JPS59212188A - Brazing filler metal and use thereof - Google Patents

Abstract

PURPOSE:To provide an inexpensive brazing filler metal for joining which can join a high melting metallic material and graphite to high strength by consisting the same of an eutectic alloy of W or Mo and Zr. CONSTITUTION:A brazing filler metal for joining a high melting metallic material and graphite consists of A W-Zr alloy such as 19% W-Zr eutectic alloy or an Mo-Zr alloy such as 31% Mo-Zr eutectic alloy obtd. as a clean refining alloy by arc melting, etc. Said brazing filler metal is clean and has good wettability as the metal is inert. The metal provides a secure joint layer free from inclusion of oxide and cavity. Production of a composite target for the rotating anode of an X-ray tube in particular is accomplished by embedding the above-mentioned brazing filler metal 6 in the revolving shaft of a W or its alloy or Mo plate 2 and/or the periphery thereon and superposing a graphite base plate 3 thereon, then heating these materials to the temp. higher than the eutectic point of the metal 6 under pressure or static pressure to form a thin joint layer having high strength. The composite target free from the stripping of the joint layer is thus easily and economically obtd.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a brazing material for joining a high-melting point metal material and graphite, and an X-ray tube made of tungsten or its alloy/graphite or tungsten or its alloy/molybdenum/graphite. The present invention relates to the use of the brazing filler metal in a composite target for a rotating anode.

[Background of the invention]

In recent years, devices using members made by bonding high-melting point metal materials and graphite have been used for various purposes. Examples include heat-resistant containers, refractory materials, and composite targets for X-ray tubes.

However, with conventional joining brazing materials and joining methods,
The wettability of the brazing filler metal was inhibited, cavities were formed in the bonding layer, and the thickness was thick and varied, which caused problems in the bonding strength.

Hereinafter, the prior art and the present invention will be explained in detail using a composite target for an X-ray tube rotating anode as an example, but the present invention is not limited thereto.

Conventionally, a single plate of tungsten (hereinafter abbreviated as W) has been used as a target for an X-ray tube rotating anode.

In order to improve its performance, a small amount of rhenium (hereinafter referred to as Re) was added to W.
) or a W alloy to which osmium or the like is added is used. Recently, X-ray CT (Co
There is a great demand for X-ray tubes for (putted tomography), and large-capacity X-ray tubes are also required to sharpen images and shorten imaging time. Therefore, it is necessary to increase the diameter and reduce the weight of the target. For this purpose, W alloy is used only on the electron impact surface of the target, and molybdenum (hereinafter abbreviated as MO) or graphite (hereinafter abbreviated as Gt), which has a low specific gravity and high specific heat, is used on the back side. Combined targets have been developed, such as W or its alloys/MO/ot or W or its alloys/Gt.

Such a composite target is shown in FIG. 1 of the accompanying drawings. That is, FIG. 1 is a schematic vertical cross-sectional view of a conventional composite target for an X-ray tube rotating anode. In Figure 1, reference numeral 1
is electron impact part (W or W alloy), 2 is Mo, 3 is G
t, 4 means the intermediate layer, and 5 means the rotation axis. Methods for manufacturing these composite targets include CvD1 thermal spraying and bonding, but bonding is particularly advantageous in terms of cost.

In the case of a bonding method, the above-mentioned 4 is a bonding layer made of a brazing filler metal for bonding.

However, conventional bonding methods have problems.

That is, since the bonding of W or its alloy or MO and Gt is the bonding of a metal and a ceramic, there are various problems in the bonding method.

