Rotor parts for X-ray rotating anodes

Abstract

1. A rotor part for an X-ray rotating anode, comprising a carrier body and a thermal sprayed coating, the carrier body being made from one of the group of materials consisting of a heat-resistant metal, a heat-resistant metal-based alloy, Fe, an Fe-based alloy or a combination thereof, the thermal sprayed coating being made from Cu or a Cu-based alloy, the carrier body being material-bonded to the thermal sprayed coating in at least some parts at a connection surface, characterized in that the microstructure of the rotor part does not have a transition zone at the connection surface between the carrier body and the thermal sprayed coating.

Description

[Technical Field]

[0001] The present invention relates to a rotor component for an X-ray rotating anode and a method for manufacturing the rotor component for an X-ray rotating anode. [Background technology]

[0002] The rotor for the X-ray rotating anode is rotatably mounted inside the vacuum housing and rotatably and fixedly connected to the X-ray rotating anode. The rotor, together with the stator, forms an electric motor that rotates the X-ray rotating anode within the vacuum housing when the stator is connected to a power source. The rotor for the X-ray rotating anode typically consists of a copper cylinder surrounding a tubular iron core. The disadvantage of this is that the materials required for the electric drive have different thermal expansion coefficients, so they must be attached to each other to maintain stable rotor alignment and withstand the temperature fluctuations that occur within the X-ray tube.

[0003] For example, from US Pat. No. 5,629,499 it is known to apply an outer rotationally symmetric section of a rotor (e.g., made of copper) as a coating to an inner rotationally symmetric section of the rotor (made of a ferromagnetic material, e.g., steel) to form a material bond between the two materials. In US Pat. No. 5,629,499, this is performed by build-up welding, in particular by laser build-up welding. In laser build-up welding, the coating material is applied as powder from a nozzle at a predetermined mass flow rate to the substrate and then immediately melted by continuous exposure to laser light, thereby forming a welded joint with the substrate. However, this creates a boundary layer where the two materials mix (as the laser locally melts the substrate). This boundary layer represents a discontinuity in the properties of the respective materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] DE 19945414

[0005] Currently, rotor components made of ferromagnetic materials (e.g., steel) coated with copper or copper alloys are primarily manufactured by backcasting. Backcasting is the metallurgical application of a material to a carrier body, whereby the carrier body is always in a solid, cohesive state relative to the process parameters used. For example, during backcasting, a solid, bulk-shaped carrier body, e.g., made of steel, is inserted into a graphite mold. The carrier body is then backcast with a second material, e.g., a melt of copper or a copper alloy. For example, the melting point of pure copper is 1083°C. Targeted solidification of the molten copper or copper alloy allows for a largely porosity-free interface or connection surface, with good direct bonding of the copper or copper alloy to the carrier body. This means that no additional joining surface, as in the case of soldering, is required. However, a disadvantage of this method is the relatively high temperature of the molten metal acting on the substrate, especially at the joining surface between the substrate and the coating. This high temperature results in the formation of a transition zone between the copper or copper alloy coating and the substrate. The transition zone is formed in the copper or copper alloy applied by backcasting by melting or dissolving the substrate material; i.e., the material on the surface of the substrate is melted and diffuses into the coating, resulting in the absence of homogeneous material properties in the transition zone. In addition, individual components of the carrier body material (e.g., Fe) can diffuse across the transition zone into the coating and thus affect the material properties of the coating. After solidification of the copper or copper alloy, the cooled rotor component exhibits a microstructure (e.g., recognizable in a cross-sectional scanning microscope image) consisting of the carrier body, the coating, and the transition zone between the two materials. In the aforementioned backcasting process, after the molten copper or copper alloy solidifies, the coated rotor component is machined or reworked by turning, milling, cutting, etc. to achieve the final part shape. This is referred to as a "top-down" machining strategy.That is, the direction of machining is "top to bottom" - subtraction or subtraction from the top to the concrete - for example, from a fully backcast part to the final part geometry by machining. The final geometry of the rotor part can only be realized in a rotationally symmetric manner due to the mechanical processing, since separate milling of non-rotationally symmetric shapes is very time-consuming and costly. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide an improved rotor part for an X-ray rotating anode, in particular a rotor part having improved electrical conductivity of both the coating and the region of the connecting surface between the carrier body and the thermal spray coating. It is also an object of the present invention to provide an improved method for manufacturing such a rotor part. [Means for solving the problem]

[0007] The technical problem of the present invention is solved by providing a rotor part for an X-ray rotating anode, comprising a carrier body and a thermal sprayed coating, the carrier body being made of a refractory metal, a refractory metal-based alloy, Fe, an Fe-based alloy or a combination thereof, the thermal sprayed coating being made of Cu or a Cu-based alloy, and the carrier body being materially bonded to the thermal sprayed coating at least in some parts of the connection surface, characterized in that the microstructure of the rotor part does not have a transition zone at the connection surface between the carrier body and the thermal sprayed coating. Furthermore, a method for producing a rotor part having the features of claim 9 is provided. Further advantageous aspects of the present invention can be found in the dependent claims, which can be freely combined with one another.

