X-ray rotating anode with two different grain structures in the focal track coating.

Abstract

A rotating X-ray anode for generating X-rays includes a carrier and at least one annular focal track coating extending along a focal track on the carrier. The carrier is made of Mo or a Mo-based alloy. The at least one annular focal track coating is made of W or a W-based alloy. The focal track coating has, starting from the carrier and perpendicular to the focal track plane, a first layer and a second layer located directly above the first layer. The first layer is characterized by a different grain structure from the second layer.

Description

[Technical Field]

[0001] The present invention relates to an X-ray rotating anode having at least one annular focal track coating extending along a focal track plane, the focal track coating having, in order from the carrier along a direction perpendicular to the focal track plane, a first layer and a second layer located directly above the first layer, the first layer having a different crystal grain structure from the second layer. [Background technology]

[0002] X-ray rotating anodes are used to generate X-rays in X-ray tubes. During operation, electrons are emitted from the cathode of the X-ray tube and accelerated in the form of a focused electron beam onto the rotating X-ray rotating anode. Inspired by the rotational movement of the X-ray rotating anode, the electron beam scans a circular path, the focal track. In the region of the focal track, the X-ray rotating anode has a focal track coating formed on a carrier. The X-ray rotating anode rotates at high speed under the focused electron beam. The global voltage state of the X-ray rotating anode is obtained when the power density at the focal point is uniformly distributed over the entire surface area to be scanned. Each direct impact of the electron beam on a particular surface element on the focal track (for a high-power anode, for example, typically lasts for a time of 10 μsec (1 μsec = 1 × 10 -6During the period (seconds), the voltage state at this surface element changes locally compared to the global voltage state of the X-ray rotating anode. Tensile and compressive stress changes typically occur (when entering or exiting the electron beam) at the focal track's direct electron beam impingement point (i.e., the focal spot). This occurs particularly whenever a surface element on the focal track moves under the electron beam. Compressive stresses arise when the surface element expands relative to the relatively cooler environment. Tensile stresses, on the other hand, arise due to plastic deformation at high temperatures and due to contraction during subsequent cooling of a previously heated surface element. As X-ray rotating anode use progresses, the focal track coating deteriorates; fatigue cracks and thermal shock cracks can occur in the focal track coating. Over the course of X-ray rotating anode use, the focal track also deteriorates due to localized melting and particle spalling. As the deterioration or roughness of the focal track surface increases, the rate of backscattered electrons decreases, so more energy is absorbed from the impinging electrode beam across the entire focal track surface. This further exacerbates the effects of degradation.

[0003] X-ray rotating anodes are typically manufactured as a composite by powder metallurgy: the carrier and focal track coating are pressed together as a composite, sintered, and then forged, typically with a lower degree of deformation compared to semi-finished products (which typically range from 60-90%). The X-ray rotating anode is then typically annealed in a recrystallization process, which results in a substantially uniform grain structure in both the carrier and the focal track coating.

[0004] As already mentioned above, fatigue cracks and thermal shock cracks occur during the use of X-ray rotating anodes and propagate along the grain boundaries on the surface of the focal track coating. In a uniform grain structure, individual grains or particles can penetrate the surface of the focal track coating through these cracks, causing thermal isolation and therefore "overheating," i.e., individual grains can melt or peel off from the surface. This causes the surface of the focal track coating to become rougher. Over the course of use, the focal track deteriorates due to gradual crack growth and increasing energy absorption from the electron beam, resulting in melting, grain (particle) peeling, and increased roughness. As a result, the service life of X-ray rotating anodes is limited.

[0005] The formation of cracks in the focal track coating and further damage to the surface of the focal track coating adversely affects the x-ray dose yield, which in turn adversely affects the quality of the x-ray image. When the x-ray dose yield falls below a critical threshold, the entire x-ray rotating anode must be replaced, or at least the damaged focal track coating must be repaired or replaced. Therefore, there is a need for x-ray rotating anodes with a long service life or long shelf life.

[0006] Patent Document 1 discloses an X-ray rotating anode having a carrier and a focal track, where the carrier and focal track are manufactured as a composite by powder metallurgy. It is therefore desirable to provide an X-ray rotating anode that enables high dose yield over extended periods of use and has a long service life. In this case, at least a portion of the focal track has a non-recrystallized and / or partially recrystallized structure. This results in the above-mentioned uniform grain structure in the focal track coating and the above-mentioned drawbacks.

[0007] Patent Document 2 discloses a method for manufacturing an anode for an X-ray tube. In this method, a focal track coating is applied to an already formed substrate by induction plasma spraying. As a result, the focal track coating forms a predominantly columnar structure. The total thickness of the focal track coating in this document is 0.4 to 0.7 mm (which typically requires 20 to 50 overlaps of individual sprayed coating layers). This reduces grain boundary penetration, which has a positive effect on anode degradation. However, this structure can lead to virtually unlimited crack growth (along the grain boundaries) within the focal track toward the base material. In some cases, this can even lead to cracks across the entire surface of the substrate. Such deep cracks limit the service life of the X-ray rotating anode.

