EP2193538B1 - X-ray anode having improved heat dissipation - Google Patents

Abstract

The invention relates to an X-ray anode having a coating and a carrier body. In addition to a region providing strength, the carrier body comprises a region comprising a diamond-metal composite material. The diamond-metal composite material comprises 40 to 90% by vol. diamond particles, 10 to 60% by vol. binding phase(s) comprising a metal or an alloy of the metals of the group consisting of Cu, Ag, AI, and at least one carbide of the elements of the group consisting of Tr, Zr, Hf, V, Nb, Ta, Cr, Mo, W, B, and Si. The highly heat-conductive region can be positively connected at the back to a heat-dissipating region, for example comprising Cu or a Cu alloy. The X-ray anode has improved heat dissipation and lower composite stress.

Description

The invention relates to an X-ray anode, which consists of a X-rays by bombardment with focused electrons generating coating, which is connected to a carrier body. The carrier body comprises a strength-giving region of a material with a strength at 500 ° C greater than 100 MPa.

When X-rays are generated by bombarding an anode material with a focused electron beam, approximately 99% of the beam energy is converted to heat. There are very high specific surface loads in the focal spot, which are on the order of 10 to 100 MW / m ² . This results in very high focal spot temperatures and, in the case of pulsed loading of X-ray rotary anodes, thermo-mechanical fatigue of the focal track. The limit of the load capacity is given by the aging of the track, associated with a progressive drop in the dose rate and / or with the loss of the high voltage stability of the tube. To slow down these effects, an optimized dissipation of the heat from the focal spot or the focal path is required.

The overwhelming majority of the radiation sources used today in X-ray computed tomography are X-ray rotary anodes in which the energy of the electron beam introduced in the line focus is distributed to a ring, the so-called focal path, by rotation of the anode at high speed. The supplied during recording energy of up to several megajoules is initially largely stored in the X-ray anode and delivered especially in the pause time between shots by radiation in rotary anodes with Gleitrillenlager also by heat conduction into the camp to the surrounding cooling medium.

Rotary anodes according to the prior art consist of a X-radiation by the bombardment with focused electrons generating coating, for example of a tungsten-rhenium alloy, on a support body, such as a disc of a Molybdenum-based material is applied. A molybdenum base material customary for this application is TZM with the composition Mo-0.5% by weight Ti-0.08% by weight Zr-0.04% by weight CI, as is known from, for example, US Pat EP 0 874 385 A1 evident. Depending on the field of application of the anode can be soldered to increase the heat storage capacity and heat radiation on the back of the metal disc a graphite body. At the outlet temperature of the tube operation (about 40 ° C), the thermal conductivities of W-10Gew.% Re, TZM and graphite are at about 85, 125 and 135 W / m · K, but decrease significantly with increasing anode temperature.

In a new generation of X-ray tubes, the so-called rotary tubes, the anode is firmly connected to the floor as a whole with a rotating tube and actively cooled at its rear. The energy balance of the anode is dominated by the heat dissipation into the cooling medium. The heat storage plays a minor role.

The DE 10 2005 039 188 B4 describes an X-ray tube with a cathode and an anode made of a first material, wherein the anode is provided on its side facing away from the cathode at least partially with a heat conducting element for removing heat, which is made of a second material having a higher heat conductivity than the first material, wherein the second material has a thermal conductivity of at least 500 W / mK and the second material is made of titanium doped graphite.

The DE 10 2004 003 370 A1 describes a high-performance anode plate for a directly cooled rotary tube, which consists of a high-temperature resistant material, such as tungsten, molybdenum or a composite of both materials, wherein formed in the Brennfteckbahn the bottom of the anode plate and / or in this another highly thermally conductive material or it is appropriate that results in an improved heat dissipation and thus a lower temperature gradient within this material range. As a material with high thermal conductivity while copper is mentioned.

There have been numerous attempts in recent years to improve heat dissipation in X-ray rotary anodes. Diamond found it despite the Excellent thermal conductivity at room temperature due to the strong declining thermal conductivity at elevated temperatures and the conversion to graphite at T> 1100 ° C only minor consideration.

So was in the US 4,972,449 proposed the use of a diamond layer, which is interposed between the lining and the carrier body. However, diamond also has a significantly lower coefficient of expansion than the adjacent materials, which induces stresses in the composite. Furthermore, the classical powder metallurgical production route for X-ray anodes, namely the powder metallurgical bonding of the track surface and carrier body, can not be used, since the sintering process would lead to a conversion of the diamond layer into graphite. X-ray anodes according to the US 4,972,449 Therefore, they can only be produced by coating methods such as CVD methods. Diamond-containing cooling structures also go from the DE 101 28 245 A1 and the JP 2002 093355 A out. That's how it describes DE 101 28 245 a heat sink for parts exposed to particle bombardment. The heat sink has a metallic matrix containing diamond particles. The metallic matrix is inserted in a dense metallic shell. The JP 2002 093355 A describes an anode for an X-ray tube, in which a heat-dissipating layer is arranged between the focal track and the main body. This layer may also comprise Cu-Ti with diamond admixtures.

