JPH04100682A - Diffusion joining method for alpha+beta type titanium alloys - Google Patents

Abstract

PURPOSE:To form coarse grains or layer structure and to improve damage admissibility for a joining defect by performing diffusion joining with material containing beta phase forming elements put between the joining faces of the alpha+beta type alloys and increasing a rate of beta phase in the vicinity of the joining interfaces at the joining temperature. CONSTITUTION:When heating and pressurizing are performed with the material 6 containing the beta phase forming elements (Ni, Fe, V, etc.) put between the joining interfaces 3, the beta phase forming elements are diffused to main phases 1 and 2 in the vicinity of the joining interfaces at the joining temperature and the rate of beta phase in the vicinity of the joining faces increases. Consequently, while the joining temperature being maintained, only the vicinity of the joining faces is formed into the coarse grains or layer structure locally and the structure where breakdown or crack propagation with the joining defect 5 as the starting point is hardly generated is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of diffusion bonding of α+β type titanium alloys, and particularly to a method of diffusion bonding of the same alloys that yields a joint with improved strength characteristics.

[Conventional technology]

Diffusion bonding of titanium alloys is performed by smoothing the joining surfaces 3 of the materials 1 and 2 to be joined, as shown in Figure 2 (a), directly overlapping the surfaces of the materials 1 and 2, and then bonding them in a vacuum or inert gas. Is going.

Diffusion bonding conditions vary slightly depending on the material, but are generally as follows.

Temperature: 900℃, bonding load: 0.3 kgf/mm'
Holding time: 2 hours [Problem to be solved by the invention] Diffusion bonding of α+β type titanium alloys is carried out at a temperature where the proportion of β phase does not exceed 50% to prevent coarsening of the structure during holding at the joining temperature. As shown in Fig. 2, etc., both the base metal part and the joint part 4 have a fine, uniform glaze grain structure that is almost the same as that before joining. Although this fine equiaxed grain structure has excellent strength, ductility, and fatigue strength, it is unfavorable from the viewpoint of fracture toughness and crack propagation characteristics (resistance). It has the disadvantage of being susceptible to destruction and crack propagation.

The present invention is within the above-mentioned state of the art and provides a diffusion bonding method for alpha+beta type titanium alloys that does not cause destruction or crack propagation at the bonded portion.

[Means to solve the problem]

In order to improve fracture toughness and crack propagation characteristics, it is preferable to form a coarse-grained or layered structure, and in order to form such a structure, heating and holding at a temperature where the proportion of β phase exceeds 50% is sufficient. . Therefore, it is possible to obtain a coarse grained or layered structure by increasing the joining temperature or by heating and holding at a high temperature after joining, but in this case, it is possible to obtain a coarse grained or layered structure. becomes a coarse grain or layered structure, which in turn causes a decrease in the static strength and ductility of the entire part.

Based on this, the present inventor developed a coarse grain or layered structure only in the vicinity of the bonding interface where defects exist without increasing the bonding temperature, and the material composition was changed to β only in the vicinity of the bonding part.
It occurred to me that it would be better to increase the ratio of the phases.

The present invention is based on the above findings, and includes:
By sandwiching a material containing a β-phase forming element between the joint surfaces of the α+β type titanium alloy to be joined and performing diffusion bonding, increasing the proportion of β phase near the joint interface at the joining temperature, the fracture toughness and This is a diffusion bonding method for α+β type titanium alloys, which is characterized by forming coarse grains and a layered structure with excellent crack propagation characteristics to improve damage tolerance against bonding defects.

[Effect]

Beta phase forming elements (for example, Ni, Fe) at the bonding interface.

When a material containing V, etc.) is sandwiched and heated and pressurized, the β phase-forming elements diffuse into the parent phase near the bonding interface at the bonding temperature, increasing the proportion of the β phase near the bonding surface.

As a result, only the vicinity of the bonding surface becomes locally coarse grained or layered while being held at the bonding temperature, resulting in a structure in which fracture or crack propagation originating from a bonding defect is difficult to occur.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

Ti-6Ai4V, a typical α→-β type titanium alloy
The alloy is heated at 900°C in vacuum (or in an inert gas) at 0.
．． Diffusion bonding is performed under the conditions of 3 kgf/mm for 22 hours.

Since this material has a β phase ratio of approximately 40% at 900°C, the growth of crystal grains during bonding is small (the bonding temperature condition of 900°C is set as the temperature at which there is little structural change). From this, the structure after bonding is the same as the above-mentioned second structure.
As shown in Figure (b), both the base material and the four bonding interfaces have fine glaze grains, and have excellent static strength characteristics.
A fine equiaxed grain structure is unfavorable from the viewpoint of fracture toughness and crack propagation characteristics, and if a bonding defect 5 exists, fracture or crack propagation is likely to occur from this as a starting point.

For this reason, in the embodiment of the present invention, as shown in FIG. By performing diffusion bonding, only the vicinity of the bonding interface 4 was formed into a coarse-grained or layered structure with excellent fracture toughness and crack propagation characteristics, as shown in FIG. 1(b).

In this example, Ni deposited on the bonding surface of the members to be bonded diffuses into the matrix at the bonding temperature, and β
Although the phase ratio is increased to form a coarse grain or layered structure, any β phase-forming element (Fe, V, etc.) can be used as the vapor deposition material, and alloys containing these elements can also be used. (contains amorphous). Further, it is not limited to vapor deposition, but it is also possible to use a plating method or a foil material, and these filler metals may be in a solid phase state or in a liquid phase at the bonding temperature.

〔Effect of the invention〕

Coarse grains and layered structures formed near the joint interface have superior fracture toughness and crack propagation characteristics compared to equiaxed microstructures, so fractures and crack propagation starting from joint defects do not occur. damage tolerance against bonding defects is greatly improved.

Materials with a coarse structure tend to have lower strength than those with a fine structure, but since the coarse grains near the joint interface in the present invention are made of a β-rich heat treatable material, it is necessary to If heat treatment is performed in accordance with the above, the strength of the joint can be made higher than the matrix strength, and in this case, a joint with excellent static strength characteristics and dynamic strength characteristics can be obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an embodiment of the present invention, (a) shows a schematic diagram of the structure before bonding, (b) shows a schematic diagram of the structure after bonding, and Fig. 2 is an explanatory diagram of a conventional diffusion bonding method. , (a) before joining, et al.
shows a schematic diagram of the structure after joining.

Claims (1)

[Claims] There is a β
A diffusion bonding method for α+β type titanium alloys, which is characterized by performing diffusion bonding by sandwiching materials containing phase-generating elements, and increasing the proportion of the β phase near the bonding interface at the bonding temperature.