[0008] Patent document 3 discloses an X-ray tube that can withstand long-term continuous use. To this end, a coating (focal track) made of an X-ray-producing metal is applied to the substrate by chemical vapor deposition (CVD). In this case, the focal track coating should have a maximum average crystal grain size of 30 μm, preferably a maximum of 10 μm, by CVD. According to this patent document, a small crystal grain size is said to have the effect of suppressing roughening of the focal track surface. The thickness of the focal track should not exceed 100 μm. Here too, a columnar crystal structure is formed. The disadvantages of such a structure have already been explained above.

[0009] Patent document 4 discloses an X-ray anode having first and second luminescent layers on a carrier. However, both luminescent layers are separated by an intermediate layer. After the first focal track wears out (and the intermediate layer is removed), a second, new focal track can be used. However, this X-ray anode does not retard the aging of each focal track. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Austrian Utility Model No. 12494 [Patent Document 2] Austrian Utility Model No. 001984 [Patent Document 3] European Patent No. 0756308 [Patent Document 4] International Publication No. 2016 / 179615 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to effectively retard the aging of the focal track of an X-ray rotating anode, thereby extending the service life of the X-ray rotating anode. In particular, fatigue cracks and thermal shock cracks should be removed as directly as possible from the focal track surface, and the generation of adiabatic grains on the focal track surface should be prevented. Furthermore, cracks should not penetrate into the base material, and their propagation toward the base material should also be suppressed. Another object of the present invention is to provide a method for manufacturing such an X-ray rotating anode. [Means for solving the problem]

[0012] These problems are solved by an X-ray rotating anode according to claim 1 and a method for manufacturing an X-ray rotating anode according to claim 10. Advantageous embodiments of the invention are defined in the dependent claims. Features and details described in connection with the X-ray rotating anode according to the invention are naturally also applicable to the method according to the invention and vice versa, so that cross-reference is always made or disclosed as such with respect to the individual aspects relevant to the present disclosure.

[0013] According to the present invention, an X-ray rotating anode for generating X-rays comprises a carrier and at least one annular focal track coating extending along a focal track on the carrier, the carrier being made of Mo or a Mo-based alloy, and the at least one annular focal track coating being made of W or a W-based alloy, wherein the focal track coating has, starting from the carrier and perpendicular to the focal track plane, a first layer and a second layer located directly above the first layer, the first layer having a different grain structure from the second layer.

[0014] The inventors have determined that in the X-ray rotating anode of the present invention, crack formation and crack propagation are desirably influenced by the deliberate tailoring of two different grain structures in the focal track coating, and further, grain melting and grain infiltration at the focal track surface are significantly reduced.

[0015] These effects can be particularly achieved when the first layer of the focal track coating has a spherical grain structure and the second layer preferably has a columnar grain structure. The oriented (columnar) grain structure (second layer) of the focal track coating formed on the surface reduces grain boundary penetration and has a positive effect on aging degradation. Fatigue cracks and thermal shock cracks are guided as directly as possible through this oriented grain structure to their depths, where they encounter a different (spherical) grain structure (first layer). This deflects cracks coming from the focal track surface from a vertical direction, slowing their progression. This effectively delays aging degradation of the focal track and extends the service life of the X-ray rotating anode by limiting crack depth. Cracks induced directly from the surface to their depths effectively reduce tensile and compressive stresses on the focal track surface when applying and removing electron beam loads, resulting in significantly reduced degradation in the immediate vicinity of the cracks.

[0016] In terms of thermal expansion, the carrier of the rotating X-ray anode consists of molybdenum or a molybdenum-based alloy (e.g., TZM and MHC). These materials have proven particularly suitable for high thermal and mechanical loads. The term "consisting of" does not, in principle, exclude the possibility that the carrier can have additional components or additional coatings, for example, made of other materials that cover part of the surface. However, the carrier preferably consists of molybdenum or a molybdenum-based alloy. Molybdenum-based alloys refer in particular to alloys that are primarily composed of molybdenum, i.e., alloys that contain a higher proportion (measured in weight percent) of molybdenum than any other element present, i.e., alloys that contain at least 50% by weight of molybdenum. In particular, the molybdenum-based alloy can contain at least 80% by weight of molybdenum, preferably at least 90% by weight of molybdenum, and particularly preferably at least 98% by weight of molybdenum.

[0017] The focal track region on the carrier is provided with at least one circumferential or annular focal track coating extending along the focal track surface. As already mentioned, further layers, such as emissive layers, or additions, such as graphite bodies, can be provided on the carrier, especially on the side facing away from the focal track.