It is therefore an object of the present invention to provide an X-ray anode which has a carrier body with improved heat dissipation. Another object is to reduce the stresses in the composite support body / covering.

The object is solved by the independent claim.

The X-ray anode consists of a coating and a carrier body, wherein the carrier body comprises a region of a diamond-metal composite material in addition to a strength-giving region. The diamond-metal composite consists of diamond grains surrounded by binder phase (s). The binder phase (s) consists of a binder metal based on copper, silver, aluminum and alloys of these materials, and optionally up to 20% by volume of carbides. By varying the diamond and binder phase content, it is possible to adapt the diamond-metal composite material with respect to thermal conductivity and thermal expansion in such a way to the surrounding materials that tailor-made solutions for a wide variety of requirements conditions are possible. Advantageously can be a gradierter

construction of
Diamond-metal composite material, wherein the proportion of diamond to the top is highest and decreases in the direction of maximum heat flow. As a result, a minimization of the bond stresses, caused by different thermal expansion coefficients of the materials used, can be achieved. Furthermore, diamond powder having a wide grain size spectrum can be processed. Preferred particle sizes are in the range of 50 to 400 μm, ideally 100 to 250 μm. In addition to natural diamonds, cheaper synthetic diamonds can also be processed accordingly. The volume fraction of the diamond grains is 40 to 90 vol.%, That of the binder phase (s) 10 to 60 vol.%. A diamond content of 40 to 90 vol.% Ensures that the bond stresses are reliably reduced to an uncritical level for the application. Particularly advantageous diamond and binder phase contents are 50 to 70% by volume and 30 to 50% by volume.

The binder metal consists of 80 to 100 At.% Of at least one matrix metal from the group Cu, Ag, Al, and preferably 0 to 20 at.% Of a metal having a solubility at room temperature in the matrix metal less than 1 At.% And 0 to 1 At. % of a metal with a solubility at room temperature in the matrix metal greater than 1 At%., Remaining impurities. Alloying elements with a solubility at room temperature in the matrix metal smaller than 1 at.% Reduce the thermal conductivity to a small extent and can therefore be present up to 20 at.%, While alloying elements with a solubility greater than 1 at.% Due to their negative influence on the thermal conductivity with 1 At% are limited.

Good bonding between the diamond and metal phases is required to ensure a transition from the phonon conductivity of the diamond to the electronic conductivity of the binder metal. This can be achieved for example by the formation of a carbide phase, which is arranged between the diamond and the metal phase. Investigations have shown that even carbide films with a thickness of a few atomic layers significantly improve the thermal conductivity. When Carbide-forming elements have the elements of the group 4b- (Ti, Zr, Hf), 5b- (V, Nb, Ta), 6b (Cr, Mo, W) metals of the periodic table, as well as B and Si proven. Particularly suitable for this purpose are the weak carbide formers Si and B. If the matrix metal is a carbide-forming element, such as aluminum, it may be possible to dispense with the addition of further carbide-forming elements. Furthermore, it is advantageous if the element forming the carbide phase is also contained in the binder metal. In this case, preference is given to the carbide-forming elements which have a solubility of less than 1 at.% In the respective matrix metal. If the solubility is greater, in turn, the thermal conductivity of the binder metal and thus the diamond-metal composite material is reduced. Present invention binder metal compositions are 0.005 to 3At% aluminum materials. one or more elements of the group V, Nb, Ta, Ti, Zr Hf, B, Cr, Mo, W and / or with 0.005 to 20 At.% Si.

On the basis of Ag, these are materials with 0.005 to 5 at.% Of one or more elements of the group Zr, Hf and / or 0.005 to 10 at% of one or more elements of the group V, Nb, Ta, Cr, Mo, W and /. or 0.005 to 20 at.% Si. Particularly advantageous properties are achieved with Cu-base matrix metals containing from 0.005 to 3 at.% Of one or more elements of the group Ti, Zr, Hf and / or 0.005 to 10 at.% Of one or more elements of the group Mo, W, B, V, Nb, Ta, Cr, and / or 0.005 to 20 At.% B are alloyed.