First, conventionally, zirconium (hereinafter abbreviated as Zr), titanium, Mo
, W, and Re are used alone or in combination. Therefore, conventional brazing filler metals have a large specific surface area per unit weight and contain a large amount of oxygen due to oxidation during powder storage. Therefore, these metal powders are subjected to pretreatment such as hydrogen reduction and used as clean powders as possible. However, it has been found that conventional bonding methods for composite targets cannot prevent the formation of brazing filler metal, especially Zr oxide, and the bonding layer always peels off. It was also discovered that the cause of this was that oxygen contained in the metal powder could not be completely removed during the joining process. Mo
-27,5W -0,5Zr-Powder compact 12 with the remaining composition
The gas components released when heated were analyzed using a mass spectrometer. The results are shown in FIG. In other words, Figure 2 shows the temperature (℃) (horizontal axis) and the partial pressure of released gas (X 10-3
mHg) (vertical axis). H
The release of ZrH2 occurs because ZrH2 decomposes and turns into metal Zr, but the decomposition of ZrH2 starts at a low temperature of about 200°C. CO2 and CO emission lines are generated due to the deoxidation reaction between carbon and oxygen in the powder during the pretreatment process of the raw material powder. What should be noted here is that ZrH
This is the point where the temperature range in which 2 decomposes and turns into metal Zr 2 and the temperature range in which carbon and oxygen undergo a deoxidation reaction and release Co 2 overlap. In other words, before the oxygen contained in the powdered brazing filler metal is sufficiently deoxidized, ZrH2 decomposes and active metal Zr is generated, and J and Zr act as getters and absorb the oxygen remaining in the powder to form Zr. (%). Therefore, since it inhibits the wettability of the brazing filler metal and causes peeling, the presence of Zr oxide reduces the amount of Zr. However, it is technically difficult to reduce active metals such as Zr with hydrogen and make them clean.

Next, in the conventional method of manufacturing composite targets, the above metal powder (I) is applied to a paste by adding an organic solvent such as ethyl cellulose to a Gt substrate, then a W alloy plate, etc. is stacked on top of it, and then vacuum In this conventional method, the oxidation of the brazing filler metal is accelerated by moisture, impurities, and dissociated oxide VC discharged from the solvent during manufacturing, and the molten metal forms an oxide layer. As a result of the enclosed shape, the wettability is significantly inhibited, resulting in the inability to form a sound bonding layer.Also, with conventional methods, it is difficult to maintain a constant composition and thickness of the bonding layer. This resulted in large cavities and oxide inclusions in the bonding layer, and variations in thickness.Furthermore, the bonding layer was generally thick, so there was a problem with bonding strength3. 5
It is said that the one with a diameter of 0 to 100 μm has the highest strength.
Journal of the Welding Society, Vol. 64, No. 8, Page 20, left column (1965)
This is because the thickness of the conventional product exceeds 100 μm, in contrast to the above. These points will be specifically explained using the attached micrographs.

That is, FIG. 3 shows Zr and M as brazing filler metals.

Figure 4 is a micrograph of the cross-sectional structure near the bonding layer of a product manufactured by the conventional method using a mixed powder of Zr, M
It is a micrograph of the cross-sectional structure near the bonding layer of a commercial product using O and W powders.

In each figure, numeral 21 means a W alloy, 5 means Gt, and 41 means a bonding layer.

As is clear from FIG. 5, the bonding layer has many cavities and is as thick as about 270 μm. Also, the bonding layer in Figure 4 is about 75
Both are unsuitable because they are thick at 0 μm.

[Purpose of the invention]

The present invention was made in order to solve the problems of the prior art), and its purpose is to create a new brazing material for joining high melting point metal materials and Gt, and to improve the joining strength using the same. An object of the present invention is to provide a composite target for an X-ray tube rotating anode, and a method for using the brazing material in its manufacture.

[Overview of the invention]

To summarize the present invention, the first invention of the present invention relates to a brazing material for joining a high melting point metal material and Gt, which is made of a eutectic alloy of W or MO and Zr. It is characterized by

Further, the second invention of the present invention is W or its alloy/Gt
Or, an invention relating to a composite target for an X-ray tube rotating anode consisting of W or its alloy/MO/Gt, wherein the W or its alloy or a brazing material for joining tJ balls 0 and 0t is the first invention of the present invention. It is characterized by being a nokki.

