An interface-enhanced liquid metal bearing for X-ray tubes

Abstract

The present invention provides an interface-enhanced liquid metal bearing for an X-ray tube, comprising a stator central shaft, a rotating component, a bearing gap formed between the stator central shaft and the rotating component, and liquid metal filled in the bearing gap; the surface of the stator central shaft and the surface of the rotating component are divided into a leakage-sensitive area, a friction and wear area, and a wetting and lubrication area; the stator central shaft and / or the rotating component are constructed with a sealing interface in the leakage-sensitive area, and the stator central shaft and / or the rotating component are constructed with a wear-resistant interface in the friction and wear area, and both the sealing interface and the wear-resistant interface are multi-layer or gradient film layer structures. The present application effectively improves the sealing, wear resistance, and lubricity of the interface-enhanced liquid metal bearing; both the sealing interface and the wear-resistant interface are multi-layer film structures, and the thermal expansion coefficient of each film layer is increased in a gradient, thereby avoiding cracking or even shedding of the film layer due to a large difference in the thermal expansion coefficient of two adjacent materials, thereby ensuring the reliability of the sealing interface and the wear-resistant interface.

Description

Technical Field

[0001] The present invention relates to the technical field of medical CT, and in particular to an interface-enhanced liquid metal bearing for an X-ray tube. Background Art

[0002] Medical CT imaging requires the X-ray tube and detector to rotate, driven by the gantry, to image the patient's target from different angles. The combined effects of gravitational acceleration generated by the high-speed rotation of the gantry and the high-speed rotation of the anode place significant stress and load on the X-ray tube's bearings. Liquid metal has been proven to effectively lubricate and dynamically support bearings, significantly reducing bearing wear, lowering noise, and enhancing heat dissipation, thereby extending bearing life. However, liquid metal bearings used in X-ray tubes face the following challenges under high-temperature, high-speed, and high-load conditions:

[0003] 1) There is a risk of liquid metal leakage, which may lead to bearing performance degradation and X-ray tube high-voltage sparking.

[0004] 2) When the liquid metal bearing is started and stopped at low speed, the bearing components may be easily subject to friction and wear due to the insufficient bearing capacity provided by the liquid metal. This may lead to a decrease in the performance and life of the liquid metal bearing, and in severe cases, the liquid metal bearing may become stuck and fail.

[0005] 3) Due to the large surface tension of liquid metal, it is not easy to fully wet the surface of the bearing material (usually Mo, tool steel, titanium alloy and other high-temperature resistant metal materials), thereby weakening the lubrication, thermal conductivity and fluid dynamics of the bearing, leading to problems such as liquid metal leakage, rotational imbalance and jamming of the bearing, and reduced life and reliability.

[0006] Based on the above-mentioned problems with liquid metal bearings, the prior art proposes designing liquid metal-resistant coatings, wear-resistant coatings, and liquid metal wetting coatings on the surfaces of liquid metal bearing parts to enhance the interface, improve the anti-wetting properties of the sealing surfaces of bearing parts, improve the wear resistance of the surfaces of relatively rotating parts, and enhance the wettability of the liquid metal contact lubrication surfaces. This effectively reduces the risk of failure of the liquid metal bearing due to liquid metal leakage or bearing component wear, thereby improving the life and reliability of the liquid metal bearing. For example, Chinese invention patent application publication number CN119480586A discloses an enhanced liquid metal sliding bearing, which enhances the sealing and wetting of the liquid metal by preparing a metal-ceramic anti-wetting film layer and a metal wetting film layer based on a micro-texture structure on the surface of the liquid metal bearing parts. For example, the Chinese invention patent application with application publication number CN113270305A discloses a liquid metal bearing, which has a titanium carbide silicon coating prepared on the inner surface of the core shaft of the part, the horizontal contact surface between the upper sleeve and the core shaft, and the horizontal contact surface between the lower sleeve and the core shaft, thereby improving the wear resistance of the bearing part surface and extending the service life.

[0007] However, in the manufacture and application of medical CT X-ray tubes, the components within the tube core (including the liquid metal bearing components) require high-temperature degassing (above 800°C) to maintain a high vacuum within the tube core. When the tube is exposed, the liquid metal bearing must withstand high temperatures (generally no more than 400°C). Under high-temperature conditions, portions of the film decompose, leading to a loss of anti-wetting properties. Furthermore, the thermal expansion coefficients of most metal-ceramic films differ significantly from those of the bearing metal substrate. Single-layer anti-wetting films or titanium silicon carbide coatings are prone to thermal stress accumulation during temperature increases and decreases. Combined with the loads and pressures of use, the film is prone to cracking and detachment, resulting in the loss of its anti-wetting and wear-resistant properties. In particular, if film fragments fall off and mix with the liquid metal, this can lead to a decrease in the liquid metal's lubrication properties or bearing failure. In addition, due to the large surface tension of gallium-based liquid metal (587~605 mN / m), its wettability with most materials is poor. Although some metal coatings can enhance wettability (such as gold, silver, copper, etc.), these metals are also easily corroded and dissolved by liquid metal, changing the composition of the gallium-based liquid metal alloy and affecting its physical properties such as viscosity and melting point, thereby weakening the dynamic behavior of the liquid metal and causing a decline in bearing performance. Specifically, the enhanced liquid metal sliding bearings covered by the Chinese invention patent application, application publication number CN119480586A, suffer from problems such as film shedding and cracking when the anti-wetting film is exposed to high-temperature operating conditions due to thermal expansion coefficient mismatch between the coating and the metal substrate, leading to thermal stress accumulation. During start-up and shutdown of the bearing, friction causes the film to wear and detach, resulting in failure of the constructed wetting interface. The metal wetting film is easily eroded and dissolved by the gallium-based liquid metal, causing coating failure and altering the liquid metal alloy composition. This, on the one hand, reduces the liquid metal viscosity, slowing its flow rate and weakening the bearing's load capacity, and on the other hand, increases the liquid metal's melting point, narrowing the liquid metal bearing's operating temperature window. In the liquid metal bearings covered by the Chinese invention patent application, application publication number CN113270305A, the film is disposed between the two axial surfaces where the liquid metal is stored. Since the axial surface of the bearing is a critical area for dynamic pressure bearing, the provision of the anti-wetting film affects the fluidity and adhesion of the liquid metal, weakening the bearing's lubrication, load capacity, and rotational stability.

[0008] In summary, existing liquid metal bearings are only considered from the perspectives of sealing, wear resistance, and lubrication. There is also a lack of consideration and design for the matching of thermal expansion coefficients between surface film layers. Ultimately, thermal stresses are easily accumulated within or between film layers, leading to film breakage or shedding, affecting bearing performance or life. Summary of the Invention

[0009] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide an interface-enhanced liquid metal bearing for an X-ray tube, which effectively prevents liquid metal leakage, reduces friction and wear, and improves bearing lubrication.

[0010] To achieve the above objectives, the present invention provides an interface-enhanced liquid metal bearing for an X-ray tube, comprising a stator central shaft, a rotating component rotatably mounted on the outer periphery of the stator central shaft, a bearing gap formed between the stator central shaft and the rotating component, and liquid metal sealed and filled in the bearing gap; the surfaces of the stator central shaft and the rotating component are divided into a leakage-sensitive area, a friction and wear area, and a wetting and lubrication area; the stator central shaft and / or the rotating component form a sealing interface in the leakage-sensitive area, the stator central shaft and / or the rotating component form a wear-resistant interface in the friction and wear area, and at least one of the opposing surfaces of the stator central shaft and the rotating component forming the bearing gap filled with liquid metal forms a wetting and lubrication interface;

[0011] The sealing interface is a multi-layer film structure, including a metal transition layer fixed on the surface of the bearing metal substrate, and an anti-wetting film layer fixed on the surface of the metal transition layer, wherein the thermal expansion coefficients of the bearing metal substrate, the thermal expansion coefficients of the metal transition layer, and the thermal expansion coefficients of the anti-wetting film layer increase in a gradient;

[0012] The wear-resistant interface is a multi-layer film structure, including a metal transition layer fixed on the surface of the bearing metal substrate, and a wear-resistant film layer fixed on the surface of the metal transition layer. The thermal expansion coefficients of the bearing metal substrate, the metal transition layer, and the wear-resistant film layer increase in gradient.