As particularly advantageous binder metals are Ag alloys with 0.1 to 12 At.% Si, and Cu alloys with 0.1 to 14 at.% Boron, balance usual impurities proved.

A particularly advantageous effect can also be achieved if already coated diamond powders (metallic or carbide coating) are used.

By using the diamond-metal composite material according to the invention, it is now possible to conically expand the heat flow and thus to increase the active cooling efficiency of actively cooled X-ray anodes. Extensive tests on such X-ray anodes have shown that the temperature is lowered so far by the solution according to the invention that the predicted low thermal conductivity of the Diamond-metal composite material at elevated operating temperatures has no function-limiting effect.

Since the inventive diamond-metal composite materials in their mechanical properties such as tensile and compressive strength, fracture toughness and fatigue strength limited, and accordingly under conditions of use of X-ray anodes as cantilevered structure are not thermally cyclable, the support body in addition to the diamond-metal composite material still a strength giving region of a structural material having a strength at 500 ° C of greater than 100 MPa. The diamond-metal composite is protected against destructive deformation or crack initiation by centrifugal forces or thermo-mechanical stresses due to the structural rigidity of the structural component. This makes it possible to optimize the diamond-metal composite on the one hand in terms of thermal conductivity, in particular by increasing the proportion of diamond. On the other hand, the thermal expansion of the diamond-metal composite material can be adapted to the structural material. In this way, the functions of the carrier body can be decoupled in terms of structural strength and bursting strength on the one hand and on heat dissipation on the other hand. Structural materials according to the invention are Mo, Mo alloys, W, W alloys, W-Cu composite materials, Mo-Cu composite materials, particle-reinforced Cu and particle-reinforced Al alloys. Particularly advantageous molybdenum alloys are TZM (Mo-0.5% by weight, titanium-0.08% by weight, zirconium-0.04% by weight C) and MHC (Mo-1.2% by weight Hf-O) , 08 wt.% C).

The area of the diamond-metal composite material can connect directly to the covering. This is possible and useful if the temperature on the backing surface can be lowered by the diamond-metal composite so far that no material damage, such as melting of the binder phase (s) of the diamond-metal composite occur. If this is not the case, it is advantageous if the strength-giving region consists of a structural material which is dimensionally stable under conditions of use, preferably molybdenum, tungsten or an alloy thereof Metals, between the
Diamond-metal composite material and the covering extends.
The diamond-metal composite material is preferably arranged under that region of the covering in which the heat is generated by the action of the electron beam. For an X-ray rotary anode, this is the annular focal track. This results in preferred embodiments for the area of the
Diamond-metal composite, namely those with axially symmetric geometry, such as a disc or a ring. The cross section is preferably approximately rectangular or trapezoidal.

Viewed in the direction of the maximum heat flow, it is further advantageous if subsequent to the area of the diamond-metal composite, a further heat-dissipating region of a highly thermally conductive metal follows, which in the final shaping, especially with regard to attachment of cooling structures with conventional machining processes can be edited shaping. As highly thermally conductive metals are copper, aluminum, silver and their alloys to mention. This heat-dissipating area is again preferably designed as a ring element or as a disk and with the
Diamond-metal composite material and / or materially bonded to the strength-giving area.

• 0,01 mm bis 1 mm Belag, 0 bis 4 mm festigkeitsgebender Bereich, 2 bis 15 mm Bereich aus dem Diamant-Metall-Verbundwerkstoff und 0 bis 10 mm wärmeableitender Bereich. Eine Mindeststärke des Belags von 0,01 mm ist aus röntgenphysikalischen Gründen erforderlich. Bei Belagsstärken über 1 mm und/oder einer Dicke des festigkeitsgebenden Bereichs über 4 mm wird die Wärmeableitung reduziert, da die üblicherweise verwendeten W-Re Legierungen und die zur Verfügung stehenden Strukturwerkstoffe eine im Vergleich zum

Following the maximum heat flow, the x-ray anode preferably has the following structure, at least in the region of the maximum heat load:

• 0.01 mm to 1 mm coating, 0 to 4 mm strength region, 2 to 15 mm diamond metal composite area and 0 to 10 mm heat dissipating area. A minimum pad thickness of 0.01 mm is required for X-ray physical reasons. For pad thicknesses greater than 1 mm and / or a thickness greater than 4 mm, heat dissipation is reduced, since the commonly used W-Re alloys and the available structural materials offer a better performance than the standard

Diamond-metal composite material have reduced thermal conductivity. It is particularly advantageous if the thickness of the covering is 0.2 to 0.4 mm or that of the strength-giving area is 0.5 to 4 mm.