[0008] The inventors have discovered that the material properties of the binding partners differ in the transition zone formed between the substrate and the coating during backcasting. Furthermore, individual components of the substrate material can diffuse across the transition zone into the coating during backcasting, affecting the material properties of the coating. These altered material properties have adverse effects when the rotor component is used (both in the transition zone and the coating). In particular, the electrical conductivity of the copper or copper alloy in the coating produced by backcasting is reduced compared to a "pure" coating (made from copper or a copper alloy), as is the electrical conductivity in the transition zone.

[0009] In rotor components according to the present invention, the electrical conductivity of copper can be fully utilized, since the presence of a dissolved carrier material in the thermal spray coating does not reduce the electrical conductivity. Furthermore, the present invention allows for resource-saving use of copper or copper alloys, for example, by directly applying the thermal spray coating with little or no post-treatment of the coating (a "bottom-up" approach to processing, i.e., during processing or manufacturing. The direction of action of the process is accumulation or addition "from bottom to top" in small units to the final product, in contrast to the "top-down" processing strategy described above). Furthermore, the layer thickness of the thermal spray coating can be reduced (resource-saving) compared to the layer thickness in a backcasting process, yet rotor components according to the present invention can achieve the same turning performance. Furthermore, the process according to the present invention also allows for the application of Cu or Cu-based alloy coatings to more complex geometries or geometries for rotor components that do not necessarily need to be rotationally symmetric.

[0010] According to the present invention, the rotor part has a carrier body and a thermal spray coating. In particular, the rotor part must be suitable for the X-ray rotating anode in order to withstand the loads in the X-ray tube. For example, imbalance must not occur. The rotor part may be a rotating part of the rotor that drives the X-ray rotating anode. However, the rotor part may also be a part of the rotor that is connected to another part, for example, by a material bond or a form fit, to drive the X-ray rotating anode.

[0011] The carrier body is made of a material consisting of a refractory metal, a refractory metal-based alloy, Fe, an Fe-based alloy (including steel), or a combination thereof. Refractory metals are refractory base metals of the 5th subgroup (vanadium, niobium, and tantalum) and the 6th subgroup (chromium, molybdenum, and tungsten). Their melting points are higher than that of platinum (1772°C). Refractory metal-based alloys can be understood as combinations of several pure refractory metals (e.g., W and Mo) as well as their alloys (e.g., W-Re) and / or their compounds. In the context of the present invention, a refractory metal-based alloy is understood to be an alloy containing at least 50% by weight, particularly at least 80% by weight, and particularly preferably at least 90% by weight, of a refractory metal or several refractory metals. Among the refractory metals, Mo and W, as well as Mo-based alloys and W-based alloys, are particularly suitable. In Mo-based or W-based alloys, the proportion of Mo (or W) is 50% by weight or more, preferably 80% by weight or more, particularly 90% by weight or more or 95% by weight or more. Molybdenum has a very high melting point, low thermal expansion, and high thermal conductivity, which is why Mo or Mo-based alloys are particularly advantageous (also from a cost perspective). Tungsten has the highest melting point of all metals, a very low thermal expansion coefficient, and high dimensional stability. A carrier body made of a combination of steel and Mo, with a steel section and a Mo section, is particularly suitable from a cost perspective.

[0012] An Fe-based alloy is understood to mean an alloy having more than 50% by weight of Fe, in particular more than 80% by weight of Fe, particularly preferably more than 90% by weight or more than 95% by weight of Fe. In particular, steels having preferably more than 97% by weight of Fe are advantageous for the carrier body according to the invention.

[0013] Thermal spray coatings according to the present invention are understood to be coatings applied by thermal spraying processes, such as plasma spraying (in air, inert gas or under low pressure), powder flame spraying, high velocity oxygen fuel (HVOF), detonation spraying (flame impact spraying), laser spraying and cold gas spraying (CGS). A common feature of all thermal spraying processes is the interaction of thermal energy with kinetic energy. The coating material is heated, for example, with a spray torch (thermal energy) and / or accelerated to high speeds (kinetic energy). Particularly preferred coatings of the present invention are cold gas spray (CGS) coatings. An alternative embodiment is plasma spraying.

[0014] Cold gas spraying is a coating process in which powder particles are applied to a substrate with very high kinetic energy and low thermal energy.