Furthermore, a sixth invention of the present invention is an invention relating to a method of using the brazing filler metal of the first invention, which uses W or its When joining the alloy or MO and the 07 substrate, the rotating shaft of the W or its alloy or Mo plate and/or
or embedding the brazing material of the first invention in the surrounding area thereof,
The method is characterized in that the Gt substrates are stacked on top of each other, and then the bonding is performed by heating to a temperature above the eutectic point of the brazing material under pressure or static pressure.

The eutectic alloy itself used as a brazing material in the present invention, including its equilibrium phase diagram, is well known.

These are obtained as clean molten alloy ingots by arc melting or the like.

However, when this is used to manufacture a composite target for an X-ray tube rotating anode according to the present invention, the temperature of the target during operation of the X-ray tube reaches 1350°C, so a material with a higher melting point is required. . Thus, examples of eutectic alloys that can be used as brazing filler metals include 19 wt% W-Zr and 31 wt% Mo-Zr eutectic alloys.

Next, the method of using the brazing filler metal of the present invention will be explained.
The brazing filler metal of the present invention is preferably used in the method according to the third aspect of the present invention described above.

An example of how to bury the brazing material according to the sixth invention will be specifically explained with reference to the attached FIGS. 5 to 7. That is, the fifth
The figure and FIG. 6 show the method of the sixth invention of the present invention.
FIG. 7 is a schematic vertical cross-sectional view showing one embodiment of the buried position of the brazing filler metal, and FIG. 7 is a plan view of the one shown in FIG. 6. In each figure, the code 2 is W or its alloy or MO, and 5 is Gt.
, 6 means the brazing filler metal of the present invention.

5 and 6 under pressurized or static pressure,
When the eutectic point of the solder is heated to a high temperature, preferably in a vacuum, the wettability is improved by the reduction effect caused by the generation of CO gas, and the small gap between the Gt substrate 3 and the metal plate 2 becomes capillary. As a result of the penetration of the wax material, a composite target with a thin bonding layer, which is advantageous in terms of strength, can be produced. Furthermore, according to the method shown in FIG. 6, the molten brazing material can sufficiently fill the gap, so that a high-output composite target with a large diameter electron irradiation surface can be obtained.

According to the third aspect of the present invention, since the bonding layer is thin and has no cavities, it has excellent thermal conductivity and is a simple method, which is economically advantageous. Furthermore, according to the method of the present invention, particularly the method shown in FIG.
It is also possible to prevent peeling due to the difference in thermal expansion coefficient from the substrate 6.

[Examples of the Invention] Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 A 51% by weight Mo-zr eutectic alloy and a 19% by weight Mo-Zr eutectic alloy were melted by arc melting to obtain each brazing filler metal of the present invention.

Example 2 The arrangement shown in Fig. 5 was adopted (however, 2 was a W-Re
The Mo-Zr or W-Zr eutectic alloy melt brazing filler metal described in Example 1 was used as the brazing filler metal (meaning an alloy plate), and the welding was performed by heating in vacuum while applying pressure. ,
A W-Re alloy/c)1 composite target was obtained. The heating temperature and time were 1600° C. for 0.5 hours in the case of the Mo-Zr eutectic alloy solder, and 1750° C. for 0.5 hour in the case of the W-Zr eutectic alloy solder.

The cross-sectional structure near the bonding layer of the obtained composite target is shown in the drawing. That is, FIG. 8 is a photomicrograph of the vicinity of the bonding layer using Mo-Zr solder, and FIG. 9 is a photomicrograph of the vicinity of the bonding layer using W-Zr solder. In each figure, numerals 21.3 and 41 have the same meaning as in FIG. 6.

As is clear from FIGS. 8 and 9, the bonding layer 41 according to the present invention has no cavities and is sound and has a thin thickness of about 50 to 70 μm. , we were able to manufacture a composite target with excellent bonding strength.

Example 6 The arrangement shown in Figure 6 was adopted (however, 2 is M).

(meaning board). Using the brazing filler metal described in Example 1 as the brazing filler metal, W alloy/Mo/
A Gt composite target was obtained.

The cross-sectional structure near the bonding layer of the obtained composite target is shown in the drawing. That is, FIG. 10 is a micrograph of the vicinity of the bonding layer using Mo-Zr solder, and FIG.
This is a microscopic photograph of the vicinity of a bonding layer using wax. In each figure, numeral 22 means Mo, 3 means Gt, and 41 means a bonding layer.