[0018] In this context, the focal track refers to the surface portion of the rotating X-ray anode that is intended to be scanned by the electron beam (and thus directed to it during use). The focal track may therefore form one or more surface portions of a focal track coating, which is typically formed annularly.

[0019] In particular, the carrier has an inclined focal track surface in the region of the focal track, preferably forming a frustoconical outer peripheral surface. The focal track surface is angled relative to a reference plane extending perpendicular to the rotation axis, so that the generated X-rays can exit through a lateral exit window in the respective X-ray device. For example, the focal track surface forms a focal track angle relative to this reference plane in the range of 2° to 16.25°, in particular 7° to 13°. In another embodiment, two focal track partial surfaces with two different angles can form the focal track surface.

[0020] According to a preferred embodiment, TZM is used as the support material. In this case, the molybdenum alloy TZM has a titanium content of 0.40-0.55% by weight, a zirconium content of 0.06-0.12% by weight, a carbon content of 0.005-0.04% by weight, an oxygen content of less than 0.03% by weight, and a molybdenum content (excluding any impurities) as the balance. In another preferred embodiment, MHC is used as the support material. In this case, MHC is understood to mean a molybdenum alloy having a hafnium content of 1.0-1.3% by weight, a carbon content of 0.05-0.12% by weight, an oxygen content of less than 0.06% by weight, and a molybdenum content (excluding impurities) as the balance. Both alloys (TZM, MHC) have high strength and hardness. These mechanical properties are retained even at high temperatures, which allows for higher operating temperatures of the X-ray rotating anode.

[0021] According to the present invention, the focal track material in the region of the focal track consists of tungsten or a tungsten-based alloy. The term "consisting of" here does not, for example, exclude in principle that the focal track material consists of two (or more) different tungsten-based alloys. In particular, at least one focal track coating formed on the carrier is made of said material. Tungsten-based alloys refer in particular to alloys that contain tungsten as the main component, i.e., a higher proportion (measured by weight) of tungsten than any other elements present, i.e., alloys that contain at least 50% by weight of tungsten. In particular, tungsten-based alloys can contain at least 70% by weight of tungsten, preferably at least 85% by weight of tungsten, and particularly preferably at least 90% by weight of tungsten.

[0022] In a preferred embodiment, the focal track coating is made of a tungsten (W)-rhenium (Re) alloy, which may have a rhenium content of up to 15% by weight. In particular, the rhenium content is in the range of 5-10% by weight. The aforementioned material is advantageous in terms of high thermal loads and the highest possible X-ray dose. The composition of the first layer of the focal track coating and the second layer of the focal track coating may be identical. However, it is also possible for the composition of the first layer of the focal track coating to differ from the composition of the second layer of the focal track coating, but in both cases it is tungsten or a tungsten-based alloy. Thus, in one embodiment, the focal track can be made from a first layer made of a W-Re alloy with 10% Re by weight and a second layer of W-Re with 5% Re by weight. This embodiment offers the advantage that the first layer (preferably produced by powder metallurgy) provides better crack resistance at moderate temperatures (e.g., 500-1000°C), and the second layer (preferably applied by plasma spraying) generates less rhenium vapor pressure at the same operating temperature during use of the X-ray rotating anode. Rhenium has a higher vapor pressure than tungsten. The lower the Re content, the lower the vapor pressure of the alloy. At high vapor pressures, localized heating can adversely affect the vacuum inside the tube and can result in voltage instabilities, such as arcing.

[0023] The focal track coating (also called the light-emitting layer) extending along the focal track surface comprises a first layer and a second layer located directly above the first layer, each layer having a different crystalline grain structure. The crystalline grain structure can be distinguished, for example, by the crystalline grain size, the crystalline grain distribution, the aspect ratio of the crystalline grains, the degree of recrystallization, etc. Preferably, the crystalline grain structure can be distinguished by the crystalline grain size or the aspect ratio of the crystalline grains. In the X-ray rotating anode according to the present invention, the focal track coating is defined starting from the carrier and extending perpendicular to the focal track surface. In particular, the focal track coating does not have an intermediate layer (barrier layer) separating or isolating the first layer from the second layer. To improve heat flow, the carrier and the first and second layers of the focal track coating are connected to each other by a material bond.

[0024] According to a further development, the first layer of the focal track coating has a spherical grain structure, and the second layer preferably has a columnar grain structure. The first layer is a layer that is applied directly to the carrier. According to the invention, a spherical grain structure means a structure with mostly uniform grains. In this case, mostly means that at least 80% of the grains observed under a microscope have a spherical structure, preferably more than 90% of the grains have a spherical structure. These characteristics are examined by cross-sectional observation using an optical or electron microscope. This microstructure or grain structure of the first layer can also be described by the so-called grain aspect ratio, which indicates the ratio of the grain length to the grain width. A spherical grain structure results in an average grain aspect ratio of less than or equal to 1 (≦1) in the focal track plane or perpendicular to the focal track plane, in particular an average grain aspect ratio of (0.5-0.95):1, preferably (0.7-0.9):1. The grain aspect ratio is measured using the line intercept method according to ASTM E112. Such a microstructure can be imparted, for example, after powder metallurgical manufacturing, preferably by subsequent forming (e.g., forging). Deformation can then result in a slight preferred orientation of the grains (parallel to the focal track surface).