[0015] The thermal spray coating is made of Cu or a Cu-based alloy. A Cu-based alloy is an alloy containing Cu, where Cu is the main component, and the Cu content is 50% by weight or more, preferably 70% by weight or more, and particularly preferably 80% by weight or more. Examples of copper alloys include CuZn (Cu: copper, Zn: zinc), CuZnSi (Si: silicon), CuMg (Mg: magnesium), CuAl (Al: aluminum), CuBe (Be: beryllium), CuCrZr (Cr: chromium, Zr: zirconium), and CuZr. Cu or Cu alloys typically contain unavoidable impurities. In Cu or Cu alloy compositions, these are, for example, elements such as iron, nitrogen, and oxygen. Carbon or hydrogen impurities are also possible. Therefore, the thermal spray coating of the present invention can contain corresponding impurities, particularly the elements mentioned above. The elements oxygen, iron, and nitrogen are preferably present in the thermal spray coating according to the present invention in the following maximum amounts: 1000 μg / g or less of oxygen, 500 μg / g or less of iron, and 200 μg / g or less of nitrogen. For oxygen, a preferred content is 500 μg / g or less, more preferably 250 μg / g or less, and particularly preferred is an oxygen content of 5 to 210 μg / g of the coating. The nitrogen content is preferably 200 μg / g or less, more preferably 100 μg / g or less of nitrogen. The nitrogen content is particularly preferred to be 0.5 to 50 μg / g. The oxygen and nitrogen contents in the thermal spray coating should be kept as low as possible. On the one hand, this can have a beneficial effect on the processability of the powder for the thermal spray coating. On the other hand, pore formation in the thermal spray coating is avoided. The iron content should be as low as possible, preferably 500 μg / g or less. More preferably, the iron content is 250 μg / g or less. The iron content of the coating is particularly preferably 100 μg / g or less, most preferably 0.5 to 50 μg / g, because Fe dissolved in Cu or Cu alloy reduces the electrical conductivity of the thermal spray coating.

[0016] The thermal spray coating according to the present invention 、C Theoretical density of Cu-based alloys 90% or more, preferablyThe coating has a relative density of 95% or more, particularly 97% or 98% or more. Therefore, pores can be present in the coating, with a porosity of 2% or less, preferably less than 1.5%. A high relative density ensures high electrical conductivity. The determination of density follows Archimedes' principle, which describes the relationship between the mass, volume, and density of a solid immersed in a liquid. Using the so-called buoyancy method, the weight lost by buoyancy is determined, and the density is calculated from this and the weight in air. The relative density is measured relative to the theoretical density of the respective material. The theoretical density of a material corresponds to the density of a 100% dense material without pores. In the present invention, the substrate body is ground after the thermal spray coating to determine the density, so that only the coating remains and can be measured.

[0017] The thermal spray coating can extend over the entire or part of the carrier body. In addition to the carrier body, the thermal spray coating can also cover parts of the rotor adjacent to the carrier body. These parts can be connected to the carrier body, for example, by a material bond or a form fit.

[0018] According to the invention, the carrier body is materially bonded to the thermal spray coating at least in part via a connecting surface, which is located between a surface or a region of the surface of the carrier body and a surface or a region of the surface of the thermal spray coating and connects the carrier body to the thermal spray coating with a material bond, so that the carrier body is permanently and inseparably connected to the thermal spray coating.

[0019] The rotor component according to the invention does not have a transition zone on the connection surface between the carrier body and the thermal spray coating.

[0020] According to the prior art, a transition zone is a zone of molten interface or diffusion zone, which can occur during the transition between the material of the carrier body and the material of the coating, for example, when back-casting a carrier body with Cu or a Cu alloy. The material is melted on the surface of the carrier body, for example, by high temperature, and diffuses into the coating. The material of the coating also diffuses into the carrier body. For example, a Cu layer and an Fe layer can form a common layer in the intermediate transition zone (typically with a composition gradient, with a higher Fe content toward the side of the Fe layer and a higher Cu content toward the side of the Cu layer), i.e., typically, there is no homogeneous material in the transition zone. Such a transition zone is usually formed during back-casting, as described above.

[0021] "No transition zone" means that the surface structure of the substrate and the surface structure of the spray coating can be clearly defined, i.e., the two materials are directly adjacent to each other at the joining interface. Essentially, there is no mass transfer between the two materials, i.e., any transition zone that may exist is no longer detectable or is completely absent. The surface structure of the carrier body may still have a slight surface roughness (Ra) or surface irregularities at the joining surface (see FIG. 4a). Such surface roughness does not represent a transition zone, since the material of the carrier body can still be clearly defined from the spray coating. Surface roughness can be measured tactilely or optically. In the case of tactile measurement, the surface is measured with a measuring probe for roughness measurement using the tactile step method (line roughness) in accordance with DIN EN ISO 4287.