The construction according to the invention of an X-ray anode can be used particularly advantageously in the case of rotating anodes and, in turn, when the rotary anode is used as the actively cooled bottom of a rotary-piston tube. In order to achieve sufficient structural strength of the rotary anode, it is proven that the center is formed only from the structural material. Furthermore, it is advantageous if the region made of the diamond-metal composite material is embedded as a ring-shaped or disc-shaped element in a corresponding recess of the strength-giving region of the carrier body and is thus supported by this with respect to the mechanical loads occurring. Advantageously, the structural material on the one hand with the coating, on the other hand, materially connected to the diamond-metal composite material. The cohesive bonding between the structural component and the diamond-metal composite can advantageously already be carried out in situ during its synthesis in suitable recesses of the strengthening region of the anode body (for example by pressure infiltration or by hot isostatic pressing). On the other hand, the composite material can be synthesized on its own and a filler material can be produced therefrom in a suitable form, which is then adhesively bonded to the structural component, for example by soldering or another known joining process.

For the production of the diamond-metal composite material, a number of processes are available in which the binder metal is bonded to the diamond either via the melt phase or via the solid phase. Over the melt phase, the processes advantageously proceed by means of pressure infiltration. Typical infiltration temperatures are about 100 ° C above the respective melting point of the binder metal. From the reactions with the diamond grain, the carbide phases which surround the diamond grains may then optionally be formed.

• ■ Herstellen eines Verbundkörpers, welcher aus dem Strukturwerkstoff und dem Belagswerkstoff gebildet ist, durch pulvermetallurgisches Verbundpressen / Sintern / Schmieden oder Aufbringen des Belagwerkstoffs auf den Strukturwerkstoff durch Vakuumplasmaspritzen;
• ■ Einbringen einer Vertiefung in den Strukturwerkstoff auf der belagsabgewandten Seite
• ■ Einfüllen von Diamantpulver mit einer Korngröße von 50 bis 400 µm in die Vertiefung, wobei das Diamantpulver unbeschichtet oder beschichtet (Schichtstärke 0,05 bis 50 µm) bevorzugt mit einem Metall oder einem Karbid eines Metalls aus der Gruppe der 4b, 5b, 6b Metalle des Periodensystems, B und Si, vorliegen kann;
• ■ Infiltrieren der Diamantpulverschüttung mit dem Bindemetall bei einem Druck von 1 bis 500 bar und einer Temperatur T, mit Liquidustemperatur des Bindemetalls < T < Liquidustemperatur des Bindemetalls plus 200°C; optional mit Überschuss des Bindemetalls zur Ausbildung des wärmeableitenden Bereichs;
• ■ Mechanische Bearbeitung.

A particularly suitable production process comprises the following production steps:

• ■ producing a composite body formed from the structural material and the facing material by powder metallurgical composite pressing / sintering / forging or applying the lining material to the structural material by vacuum plasma spraying;
• ■ introducing a depression into the structural material on the side facing away from the lining
• ■ filling of diamond powder with a grain size of 50 to 400 microns in the well, the diamond powder uncoated or coated (layer thickness 0.05 to 50 microns) preferably with a metal or a carbide of a metal from the group of 4b, 5b, 6b metals of the periodic table, B and Si may be present;
• ■ infiltrating the diamond powder spill with the binder metal at a pressure of 1 to 500 bar and a temperature T, with the liquidus temperature of the binder metal <T <liquidus temperature of the binder metal plus 200 ° C; optionally with excess of binder metal to form the heat-dissipating area;
• ■ Mechanical processing.

In the production of the bond between diamond grain and binder metal in the solid phase, the attachment of the diamond grain to the binder metal is caused by diffusion. The required diffusion paths can already be achieved at temperatures T - 0.5 to 0.8 T _m (T _m = melting point of the binding metal in degrees Kelvin) and holding times of a few hours. Suitable methods are, for example, hot pressing or hot isostatic pressing of
Diamond-metal powder mixtures. The connection is advantageously improved or accelerated by suitable coatings of the diamond grains. In the case of the solid-phase reaction, the contents of filler metals can be reduced orders of magnitude or possibly completely omitted with suitable pretreatment of the diamond grains and choice of consolidation conditions, whereby the high thermal conductivity of the pure binder phase can be largely maintained.

Combinations of both reaction paths, for example passing through the melt phase under pressure for pore-free backfilling of the diamond bed followed by a solid-pressure diffusion phase at lowered temperatures, may also be advantageous, in particular for realizing high diamond fractions of the composite material.