[0025] If the first layer is produced by a powder metallurgical process (P / M process), the microstructure of the first layer may contain pores distributed across the entire cross section of the focal track coating. These are visible, for example, under an optical microscope as small black dots. The average grain size of the first layer is, for example, in the range of 10 to 75 μm, in particular 20 to 70 μm, preferably 20 to 45 μm (from micrographs according to ASTM E112). In a further embodiment, this first layer may be composed of various W alloys.

[0026] Preferably, the first layer of the focal track coating is produced as a composite with the carrier by powder metallurgy. Powder metallurgical production is understood to include pressing the corresponding starting powders to form a green compact and sintering the green compact. In addition, the production process may include further steps, such as mixing and homogenizing the powders to be pressed (e.g., by a plowshare mixer). The sintered part is preferably subjected to further processing steps, such as shaping (rolling, forging, etc.), which then results in a shaped structure, followed by annealing (typically recrystallization), etc.

[0027] The second layer of the focal track coating has a predominantly columnar or columnar grain structure, with the individual grains having a common growth direction, i.e., oriented in approximately the same direction. The columnar grain structure is preferably oriented approximately perpendicular to the focal track plane. The average aspect ratio of the grains perpendicular to the focal track plane is 1 or greater, in particular (1.5-5):1, preferably (1.5-3):1. The average grain size is 5-35 μm, preferably 10-15 μm (from microscopic grinding photographs according to ASTM E112).

[0028] Preferably the second layer of the focal track coating is produced by thermal spraying, in particular plasma spraying, for example vacuum plasma spraying (VPS).

[0029] The inventors have determined that an X-ray rotating anode according to the present invention having two different grain structures in the focal track coating provides the following advantages:

[0030] The columnar grain structure, i.e., the second layer, directs fatigue cracks and thermal shock cracks in this grain structure directly into the depths, i.e., away from the surface of the focal track. This reduces the formation of insulating grains at the focal track surface. The spherical grain structure, i.e., the first layer, can deflect cracks coming from the focal track surface at the grain boundaries, slowing their progression. Heat dissipation from the focal track surface is barely affected, even at longer distances from the focal track surface. In this way, the service life of the X-ray rotating anode according to the present invention can be significantly extended.

[0031] In one embodiment of the present invention, the different grain structures of the focal track coating are achieved by having the first layer of the focal track coating manufactured by powder metallurgy and preferably the second layer of the focal track coating manufactured by plasma spraying, particularly vacuum plasma spraying.

[0032] In a preferred embodiment, the second layer of the focal track coating has a thickness of at least 250 μm. As already mentioned, in X-ray rotating anodes, each movement of the surface member under the electron beam creates additional tensile and compressive stresses near the surface. For high-performance anodes, these changes, relative to the overall voltage state of the anode, typically extend up to 200 μm perpendicular to the focal track surface in the depth direction, resulting in higher voltages or additional periodic voltage changes in the microsecond (μsec) range in this region, relative to the overall voltage state of the anode.

[0033] The grain structure of the second layer (at this layer thickness) and the direct induction of cracks deep within it effectively reduce tensile and compressive stresses in the focal track surface (caused by electron beam loading and discharge), significantly reducing deterioration (or roughening) in the immediate vicinity of the cracks. To fully utilize the surface relaxation effect, the layer with a columnar grain structure must have a thickness or depth of at least 250 μm, especially in the area affected by the electron beam sweep. Within this depth range, crack deflection plays an increasingly small role in local overheating and thus accelerated aging of the focal track surface. Direct propagation of cracks into the support material must be avoided. Otherwise, the electron beam may strike the Mo-based alloy, which, because its melting point is much lower than that of the focal track alloy, could promote unacceptable evaporation within the electron beam and potentially lead to voltage flashover (so-called arcing).

[0034] The total thickness of the focal track coating, i.e., the thickness of the first and second layers, of the X-ray rotating anode according to the present invention is preferably 0.5 to 1.3 mm, more preferably 0.7 to 1.0 mm, which also results in a minimum thickness of the first layer of the focal track coating of 0.25 to 1.05 mm, preferably 0.45 to 0.75 mm.