[0022] The invention described herein eliminates the drawbacks identified by the inventors regarding the transition zone formed between the carrier body and the coating during backcasting. Furthermore, there is no contamination of the coating with dissolved carrier material. The properties of the material in the coating, such as the electrical conductivity of copper, are significantly impaired by both the occurrence of the transition zone and any impurities that may be present. As already explained above, "no transition zone" means that the material of the thermal spray coating is directly adjacent to the material of the substrate at the joining interface. As a result, the electrical conductivity of the joining interface is determined solely by the material of the thermal spray coating and the material of the carrier body, but is not adversely affected by impurities in the transition zone or the coating, which typically has a lower electrical conductivity. Furthermore, thermal spray coating has the advantage of a thinner coating thickness compared to the backcasting process, allowing for more complex geometries for rotor components that do not necessarily have to be rotationally symmetric.

[0023] In a preferred embodiment of the present invention, the thermal spray coating is a cold gas spray (CGS) coating. When a thermal spray coating is applied to a substrate by cold gas spraying, it can be seen under a microscope that the coating consists of individual particles. The particles in a coating applied by low-temperature irradiation do not exhibit a molten phase and are still clearly recognizable in the deposited coating. The particles undergo deformation due to the high kinetic impact energy, so that the coating contains cold-formed Cu particles or Cu-based alloy particles in at least some regions. Cold deformation should be understood by the metallurgical definition as the particles being deformed by impact with the substrate under conditions (temperature / time) that do not lead to recrystallization. Cold-worked structures are characterized by characteristic dislocation structures, as is well known to all experts and described in detail in specialized textbooks. Dislocation structures can be visualized, for example, using a TEM (transmission electron microscope).

[0024] The cold-formed particles of the coating are at least partially elongated in a direction parallel to the substrate surface (transversely), resulting in an average (average value of at least 100 elongated particles) particle aspect ratio (GAR; corresponding to the particle's length divided by its width) greater than 1. The aspect ratio is determined metallographically by analyzing images using the line section method (see ASTM E112-96). For this purpose, a section embedded in an embedding medium, such as epoxy resin, is first prepared. After a curing period, the sample is metallographically prepared, i.e., the cross section can be subsequently analyzed. Preparation involves the following steps: grinding with bonded SiC paper with a grit size between 220 and 1200; polishing with a diamond suspension with a grit size of 3 μm; final polishing with OPS (oxide polishing suspension) with a grit size of 0.04 μm; cleaning the sample in an ultrasonic bath and drying the sample. The cross section is then etched. Scanning electron microscopy is used to determine the aspect ratio by the width-to-height ratio of the particles.

[0025] In a further embodiment of the present invention, thermal spray coatings are recrystallized or recovered by annealing after low-temperature spray coating, resulting in a fine-grained, more equiaxed microstructure that is significantly different from backcast coatings. After annealing, the low-temperature spray coating exhibits a recrystallized microstructure of Cu or Cu-based alloy grains with an average grain size of 150 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and particularly preferably 1 μm to 10 μm. The average grain size can be easily analyzed using a line-section method on optical microscope images of longitudinal metallographic cross sections (the forming direction and the normal direction form the image plane). For this purpose, the longitudinal cross sections are prepared by etching to visualize the grain boundaries. At 500x magnification (image section 240 × 100 μm), five lines are placed in the image at equal intervals from edge to edge, and the maximum grain size is measured in both directions (forming direction and normal direction), and the average value ((a + b) / 2) is obtained. The recrystallization increases the electrical conductivity of the rotor component according to the invention. Furthermore, the adhesion of the copper or Cu-based alloy layer to the carrier material is improved.

[0026] The thickness of the thermal spray coating is preferably 0.025 mm to 5 cm. In particular, the thickness is advantageously 0.1 mm to 4 mm, more preferably 0.5 mm to 2 mm, and particularly preferably 0.8 mm to 1.2 mm. The layer can consist of a single layer or, preferably, multiple layers. The layer thickness can be determined using a scanning electron microscope. A metallographic section is taken perpendicular to the plane of the intermediate layer, and the layer thickness is then measured under a scanning electron microscope at an appropriate magnification. The layer thickness should be determined at a representative point on the section. At least 10 different representative points should be analyzed for their coating thickness and an average value should be determined, which provides the value for the average thickness of the coating.

[0027] According to a further advantageous embodiment of the present invention, the thermal spray coating has a conductivity of 26 MS / m (megasiemens per meter) or more. Preferably, the conductivity is 40 MS / m or more, more preferably 50 MS / m or more, and particularly preferably 55 MS / m or more. The conductivity is measured in accordance with DIN EN 16813 (2017).

[0028] The rotor component according to the present invention exhibits good adhesion strength of the thermal spray coating. The adhesion strength was measured according to ASTM C633-13(2016). The adhesion strength of the rotor component according to the present invention is greater than 10 MPa, preferably greater than 20 MPa.