[0013] Furthermore, the rotating component includes a thrust flange and a shaft sleeve that are fixedly connected to each other; the outer periphery of the stator central shaft is provided with an axial limiting boss that protrudes radially and is distributed at the connection between the thrust flange and the shaft sleeve; the stator central shaft also includes a first shaft segment and a second shaft segment respectively provided on both sides of the axial limiting boss; a flange hole for accommodating the first shaft segment is provided in the thrust flange; a first shaft sleeve hole for accommodating the axial limiting boss and a second shaft sleeve hole for accommodating the second shaft segment are provided in the shaft sleeve;

[0014] The bearing clearance includes a first axial clearance formed between the thrust flange and the outer periphery of the first shaft segment, a first radial clearance formed between the thrust flange and the end of the axial limiting boss, a second axial clearance formed between the shaft sleeve and the outer periphery of the axial limiting boss, a second radial clearance formed between the shaft sleeve and the end of the axial limiting boss, a third axial clearance formed between the shaft sleeve and the outer periphery of the second shaft segment, and a third radial clearance formed between the shaft sleeve and the end of the second shaft segment;

[0015] The leakage sensitive area includes the surface of the stator center shaft and the thrust flange located at the first axial gap, the flange sealing surface of the thrust flange that contacts and cooperates with the shaft sleeve surface, and the sleeve sealing surface of the shaft sleeve that contacts and cooperates with the thrust flange surface;

[0016] The friction and wear area includes a surface of the thrust flange located at the first radial gap, and a surface of the sleeve located at the second axial gap and the second radial gap;

[0017] The wet lubrication area includes surfaces on the stator center shaft located at the first radial gap, the second axial gap, the second radial gap and the third axial gap, and a surface on the sleeve located at the third axial gap.

[0018] Furthermore, the material of the metal transition layer is any one or more of Cr, Ti, Zr, CrTi, CrAl, CrZr, CrMo, TiAl, TiZr, and TiMo.

[0019] Furthermore, the material of the anti-wetting film layer is any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN.

[0020] Furthermore, the material of the wear-resistant film layer is any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN.

[0021] Furthermore, the sealing interface and the wear-resistant interface have the same structure, the metal transition layer is a Cr film layer, and the anti-wetting film layer and the wear-resistant film layer are both A k N (1-k) 、A k B l N (1-k-l) 、A k B l C m N (1-k-l-m) 、A k B l C m D n N (1-k-l-m-n)Any one of the elements, element A is any one of Ti, Cr, Zr, Mo, W, and Nb, element B, element C, and element D are all any one of C, Si, Al, Ti, Cr, Fe, Ni, Zr, Mo, W, and Nb, and element A, element B, element C, and element D are different elements; the value ranges of k, l, m, and n are all 0.05-0.75, and the k value decreases outwardly along the normal direction of the anti-wetting film layer and the wear-resistant film layer, so that the N content in the anti-wetting film layer and the wear-resistant film layer increases outwardly along the normal direction of the anti-wetting film layer and the wear-resistant film layer.

[0022] Furthermore, the thickness of the anti-wetting film layer and the wear-resistant film layer are both 0.2μm-10μm, the thickness of the metal transition layer in the sealing interface does not exceed 0.5 times the thickness of the anti-wetting film layer, and the thickness of the metal transition layer in the wear-resistant interface does not exceed 0.5 times the thickness of the wear-resistant film layer.

[0023] Furthermore, the surface of the stator central shaft and / or rotating component in the wetting and lubrication area is cleaned by plasma or electron beam etching to construct a liquid metal wetting interface, removing surface carbon, hydrogen pollutants or metal oxides, thereby obtaining a highly active surface, thereby contacting with the liquid metal to construct a wetting and lubrication interface.

[0024] Furthermore, during plasma etching cleaning, a H2 / Ar mixed gas is used, and the Ar ratio does not exceed 20%, the gas inlet speed is 100-300 mL / min, the gas pressure is maintained at 10~50 Pa, the RF power supply power is 200~600 W, and the cleaning time is 10~30 min.

[0025] Furthermore, during electron beam etching and cleaning, the workpiece rotation speed is 200-1500 rpm, the workpiece translation speed is 0.5-5 mm / s, and the vacuum degree of the workpiece is within 5x10 -5 Pa or less; the electron gun used: the incident angle of the electron beam focused on the surface to be etched of the workpiece is 0°~15°, the filament current is 10~20A, the tube voltage is 30~60kV, the tube current is 3~6.5mA, the focal spot size is 0.8~3mm, and the focus traverses the surface to be etched at least once.

[0026] As described above, the interface-enhanced liquid metal bearing for an X-ray tube according to the present invention has the following beneficial effects.

[0027] 1. This application divides the surface of the stator center shaft and rotating components into a leakage-sensitive area, a friction and wear area, and a wetting and lubrication area based on the working state and structure of the interface-enhanced liquid metal bearing. In the leakage-sensitive area, a sealing interface is constructed to prevent liquid metal leakage, thereby improving the anti-wetting performance of the interface-enhanced liquid metal bearing. In the friction and wear area, a wear-resistant interface is constructed to reduce friction and wear, thereby improving the wear resistance of the interface-enhanced liquid metal bearing. The film layers of the sealing interface and the wear-resistant interface do not affect the fluidity and adhesion of the liquid metal in the wetting and lubrication area, thereby ensuring the lubricity of the interface-enhanced liquid metal bearing. In this way, this application effectively improves the sealing, wear resistance, and lubricity of the interface-enhanced liquid metal bearing.

[0028] 2. The sealing interface and wear-resistant interface constructed in this application are both multi-layer film structures, which realizes a gradient increase in the thermal expansion coefficient from the inside to the outside between each film layer or within the film layer, avoiding cracks or even falling off of the anti-wetting film layer or the wear-resistant film layer due to the large difference in the thermal expansion coefficients of the two adjacent materials, greatly reducing the risk of failure of the sealing interface and the wear-resistant interface; secondly, the gradual change of composition between the film layers or within the film layers also enhances the bonding force of the interface between the film layers, and improves the toughness and wear resistance of the film layer; in addition, the multi-layer film structure is denser than the single-layer film structure, and is a reinforced interface, which can effectively delay the diffusion of liquid metal atoms to the inside and destroy the structure and function of the sealing interface and the wear-resistant interface, thereby improving the corrosion resistance of the sealing interface and the wear-resistant interface and ensuring the reliability of the sealing interface and the wear-resistant interface.

[0029] 3. The wetting and lubrication interface constructed in this application does not require a coating. The wetting interface is directly constructed by increasing the surface activity of the substrate. The method is simple and easy to implement. At the same time, it avoids the erosion and failure of the coating material, and also avoids the doping or contamination of the liquid metal by the dissolution of the coating. It not only enhances the reliability of the wetting interface, but also ensures the stable performance of the liquid metal bearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of the medical CT X-ray tube used in this application.

[0031] Figure 2 This is a schematic structural diagram of the interface-enhanced liquid metal bearing used in the X-ray tube of this application.

[0032] Figure 3 and Figure 4 for Figure 2 Schematic diagram of the structure of the central axis of the stator at different perspectives.

[0033] Figure 5 and Figure 6 for Figure 2 Schematic diagram of the structure of the thrust flange from different perspectives.

[0034] Figure 7 and Figure 8 for Figure 2 Schematic diagram of the structure of the middle shaft sleeve from different perspectives.

[0035] Figure 9 This is a schematic structural diagram of the sealing interface and wear-resistant interface constructed in Example 1 of the interface-enhanced liquid metal bearing of this application.

[0036] Figure 10 This is a schematic structural diagram of the sealing interface and wear-resistant interface constructed in Example 2 of the interface-enhanced liquid metal bearing of this application.

[0037] Figure 11 This is a schematic structural diagram of the sealing interface and wear-resistant interface constructed in Example 3 of the interface-enhanced liquid metal bearing of this application.

[0038] Figure 12 This is a schematic structural diagram of the sealing interface and wear-resistant interface constructed in Example 4 of the interface-enhanced liquid metal bearing of this application.

[0039] Figure 13 Schematic diagram of the wetting state between the surface of the wetting and lubrication area of ​​the stator central axis and the liquid metal in Example 1 of the present application.

[0040] Figure 14 Schematic diagram of the wetting state between the surface of the wetting and lubrication area of ​​the stator central axis and the liquid metal in Example 2 of the present application.

[0041] Figure 15 Schematic diagram of the wetting state between the leakage sensitive area surface of the sleeve and the liquid metal in Example 4 of the present application.

[0042] Figure 16 Schematic diagram of the wetting state between the surface of the second shaft section of the stator central shaft and the liquid metal in Comparative Example 3 of the present application.

[0043] Figure 17 Schematic diagram of the surface morphology of the multilayer film structure of Example 1 of the present application after thermal shock testing.

[0044] Figure 18 Schematic diagram of the surface morphology of the single-layer film structure of Comparative Example 1 of the present application after thermal shock testing.

[0045] Figure 19 Schematic diagram of the wetting state of the multilayer film structure of Example 1 of the present application with liquid metal after thermal shock testing.

[0046] Figure 20 Schematic diagram of the wetting state of the single-layer film structure of Comparative Example 1 of the present application with liquid metal after thermal shock testing.

[0047] Figure 21 Schematic diagram of the surface morphology of the multilayer film structure of Example 5 of the present application after high temperature resistance testing.

[0048] Figure 22 Schematic diagram of the surface morphology of the single-layer film structure of Comparative Example 2 of the present application after high temperature resistance test.