[0035] In an alternative embodiment, the rotating anode according to the present invention has multiple slots / relief slots. These slots / relief slots are uniformly distributed around the circumference, pass through the thickness of the carrier and the thickness of the focal track coating, and extend radially between the outer periphery of the carrier (i.e., the slots open to the outer periphery) and the carrier bore (i.e., the slots terminate radially outside the carrier bore). Such slots allow the material of the rotating anode to expand in the outer region at the high temperatures encountered during use, reducing plastic deformation. This reduces stress within the material, and therefore fatigue, and avoids material failure. Such slots can extend exactly radially (the terms "radial" and "axial" refer to the predetermined rotation axis of the rotating anode). Alternatively, however, they can extend slightly obliquely to the radial direction (e.g., at an angle of >0° to 5°). The radial gradient, the axial gradient (which may also be slightly inclined relative to the axial direction, for example by an angle ranging from 1° to 10°), and / or the width of the slots may vary according to a predetermined profile. Furthermore, the ends of the slots (i.e., the radially inner ends) may be provided with end bores, each having a diameter greater than the width of the open slot, preferably extending through the thickness of the support, and / or end bores with circumferential grooves. Preferably, all of the slots are formed symmetrically with respect to one another relative to the rotation axis. Providing such slots is particularly advantageous when the thickness of the support increases toward the rotation axis.

[0036] The present invention further relates to a method for manufacturing an X-ray rotating anode, in particular an X-ray rotating anode according to the invention, which method can be designed according to one or more of the above-mentioned developments and / or variants, comprising the following steps: a) providing an X-ray rotating anode substrate comprising a carrier made of Mo or a Mo-based alloy and at least one focal track coating made of W or a W-based alloy, the focal track coating being annularly formed on the carrier and extending along a focal track surface, wherein the focal track coating has a first layer starting from the carrier in a direction perpendicular to the focal track surface of the X-ray rotating anode substrate; b) applying a second layer of W or a W-based alloy directly to the first layer of the focal track coating by a thermal cladding process, so that the focal track coating has, in a direction perpendicular to the focal track plane of the X-ray rotating anode substrate, the first layer and the second layer directly on top of it, the first layer having a different grain structure than the second layer.

[0037] The X-ray rotating anode substrate has a carrier and at least one annularly formed focal track coating. In this case, the X-ray rotating anode substrate may be a newly manufactured substrate, a scrap substrate (e.g., having defects in the focal track coating after manufacture), or an already aged or used substrate. In this context, "used" means that the focal track has already been in contact with the electron beam. If a newly manufactured substrate is provided, it is preferably produced by powder metallurgy by compacting and sintering the corresponding starting powder, and preferably subsequently shaping (e.g., hot forging, cold forging, etc.).

[0038] Furthermore, X-ray rotating anodes that have already been used and therefore have a deteriorated surface of the focal track coating can also be reprocessed by the method according to the invention (also called "rework"; for example, removal and reapplication of the focal track or focal lane). Aged focal track coating refers to the fatigue of the focal track coating due to the load / use of the X-ray rotating anode. This type of aged focal track coating can be repaired or renewed. In this case, the used focal track coating is removed until a crack-free surface is obtained, i.e., specifically the layer of focal track coating present on the surface. This does not involve removing the entire focal track coating down to the carrier, so that part of the focal track coating (the first layer) is retained. The used focal track coating can also be removed in the form of a calotte (spherical cap). A calotte is the curved surface of the ball part on which the focal track coating is machined. This saves material and further improves sustainability.

[0039] Thus, an advantage of the present invention is not only the renewal of the focal track coating, but also that the special grain structure of the focal track coating increases the loading capacity of the focal track coating, thus slowing down the aging of the X-ray rotating anode.

[0040] From an ecological, sustainability and cost perspective, it is desirable to provide an X-ray rotating anode that can be further used or adjusted.

[0041] In the method according to the present invention, the aged / used surface of the focal track coating is removed from the used substrate, and then a focal track layer (second layer) having a columnar grain structure is applied by plasma spraying. As a result, the used X-ray rotating anode can be reused and even the aging of the conditioned X-ray rotating anode can be delayed, which significantly saves resources.

[0042] Furthermore, the method according to the invention can also be used on X-ray rotary anode substrates (so-called scrap anodes) that have been manufactured by pressing, sintering, preferably by forging and mechanical processing, and subsequently suffer damage to the surface of the focal track coating. For this purpose, the surface of the focal track coating is similarly removed to remove the damage, and then a focal track layer (second layer) with a columnar grain structure is formed by plasma spraying.

[0043] The second layer of focal track coating is preferably applied by a thermal spray process such as plasma spraying.

[0044] Although the second layer can be applied as a single layer by plasma spraying, the focal track coating can also consist of several superimposed sprayed layers. In one embodiment of the method of the present invention, the second layer is applied in multiple layers by a thermal coating process or plasma spraying. In this case, one plasma layer corresponds to one rotation of the X-ray rotating anode by the plasma beam. The superposition of this first layer and optionally subsequent layers then results in a multi-layer sprayed layer. Particularly preferably, this sprayed layer, i.e., the second layer, has a thickness of 250 μm or more.