[0029] The present invention also relates to a method for manufacturing a rotor part for an X-ray rotating anode having a carrier body and a thermal spray coating, the method being characterized by the following steps: - providing a support comprising a refractory metal, a refractory metal-based alloy, Fe, an Fe-based alloy, or a combination thereof; - coating a carrier with a thermal spray coating using a powdered coating material, thereby producing a rotor component having at least a partial material bond connection at the connection surface between the carrier body and the thermal spray coating, wherein the thermal spray coating consists of Cu or a Cu-based alloy, and the microstructure of the rotor component does not have a transition zone at the connection surface between the carrier body and the thermal spray coating.

[0030] The method according to the invention for manufacturing a rotor part ensures that the advantages described above for the part according to the invention are achieved reliably and with process reliability. Furthermore, the advantageous embodiments of the invention described above are also advantageous for the method according to the invention.

[0031] Thermal spray coatings are particularly preferably applied using cold gas spraying (CGS). As described above, powder particles with very high kinetic energy and low thermal energy are applied to the carrier body. A process gas under high pressure (e.g., air, helium (He), nitrogen (N), water vapor, or a mixture thereof) is expanded using a convergent-divergent nozzle (also known as a supersonic nozzle). A typical nozzle shape is a Laval nozzle. Depending on the process gas used, gas velocities of 300 to 1200 m / s (meters per second) (for N) or up to 2500 m / s (for helium) can be achieved. The coating material is injected into the gas stream, for example, upstream of the narrowest cross section of the convergent-divergent nozzle forming part of the spray gun, accelerated to a speed typically between 300 and 1200 m / s, and deposited onto the carrier body. By heating the gas upstream of the convergent-divergent nozzle, the gas flow rate, and therefore the particle velocity, increases as the gas expands within the nozzle. Typically, gas temperatures between room temperature (RT), especially 20°C, and 1000°C are used for low-temperature gas spraying according to the present invention. Low-temperature gas spraying can be used to spray ductile materials, especially those with face-centered cubic and hexagonal close-packed lattices, to form dense, well-adhered layers. Low-temperature irradiation is typically used to apply metal layers to metal substrates. In low-temperature gas spraying, coatings are built up layer by layer from individual particles of the coating material. The adhesion of the coating material to the substrate and the cohesion between the coating material particles are crucial for the quality of the low-temperature gas sprayed coating. In principle, adhesion is a combination of several physical and chemical adhesion mechanisms, both in the area of ​​the coating material / substrate bonding surface and between the coating material particles. Due to the low process temperature, the powder does not melt during low-temperature gas spraying; instead, it impinges on the substrate to be coated in an unmolten state, building up a layer. The high kinetic energy resulting from the high velocity of the powder moving through the gas stream causes mechanical interlocking when the powder strikes the surface of the substrate, the interlocking being assisted by the process temperature. Coatings produced in this manner using low-temperature gas spraying can be recognized under a microscope by the fact that the coating consists of individual particles with a "pancake" shape (i.e., a structure in which the length and width of the individual particles are large compared to their thickness).The particles are deformed by the high kinetic impact energy and exhibit an aspect ratio greater than one.

[0032] According to an advantageous production method of the invention, low-temperature gas spraying is carried out at a pressure of 10 to 100 bar, preferably 20 to 80 bar, particularly preferably 30 to 60 bar, and at a gas temperature of room temperature (RT) to 1000°C (room temperature is particularly 20°C). The gas temperature is preferably 300 to 1000°C, particularly preferably 400 to 800°C.

[0033] According to an advantageous manufacturing method of the present invention, the rotor part is annealed in a vacuum or protective gas atmosphere after the coating step. This process step improves the electrical conductivity of the coating and reduces residual stresses in the coating. Preferably, the rotor part is annealed at 400-750°C for up to 5 hours. More preferably, the rotor part is annealed at 500-600°C for 0.5-3 hours.

[0034] According to an advantageous manufacturing method of the present invention, the carrier body is surface-treated before the coating process. This can be a chemical or physical surface treatment. It can be a surface treatment with alcohol, blasting, etc. Surface treatment with a powder jet is preferred, as this allows for better adhesion of the low-temperature sprayed coating to the substrate.

[0035] The method according to the invention as well as preferred embodiments thereof achieve, inter alia, the following advantageous effects: - Improved electrical conductivity of thermally sprayed coatings on rotor components; - Reduction of layer residual stresses and improvement of thermal spray coating adhesion; - the absence of a transition zone between the carrier body and the thermal spray coating, which improves the electrical conductivity at the connecting surface between the carrier body and the thermal spray coating;

[0036] Coating materials are composed of particles. A large number of particles is called a powder. A large number of powder particles can be converted into powder granules by granulation. The size of the powder particles or powder granule particles is called particle size and is usually measured using laser diffraction methods. The measurement results are given as a distribution curve. d 50The values ​​indicate the average particle size. 50 means that 50% by volume of the particles are smaller than the specified value.