[0049] Figure 23 Schematic diagram of the wetting state of the multilayer film structure of Example 5 of the present application with liquid metal after high temperature resistance test.

[0050] Figure 24 Schematic diagram of the wetting state of the single-layer membrane structure of Comparative Example 2 of the present application with liquid metal after high temperature resistance test. DETAILED DESCRIPTION

[0051] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0052] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0053] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element through an intervening element.

[0054] In addition, the descriptions of "first", "second", etc. in this application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0055] The present application provides an interface-enhanced liquid metal bearing for an X-ray tube, wherein the interface-enhanced liquid metal bearing is used for assembly in an X-ray tube for medical CT.

[0056] like Figure 1 As shown, the medical CT X-ray tube involved in the present application includes a tube shell 110, and a cathode assembly 120 and an anode assembly 130, both of which are sealed and mounted in the tube shell 110. The tube shell 110 is used to provide a vacuum environment, and a window 111 is provided on the tube shell 110. The cathode assembly 120 includes a cathode ceramic insulator 121, a metal support arm 122, and a cathode head tungsten filament 123. The cathode head tungsten filament 123 is mounted at the end of the metal support arm 122. The metal support arm 122 is used to connect to the negative electrode. The other end of the metal support arm 122 is mounted in the tube shell 110 through the cathode ceramic insulator 121. The cathode ceramic insulator 121 realizes high-voltage insulation between the tube shell 110 and the metal support arm 122. The anode assembly 130 includes an anode target plate 131, a rotor 132, an interface-enhanced liquid metal bearing 133, a high-voltage shielding cover 134 and an anode ceramic insulator 135. The anode target plate 131 is a tungsten alloy target plate and is arranged at one end of the interface-enhanced liquid metal bearing 133. The other end of the interface-enhanced liquid metal bearing 133 is connected to the positive electrode. The rotor 132 is connected to the anode target plate 131 through the interface-enhanced liquid metal bearing 133 to provide a rotational driving force to drive the anode target plate 131 to rotate. The high-voltage shielding cover 134 is installed on the outer periphery of the rotor 132 and the interface-enhanced liquid metal bearing 133. The anode ceramic insulator 135 is fixed between the tube shell 110 and the high-voltage shielding cover 134 to achieve high-voltage insulation between the tube shell 110 and the high-voltage shielding cover 134. When a medical CT X-ray tube is operating, the cathode head tungsten filament 123 is heated by a low-voltage current, exciting an electron beam. Under the action of the positive and negative high-voltage electric fields, the electron beam is focused and accelerated to bombard the focal ring orbit of the anode target disk 131, thereby exciting X-rays. The X-rays pass through the window 111 on the tube shell 110 and then emit toward the target to be measured. During this process, the rotor 132 drives the anode target disk 131 to rotate at high speed through the interface-enhanced liquid metal bearing 133, increasing the bombardment area of ​​the electron beam and the heat distribution area, effectively improving the power of the X-ray tube.

[0057] like Figure 2As shown, the interface enhanced liquid metal bearing 133 for an X-ray tube involved in the present application includes a stator central shaft 10, a rotating component rotatably assembled on the outer periphery of the stator central shaft 10, a bearing gap formed between the stator central shaft 10 and the rotating component, and liquid metal sealed and filled in the bearing gap, an anode target plate 131 is fixedly connected to one end of the rotating component, and a rotor 132 is fixedly connected to the other end of the rotating component. According to the actual working state and structure of the interface-enhanced liquid metal bearing 133, the present application distinguishes the surface of the stator central shaft 10 and the surface of the rotating component, dividing the surface of the stator central shaft 10 and the surface of the rotating component into a leakage-sensitive area 21, a friction and wear area 22, and a wetting and lubrication area 23. In addition, the stator central shaft 10 and / or the rotating component construct a sealing interface 30 in the leakage-sensitive area 21 to prevent liquid metal leakage and improve the anti-wetting performance of the interface-enhanced liquid metal bearing 133. The stator central shaft 10 and / or the rotating component construct a wear-resistant interface 40 in the friction and wear area 22 to reduce friction and wear and improve the wear resistance of the interface-enhanced liquid metal bearing 133. By distinguishing the surface of the components of the interface-enhanced liquid metal bearing 133 and constructing interfaces only in the leakage-sensitive area 21 and the friction and wear area 22, the film layers of the sealing interface 30 and the wear-resistant interface 40 do not affect the fluidity and adhesion of the liquid metal in the wetting and lubrication area 23, thereby ensuring the lubricity of the interface-enhanced liquid metal bearing 133. In this way, the present application effectively improves the sealing, wear resistance and lubricity of the interface enhanced liquid metal bearing 133 , thereby improving the performance and life of the interface enhanced liquid metal bearing 133 .

[0058] In particular, the sealing interface 30 constructed in the leakage sensitive area 21 and the wear-resistant interface 40 constructed in the friction and wear area 22 of the present application are both multi-layer film structures. Specifically, Figures 9 to 12As shown in any of the views in the figure, the sealing interface 30 includes a metal transition layer 52 fixed on the surface of the bearing metal substrate 51, and an anti-wetting film layer 31 fixed on the surface of the metal transition layer 52. The anti-wetting film layer 31 suppresses the leakage of liquid metal to achieve a sealing effect; and the thermal expansion coefficient of the bearing metal substrate 51, the thermal expansion coefficient of the metal transition layer 52 in the sealing interface 30, and the thermal expansion coefficient of the anti-wetting film layer 31 are gradually increased, that is, the thermal expansion coefficient of the bearing metal substrate 51 is less than the thermal expansion coefficient of the metal transition layer 52 and the thermal expansion coefficient of the anti-wetting film layer 31. The wear-resistant interface 40 includes a metal transition layer 52 fixed on the surface of the bearing metal substrate 51, and a wear-resistant film layer 41 fixed on the surface of the metal transition layer 52. The wear-resistant film layer 41 strengthens the surface of the bearing metal substrate 51, reduces the friction coefficient, and reduces the surface wear of the bearing metal substrate 51; and the thermal expansion coefficient of the bearing metal substrate 51, the thermal expansion coefficient of the metal transition layer 52 in the wear-resistant interface 40, and the thermal expansion coefficient of the wear-resistant film layer 41 are gradually increased, that is, the thermal expansion coefficient of the bearing metal substrate 51 in the wear-resistant interface 40 is less than the thermal expansion coefficient of the metal transition layer 52 and the thermal expansion coefficient of the wear-resistant film layer 41. In this way, when constructing the sealing interface 30 and the wear-resistant interface 40, the thermal expansion coefficient of the metal transition layer 52 of the present application is close to the thermal expansion coefficient of the bearing metal substrate 51, and is between the thermal expansion coefficient of the bearing metal substrate 51 and the thermal expansion coefficients of the anti-wetting film layer 31 and the wear-resistant film layer 41. By adding the metal transition layer 52, the large difference in thermal expansion coefficients between the bearing metal substrate 51 and the anti-wetting film layer 31, and between the bearing metal substrate 51 and the wear-resistant film layer 41 is avoided, so that the thermal expansion coefficient gradient of each film layer in the sealing interface 30 and the wear-resistant interface 40 is increased, forming a transition change, and reducing the thermal stress between the two adjacent layers, thereby effectively avoiding cracks or even falling off of the anti-wetting film layer 31 or the wear-resistant film layer 41, and greatly reducing the risk of failure of the sealing interface 30 and the wear-resistant interface 40. Secondly, between the metal transition layer 52 and the anti-wetting film layer 31 and the wear-resistant film layer 41, the content of different elements in the film layers within the anti-wetting film layer 31 and the wear-resistant film layer 41 gradually increases or decreases outward. By reducing the difference in the content of the components between the different layers, the bonding force between the film layers is enhanced, and the overall toughness and wear resistance of the film layers are improved. In addition, the multi-layer film structure is denser than the single-layer film structure and has a reinforced interface. It can effectively delay the diffusion of liquid metal atoms into the interior and damage the structure and function of the sealing interface 30 and the wear-resistant interface 40, thereby improving the corrosion resistance of the sealing interface 30 and the wear-resistant interface 40 and ensuring the reliability of the sealing interface 30 and the wear-resistant interface 40. In addition, the bearing metal substrate 51 is the substrate of the stator center shaft 10 and the rotating components.

[0059] Preferably, if Figure 2 As shown, the stator central shaft 10 is a hollow structure, which is beneficial to the heat dissipation of the anode target plate 131.

[0060] Optionally, the liquid metal is gallium-based liquid metal. Gallium-based liquid metal has the advantages of high vapor pressure, excellent thermal and electrical conductivity, and a low melting point. Gallium-based liquid metal is selected to be filled between the stator central shaft 10 and the rotating member to further enhance the thermal conductivity, electrical conductivity, and lubricity of the interface-enhanced liquid metal bearing 133.