[0045] In one embodiment, the X-ray rotating anode is subjected to a heat treatment after the application of the second layer. The purpose of this heat treatment is both to further improve the bond structure by a diffusion process and to degas the anode. The temperature of the annealing treatment depends, inter alia, on the material from which the substrate is made. The heat treatment is usually carried out at a temperature of 1350°C or higher, preferably 1600°C or higher, particularly preferably 1700°C or higher, typically for 1 hour or more. In particular, the higher the annealing temperature, the shorter the heat treatment duration. [Brief explanation of the drawings]

[0046] Further advantages and suitability of the present invention will become apparent from the following description of an embodiment with reference to the accompanying drawings.

[0047] [Figure 1] 1 shows a schematic cross-sectional view of a rotating X-ray anode according to the present invention; [Figure 2] An X-ray electron microscope cross section (approximately 50x magnification) of the focal track on the substrate is shown. [Figure 3a] X-ray electron microscope cross section (approximately 50x magnification) of the focal track on the substrate, with the grain boundaries easily discernible using a software program. [Figure 3b] This is an exploded view of FIG. 3a without the carrier, magnified (approximately 250 times). [Figure 4a] 1 shows a schematic cross-sectional view of the rework sequence on a used X-ray rotating anode. [Figure 4b] 1 shows a schematic cross-sectional view of the rework sequence on a used X-ray rotating anode. [Figure 5a] 1 shows a schematic cross-sectional view of the rework sequence on a used X-ray rotating anode. [Figure 5b] 1 shows a schematic cross-sectional view of the rework sequence on a used X-ray rotating anode. [Figure 5c] An optical microscope view (approximately 35x) of Figure 5b is shown. DETAILED DESCRIPTION OF THE INVENTION

[0048] FIG. 1 shows a schematic cross-sectional structure of an X-ray rotating anode according to the present invention. The X-ray rotating anode 8 is rotationally symmetrical with respect to an axis of rotational symmetry 4. The X-ray rotating anode has a disk- or dish-shaped carrier 2 that can be mounted on the corresponding axis. The lid side of the carrier is provided with a focal track coating 3, which comprises a first layer 6 and a second layer 5 located directly thereon. In the region of the focal track coating, the carrier 2 has a circumferentially chamfered focal track surface 10 that is angled (at an angle α) with respect to a reference plane 7 that extends perpendicular to the axis of rotation 4. As is known in the art, the geometry and structure of the X-ray rotating anode 8 may differ from the X-ray rotating anode shown.

[0049] Figure 2 shows a REM-SE (secondary electron contrast) image. At approximately 50x magnification, Figure 2 shows a TZM substrate C on which a two-layer W-Re focal track coating is disposed. The two layers of the focal track coating are made from the same W-Re alloy (90% W by weight, 10% Re by weight). The first layer A of the focal track coating was manufactured by powder metallurgy in combination with the substrate. The second layer B of the focal track coating was applied by plasma spraying. The spherical grain structure of the first layer A and the columnar structure of the second layer B are clearly distinguishable.

[0050] Figures 3a and 3b show REM-SE (Range of Emission Secondary Electron Microscopy) images obtained by EBSD analysis. For this purpose, we briefly describe EBSD analysis (electron backscatter diffraction). This EBSD analysis allows for characterization of the respective structures at the microscopic level. In particular, this EBSD analysis allows for the determination of the respective structure of the layers and the specific texturing occurring within the structure. For this EBSD analysis, a cross section extending perpendicular to the focal plane (see Figure 1) through the X-ray rotating anode is generated within the sample preparation. The corresponding ground surface is prepared, in particular, by embedding, grinding, polishing, and etching at least a portion of the resulting X-ray rotating anode cross section. Optionally, the surface of the ground surface can be subsequently ion-polished (to remove surface deformation structures arising during the grinding process). In this case, the ground surface to be inspected is selected to include part of the focal track and part of the X-ray rotating anode carrier, allowing both parts to be inspected. The measuring device is configured so that the electron beam strikes the prepared ground surface at an angle of 30°. In the case of the scanning electron microscope (here, a Carl Zeiss "Ultra Plus"), the distance between the electron source (here, a field-emission cathode) and the sample was 22.5 mm, and the distance between the sample and the EBSD camera (here, a "Hikari XP CCD") was 16.8 mm. The bracketed indications refer to the type of equipment used by the applicant; other types of equipment that allow the described functionality in principle can also be used in a corresponding manner. The acceleration voltage was 20 kV, the magnification was set to 50x, and the distance between individual pixels on the successively scanned sample was 1 μm. For this purpose, additional display software (here, OIM7.3.1 from EDAX) was used. To determine the illustrated grain boundaries, a grain tolerance angle of 15° was set (this is the usual value for measuring grain boundaries with large angles). No cleanup was performed in the software. Regarding the software, for visualization of the grain structure, both the grayscale map type and the color-coded map type were set to "None," and a "rotation angle" of 15 to 180° was specified for the "boundaries."In these images, the grain boundaries of the focal track coating are clearly visible. The spherical grain structure of the first layer A is clearly distinguishable from the columnar grain structure of the second layer B. Figure 3a shows an image with a magnification of approximately 50x, and a portion of carrier C can also be identified. Figure 3b shows the same image at a magnification of approximately 250x. The grain structure of the second layer B is clearly distinguishable from the grain structure of the first layer A. Also at this magnification, the pores in the first layer A, which result from powder metallurgy manufacturing, are visible.