[0037] Furthermore, particles with a particle size d of 5 μm or more and 150 μm or less 50 It is advantageous to have d 50 is measured by laser diffraction using the standard (ISO 13320-2009). Another advantageous range is 10 μm≦d 50 ≦100μm or 15μm≦d 50 ≦80 μm.

[0038] According to an advantageous manufacturing method of the present invention, the spray coating can be applied in several layers of powdered Cu or several layers of powdered Cu-based alloy. The final thickness of the coating is between 25 μm and 5 cm. The thickness of the coating is determined using conventional metallographic methods.

[0039] Further advantages and benefits of the present invention will be apparent from the following description of the embodiments, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0040] [Figure 1] Schematic diagram of a longitudinal section of a state-of-the-art X-ray tube with a rotating X-ray anode [Figure 2] Scanning electron microscope image (100x magnification) of the transition zone between the steel body and copper in sample number 1 using state-of-the-art technology [Figure 3] Scanning electron microscope image (100x magnification) of the transition zone between the steel body and copper in sample number 2 according to the invention [Figure 4a] Scanning electron microscope image (500x magnification) of the transition zone between the steel body and copper in sample number 2 according to the invention [Figure 4b] Scanning electron microscope image (500x magnification) of the transition zone between the steel body and copper in sample number 1 using state-of-the-art technology [Figure 4c] Line scan of the transition zone between the steel body and copper based on Fig. 4(b) [Figure 5]Scanning electron microscope image (100x magnification) of the copper coating on sample No. 2 according to the invention before the annealing step [Figure 6] Optical microscope image (200x magnification) of the copper coating on sample number 2 according to the invention after etching and before the annealing step. [Figure 7] Optical microscope image (200x magnification) of the copper coating on sample number 2 according to the invention after etching and annealing steps [Figure 8] Optical microscope image (50x magnification) of the copper coating on sample number 2 according to the invention after etching and after annealing [Figure 9] Optical microscope image (50x magnification) of the copper coating on sample number 1 using state-of-the-art techniques after etching

[0041] FIG. 1 shows a longitudinal section of an X-ray tube with a rotor and an X-ray rotating anode, as known in the prior art. X-ray tubes typically consist of a glass bulb (5) with a vacuum interior (4). The glass bulb contains a cathode (3) with a heating coil (6) that emits electrons (7). Opposite the cathode (3) is the X-ray rotating anode (2), which has an anode disk (11) connected to the rotor (1) of an electric motor by a shaft (12). Stators (9, 10) are positioned outside the glass bulb (5) to drive the rotor. When connected to electricity, the stators (9, 10) generate a magnetic field that rotates around the glass bulb (5), which exerts a torque on the rotor (1), thus rotating the X-ray rotating anode (2). The rotor (1) and X-ray rotating anode (2) are placed in a high vacuum (4) within the glass flask (5). Electrons (7) emitted by the cathode (3) are accelerated towards the anode disk, where they decelerate to produce X-rays (8), which exit the X-ray tube through an emission window in the glass bulb.

[0042] [Example] Sample No. 1 was manufactured using a state-of-the-art backcasting process. A steel tube with a length of 103 mm, an outer diameter of 62 mm, and an inner diameter of 44 mm was provided for this purpose. The steel tube had a composition of 0.08–0.15 wt.% C, 1.00 wt.% Si, 1.50 wt.% Mn, 0.040 wt.% P, 0.030 wt.% S, 11.5–13.5 wt.% Cr, with the remainder being Fe and normal impurities. The steel tube was inserted into a graphite mold and then backcast with a copper melt (containing at least 99.95 wt.% Cu, with the remainder consisting of normal impurities totaling up to 0.05 wt.%). The steel tube was then ground so that the copper coating (on the outer sheath surface of the steel tube) had a thickness of 2 mm.

[0043] For sample number 2 of the present invention, a Cu powder was prepared having 99.95 atomic % Cu and 28 μg / g C, less than 10 μg / g Fe, 4 μg / g H, less than 5 μg / g N, and 201 μg / g O. The average particle size d 50 The thickness was 26.53 μm. A 25 mm diameter, 7 mm high steel part with a composition of 0.20–0.22 wt% C, 0.55 wt% Si, 1.60 wt% Mn, 0.025 wt% P, 0.025 wt% S, 0.55 wt% Cu, with the remainder being Fe and other common impurities, was prepared and its surface pre-cleaned. The steel part was then coated with Cu powder using a low-temperature gas spray process. The following low-temperature gas spray process parameters were used: pressure 32 bar, gas temperature 400°C, and process gas N2. After coating, the sample was annealed in high vacuum at 550°C for 1 hour. The coating was ground to 1 mm, resulting in a total sample thickness of 8 mm.