[0061] Furthermore, the metal transition layer 52 is made of any one or more of Cr, Ti, Zr, CrTi, CrAl, CrZr, CrMo, TiAl, TiZr, and TiMo. The metal transition layer 52 is prepared by electroplating, PVD (vacuum evaporation, magnetron sputtering, ion plating), or laser cladding.

[0062] Furthermore, if Figures 9 to 12 As shown in any of the views in the figure, the materials of the anti-wetting film layer 31 and the wear-resistant film layer 41 can be the same or different. In the present application, the anti-wetting film layer 31 and the wear-resistant film layer 41 are both nitride film layers, preferably both metal nitride film layers 54. The metal nitride film layer 54 has the characteristics of high hardness and low friction coefficient, and does not wet with liquid metal, and does not react with liquid metal under high temperature conditions. Therefore, the metal nitride film layer 54 can be used as both the anti-wetting film layer 31 and the wear-resistant film layer 41 in the present application. The preparation method of the anti-wetting film layer 31 and the wear-resistant film layer 41 is any one of PVD (vacuum evaporation, magnetron sputtering, ion plating), CVD, ALD, and ion implantation. In addition, the anti-wetting film layer 31 and the wear-resistant film layer 41 can be non-gradient homogeneous film layers to achieve a gradient change in the expansion coefficient between different film layers; they can also be gradient film layers with a gradient change in internal composition to achieve a gradient change in the expansion coefficient within a single film layer.

[0063] When both the anti-wetting film layer 31 and the wear-resistant film layer 41 are non-gradient homogeneous film layers, the material of the anti-wetting film layer 31 is preferably any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN. The material of the wear-resistant film layer 41 is preferably any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN.

[0064] When the anti-wetting film layer 31 and the wear-resistant film layer 41 are both gradient film layers, the anti-wetting film layer 31 and the wear-resistant film layer 41 are preferably A k N (1-k) 、A k B l N (1-k-l) 、A k Bl C m N (1-k-l-m) 、A k B l C m D n N (1-k-l-m-n) Element A is any one of Ti, Cr, Zr, Mo, W, and Nb; Element B, Element C, and Element D are all any one of C, Si, Al, Ti, Cr, Fe, Ni, Zr, Mo, W, and Nb; and Element A, Element B, Element C, and Element D are mutually exclusive. The values ​​of k, l, m, and n are all in the range of 0.05-0.75. The k value decreases outwardly along the normal direction of the anti-wetting film layer 31 and the wear-resistant film layer 41, causing the nitrogen content in the anti-wetting film layer 31 and the wear-resistant film layer 41 to increase outwardly along the normal direction of the anti-wetting film layer 31 and the wear-resistant film layer 41.

[0065] Furthermore, the thickness of both the anti-wetting film layer 31 and the wear-resistant film layer 41 is 0.2 μm to 10 μm, which avoids both poor wetting and wear resistance due to thin films and increased manufacturing costs due to excessively thick films resulting in prolonged coating times. The thickness of the metal transition layer 52 in the sealing interface 30 is no more than 0.5 times the thickness of the anti-wetting film layer 31, and the thickness of the metal transition layer 52 in the wear-resistant interface 40 is no more than 0.5 times the thickness of the wear-resistant film layer 41. The thickness of the metal transition layer 52 is 0.1 μm to 5 μm, improving the bonding strength and mechanical properties of the multilayer films in the sealing interface 30 and the wear-resistant interface 40.

[0066] Based on the different structures of the stator central shaft 10 and the rotating components, as well as the different structures of the sealing interface 30 and the wear-resistant interface 40 in the interface-enhanced liquid metal bearing 133, the interface-enhanced liquid metal bearing 133 has multiple preferred embodiments. The following provides multiple preferred embodiments of the interface-enhanced liquid metal bearing 133.

[0067] Example 1.

[0068] like Figure 2As shown, the rotating component includes a thrust flange 60 and a shaft sleeve 70 fixedly connected by several bolts, and a radially protruding axial limit boss 11 is provided on the outer periphery of the stator central shaft 10. The axial limit boss 11 is distributed at the connection between the thrust flange 60 and the shaft sleeve 70, and the axial limit boss 11 is used to limit the axial movement of the thrust flange 60 and the shaft sleeve 70; the stator central shaft 10 also includes a first shaft segment 12 and a second shaft segment 13 respectively arranged on both sides of the axial limit boss 11; the first shaft segment 12 is inserted into the thrust flange 60, and a flange hole 61 for accommodating the first shaft segment 12 is provided in the thrust flange 60; the axial limit boss 11 and the second shaft segment 13 are both inserted into the shaft sleeve 70, and a first shaft sleeve hole 71 for accommodating the axial limit boss 11 and a second shaft sleeve hole 72 for accommodating the second shaft segment 13 are provided in the shaft sleeve 70. The aperture of the first shaft sleeve hole 71 is larger than the aperture of the second shaft sleeve hole 72, and the two are connected to form a stepped hole. Furthermore, the shaft sleeve 70 has a single opening, meaning the end of the shaft sleeve 70 facing away from the thrust flange 60 is closed. The thrust flange 60 and the shaft sleeve 70 each have a sealing surface where they meet. Specifically, the end surface of the thrust flange 60 facing the shaft sleeve 70 has a flange sealing surface, while the end surface of the shaft sleeve 70 facing the thrust flange 60 has a shaft sleeve sealing surface. The flange sealing surface and the shaft sleeve sealing surface are in surface contact, forming a tight seal. The rotor 132 is fixedly connected to the thrust flange 60 by several bolts, and the anode target 131 is fixedly connected to the shaft sleeve 70 by several bolts.

[0069] like Figure 2 As shown, based on the mating structure of the stator central shaft 10, the thrust flange 60, and the sleeve 70, the bearing clearances formed therebetween include a first axial clearance 81 formed between the thrust flange 60 and the outer periphery of the first shaft segment 12, a first radial clearance 82 formed between the thrust flange 60 and the end of the axial limiting boss 11, a second axial clearance 83 formed between the sleeve 70 and the outer periphery of the axial limiting boss 11, a second radial clearance 84 formed between the sleeve 70 and the end of the axial limiting boss 11, a third axial clearance 85 formed between the sleeve 70 and the outer periphery of the second shaft segment 13, and a third radial clearance 86 formed between the sleeve 70 and the end of the second shaft segment 13. The first axial clearance 81, the second axial clearance 83, and the third axial clearance 85 are clearances extending in the axial direction of the interface-enhanced liquid metal bearing 133, while the first radial clearance 82, the second radial clearance 84, and the third radial clearance 86 are clearances extending in the radial direction of the interface-enhanced liquid metal bearing 133.

[0070] Preferably, if Figure 3 As shown, the stator center shaft 10 is provided with a herringbone groove 91 on the outer peripheral surface of the second shaft section 13 inserted into the shaft sleeve 70; Figure 5 As shown, a spiral groove 92 is provided on the end surface of the thrust flange 60 facing the axial limiting boss 11; Figure 7As shown, a spiral groove 92 is provided on the end surface of the sleeve 70 facing the axial limiting boss 11. Both the herringbone groove 91 and the spiral groove 92 have a grain tip, and the herringbone groove 91 and the spiral groove 92 seal the liquid metal in the bearing gap to prevent the liquid metal from leaking out.

[0071] When the interface enhanced liquid metal bearing 133 is working, the stator center shaft 10 remains fixed, the thrust flange 60 and the sleeve 70 rotate at high speed around the stator center shaft 10, and the liquid metal converges at the tips of the herringbone grooves 91 on the surface of the stator center shaft 10, the spiral grooves 92 on the end face of the sleeve 70, and the spiral grooves 92 on the end face of the thrust flange 60 under the action of dynamic pressure, thereby supporting and fixing the rotating thrust flange 60 and the sleeve 70, and confining the liquid metal to the bearing gap between the rotating component and the stator center shaft 10. In the long-term use environment of the interface enhanced liquid metal bearing 133 under high temperature, high speed and high load, the liquid metal pressure in the bearing gap is relatively high. When the speed change of the rotating component causes pressure imbalance, there is a risk of liquid metal leaking outward. The risk paths for liquid metal to leak outward are from the first axial gap 81 near the bearing gap outlet, and from the gap between the flange sealing surface of the thrust flange 60 and the sleeve sealing surface of the sleeve 70. Therefore, if Figures 3 to 8 As shown, the leakage-sensitive area 21 includes a surface on the first shaft section 12 of the stator central shaft 10 located outside the first axial gap 81, a surface on the thrust flange 60 located inside the first axial gap 81 (i.e., the wall of the flange hole 61), a flange sealing surface at the end of the thrust flange 60, and a sleeve sealing surface at the end of the sleeve 70. A sealing interface 30 is constructed on these four surfaces. The anti-wetting film layer 31 on the outermost layer of the sealing interface 30 suppresses outward leakage of liquid metal, thereby achieving a sealing effect, ensuring the load-bearing capacity of the interface-enhanced liquid metal bearing 133, preventing the interface-enhanced liquid metal bearing 133 from getting stuck due to liquid metal leakage, and preventing the leaked liquid metal from contaminating the vacuum environment of the tube shell 110 of the medical CT X-ray tube, reducing the vacuum degree due to high-temperature evaporation, or failing the insulation component, thereby preventing the X-ray tube from igniting or failing.