[0051] Working Example: Example 1: The manufacturing of an X-ray rotating anode according to the present invention will be described below based on an embodiment of the present invention. First, starting powder for the carrier and starting powder for the focal track coating (first layer) are mixed. The starting powder for the carrier is selected so that the composition of the carrier (excluding impurities) is 0.5 wt. % Ti, 0.08 wt. % zirconium, 0.005-0.04 wt. % carbon, less than 0.03 wt. % oxygen, and the balance molybdenum (i.e., TZM) (after all processes and heat treatments performed in the powder metallurgy manufacturing method are completed). Furthermore, the starting powder for the focal track coating is selected so that the composition is 10 wt. % rhenium and 90 wt. % tungsten (excluding impurities). The starting powder is mixed as a composite of 400 t (4 × 10 5The resulting mass was compressed to approximately 1000 kg (equivalent to 10 ... Specifically, the axis of the plasma gun was moved continuously past the centerline, alternating between both sides. The maximum deviation from the centerline was 5 mm, and the movement speed was 2 mm / s. The coating process lasted approximately 3 minutes, resulting in a focal track coating with a total thickness of approximately 250 μm and a width of 25 mm, formed by depositing approximately 20 individual layers. After the coating process was completed, the rotating anode was cooled to below 100°C and removed from the vacuum chamber. The focal track coating was then ground to a thickness of 0.7 mm. Finally, the completed rotating anode was subjected to high-vacuum annealing at a temperature of 1600°C for at least 1 hour.

[0052] The focal track of an X-ray rotating anode according to the present invention was examined at the end of its service life. It was found that cracks propagating along the columnar grain structure (or columnar grain boundaries) were deflected along the grain boundaries of the spherical structure, thereby changing their propagation direction several times. This deflection of cracks along the spherical structure prevented cracks from propagating deep into the focal track. At the end of the service life of the focal track, a uniformly distributed crack pattern with uniformly formed cracks was also observed on the surface. In contrast, in the X-ray rotating anode whose focal track was produced solely by vacuum plasma spraying, cracks were observed to propagate along the grain boundaries indefinitely deep into the focal track (even behind the substrate). Furthermore, the focal track coating of the X-ray rotating anode according to the present invention showed no grain spalling and a reduced number of melting events.

[0053] Example 2: Figures 4a and 4b show a schematic diagram of the reconditioning of a previously used or used (or aged) X-ray rotating anode, where the focal track coating 6 already has clear traces of aging 7. Figure 4a shows the focal track coating 6 placed on the carrier 2, already bearing clear traces of aging 7 on its surface 11. Furthermore, the X-ray rotating anode includes a graphite body 9. The focal track coating 6 is then polished so that there are no longer any cracks / signs of aging, i.e., the coating bearing the traces of aging 7 is completely polished. Finally, only a portion of the focal track coating 6 remains (see Figure 4b). Specifically, the focal track coating 6 is polished with a polishing plane parallel to the focal track surface to a residual thickness of 0.5–0.7 mm (depending on the initial thickness of the focal track coating and the depth of the aging traces). The resulting ground surface is then electropolished several times, at least twice, to remove any deformed structures caused by the grinding process. Thus, a portion of the focal track coating 6 produced by powder metallurgy is preserved (i.e., only the coating with the traces 7 is renewed). The second layer 5 is then applied by induction plasma spraying, resulting in a new focal track surface. The total thickness of the focal track coating preferably corresponds to the total thickness of the focal track coating before the initial aging or grinding, so that when the X-ray rotating anode is used after reworking, the X-ray formation point is identical to that of an X-ray rotating anode that has not yet been aged. Figure 4a shows a schematic cross-section of the focal track 6 with the traces 7 of use, while Figure 4b shows the already renewed focal track coating consisting of the first layer 6 and the second layer 5, resulting in the entire focal track coating 3.