• ■ Herstellen eines Verbundkörpers, welcher aus dem Strukturwerkstoff und dem Belagswerkstoff gebildet ist, durch pulvermetallurgisches Verbundpressen / Sintern / Schmieden oder Aufbringen des Belagwerkstoffs auf den Strukturwerkstoff durch Vakuumplasmaspritzen;
• ■ Einbringen einer Vertiefung in den Strukturwerkstoff auf der belagsabgewandten Seite;
• ■ Einfüllen einer Mischung aus Diamantpulver und dem Bindemetall in die Vertiefung, wobei das Diamantpulver eine Korngröße von 50 bis 400 µm aufweist und unbeschichtet oder beschichtet (Schichtstärke 0,05 bis 50 µm) bevorzugt mit einem Metall oder einem Karbid eines Metalls aus der Gruppe der 4b, 5b, 6b Metalle des Periodensystems, B und Si vorliegen kann;
• ■ Heißpressen der Mischung bei einem Druck von 10 bis 200 MPa und einer Temperatur T, mit 0,6 x Solidustemperatur des Bindemetalls < T < Solidustemperatur des Bindemetalls; optional mit Überschuss des Bindemetalls zur Ausbildung des wärmeableitenden Bereichs;
• ■ Mechanische Bearbeitung.

A particularly suitable method here comprises the production steps:

• ■ producing a composite body formed from the structural material and the facing material by powder metallurgical composite pressing / sintering / forging or applying the lining material to the structural material by vacuum plasma spraying;
• ■ introducing a depression into the structural material on the side facing away from the lining;
• ■ filling a mixture of diamond powder and the binder metal in the well, wherein the diamond powder has a particle size of 50 to 400 microns and uncoated or coated (layer thickness 0.05 to 50 microns) preferably with a metal or a carbide of a metal from the group 4b, 5b, 6b metals of the Periodic Table, B and Si may be present;
• ■ hot pressing of the mixture at a pressure of 10 to 200 MPa and a temperature T, with 0.6 x solidus temperature of the binder metal <T <solidus temperature of the binder metal; optionally with excess of binder metal to form the heat-dissipating area;
• ■ Mechanical processing.

• ■ Herstellen einer eines Verbundkörpers, welcher aus dem Strukturwerkstoff und dem Belagswerkstoff gebildet ist, durch pulvermetallurgisches Verbundpressen / Sintern / Schmieden oder Aufbringen des Belagwerkstoffs auf den Strukturwerkstoff durch Vakuumplasmaspritzen;
• ■ Einbringen einer Vertiefung in den Strukturwerkstoff auf der belagsabgewandten Seite;
• ■ Herstellen eines Grünlings durch das Pressen einer Mischung aus Diamant- und Bindemetallpulver, wobei das Diamantpulver eine Korngröße von 50 bis 400 µm und das Bindemetallpulver von 0,5 bis 600 µm aufweist und das Diamantpulver unbeschichtet oder beschichtet (Schichtstärke 0,05 bis 50 µm) bevorzugt mit einem Metall oder einem Karbid eines Metalls aus der Gruppe der 4b, 5b, 6b Metalle des Periodensystems, B und Si vorliegen kann, bei einem Druck bevorzugt von 70 bis 700 MPa;
• ■ Einbringen des Grünlings in die Vertiefung des Strukturwerkstoffs und Kannen des so hergestellten Zusammenbaus unter Verwendung üblicher Kannenwerkstoffe (beispielsweise Stahl, Titan);
• ■ Heißisostatisches Pressen des gekannten Zusammenbaus bei einem Druck von 50 bis 300 MPa und einer Temperatur T, mit 0,6 x Solidustemperatur des Bindemetalls < T < Liquidustemperatur des Bindemetalls plus 200°C; optional mit Überschuss des Bindemetalls zur Ausbildung des wärmeableitenden Bereichs;
• ■ Mechanische Bearbeitung.

Another suitable method comprises the production steps:

• ■ producing a composite body formed of the structural material and the facing material by powder metallurgy composite pressing / sintering / forging or applying the lining material to the structural material by vacuum plasma spraying;
• ■ introducing a depression into the structural material on the side facing away from the lining;
• Producing a green compact by pressing a mixture of diamond and binder metal powder, wherein the diamond powder has a particle size of 50 to 400 .mu.m and the binding metal powder of 0.5 to 600 .mu.m and the diamond powder uncoated or coated (layer thickness 0.05 to 50 microns ) may preferably be present with a metal or a carbide of a metal from the group of 4b, 5b, 6b metals of the Periodic Table, B and Si, at a pressure preferably from 70 to 700 MPa;
• ■ introduction of the green compact into the recess of the structural material and pitching of the assembly thus produced using conventional can materials (for example steel, titanium);
• ■ hot isostatic pressing of the known assembly at a pressure of 50 to 300 MPa and a temperature T, with 0.6 x solidus temperature of the binder metal <T <liquidus temperature of the binder metal plus 200 ° C; optionally with excess of binder metal to form the heat-dissipating area;
• ■ Mechanical processing.