[0072] When the interface enhanced liquid metal bearing 133 is started and decelerated to a stop, when the rotation speed is lower than the take-off speed of the interface enhanced liquid metal bearing 133, the liquid metal in the bearing gap cannot provide sufficient supporting force, which will cause the eccentric distance between the rotating component and the stator center shaft 10 to be large during relative rotation, thereby causing the axial limit boss 11 of the stator center shaft 10 to easily undergo friction and wear with the thrust flange 60 and the shaft sleeve 70. The risk areas prone to friction and wear are the relative surface areas of the thrust flange 60 and the axial limit boss 11 (i.e., the areas at the first radial gap 82), and the relative surface areas of the shaft sleeve 70 and the axial limit boss 11 (i.e., the areas at the second axial gap 83 and the second radial gap 84). Therefore, if Figures 5 to 8 As shown, the friction and wear zone 22 includes a surface on the thrust flange 60 at the first radial gap 82 (i.e., a partial end face of the thrust flange 60), a surface on the shaft sleeve 70 at the second axial gap 83 (i.e., the hole wall of the first shaft sleeve hole 71), and a surface on the shaft sleeve 70 at the second radial gap 84 (i.e., the hole bottom surface of the first shaft sleeve hole 71). Wear-resistant interfaces 40 are constructed on these three surfaces. The high-hardness wear-resistant film layer 41 on the outermost layer of the wear-resistant interface 40 strengthens the surface of the bearing metal substrate 51 at these three locations, reduces wear, and extends the service life of the interface enhanced liquid metal bearing 133. In particular, the surface of the thrust flange 60 at the first radial gap 82 and the surface of the sleeve 70 at the second radial gap 84 are both provided with spiral grooves 92 for guiding the flow of liquid metal and providing thrust. A wear-resistant interface 40 is constructed on the surfaces of these two locations, which can better avoid wear of the spiral groove 92 structure, avoid the resulting changes in the fluid dynamics of the liquid metal, the weakening of the axial thrust of the interface-enhanced liquid metal bearing 133, the uneven thrust of the stator center shaft 10 on its axial limit boss 11, etc., and better avoid the possibility of friction wear.

[0073] When the medical CT X-ray tube is in operation, the thrust flange 60 and sleeve 70 in the interface-enhanced liquid metal bearing 133, as well as the support force of the anode target plate 131 and the drive rotor 132 fixed to the end of the sleeve 70, mainly converge the liquid metal through the herringbone groove 91 on the surface of the stator central shaft 10. Therefore, the wetted and lubricated area 23 includes at least the portion of the surface of the stator central shaft 10 provided with the herringbone groove 91; that is, the wetted and lubricated area 23 includes the surface of the stator central shaft 10 provided at the third axial gap 85 and the surface of the sleeve 70 provided at the third axial gap 85. The surface of the stator central shaft 10 provided with the herringbone groove 91 and the inner surface of the sleeve 70 opposite thereto are fully wetted by the liquid metal, which is conducive to the flow of the liquid metal and the formation of a stable lubricating liquid film, thereby providing sufficient lubrication for the stable and smooth operation of the interface-enhanced liquid metal bearing 133. In addition, since a wear-resistant film layer 41 is provided on the surface of the thrust flange 60 and the shaft sleeve 70 opposite to the axial limit boss 11, which does not wet the liquid metal, the wetted lubrication area 23 also includes at least the surface of the axial limit boss 11, that is, the wetted lubrication area 23 also includes the surface of the stator center shaft 10 provided at the first radial gap 82, the second axial gap 83, and the second radial gap 84, thereby constructing a sufficient wetted lubrication interface 140 for the surface of the axial limit boss 11 on the stator center shaft 10, and utilizing surface tension to adsorb the liquid metal in the bearing gap to prevent overflow to the outside of the bearing gap, while helping the axial flow of liquid metal in the bearing gap to automatically balance and form a lubricating liquid film.

[0074] Preferably, the stator center shaft 10 and the sleeve 70 are cleaned by plasma or electron beam etching to construct a liquid metal wetting interface on the surface of the wetted lubricating area 23. Plasma etching cleaning uses H2 / Ar mixed gas, and the Ar ratio does not exceed 20%, preferably 10%, the air intake speed is 100-300mL / min, the air pressure is maintained at 10~50pa, the RF power is 200~600W, the cleaning time is 10~30min, and the adsorbed gas molecules, oxides, etc. are effectively removed to effectively remove the organic adsorbents that hinder the wetting of the stator center shaft 10 and / or the rotating component surface in the wetted lubricating area 23, and obtain a liquid metal wettable substrate surface in the wetted lubricating area 23 to improve lubricity. During electron beam etching cleaning, the rotation speed of the workpiece is 200-1500rpm, the translation speed of the workpiece is 0.5~5mm / s, and the vacuum degree of the vacuum environment in which the workpiece is located is 5x10 -5 Pa or less; the electron gun used: the incident angle of the electron beam focused on the surface to be etched of the workpiece is 0°~15°, the filament current is 10~20A, the tube voltage is 30~60kV, the tube current is 3~6.5mA, the focal spot size is 0.8~3mm, and the focus traverses the surface to be etched at least once.

[0075] Furthermore, the stator center shaft 10, thrust flange 60, and sleeve 70 are all made of Mo, meaning the bearing metal substrate 51 is Mo. This application utilizes the thermal expansion coefficient, hardness, and composition gradient of the bearing metal substrate 51, along with the multi-layer structure of the sealing interface 30 and the wear-resistant interface 40, to reduce cracking or shedding of the surface film layers at the sealing interface 30 and the wear-resistant interface 40 caused by thermal stress. Table 1 below lists the thermal expansion coefficients of some metals and some metal nitrides.

[0076] Table 1 Thermal expansion coefficients of some metals and some metal nitrides

[0077]

[0078] In Example 1, Figure 9 As shown, the leakage sensitive area 21 and the friction and wear area 22 are both multi-layer interface structures of bearing metal substrate 51 / metal transition layer 52 / gradient film layer 53 / metal nitride film layer 54, and the structure and material of the sealing interface 30 and the wear-resistant interface 40 are the same. In this way, the sealing interface 30 and the wear-resistant interface 40 are obtained by the same multi-layer film structure on different surface areas of the same part. During the manufacturing process, the coating can be done at one time to take into account both interface enhancements, which can improve manufacturing efficiency. The preferred structure of the sealing interface 30 and the wear-resistant interface 40 is: a multi-layer interface structure of bearing metal substrate 51 / metal transition layer 52 / gradient film layer 53 / metal nitride film layer 54, the metal transition layer 52 is a Cr film layer, the anti-wetting film layer 31 and the wear-resistant film layer 41 are both fixed from the inside to the outside with a gradient film layer 53 and a metal nitride film layer 54, which are Cr fixed on the surface of the Cr film layer respectively. k N (1-k) Gradient film layer, and fixed on Cr k N (1-k) CrAlN film on the surface of gradient film, Cr k N (1-k) The film layer is a gradient film layer 53 with a Cr content that decreases from the inside to the outside, which can gradually connect the composition content and thermal expansion coefficient between the metal transition layer 52 and the metal nitride film layer 54, and enhance the bonding strength of the metal transition layer 52 / gradient film layer 53 interface and the gradient film layer 53 / metal nitride film layer 54 interface, thereby achieving the construction of a sealing and wear-resistant enhanced interface on different surfaces of the interface-enhanced liquid metal bearing 133. Therefore, the sealing interface 30 and the wear-resistant interface 40 in Example 1 are Cr film layer, Cr film layer, and Cr film layer from the inside to the outside. k N (1-k) film layer and CrAlN film layer.

[0079] Furthermore, the atomic ratio of the metal nitride film layer 54 can be controlled according to the target alloy composition ratio, the Ar / N2 ratio, the substrate bias, and the excitation power supply parameters (power, current, voltage, pulse characteristics, etc.).

