JPH04188551A - Rotary anode for x-ray tube - Google Patents

Abstract

PURPOSE:To prevent a crack from reaching a graphite base board to damage it, by dispersing the crack with polycrystals of W or W alloy. CONSTITUTION:After formation of Re 21, a polycrystal film 23 of W is generated, and columnar crystals 22 of W are provided as an over-layer. In this manner the substratum of W or W alloy is made in polycrystals, so that a crack propagates along the crystalline grain boundary, and the columnar crystalline grain boundary stretches straight in the direction of a graphite base board. In polycrystal, on the other hand, the grain boundaries exist in other directions out of order, so that crack 3 initiated in columnar crystal digerges in other direction when it reaches the polycrystalline part. Thereby the crack 3 is hindered from propagating to the graphite base board 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an X-ray generating material of a rotating anode for an X-ray tube.

[Conventional technology]

Conventional rotating anodes for X-ray tubes have a structure in which rhenium and the X-ray generating material tungsten or tungsten alloy are provided on a disc-shaped graphite substrate, but the surface of the X-ray generating material cannot be irradiated with an electron beam. X-rays are generated. In this case, the temperature of the tungsten alloy, which is the X-ray generating material, increases rapidly compared to the graphite substrate, so thermal stress occurs due to the difference in thermal expansion between graphite and tungsten alloy, and the stress causes disorder in the tungsten. A rack will occur. In Japanese Patent Application Laid-Open No. 1-209641, slits are cut in advance in the radial direction of the rotating anode in order to prevent cracks from occurring randomly. However, if the electron beam is powerful, it is not only impossible to completely prevent cracks from occurring.

There is a drawback that cracks start from the bottom of the slit and propagate in the depth direction.

[Problem to be solved by the invention]

The above conventional technology not only cannot completely prevent cracks from occurring when the electron beam is strong, but also causes cracks to propagate inside the graphite substrate starting from the bottom of the slit, resulting in centrifugal stress generated by rotation and electron There was a problem in that the rotational fracture strength of the rotating anode decreased because the thermal stress caused by irradiation was concentrated at the tip of the crack.

An object of the present invention is to provide a rotating anode for an X-ray tube in which cracks caused by thermal stress generated by electron beam irradiation do not develop in a graphite substrate.

[Means to solve the problem]

In order to achieve the above object, the crystal structure of the lower layer of tungsten or tungsten alloy in contact with the rhenium of the X-ray generating material is a polycrystalline grain structure, and the upper layer of tungsten or tungsten alloy is made of columnar crystals.

Furthermore, a fine polycrystalline layer is provided on the top layer of a tungsten alloy which is an X-ray generating material.

[Effect]

Cracks on the surface of tungsten or tungsten alloy, which is an X-ray generating material, are caused by thermal stress generated by electron beam irradiation and propagate in the depth direction. By making tungsten or tungsten alloy into columnar crystals, cracks are likely to occur at any location, so the cracks that occur are small, but on the other hand, cracks can easily propagate, reaching all the way to the lowest layer of rhenium.

As a result, cracks will develop in the graphite substrate. However, by making the lower layer of tungsten or tungsten alloy polycrystalline, cracks are estimated to occur along grain boundaries, so while columnar grain boundaries extend directly toward the graphite substrate, polycrystalline grains extend in the other direction. Due to the existence of grain boundaries in a disordered manner, when cracks generated in the columnar crystals reach the polycrystalline part, the cracks branch in other directions, and it is possible to prevent the cracks from propagating to the graphite substrate.

〔Example〕

An embodiment of the present invention will be described below.

FIG. 1 is a sectional view of a rotating anode for an X-ray tube.

It is obtained by forming a film of rhenium, tungsten, tungsten-rhenium, etc. 2 on the outer periphery of a disk 1 made of graphite by the CVD method.

Figure 2 shows an example of a conventional film structure, in which rhenium 21 is coated with a thickness of 10 μm on a graphite substrate 1, and tungsten rhenium columnar crystals 22 are coated.
is formed with a thickness of 300 μm. When a film with this structure is irradiated with an electron beam, a crank 3 is formed due to the thermal stress that causes tungsten to turn to rhenium, and as shown in FIG. 4, the crack 3 reaches the graphite substrate 1. Crack 3 varies depending on the electron beam density, but 14
At 0KUX 200mA, continuous irradiation for 3 seconds with focal size 1.5 x 1.5m was repeated with cooling for 10 seconds.The width of crack 3 was about 0.3m at 1.000 scans, and the crack reached about 1 inch from the graphite surface. It was known that the tip of 3 had reached the tip. The rotating anode is usually 10. This crack is extremely dangerous because a large stress is generated in the graphite substrate due to rapid acceleration and rotation of 1 see to OOOrpm.

FIG. 3 shows this embodiment. After forming rhenium 21, a tungsten polycrystalline film 23 was formed, and tungsten columnar crystals 22 were provided as an upper layer. As shown in Fig. 5, the cracks 3 that occurred after performing the same evaluation as in Fig. 2 pass through the tungsten columnar crystals 22, and are dispersed by branching in the tungsten polycrystals. ] was never reached.

FIG. 6 shows an example in which fine polycrystals of tungsten rhenium were provided in the uppermost layer in the embodiment shown in FIG. 5, and the same effect as in FIG. 5 was obtained.

〔Effect of the invention〕

According to the present invention, the polycrystalline tungsten or tungsten alloy has the effect of dispersing cracks, so that the cracks do not reach the graphite substrate and damage the graphite substrate. Highly reliable X that will not break due to centrifugal stress that sometimes occurs
A rotating anode for wire tubes is obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a rotating anode according to an embodiment of the present invention, and FIG.
The figure is a cross-sectional view of the membrane of a conventional rotating anode, FIG. 3 is a cross-sectional view of the membrane of an embodiment of the present invention, FIG. 4 is a cross-sectional view of the membrane when a crack occurs in the conventional rotating anode, and FIG. , FIG. 6 is a cross-sectional view of a membrane when cracks occur in an embodiment of the present invention.゛ 1...Graphite substrate, 2...X-ray generating material, 3...
・Crack, 21... Rhenium layer, 22... Tungsten or tungsten rhenium columnar crystal, 23...
・Tungsten polycrystal, 24...Tungsten rhenium alloy fine polycrystal 6

Claims (1)

[Claims] 1. A rotating anode comprising a rhenium layer provided on the outer periphery of a disc-shaped substrate made of a non-metallic material, and two or more layers of tungsten or tungsten alloy, which is an X-ray generating material, provided on top of the rhenium layer. A rotating anode for an X-ray tube, characterized in that the tungsten or tungsten alloy layer has two layers, the lower layer in contact with rhenium has a polycrystalline granular crystal structure, and the upper layer has a columnar crystal structure. 2. The rotating anode for an X-ray tube according to claim 1, wherein the tungsten or tungsten alloy has three layers, the lower layer in contact with rhenium is polycrystalline, the middle layer is columnar crystal, and the uppermost layer is fine polycrystalline. 3. The rotating anode for an X-ray tube according to claim 2, wherein the lower layer and the intermediate layer are made of tungsten material, and the uppermost layer is made of a tungsten alloy.