achieved considerable results. , this kind of heat-resistant superalloy plays the main role in the formation of the γ″ phase.
Since it contains a large amount of Al and Ti, the bonding surface is easily oxidized, and oxides may remain on the bonding surface. If oxide remains, there is a risk that the bonding surface will easily break due to the weak oxide becoming a starting point. Furthermore, since it contains a large amount of elements with low diffusion rates, it is not possible to shorten the bonding time considering the liquid-phase diffusion between a liquid and a solid. Furthermore, there is still room to improve the size and distribution of the γ'' phase and crystal grains in and around the joint to increase the joint strength. To provide a diffusion bonding method capable of increasing the bonding strength by dispersing the insert material, melting the insert material early, and speeding up the subsequent diffusion to uniformly refine the structure of the bonded portion and its vicinity. The present invention relates to a diffusion bonding method in which an insert material is interposed between members to be joined made of a precipitation hardening Ni-based superalloy containing Al and Ti, and the members are joined by heating and pressurizing in a non-oxidizing atmosphere. Amorphous insert material containing B and Si with the same composition as Ni-based superalloy
Formed from a Ni-based alloy, the joint surfaces between the members to be joined are heated and pressurized, and while the insert material is melting, ultrasonic vibrations of at least 3500 VPM are applied to the joint surfaces, and then heated and held at a predetermined temperature to diffuse. After joining, the structure is such that solution treatment and aging treatment are performed. The present invention will be explained in more detail below. In the present invention, a heat-resistant alloy, general carbon steel, alloy steel, etc. can be used for the joining member. As heat-resistant alloys, γ″ phase precipitation strengthened super heat-resistant alloys (Co-based, Ni
It is particularly effective for materials that require extremely high bonding strength, such as (Fe-based, Fe-based). The insert material can be made of metal or alloy, and its form is powder,
It may be either foil-like or ribbon-like. When a non-membrane ribbon is used as an insert material, in addition to the effect obtained by imparting kinetic energy of metal atoms, the following advantages are provided by the properties of the non-metamorphic ribbon itself. In other words, the first reason is that the non-corrosive ribbon has high bonding strength because it has corrosion resistance, and the second reason is that the non-corrosive ribbon has high bonding strength.
Since it can be made extremely thin and uniform in thickness, the bonding time is short and the bonding strength is high.
Thirdly, since it has high strength, it can be easily manufactured into a shape that can be inserted between joining members, and the operation for inserting it is simple. When an insert material is interposed between joining members and a diffusion bonding process is performed, an arbitrary surface pressure is applied under vacuum or in a protective atmosphere. Ar, Ne, as a protective atmosphere
It is preferable to use an atmosphere of He, H ₂ , CO, etc. In the present invention, in such an atmosphere,
It imparts thermal energy and energy other than thermal energy (hereinafter simply referred to as energy A) for increasing the kinetic energy of metal atoms. Energy A reduces the activation energy of metal atoms and facilitates their movement. Such energy A includes vibration energy, electromagnetic induction energy, high frequency induction energy, and the like. Next, the effect of such energy A will be explained, particularly taking vibration energy as an example. The vibrational energy enhances the motion of the metal atoms, resulting in extremely rapid melting of the insert material compared to the static state. The melting speed of the insert material is related to the adhesion of the joint surfaces, and if the insert material melts slowly, the portion that becomes a liquid phase is small in quantity, so isothermal solidification begins before the melt penetrates to the extreme. There is a risk of Therefore, in order to achieve close contact, it is important that the insert material melts instantly, and in this respect, vibration is extremely effective. Also, when vibration temporarily becomes a liquid phase, it prevents the oxides (especially Al, Ti, and Cr systems) mixed therein from accumulating at the bonding interface, disperses them, and changes the shape of the oxides. It was also discovered that it has the ability to cause division. This greatly reduces the risk that the fragile oxide will become a starting point and break when stress is applied. According to experiments conducted by the present inventors, when joining pure metals, carbon steel, low-alloy steel, etc., the above-mentioned problems are almost non-existent if the insert material does not contain any oxide-forming elements. When a highly oxidizing element is present in the components, the effect of vibration is clear, and almost no oxides are observed on the structure of the bonding interface. Therefore, the insert material contains Al,
The vibration effect is most effective when large amounts of Ti and Cr are included. Applying vibrational energy to the bonding material accelerates the melting of the insert material, so that the melt enters the extreme regions and then solidifies. Therefore, since isothermal solidification is accelerated, the joining process can be performed at a temperature lower than the temperature at which the insert material was melted. This is aimed at preventing the structure and crystal grains in and around the joint from becoming coarse, and is effective for members where joint strength is strictly required. The purpose of applying vibrational energy in addition to thermal energy is to promote early melting and isothermal solidification of the insert material. Therefore, it is not necessary to apply vibrational energy before the insert material begins to melt due to the application of thermal energy and after isothermal solidification is completed. FIG. 1 is a schematic diagram showing temperature, pressure, and vibration timing over time. As shown in Figure 1, the application of vibrational energy is started (t ₁ ) just before the joining temperature T reaches the insert material melting temperature Ti, and it is determined that the molten insert material has acquired the components of the base material and solidification has been completed. It is desirable to stop applying vibrational