In principle, other processes are also used for the production of the diamond-metal composite, in particular also those for the production of composite materials, such as e.g. the gas phase infiltration of the binding metal, into consideration.

Figur 1

zeigt skizzenhaft den Querschnitt der erfindungsgemäßen Röntgenanode gemäß Beispiel 4

Figur 2

zeigt skizzenhaft den Querschnitt der Röntgenanode gemäß Beispiel 5

Figur 3

zeigt skizzenhaft den Querschnitt der Röntgenanoden gemäß Beispiel 6 und 7

In the following the invention is explained in more detail by examples.

FIG. 1

shows a sketch of the cross section of the X-ray anode according to the invention according to Example 4

FIG. 2

shows in sketchy the cross section of the X-ray anode according to Example 5

FIG. 3

shows a sketch of the cross section of the X-ray anodes according to Example 6 and 7

example 1

To adjust the Cu-based binder phase, blanks were made of the high-strength Mo alloy TZM (Mo-0.5 wt% Ti-0.08 wt% Zr-0.01 to 0.06 wt% C) with a diameter of 50 mm and a thickness of 30 mm in the usual powder metallurgical way via powder pressing / sintering / forging. In these rounds, a cylindrical recess having a diameter of 30 mm and a depth of 20 mm was incorporated. In the following step, in each case a diamond bed having a mean grain diameter (determined laser-optically) of 150 μm was introduced into the resulting recess for the production of the diamond-metal composite material and the ring mold was infiltrated via gas pressure infiltration with Cu alloys of the following compositions: Cu-O, 5At.% B, Cu-2At.% B and Cu-8At.% B.

In addition, diamond powder with a mean grain diameter (determined by laser optics) of 150 .mu.m coated with Nb (layer thickness about 1 .mu.m) was introduced into the ring mold and above that pure Cu was positioned in lumpy form. Idente experiments were carried out with Cr, Ti and Mo coated powders. The gas pressure infiltration was carried out in each case under Ar protective gas atmosphere at 1100 ° C with a gas pressure of 2 bar. The volume fraction diamond was about 55% for all samples. The thermal conductivity of the Cu-diamond composites at 500 ° C was between 290 and 350 W / m.K.

Example 2

To set the binder phase based on Ag blanks were prepared according to Example 1. Into the depression was used for the production of the

Diamond-metal composite material in each case a diamond bed with a mean grain diameter (determined by laser optics) of 150 microns introduced and the ring mold infiltrated via gas pressure infiltration with Ag alloys of the following compositions: Ag-0.5At.% Si, Ag-3At.% Si, Ag-11At.% Si and Ag-18At.% Si.

In addition, diamond powder with a mean grain diameter (determined laser-optically) of 150 .mu.m coated with Nb was introduced into the ring mold and above this pure Ag was positioned in lumpy form. Idente experiments were carried out with Cr, Ti and Mo coated powders. The gas pressure infiltration was carried out under Ar protective gas atmosphere at 1000 ° C with a gas pressure of 2 bar. The volume fraction diamond was about 55% for all samples.

The thermal conductivity of Ag-diamond composites was between 340 and 440 W / mK at 500 ° C.

Example 3

To set the Al-based binder phase, blanks were prepared according to Example 1. For the production of the diamond-metal composite material, a diamond bed having a mean grain diameter (determined laser-optically) of 150 μm was introduced into the depression and the ring mold was infiltrated by gas pressure infiltration with Al materials of the following compositions: Al, Al-3At.% Si, Al-12At.% Si and Al-15At.% Si. In addition, diamond powder with a mean grain diameter (determined by laser optics) of 150 μm coated with Nb (layer thickness about 1 μm) was introduced into the ring mold and above this Rein-Al was positioned in lumpy form. Idente experiments were carried out with Cr, Ti and Mo coated powders.

The gas pressure infiltration was carried out in each case under Ar protective gas atmosphere at 700 ° C with a gas pressure of 2 bar. The volume fraction diamond was about 55% for all samples.

The thermal conductivity of the Al-diamond composites at RT was between 400 and 450 W / m.K.