[0080] Furthermore, in Example 1, the sealing interface 30 and the wear-resistant interface 40 are prepared by multi-arc ion plating, which includes the following steps: 1. The surfaces of the stator center shaft 10, the thrust flange 60 and the shaft sleeve 70 are ground and polished to a roughness of Ra ≤ 0.2 μm. 2. The stator center shaft 10, the thrust flange 60 and the shaft sleeve 70 are chemically cleaned and degreased, and then ultrasonically treated with alcohol and dried. 3. The non-coated areas on the stator center shaft 10, the thrust flange 60 and the shaft sleeve 70 are shielded and the coated parts are placed in a vacuum chamber with a vacuum degree of <1x10-3Pa, heated to 250°C, and Ar gas is introduced at 50mL / min. A bias voltage of -300V is applied to the bearing metal substrate 51 of each coated part, and the surface is etched with Ar ions for 15 minutes. 4. Use cathode power supply to control Cr target, adjust Ar gas flow rate to 200ml / min, apply bias voltage -60V to substrate, target current 60A, and deposit 0.1μm thick Cr film as metal transition layer. 5. Then, introduce 200ml / min N2 / Ar mixed gas, wait until N2 / Ar flow ratio is 20%, start Cr target power supply, apply bias voltage -80V to bearing metal substrate 51, target current 60A, then control N2 / Ar flow ratio to increase linearly, coating time is 8min, at the end of coating, N2 / Ar gas flow ratio reaches 100%, and 0.4μm thick Cr film is deposited on the surface of Cr transition layer. k N (1-k) Gradient film layer, in which the k value gradually decreases from 0.7 to 0.57 from the inside to the outside. 6. Turn off the Ar gas, introduce 400ml / min of N2, turn off the Cr target power supply, start the CrAl target power supply, bias -70V, target current 100A, in Cr k N (1-k) A 2μm thick CrAlN film layer is deposited on the surface of the gradient film layer.

[0081] Furthermore, the outer surface of the portion of the stator center shaft 10 inserted into the sleeve 70, as well as the uncoated inner surface of the sleeve 70, were plasma-etched and cleaned. A H2 / Ar gas mixture was introduced to ignite the plasma, with the H2 / Ar mixture comprising 90% H2. The plasma power supply output was 400W, the gas flow rate was 150mL / min, the pressure was maintained at 30Pa, and the cleaning time was 15 minutes. Plasma etching only enhances the wettability of the uncoated surface and has little effect on the metal nitride film 54 (i.e., the anti-wetting film 31 and the wear-resistant film 41), thereby achieving precise control over the enhancement of the wetting and lubrication interface 140.

[0082] Example 2.

[0083] The difference between Example 2 and Example 1 is that in Example 2, Figure 10As shown, both the leakage-sensitive area 21 and the friction and wear area 22 have a multilayer interface structure of a bearing metal substrate 51 / metal transition layer 52 / metal nitride film layer 54. In the sealing interface 30, the metal transition layer 52 is a Ti film layer, and the anti-wetting film layer 31 is a TiAlSiN film layer. In the wear-resistant interface 40, the metal transition layer 52 is a Ti film layer, and the wear-resistant film layer 41 is a TiAlN film layer. Therefore, the sealing interface 30 in Example 2 is composed of a Ti film layer and a TiAlSiN film layer from the inside to the outside, and the wear-resistant interface 40 in Example 2 is composed of a Ti film layer and a TiAlSiN film layer from the inside to the outside.

[0084] Furthermore, each film layer in the sealing interface 30 and the wear-resistant interface 40 in Example 2 is prepared by a magnetron sputtering coating method, including the following steps: 1. Before coating, the surface of the bearing metal substrate 51 of the stator center shaft 10, the thrust flange 60 and the shaft sleeve 70 is ground and polished, and the roughness Ra ≤ 0.2μm. 2. The stator center shaft 10, the thrust flange 60 and the shaft sleeve 70 are degreased, cleaned, ultrasonically treated with anhydrous alcohol and then dried. 3. Constructing the sealing interface 30: shielding the surface of the non-leakage sensitive area 21, placing the coating workpiece into a vacuum chamber, evacuating the vacuum and heating it to 500°C, introducing Ar, the vacuum degree is 0.1Pa, and the surface of the bearing metal substrate 51 is cleaned with a bias voltage of -200V plasma for 20 minutes; the vacuum temperature is maintained at 500°C, and a DC pulse power supply is used to control the Ti target and Ti 30 Al 60 Si 10 Target material, first use Ti target to deposit metal transition layer 52, bias voltage -100V, peak current 200A, peak voltage 1200V, frequency 1100Hz, pulse time 100μs, the thickness of metal transition layer 52 is about 0.5μm; then introduce Ar / N2 mixed gas (6:1) to deposit Ti 30 Al 60 Si 10The target deposits an anti-wetting film layer 31 with a bias voltage of -120V, a peak current of 250A, a peak voltage of 1200V, a frequency of 1100Hz, and a pulse duration of 100μs. A TiAlSiN film layer is deposited with a thickness of 3μm. The workpiece is removed after coating. 4. Constructing a wear-resistant interface 40: The surface of the non-friction wear zone 22 is shielded. The coated workpiece is placed in a vacuum chamber, evacuated, and heated to 400°C. Ar plasma cleaning is repeated in the same manner as described above. A DC pulse power supply is used to control the Ti and TiAl targets. A Ti metal transition layer 52 and a TiAlN wear-resistant film layer 41 are deposited in the same manner. The Ti film layer has a thickness of 0.5μm, and the TiAlN film layer has a thickness of 3μm. 5. Constructing the wetting and lubrication interface 140: The outer surface of the portion of the stator central shaft 10 inserted into the sleeve 70 and the inner surface of the sleeve 70 that is not coated are cleaned by electron beam etching. The coated stator central shaft 10 and the sleeve 70 are fixed on a rotating bracket of the vacuum chamber. The parts can be controlled to rotate or translate uniformly along the axis. The rotation speed is 1000 rpm and the translation speed along the axis is 1 mm / s. The vacuum is drawn to 5x10 -5 Pa, adjust the incident direction of the electron gun so that the incident angle between the electron beam and the surface to be etched and cleaned of the stator central axis 10 is 0°, and the incident angle between the electron beam and the surface to be etched and cleaned of the sleeve 70 is 4°. Control the electron gun filament current to 20A, tube voltage to 50kV, tube current to 5mA, and focal spot size to 1mm, so that the electron beam focus traverses the surface to be cleaned once.

[0085] Example 3.

[0086] The difference between Example 3 and Example 1 is that in Example 3, Figure 11 As shown, the leakage sensitive area 21 and the friction wear area 22 are both multi-layer interface structures of bearing metal substrate 51 / metal transition layer 52 / gradient film layer 53, and the gradient film layer 53 is Cr k Al l N (1-k-l) The composition of the gradient film layer 53 changes gradually, specifically, k decreases from the inside to the outside.

[0087] Furthermore, in Example 3, each film layer in the sealing interface 30 and the wear-resistant interface 40 is prepared by multi-arc ion plating. The structure and material of the sealing interface 30 and the wear-resistant interface 40 are the same. The preparation steps before coating are the same as those in Example 1. The difference is that: the workpiece to be coated is placed in the coating vacuum chamber, evacuated to the local vacuum of the coating machine, and then the workpiece is heated to 350°C, 50ml / min of Ar is introduced, the bias voltage is -200V, and Ar ion cleaning is performed for 15 minutes; then two cathode power supplies are used to control the Cr target and the Al target, the target current is 80A, and the substrate The bias voltage was increased to -250V, and a 0.2μm thick CrAl alloy transition layer was co-deposited on the surface of the bearing metal substrate 51; then, 400ml / min of N2 / Ar mixed gas was introduced, the N2 / Ar flow ratio was controlled to be stable at 60%, the vacuum was 0.4Pa, the substrate bias voltage was -70V, the target current of the Cr cathode was linearly reduced from 80A at a rate of 1A / min, and the target current of the Al cathode was linearly increased from 80A at a rate of 0.8A / min. The coating time was 20min, and a Cr with a composition gradient was deposited on the surface of the CrAl transition layer. k Al l N (1-k-l) The film layer, wherein x decreases from 0.45 to 0.2 from the inside to the outside. l changes from 0.2 to 0.4 from the inside to the outside. Therefore, the sealing interface 30 and the wear-resistant interface 40 in Example 3 are CrAl alloy film layer and CrAl alloy film layer from the inside to the outside. k Al l N (1-k-l) Gradient film.

[0088] Example 4.

[0089] The difference between Example 4 and Example 1 is that in Example 4, Figure 12 As shown, the leakage sensitive area 21 and the friction and wear area 22 are both multi-layer interface structures of bearing metal substrate 51 / metal transition layer 52 / first gradient film layer 55 / second gradient film layer 56.