energy at the time when vibration energy is to be obtained (t ₂ ). This is because if the insert material is subjected to vibration after solidification, there is a risk that the unfinished region at the bonding boundary will be destroyed both in terms of composition and structure. Furthermore, since the destruction of the unfinished area depends on the vibration frequency, amplitude, and excitation position, in order to stabilize the joint strength, the vibration energy must be adjusted according to the constituent components of the joining base material and insert material and the insert melting temperature. The timing of stopping should be selected. The bonding force according to the present invention may be a small load because the bonding force is promoted by vibration. For example, for heat-resistant superalloys, at least 2 Kgf/cm ² is sufficient. However, machining a curved joint surface is more difficult than machining a flat surface, and it is also difficult to obtain surface accuracy. In joining such curved surfaces, in order to ensure the reliability of the strength of the joint, it is advantageous to increase the pressing force from the beginning shortly after the insert material has melted. The reason for this is that the molten insert material fills the void and bonds the surfaces together.
This is because the bonding strength is improved. It also has the effect of discharging excess solution that is not necessary for surface bonding from the bonding surface as burrs. In addition, if the base material and the insert material differ greatly in composition and melting point, or if there is a weak compound remaining at the bonding interface due to a component reaction between the base material and the insert material, In order to discharge excess solution as burrs, it is necessary to increase the pressing force slightly. The timing of secondarily increasing the pressing force is important in order to reliably achieve the above effects. FIG. 2 is a schematic diagram showing the relationship between bonding temperature (insert melting temperature), vibration timing, and pressurization timing over time. As is clear from this figure, the secondary pressurization (P ₂ ) starts after the insert material melts and before the vibration stops, and the effect of the secondary pressurization is not clear at timings other than this. Next, although there are no particular restrictions on the means for exciting vibration energy into the joining base material, ultrasonic waves are substantially preferable. The direction of vibration is not particularly limited either, and good results can be obtained either in a direction parallel to the stress axis (longitudinal vibration) or in a direction perpendicular to the stress axis (transverse vibration). The frequency is preferably 3500 VPM or higher, preferably as high as possible. Note that VPM indicates the frequency of vibration per minute, and 1 VPM corresponds to 1/60Hz. Example Precision casting Ni-based heat-resistant superalloy (Cr; 16% by weight,
Co: 8% by weight, W: 2.5% by weight, Mo: 2% by weight,
Ta: 1.5% by weight, Al and Ti: 3.4% by weight, remaining Ni)
The bonding base material is a non-selective ribbon (non-selective Ni) containing B (3.2% by weight) and Si (2.5% by weight) in the same composition as the bonding material to lower the melting point.
base alloy) was used. In FIG. 3, 1 is a chamber, 2 is a pressure shaft, and the bonding base materials 3 of the above components are mounted on a pressure jig 4 fixed to the pressure shaft 2, and these bonding base materials 3 are The amorphous ribbon 5 was interposed between the curved surfaces. The applied pressure was 0.5 Kgf/cm ² , and heating was started using the heating element 6 under a vacuum of 5×10 ⁻⁴ Torr. The bonding temperature was 1170°C, but after the temperature reached 900°C, the ultrasonic vibrator 7 continued to apply vibrations of 15000 VPM to the bonding material. After that, when the temperature reached 1170℃, the pressure was increased to 1.5Kgf/ ^cm2 , and after 30 minutes determined from the preliminary experiment, the vibration was stopped.
A time bonding process was performed. After bonding, the bonding material was taken out of the furnace body and subjected to solution treatment at 1120°C for 2 hours, then at 840°C for 24 hours.
After aging heat treatment, the microstructure and tensile properties of the joint were investigated. As a result, it was confirmed that the size and distribution of the γ'' precipitated phase at and near the bonding interface were almost the same as the base metal in terms of the microstructure, and that the crystal grains did not become coarse and were rather finer than the base metal. The tensile properties of the joints are shown in Table 1. In Table 1, the comparative examples are the same as the examples except that no vibration energy is applied during the joining process. The Example has excellent tensile properties compared to the Comparative Example, and the improvement in elongation is particularly remarkable.From these results, it is confirmed that the present invention can be fully applied to joining gas turbine rotor blades with complex inner holes. did it.

[Table] As described above, according to this example, by applying thermal energy and ultrasonic energy, early melting of the insert material and promotion of isothermal solidification are promoted, and the dispersion of oxides at the bonding interface is It is possible to obtain a stable and strong joint between the joining member made of a heat-resistant alloy and the insert material under low pressure.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams showing the relationship between bonding time, temperature, pressure, and vibration, and FIG. 3 is a schematic diagram of an apparatus showing an embodiment of the present invention. 3... Bonding base material, 5... Insert material, 6...
Heating element, 7... Ultrasonic vibrator.

Claims (1)

[Claims] 1 An insert material is interposed between the members to be joined made of a precipitation hardening type Ni-based superalloy containing Al and Ti,
In the diffusion bonding method of bonding by heating and pressurizing in a non-oxidizing atmosphere, the insert material is an amorphous material containing B and Si with the same composition as the Ni-based superalloy.
The insert material is made of a Ni-based alloy, and the joining surfaces between the members to be joined are heated and pressurized, and at least
A diffusion bonding method characterized by applying ultrasonic vibration of 3500 VPM, then heating and holding at a predetermined temperature to perform diffusion bonding, followed by solution treatment and aging treatment.