[0044] The conductivity of the coatings was then measured according to DIN EN 16813 (2017). Sample No. 1 had a conductivity of 24 MS / m. Sample No. 2 had a conductivity of 56 MS / m. For pure copper, the conductivity is 58 MS / m (according to IACS). As a result, the cold gas spray coated steel parts have almost twice the conductivity of steel parts produced by backcasting. In addition, the samples according to the present invention have a conductivity almost equivalent to that of pure copper.

[0045] Also, the adhesive strength of the copper sprayed coating film to the steel part of sample number 2 was tested. Also, the adhesive strength of the copper sprayed coating film to the steel part of sample number 2 was tested.

[0046] To analyze the interface and the applied coating, polished sections were prepared whose image surface was at a 90° angle to the coating surface, thus depicting the two base materials and their interface. These polished sections were examined and images were taken under a scanning electron microscope at 100x and 500x magnification. Meanwhile, optical microscope images of the polished sections were also taken, and the sections were pre-etched to reveal the grain structure of the thermal sprayed coating.

[0047] Figure 2 shows the transition from steel to copper coating in a cross-sectional section of sample No. 1, a state-of-the-art example (Cu backcasting on steel), in a scanning electron microscope image at 100x magnification. Figure 2 shows the steel body (A, dark area) in the lower half of the image and the copper coating (C, light area) in the upper half of the image. The copper coating is bonded to the steel over the entire surface via a transition zone (B), and the loosening of the steel surface due to the copper backcasting is clearly visible. The transition zone (B) shows an approximate thickness of about 50 μm. It is clearly visible that the copper coating penetrates the steel surface and that steel components are also present in the copper coating, i.e., both materials diffuse between each other and there is no homogeneous material property in the transition zone.

[0048] Figure 3 shows the transition from steel to copper coating in a cross-sectional section of sample number 2, an example (low-temperature gas spray coating on steel) according to the invention, in a scanning electron micrograph at 100x magnification. Figure 3 shows the steel body (A, dark areas) in the lower half of the image and the copper coating (C, light areas) in the upper half of the image. Bonding of the copper coating to the steel is complete across the entire surface, with no intermixing of the materials discernible, i.e., there is no transition zone.

[0049] Figure 4a is an enlarged image of Figure 3, showing the transition from steel to copper coating in a cross-sectional section of sample No. 2, an example of an embodiment (low-temperature gas-sprayed coating on steel) according to the present invention, at 500x magnification in a scanning electron microscope image. Figure 4a shows the steel body (A, dark area) in the lower half of the image and the copper coating (C, light area) in the upper half of the image. The steel surface is clearly visible and exhibits irregularities. These irregularities can be caused either by surface treatment of the steel before low-temperature irradiation or by impingement of copper on the steel surface. In the image shown, the surface irregularities reach a maximum of 10 μm. However, it is clearly visible that the steel surface is not melted and no intermixing of the materials has occurred. There is a clear boundary between the steel body (A) and the copper coating (C).

[0050] Figure 4b is an enlarged image of Figure 2, showing the transition from steel to copper coating in a cross-sectional section of sample number 1 of the state-of-the-art example (backcasting on steel) at 500x magnification in a scanning electron microscope image. Figure 4b shows the steel body (A, dark area) in the right half of the image and the copper coating (C, light area) in the left half of the image. The transition zone (B) is clearly visible. Copper has partially penetrated deep into the steel surface. The steel surface shows clear signs of melting, which means that steel is present in the copper layer.

[0051] Figure 4c shows a line scan of the copper-to-steel transition zone based on Figure 4b. For this purpose, the elemental concentrations of chromium, iron, and copper are measured along a line starting from the copper coating (C, light area) and moving toward the steel body (A, dark area). The peak intensities after excitation with the Cu K(α) radiation used in the evaluation are iteratively corrected for atomic number, absorption, and fluorescence in this method, thus enabling quantitative calculation of the elemental composition (atomic %) without the use of standards. In the region of the transition zone (B), the presence of a large amount of iron in the copper coating and the deep penetration of a large amount of copper into the surface of the steel body are clearly visible. The high Cu content in the region of the Cu layer (C) before the transition zone (B) and the high Fe content in the steel body (A) after the transition zone (B) are clearly recognizable. In the region of the Cu layer (C), a higher Fe content (especially compared to the Cu content in the steel body (A)) is also recognizable. This indicates that Fe can also penetrate beyond the transition zone into the Cu coating (C). It can also be seen that the steel body contains a certain proportion of chromium.

[0052] Figure 5 shows a scanning electron microscope image at 500x magnification of the copper coating before the annealing step in a cross-sectional section of sample number 2 of an example (low-temperature thermal spray coating on steel) according to the invention. The copper coating shows a homogeneous layer with a density of 97% or more (97-98.66%) of the theoretical density of copper. Individual layers are not discernible.