[0090] Furthermore, in Example 4, each film layer in the sealing interface 30 and the wear-resistant interface 40 is prepared by multi-arc ion plating. The structure and material of the sealing interface 30 and the wear-resistant interface 40 are the same. The substrate treatment method before coating is consistent with the method in Example 1, except that: the workpiece to be coated is placed in the vacuum chamber of the coating machine, evacuated to the coating background vacuum, heated to 250°C, Ar gas is introduced into the vacuum chamber, the air flow rate is 30ml / min, a bias voltage of -250V is applied to the substrate metal, and the surface of the workpiece to be coated is cleaned with Ar ions for 20min; the coating cathode target materials are Cr target, CrAl target and CrMo target, which are independently controlled by three power supplies to deposit a Cr metal transition layer: the Ar gas flow rate is adjusted to 200ml / min, the Cr target power supply is turned on, the target current is 60A, the bias voltage is -300V, and a Cr metal transition layer with a thickness of 0.4μm is deposited; Cr is deposited k Al l N (1-k-l) First gradient film layer: Turn off the Cr target power supply, introduce N2 / Ar mixed gas, the gas flow rate is 400ml / min, control the N2 / Ar flow ratio to increase linearly with the function F=(0.2+0.02t), start the CrAl target power supply, bias voltage -70V, target current 60A, coating time 20min, and deposit 0.8μm Cr on the surface of the Cr metal transition layer. k Al l N (1-k-l) Gradient film layer, in which k and l decrease from 0.4 to 0.25 from the inside to the outside; Cr is deposited k Al l Mo m N (1-k-l-m) Second gradient film layer: N2 / Ar mixed gas was introduced, the gas flow rate was maintained at 500 ml / min, the N2 / Ar flow ratio was stable at 100%, the CrAl target power supply and the CrMo target power supply were started, the bias voltage was -70 V, the CrAl target current was gradually linearly reduced from 100 A to 80 A, and the Mo target current was gradually linearly increased from 60 A to 80 A. The deposition time was 60 min, and the second gradient film layer CrMo was deposited with a film thickness of 3.1 μm. k Al l Mo m N (1-k-l-m) , where k, l decreases gradually from 0.25 to 0.2 from inside to outside, and m increases gradually from 0.1 to 0.15 from inside to outside. Therefore, the sealing interface 30 and the wear-resistant interface 40 in Example 4 are Cr metal transition film layer / Cr k Al l N (1-k-l) First gradient film layer / Cr k Al l Mo m N (1-k-l-m) The second gradient film layer.

[0091] Furthermore, the film layers in the sealing interface 30 and the wear-resistant interface 40 in Example 4 are prepared by multi-arc ion plating. The structures and materials of the sealing interface 30 and the wear-resistant interface 40 are the same. The steps before plating are the same as those in Example 1, except that: a Cr metal transition layer 52 is first deposited on the surface of the bearing metal substrate 51 using a Cr target, and the thickness of the Cr film layer is 0.5 μm; then the Ar gas is turned off, N2 is introduced, and a CrN film layer is deposited, and the thickness of the CrN film layer is 0.5 μm; finally, a CrAlMoN film layer is co-deposited using a CrAl target and a CrMo target, with a bias voltage of -70 V, a target current of 80 A, and a thickness of the CrAlMoN film layer of 1.5 μm.

[0092] Example 5.

[0093] In Example 5, both the leakage-sensitive area 21 and the friction and wear area 22 have a multilayer interface structure of a bearing metal substrate 51 / Ti film layer / TiN film layer. Similar to Example 2, Example 5 uses magnetron sputtering to deposit a sealing interface 30 and a wear-resistant interface 40 of identical composition and structure. The difference from Example 2 is that the structure is heated to 250°C, and a Ti metal transition layer 52 is first deposited on the surface of the area to be coated using a Ti target at a sputtering power of 5kW and a thickness of 0.2μm. An Ar / N2 (1:1) mixed gas is then introduced to sputter-deposit a TiN film layer with a thickness of 1.8μm. Therefore, in Example 5, the sealing interface 30 and the wear-resistant interface 40 are, from the inside to the outside, a Ti film layer and a TiN film layer, respectively.

[0094] The following comparative examples are provided to further illustrate the advantages of the embodiments of the present application.

[0095] Comparative Example 1: A CrAlN film layer is prepared on the surface of a bearing metal substrate 51 using the same arc ion plating method as in Example 1. The difference is that a cathode power supply is used to control the CrAl target, there is no metal transition layer 52, and a single-layer CrAlN film layer with a thickness of 2 μm is deposited directly on the surface of the bearing metal substrate 51.

[0096] Comparative Example 2: A TiN film is prepared on the surface of the bearing metal substrate 51 using the same magnetron sputtering method as in Example 5. The difference is that the Ti target is controlled by a DC power supply, there is no metal transition layer 52, and a single-layer TiN film with a thickness of 3 μm is directly prepared on the surface of the bearing metal substrate 51.

[0097] Comparative Example 3: The non-coated surface of the wetting and lubrication area 23 of the stator central shaft 10 in Example 1 is not subjected to plasma or electron beam etching cleaning treatment, and a liquid metal wetting interface is not constructed, and a wettability test with liquid metal is performed on the surface.

[0098] Comparative Example 4: The stator central shaft 10 , the thrust flange 60 and the sleeve 70 are not subjected to any coating.

[0099] Performance evaluation comparison.

[0100] First, the enhanced surface interfaces prepared in the above examples and comparative examples were compared in terms of film hardness, bonding force, friction coefficient, wear loss, heat resistance, thermal shock resistance, sealing effect, and liquid metal wettability.

[0101] 1. Film Hardness: According to GB / T 25898-2010, the films at the sealing interface 30 and the wear-resistant interface 40 in Examples 1-5, as well as the films in Comparative Examples 1-2, were tested using nanoindentation to measure the changes in indentation depth and load, thereby determining the nanohardness of the films. To minimize the effect of the bearing metal substrate 51 on the film hardness, the indenter's indentation depth did not exceed 10% of the film thickness. The test results are shown in Table 2.

[0102] 2. Adhesion: According to ASTM C1624-05, the adhesion of the films of Examples 1-5 and Comparative Examples 1-2 was measured using a scratch test method. The test results are shown in Table 2.

[0103] 3. Friction coefficient and wear rate: According to the dry friction test method in ASTM G133-05, reciprocating friction tests were performed on the films of Examples 1-5 and Comparative Examples 1-2. A 4 mm diameter Si3N4 ball was used as the friction pair. The friction coefficient was measured, the wear scratch morphology was measured, and the wear rate was calculated. The test results are shown in Table 2.

[0104] 4. Wettability: Referring to ISO 15989:2004, the interfacial wetting angles between the film surfaces of Examples 1-5 and Comparative Examples 1-3 and the liquid metal were measured. The test results are shown in Table 2.

[0105] Table 2 Test results of film hardness, adhesion, friction coefficient, wear rate and wetting angle

[0106]

[0107] The wettability of the interface is determined by the wetting angle θ between the liquid metal and the contact interface. When the wetting angle θ is less than 90°, the contact interface is determined to be in a wettable state; when the wetting angle θ is greater than 90°, the contact interface is determined to be in a non-wetting state; and when the wetting angle θ is greater than 150°, the contact interface is determined to be a super-hydrophobic surface with excellent anti-wetting properties. The wettability of the surface of the wetted lubrication area 23 of the stator central shaft 10 and the liquid metal in Example 1 is as follows: Figure 13 As shown, the wetting state of the surface of the wetting and lubrication area 23 of the stator central shaft 10 and the liquid metal in Example 2 is as follows: Figure 14As shown, the leakage sensitive area 21 of the sleeve 70 in Example 4 is coated to form a sealing interface 30 and the wetting state of the liquid metal is as follows: Figure 15 As shown, the wetting state of the surface of the second shaft section 13 of the stator central shaft 10 and the liquid metal in Comparative Example 3 is as follows: Figure 16 As shown; it can be seen that the wetting angle θ in Example 1 is 28.7°, and the wetting angle θ in Example 2 is 27.5°, the adsorption force on liquid metal is strong, the liquid metal is easy to wet and spread, and the wetting and lubrication performance is good; the wetting angle θ in Example 4 is 155.4°, the adsorption force on liquid metal is small, the liquid metal is not easy to wet and spread, and it is an anti-wetting property; the wetting angle θ in Comparative Example 3 is 132.4°, and it does not wet the liquid metal.

[0108] Furthermore, after the wetting and lubrication area 23 of the stator central shaft 10 in Examples 1 and 2 was cleaned by plasma and electron beam etching, respectively, compared with the surface of the wetting and lubrication area 23 that was not etched and cleaned in Comparative Example 3, it can be seen that the wetting state with liquid metal after plasma or electron beam cleaning is significantly better than the wetting state of the surface without etching and cleaning.

[0109] Furthermore, the leakage sensitive area 21 of the sleeve 70 in Example 4 forms a super-hydrophobic anti-wetting state with the liquid metal after coating. Compared with the uncoated and unetched and cleaned surface of the wetted lubrication area 23 in Comparative Example 3, it can be seen that the surface prepared with the metal nitride film layer has better anti-wetting ability to liquid metal than the uncoated substrate surface.