Example 4

A rotary anode -1- with a structure according to Fig. 1 The strengthening region -4- of the support body -3- was prepared from TZM by the usual powder metallurgical method via powder pressing / sintering / forging and overdriving the precontour (with external diameter 125 mm). Then the X-ray generating coating -2- from W-5Gew.% Re was applied by means of vacuum plasma spraying. From the strength-giving area -4- of the support body -3- below the covering -2- an annular area of 25 mm width was turned out with a residual thickness of the festigkeitsgebenden range -4- of 1 mm. In the following step was in the resulting annular groove for the production of the area -5- of the diamond-metal composite material Diamond bed with a mean grain diameter (determined by laser optics) of 150 microns introduced and the ring mold infiltrated by gas pressure infiltration with a Cu-4At.% B alloy, which was positioned in a lumpy form on the Diamantpullobüttung. The gas pressure infiltration was carried out under Ar protective gas atmosphere at 1100 ° C with a gas pressure of 2 bar. Using a suitable graphite tool, the Diamantverbund was infiltrated simultaneously with the infiltration of the heat-dissipating portion -6- in the form of a Cu-4At.% B back plate with a thickness of 3.7 mm. In this back plate, a fin structure was incorporated to improve the heat transfer to the cooling medium.

The resulting diamond-metal composite region -5- had a volume fraction of about 55% diamond and an expansion coefficient at RT of 6.5 E ^-6 / ° K. The thermal conductivity of the Cu-diamond composite was 480 W / mK at 22 ° C and 350 W / mK at 500 ° C, respectively.

Example 5

A rotary anode -1- with a structure according to Fig. 2 was made as follows. The festigkeitsgebende range -4- of the support body -3- was made of the high-strength Mo alloy MHC (Mo-1.2Gew.% Hf-0.04 to 0.15 wt.% C), wherein the X-ray generating coating - 2- from W10Gew.% Re was bonded by the usual powder metallurgical method via co-pressing / sintering and composite forging with the strength-giving range -4-. The production of the annular groove was carried out as described in Example 4.

In the following step, a diamond bed with a mean grain diameter of 150 (determined by laser optics) was introduced into the machined annular groove to produce the region -5- of the diamond-metal composite material. On the diamond bed, an Ag-11 At.% Si alloy was positioned in particulate form. The infiltration was carried out under Ar protective gas atmosphere at 1000 ° C with a gas pressure of 2 bar. The area -5- was completed on the underside of the rotary anode -1- with an excess of molten metal with a thickness of about 2 mm. By using the Ag matrix, a thermal conductivity of 590 W / mK at 22 ° C or 420 W / mK at 500 ° C was achieved.

Example 6

A rotary anode -1- with a structure according to Fig. 3 was prepared as follows. The production of the strength-giving area -4- from TZM (thickness 15 mm, diameter 140 mm) and the application of the coating -2- from W-5Gew.% Re was carried out according to Example 4. The strength-giving area -4- of the support body -3- was turned in the diamond-metal composite to be backfilled ring area (outer diameter 125 mm, inner diameter 80 mm) to a residual thickness of the TZM of 1 mm. The strength-giving area -4- formed together with an annular washer built thereon a portion of the hot-pressing tool, with a mixture of 50 vol.%. Diamond and 50 vol.% Of high purity copper to form the

Area -5- was backfilled. The diamond grains had a diameter of 150 μm (measured by laser optics) and were coated with 1 μm SiC for subsequent attachment of the matrix. The high-purity Cu powder likewise had a grain diameter of 150 μm. Finally, a cover fill of 3 mm copper powder of the same grain size was used to form the heat-dissipating area -6-. This bed was pre-pressed at room temperature and hot-pressed at a temperature of 900 ° C for 1.5 hours at a pressure of 40 MPa and thereby compressed to 99.8% of the theoretical density. At the same time by diffusion between SiC and Cu, a firm and good thermal conductivity bond of the diamond grains to the copper matrix, and the matrix to the support body -3-.

The thermal conductivity measured on the copper-diamond composite thus obtained was 490 W / m.K (at 22 ° C).

Example 7

A rotary anode -1- with a structure according to Fig. 3 was prepared as follows. The production of the strength-giving area -4-, application of the lining - 2- and production of the ring area was carried out as described in Example 5. A powder bed of a mixture of 70% by volume of diamond and 30% by volume of silver to form the region -5- was made into a compact by means of die pressing in the approximate shape of the twisted ring area of the strength-giving area -4- and inserted into the twisted ring area. The diamond grains had a diameter of 300 μm and were coated with 3 to 5 μm SiC. The Ag powder had a grain diameter of 150 μm. On the back side of the diamond Ag greenware was placed an Ag sheet with a diameter of 140 mm and a thickness of 3 mm. The entire structure was vacuum-sealed in a steel can and evacuated. The Ag contents were melted in the HIP process by heating to 980 ° C with a 2 minute hold time under a pressure of 50 MPa, while backfilling the cavities of the green body with Ag melt. Subsequently, the temperature was lowered to 650 ° C and held the known component for 1 h under a pressure of 70 MPa. The cooling to room temperature was also carried out under pressure in the range of about 70 MPa, with a holding time of 2 h at 400 ° C. The resulting silver-diamond composite had a thermal conductivity of 610 W / mK.