[0054] Example 3: Figures 5a and 5b show a schematic representation of the reconditioning of a previously used or utilized X-ray rotating anode, whose focal track coating shows clear signs of aging. Figure 5a shows a focal track coating 6 placed on a carrier 2, which already shows clear signs of aging 11 on its surface. The X-ray rotating anode also includes a graphite body 9. The focal spot or focal track, i.e., the electron impact point on the focal track, is polished with a spherical cap having a radius R, so that cracks / signs of aging no longer exist. In particular, the focal track is polished so that part of the focal track coating 6, i.e., the part of the focal track coating 6 prepared by powder metallurgy, is preserved; only the used focal track coating is renewed. A second layer 5 is then applied by induction plasma spraying, resulting in a flat focal track surface again. The total thickness of the focal track coating after rework corresponds to the total thickness of the focal track coating before grinding. Therefore, when the X-ray rotating anode is used after reworking, the location of the X-ray formation is identical to that of an X-ray rotating anode that has not yet been aged (i.e., an X-ray rotating anode before the initial aging). Figure 5a shows a schematic cross-section of the focal track coating 6 after the focal track surface 11 has been removed by the spherical cap, while Figure 5b shows the already renewed focal track 5, 6. Preferably, the thickness of the focal track 5, i.e., the second layer, is at least 250 μm at the maximum material removal point. This maximum material removal point corresponds to the deepest point within the spherical cap. Figure 5c shows an optical microscope image of the carrier 2 with the powder metallurgical first layer 6 and the plasma sprayed second layer 5. The focal track surface 11 is indicated by an arrow.

Claims

1. An X-ray rotating anode (8) for generating X-rays, a carrier (2) and at least one annular focal track coating (3) extending along a focal track surface (10) on the carrier; The support (2) is made of Mo or a Mo-based alloy, the at least one annular focal track coating (3) is made of W or a W-based alloy; wherein the focal track coating (3) comprises, in order from the carrier (2) along a direction perpendicular to the focal track plane (10), a first layer (6) and a second layer (5) located directly above the first layer (6); The first layer (6) has a different grain structure from the second layer (5). A rotating X-ray anode.

2. the first layer (6) of the focal track coating has a spherical grain structure; The second layer (5) has a columnar grain structure.

2. The X-ray rotating anode according to claim 1.

3. the spherical grain structure extends from the carrier (2) along a direction perpendicular to the focal track plane (10), and the average grain aspect ratio is 1 or less; 4. A rotating X-ray anode according to any preceding claim.

4. the columnar grain structure extends from the carrier (2) along a direction perpendicular to the focal track plane (10), and the average grain aspect ratio is greater than 1; 4. A rotating X-ray anode according to any preceding claim.

5. The second layer (5) has a layer thickness of at least 250 μm.

4. A rotating X-ray anode according to any preceding claim.

6. The Mo-based alloy is TZM or MHC; 10. The X-ray rotating anode according to any preceding claim.

7. The W-based alloy is a W—Re alloy.

4. A rotating X-ray anode according to any preceding claim.

8. characterised in that the composition of the first layer (6) of the focal track coating is different from the composition of the second layer (5) of the focal track coating, 10. The X-ray rotating anode according to any preceding claim.

9. the first layer (6) of the focal track coating is manufactured by powder metallurgy, the second layer (5) of the focal track coating is produced by plasma spraying; 4. A rotating X-ray anode according to any preceding claim.

10. A method for manufacturing an X-ray rotating anode (8), comprising the steps of: a) providing an X-ray rotating anode substrate comprising a carrier (2) made of Mo or a Mo-based alloy and at least one annular focal track coating (6) made of W or a W-based alloy extending on the carrier along a focal track plane, the focal track coating (6) having a first layer (6) originating from the carrier along a direction perpendicular to the focal track plane of the X-ray rotating anode substrate; and b) applying a second layer (5) of W or a W-based alloy directly onto the first layer of the focal track coating by a thermal coating process, so that the focal track coating has the first layer and a second layer disposed directly above it along a direction perpendicular to the focal track plane of the rotating X-ray anode substrate, the first layer (6) having a different grain structure from the second layer (5); A method for manufacturing an X-ray rotating anode (8), comprising:

11. the step of preparing an X-ray rotating anode substrate having the first layer includes a step of manufacturing the carrier (2) and the first layer (6) as a composite by a powder metallurgical method; The method of claim 10.

12. The step of preparing an X-ray rotating anode substrate having the first layer includes: a step of preparing a used X-ray rotating anode substrate having the carrier and the first layer, wherein the carrier (2) and the first layer (6) are manufactured as a composite by a powder metallurgical method; removing the used portion of the first layer; The method of claim 10, comprising:

13. the second layer (5) being applied by plasma spraying; 13. The method according to any one of claims 10 to 12.

14. the second layer (5) is applied in multiple layers by plasma spraying, 14. The method according to any one of claims 10 to 13.

15. a heat treatment of the X-ray rotating anode after applying the second layer; 15. The method according to any one of claims 10 to 14.

16. After applying the second layer, the X-ray rotating anode is subjected to a heat treatment at 1350° C. or higher.

16. The method according to any one of claims 10 to 15.

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