[0110] 5. Thermal shock resistance: The bearing metal substrates 51 of Example 1, Example 5, Comparative Example 1 and Comparative Example 2 were rapidly heated to 400°C (the interface enhanced liquid metal bearing 133 generally does not exceed 400°C during operation), kept at this temperature for 5 minutes, and then directly immersed in deionized water for cooling. This cycle was repeated 20 times. The surface of the test film layer was observed for discoloration, cracks, or shedding, and the wettability of the liquid metal and the surface film layer. The results are shown in Table 3. The surface morphology of the multilayer film structure of Example 1 after the thermal shock test is as follows: Figure 17 As shown in FIG. 1 , the multilayer film structure did not show any discoloration, cracking, or shedding. The surface morphology of the single-layer film structure of Comparative Example 1 after the thermal shock test was as shown in FIG. Figure 18 As shown in FIG, the single-layer film structure shows discoloration, cracking, and shedding. The wetting state of the multilayer film structure of Example 1 with the liquid metal after the thermal shock test is as follows: Figure 19 As shown, the wetting state of the single-layer film structure of Comparative Example 1 with the liquid metal after the thermal shock test is as follows Figure 20 As shown, it can be seen that the multilayer film structure has good anti-wetting performance.

[0111] 6. High temperature resistance: The anti-wetting film layer 31 and the bearing metal substrate 51 of Example 1, Example 5, Comparative Example 1 and Comparative Example 2 were heated to 800°C under vacuum (the degassing process of bearing parts in medical CT X-ray tubes is higher than this temperature), kept at this temperature for 2 hours, cooled to room temperature, and the test surface was observed for discoloration, cracks, or shedding, and the wettability of the liquid metal and the surface film layer. The results are shown in Table 3. In addition, the surface morphology of the multilayer film structure of Example 5 after the high temperature resistance test is as follows: Figure 21 As shown in FIG. 1 , the multilayer film structure did not show any discoloration, cracking, or shedding. The surface morphology of the single-layer film structure of Comparative Example 2 after the high temperature resistance test was as shown in FIG. Figure 22 As shown in FIG, the single-layer film structure shows discoloration, cracking, and shedding. The wetting state of the multi-layer film structure of Example 5 with the liquid metal after the high temperature resistance test is as follows: Figure 23 As shown, the wetting state of the single-layer film structure of Comparative Example 2 with the liquid metal after the high temperature resistance test is as follows Figure 24 As shown, it can be seen that the multilayer film structure has good anti-wetting performance.

[0112] 7. Sealing Effect: The bearing parts of Example 1 and Comparative Example 5 were assembled into an interface-enhanced liquid metal bearing 133, and a high-speed rotation test was performed on a test platform. The interface-enhanced liquid metal bearing 133 had a rotation speed of 8400 rpm, an equivalent gravitational acceleration of 25 G, and a start-stop continuous rotation time of 10 hours. The test was performed to observe whether the liquid metal leaked from the leakage-sensitive area 21 of the interface-enhanced liquid metal bearing 133. The results are shown in Table 3.

[0113] Table 3 Surface state of the film

[0114]

[0115] In summary, the present invention divides the bearing surface into a leakage-sensitive area 21, a friction and wear area 22, and a lubrication area 23 based on the actual operating conditions of the interface-enhanced liquid metal bearing 133. A multilayer film structure is constructed in the leakage-sensitive area 21 and the friction and wear area 22 to enhance the interface reliability, effectively prevent liquid metal leakage, reduce friction and wear, and improve bearing lubrication. This improves the performance and reliability of the interface-enhanced liquid metal bearing 133 and extends its service life. This method is low-cost and simple to implement.

[0116] In summary, the present invention effectively overcomes various shortcomings of the prior art and has high industrial utilization value.

[0117] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. An interface-enhanced liquid metal bearing for an X-ray tube, comprising a stator central shaft, a rotating member rotatably mounted on the outer periphery of the stator central shaft, a bearing gap formed between the stator central shaft and the rotating member, and liquid metal sealed and filled in the bearing gap, characterized in that: The surface of the stator central shaft and the surface of the rotating component are divided into a leakage-sensitive area, a friction and wear area, and a wetting and lubrication area. The stator central shaft and / or the rotating component are provided with a sealing interface in the leakage-sensitive area, and a wear-resistant interface in the friction and wear area. The sealing interface is a multi-layer film structure, including a metal transition layer fixed on the surface of the bearing metal substrate, and an anti-wetting film layer fixed on the surface of the metal transition layer, wherein the thermal expansion coefficients of the bearing metal substrate, the thermal expansion coefficients of the metal transition layer, and the thermal expansion coefficients of the anti-wetting film layer increase in a gradient; The wear-resistant interface is a multi-layer film structure, including a metal transition layer fixed on the surface of the bearing metal substrate, and a wear-resistant film layer fixed on the surface of the metal transition layer. The thermal expansion coefficients of the bearing metal substrate, the metal transition layer, and the wear-resistant film layer increase in gradient.

2. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, characterized in that: The rotating component includes a thrust flange and a shaft sleeve that are fixedly connected. The outer periphery of the stator central shaft is provided with an axial limiting boss that protrudes radially and is distributed at the connection between the thrust flange and the shaft sleeve. The stator central shaft also includes a first shaft segment and a second shaft segment respectively provided on both sides of the axial limiting boss. The thrust flange is provided with a flange hole for accommodating the first shaft segment. The shaft sleeve is provided with a first shaft sleeve hole for accommodating the axial limiting boss and a second shaft sleeve hole for accommodating the second shaft segment. The bearing clearance includes a first axial clearance formed between the thrust flange and the outer periphery of the first shaft segment, a first radial clearance formed between the thrust flange and the end of the axial limiting boss, a second axial clearance formed between the shaft sleeve and the outer periphery of the axial limiting boss, a second radial clearance formed between the shaft sleeve and the end of the axial limiting boss, a third axial clearance formed between the shaft sleeve and the outer periphery of the second shaft segment, and a third radial clearance formed between the shaft sleeve and the end of the second shaft segment; The leakage sensitive area includes the surface of the stator center shaft and the thrust flange located at the first axial gap, the flange sealing surface of the thrust flange that contacts and cooperates with the shaft sleeve surface, and the sleeve sealing surface of the shaft sleeve that contacts and cooperates with the thrust flange surface; The friction and wear area includes a surface of the thrust flange located at the first radial gap, and a surface of the sleeve located at the second axial gap and the second radial gap; The wet lubrication area includes surfaces on the stator center shaft located at the first radial gap, the second axial gap, the second radial gap and the third axial gap, and a surface on the sleeve located at the third axial gap.

3. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The material of the metal transition layer is any one or more of Cr, Ti, Zr, CrTi, CrAl, CrZr, CrMo, TiAl, TiZr, and TiMo.

4. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The material of the anti-wetting film layer is any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN.

5. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The material of the wear-resistant film layer is any one or more of CrN, TiN, CrAlN, TiZrN, TiCrN, TiSiN, TiCN, CrSiN, CrAlSiN, TiAlSiN, CrAlMoN, and TiAlCrSiN.

6. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The sealing interface and the wear-resistant interface have the same structure, and the anti-wetting film layer and the wear-resistant film layer are both A k N (1-k) 、A k B l N (1-k-l) 、A k B l C m N (1-k-l-m) 、A k B l C m D n N (1-k-l-m-n) Any one of the elements, element A is any one of Ti, Cr, Zr, Mo, W, and Nb, element B, element C, and element D are all any one of C, Si, Al, Ti, Cr, Fe, Ni, Zr, Mo, W, and Nb, and element A, element B, element C, and element D are different elements; the value ranges of k, l, m, and n are all 0.05-0.75, and the k value decreases outwardly along the normal direction of the anti-wetting film layer and the wear-resistant film layer, so that the N content in the anti-wetting film layer and the wear-resistant film layer increases outwardly along the normal direction of the anti-wetting film layer and the wear-resistant film layer.

7. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The thickness of the anti-wetting film layer and the wear-resistant film layer are both 0.2μm-10μm, the thickness of the metal transition layer in the sealing interface does not exceed 0.5 times the thickness of the anti-wetting film layer, and the thickness of the metal transition layer in the wear-resistant interface does not exceed 0.5 times the thickness of the wear-resistant film layer.

8. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 1, wherein: The surfaces of the stator central shaft and / or the rotating components in the wetting and lubrication area are cleaned by plasma or electron beam etching to form a liquid metal wetting interface.

9. The interface-enhanced liquid metal bearing for an X-ray tube according to claim 8, characterized in that: During plasma etching cleaning, use H2 / Ar mixed gas with an Ar ratio not exceeding 20%, an inlet speed of 100-300 mL / min, a gas pressure maintained at 10-50 Pa, an RF power supply of 200-600 W, and a cleaning time of 10-30 min.

10. The interface enhanced liquid metal bearing for an X-ray tube according to claim 8, characterized in that: During electron beam etching and cleaning, the workpiece rotation speed is 200-1500rpm, the workpiece translation speed is 0.5-5mm / s, and the vacuum degree of the workpiece is 5x10 -5 Pa or less; the electron gun used: the incident angle of the electron beam focused on the surface to be etched of the workpiece is 0°~15°, the filament current is 10~20A, the tube voltage is 30~60kV, the tube current is 3~6.5mA, the focal spot size is 0.8~3mm, and the focus traverses the surface to be etched at least once.

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