[0053] Figure 6 shows an optical microscope image at 200x magnification of the copper coating (C) before the annealing process in a cross-sectional section of sample No. 2 of an example (low-temperature gas spray coating on steel) according to the invention. The grain boundaries were highlighted by etching the Cu particles so that the microstructure was clearly visible. The elongated shape of the Cu particles and many layers can be recognized. This coating is clearly different from the Cu coating obtained using back-casting (see Figure 9).

[0054] Figure 7 shows an optical microscope image at 200x magnification of the copper coating (C) after the annealing step in a cross-sectional section of sample number 2 of an example (low-temperature gas sprayed coating on steel) according to the invention. The grain boundaries were highlighted by etching the Cu particles so that the microstructure was clearly visible. The fine-grained, equiaxed microstructure of the coating can be recognized.

[0055] Figure 8 shows the copper coating (C) after the annealing process in a cross-sectional section of sample No. 2 of an example (low-temperature gas spray coating on steel) according to the present invention, at 50x magnification in an optical microscope image. This low magnification was chosen for direct comparison with the grain size in the back-casting process. After etching the Cu particles, the fine and uniform microstructure of the copper coating (C) can be seen. The steel body (A, dark area) can also be seen.

[0056] Figure 9 shows an optical microscope image of the copper coating (C) in a cross-sectional section of sample number 1 of the state-of-the-art example (Cu backcasting on steel) at 50x magnification. The formation of a large grain structure of the copper coating during backcasting is clearly visible after etching the copper particles.

Claims

1. 1. A rotor part for an X-ray rotating anode, comprising a carrier body and a thermal sprayed coating, wherein the carrier body is made of one of the group of materials consisting of a heat-resistant metal, a heat-resistant metal-based alloy, Fe, an Fe-based alloy or a combination thereof, the thermal sprayed coating is made of Cu or a Cu-based alloy, and the carrier body is material-bonded to the thermal sprayed coating in at least some portions of a connecting surface, characterized in that the microstructure of the rotor part does not have a transition zone at the connecting surface between the carrier body and the thermal sprayed coating.

2. The rotor component of claim 1, wherein the thermal spray coating is a low-temperature gas thermal spray coating.

3. 3. The rotor component according to claim 2, characterized in that the low-temperature gas spray coating comprises cold-formed Cu particles or Cu-based alloy particles that are at least partially elongated parallel to the surface of the carrier body in at least certain regions and have an elongation ratio of more than 1.

4. The rotor component according to claim 2, wherein the low-temperature gas sprayed coating after annealing has a recrystallized microstructure of the Cu particles or Cu-based alloy particles with an average grain size of 150 μm or less.

5. 2. The rotor component according to claim 1, wherein the composition of the Cu thermal spray coating or the Cu-based alloy thermal spray coating contains 1000 μg / g or less of oxygen, 500 μg / g or less of iron, and 200 μg / g or less of nitrogen.

6. 2. The rotor component according to claim 1, wherein the thermal spray coating has a layer thickness of 25 μm to 5 cm.

7. The rotor component of claim 1 , wherein the thermal spray coating of the rotor component has a conductivity of 26 MS / m or greater in the coating.

8. 2. The rotor component according to claim 1, wherein the thermal spray coating has a density of 90% or more of the theoretical density of the Cu or Cu-based alloy.

9. A method for manufacturing a rotor part for an X-ray rotating anode, comprising a carrier body and a thermal spray coating, characterized by the following steps: - Providing a support comprising a refractory metal, a refractory metal-based alloy, Fe, an Fe-based alloy, or a combination thereof. - coating the carrier body by thermal spray coating using a powdered coating material to produce a rotor component having at least a partial material bond connection at the connection surface between the carrier body and the thermal spray coating, wherein the thermal spray coating consists of Cu or a Cu-based alloy and the microstructure of the rotor component does not have a transition zone at the connection surface between the carrier body and the thermal spray coating.

10. 10. The method of claim 9, wherein the thermal spray coating is applied by low temperature gas spraying.

11. 11. The method of claim 10, wherein the low-temperature gas spraying is carried out at a pressure of 10 to 100 bar and a gas temperature of room temperature to 1000°C.

12. 10. The method according to claim 9, characterized in that the rotor part is annealed in vacuum or in a protective gas atmosphere after the coating step.

13. 10. The method of claim 9, wherein the rotor part is annealed after the coating step at 400-750°C for up to 5 hours.

14. 10. The method of claim 9, wherein the carrier body is surface treated prior to the coating step.

15. 10. The method according to claim 9, characterized in that the powdered coating material of Cu or Cu-based alloy has a powder particle size of 5 to 150 μm.

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