As is clear from FIGS. 10 and 11, the bonding layer according to the present invention has no cavities and has a thickness of approximately 30 to 40 μm.
Since the target is as thin as m, the present invention was able to obtain a composite target with excellent bonding strength.

Test Example 1 The composite targets of the present invention of Examples 2 and 3 were subjected to a peel test using tensile strength, and as a result, both were broken at Gt. This is evidence that the bonding strength of the bonding layer is high.

Comparative example 1 For comparison, welding was performed using a conventional method.

First, the zr and Mo powders were mixed together, which was dispersed in a nitrocellulose-containing solvent and then applied to a Ct substrate. A gold plate with a W composite layer was placed on this and heated in vacuum at 1600°C for 0.5 hours to obtain a W alloy/Gt composite target.The micrograph of the cross-sectional structure near the joint layer is shown below. Already 4・
FIG. 3 is a diagram illustrating the drawings. Bonding layer in terms of cavity and thickness
It was less useful.
[Effect of invention]
As explained above, the brazing filler metal of the present invention is
Improved wettability and oxidation resistance due to inertness under pressure and purification
A bonding layer without any cavities can be obtained without the entrainment of conventional products.

In addition to being a subassembly, this brazing filler metal itself has high strength and is inexpensive, making it economically advantageous. Therefore, the brazing material according to the present invention is useful as a joining brazing material in a composite target for an X-ray tube rotating anode.
Further, according to the method of using the brazing filler metal of the present invention, 1: Reduction effect due to generated CO gas and capillary current Mo.

Strong 4
:0 which can form a thin bonding layer with excellent strength
It does not explode and has good thermal conductivity, there is no bond separation due to differences in thermal expansion coefficients, and the method is simple, so a remarkable effect has been achieved in economically advantageous manufacturing of composite targets.

Brief explanation of Figure 1 is a schematic vertical cross-sectional view of a conventional composite target for an X-ray tube rotating anode, Figure 2 is a graph showing the relationship between temperature and amount of released gas when Mo-W-Zr compacted powder is heated. 3 and 4 are microscopic photographs of the weaving near the bonding layer of the composite target obtained by the method, and FIGS. 5 and 6 are longitudinal cross-sectional schematic diagrams showing one embodiment of the buried position of the brazing material in the non-explosion method, Figure 7 is the 6th
The top view of the figure and FIGS. 8 to 11 are mirror photographs of the cross-sectional structure near the bonding layer of the composite target according to the method of the present invention.

Electron impact part, 2: W or its alloy, or 21: W alloy, 22: Mo, 3: Gt.

Intermediate layer, 41: Bonding layer, 5: Rotating shaft, 6: Light brazing material Figure 5 Figure 6 Figure 8 Figure 9 50 offices Figure 10

Claims (1)

[Claims] 1. A brazing material for joining a high-melting point metal material and graphite, characterized in that it is made of tungsten or a eutectic alloy of molybdenum and zirconium. 2. In a composite target for an X-ray tube rotating anode consisting of tungsten or its alloy/graphite or tungsten or its alloy/molybdenum/graphite,
A composite target for an X-ray tube rotating anode, characterized in that the brazing material for bonding tungsten or its alloy or molybdenum and graphite is made of tungsten or a eutectic alloy of molybdenum and zirconium. 3. When bonding tungsten or its alloy or molybdenum to a graphite substrate in the production of a composite target for an X-ray tube rotating anode consisting of tungsten or its alloy/graphite or tungsten or its alloy/molybdenum/graphite, the tungsten or A brazing material made of tungsten or a eutectic alloy of molybdenum and zirconium is embedded in the rotating shaft of the alloy or molybdenum plate and/or its surroundings, a graphite substrate is placed on top of the brazing material, and then the eutectic point of the brazing material is A method of using the brazing filler metal described above, characterized in that joining is performed by heating at high temperature under pressure or static pressure.