As a reference anode for comparative tests in X-ray tubes, an anode of the same design for rotary-tube tubes, but backfilled with copper instead of diamond-metal composite, was used.

All in accordance with Examples 4 to 7 with diamond metal composite back-filled rotary anodes showed in the test in rotary tubes under tightened compared to today's limit load test conditions (increase in electrical power by 20% compared to the reference anodes according to the prior art) an excellent use behavior, in a in spite of the increased load significantly slowed down the decrease in the X-ray dose over the test period compared to the reference anodes. The reduction of the Brennbahnaufrauung, which is responsible for the decrease in the X-ray dose over the life of the anode correlated in good approximation with the relative increase in the thermal conductivity of the respective present diamond-metal composites. In destructive analyzes of the different anodes after the end of the test, no damage to the bond between the strength - giving component and the Diamond-metal composite or can be found within the same between diamond grains and binder metal.

Claims (8)

1. X-ray anode (1) for generating X-rays, consisting of a coating (2) generating the X-radiation as a result of bombardment with focused electrons, said coating being connected to a support body (3) which includes a strength-imparting region (4) consisting of a material with a strength at 500 °C greater than 100 MPa from the group comprising Mo, Mo alloy, W, W alloy, W-Cu composite, Cu composite, particle-reinforced Cu alloy and particle-reinforced A1 alloy, the support body (3) including, in addition, a region (5) consisting of a diamond-metal composite that contains 40 vol.% to 90 vol.% of diamond grains and 10 vol.% to 60 vol.% of binding phase(s), the binding phase(s) consisting of 80 vol.% to 100 vol.% of binding metal based on copper, silver, aluminium or alloys of these materials and optionally up to 20 vol.% of at least one carbide of an element from the group comprising B, Si and metals pertaining to subgroups 4b, 5b and 6b of the periodic table,
   characterised in that
   if Cu is the basis, the binding metal contains 0.005 at.% to 3 at.% of one or more elements from the group comprising Ti, Zr, Hf and/or 0.005 at.% to 10 at.% of one or more elements from the group comprising Mo, W, V, Ta, Nb, Cr and/or 0.005 at.% to 20 at.% B; if Ag is the basis, the binding metal contains 0.005 at.% to 5 at.% of one or more elements from the group comprising Zr, Hf and/or 0.005 at.% to 10 at.% of one or more elements of the group comprising V, Nb, Ta, Cr, Mo, W and/or 0.005 at.% to 20 at.% Si; and if A1 is the basis, the binding metal contains 0.005 at.% to 3 at.% of one or more elements from the group comprising V, Nb, Ta, Ti, Zr, Hf, Cr, Mo, W, B and/or 0.005 at.% to 20 at.% Si.
2. X-ray anode (1) according to Claim 1, characterised in that the region (5) beneath the coating (2) is arranged in the region of maximal thermal load.
3. X-ray anode (1) according to Claim 1 or 2, characterised in that the regions (4, 5) are integrally connected, at least in subregions, by a backing process, pressure-infiltration process, diffusion-welding process or soldering process.
4. X-ray anode (1) according to one of Claims 1 to 3, characterised in that the thickness of the strength-imparting region (4) amounts to 0.5 mm to 3 mm.
5. X-ray anode (1) according to Claim 4, characterised in that the strength-imparting region (4) consists of 0.5 wt.% Mo, 0.08 wt.% Ti, 0.01 wt.% to 0.06 wt.% Zr, C or 1.2 wt.% Mo, 0.04 wt.% to 0.15 wt.% Hf, C.
6. X-ray anode (1) according to one of Claims 1 to 5, characterised in that the coating (2) consists of a W-Re alloy with 1 wt.% to 10 wt.% Re.
7. X-ray anode (1) according to one of Claims 1 to 6, characterised in that said X-ray anode is constructed as an axially symmetrical rotating anode and the strength-imparting region (4) and region (5) are arranged in axially symmetrical manner.
8. X-ray anode (1) according to Claim 7, characterised in that region (5) takes the form of a ring or disc, is positioned in a geometrically corresponding depression of the strength-imparting region (4) and is integrally connected to said strength-imparting region at least in the region below the focal track.

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