Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
  • H01J9/14—Manufacture of electrodes or electrode systems of non-emitting electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J35/00—X-ray tubes
  • H01J35/02—Details
  • H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
  • H01J35/08—Anodes; Anti cathodes
  • H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2235/00—X-ray tubes
  • H01J2235/08—Targets (anodes) and X-ray converters
  • H01J2235/085—Target treatment, e.g. ageing, heating

Definitions

• the invention relates to a method for producing an X-ray rotary anode with an annular focal path region made of refractory metals, e.g. by powder metallurgy or CVD or PVD methods. Tungsten or tungsten rhenium.
• X-ray rotary anodes Today, high-melting metals or graphite, or a combination of both materials, are used as the base material for X-ray rotary anodes.
• the actual generation area of the X-rays, the focal path area consists of tungsten, molybdenum or their alloys.
• Metallic X-ray rotary anodes are manufactured according to sintered metallurgical processes for reasons of shape, the materials used and the required properties; the focal path area itself is produced using sintered metallurgical processes or more recently also using CVD or PVD coating processes.
• Such rotating anodes or focal path areas have a residual porosity in the range of 0.1-10% in the finished state, measured on the theoretical density.
• Such an X-ray rotating anode is described in EP-A1-0 116 385, with the rotating anode optionally being post-treated and heat-treated after the focal path layer has been applied in accordance with the process there.
• This residual porosity has a number of disruptive disadvantages for the operation of X-ray rotary anodes, which is generally carried out in a high vacuum.
• the porosity causes the release of gases trapped in the pores. This in turn leads to gas discharges in the high vacuum of the tube with undesirable tube short circuits, which in turn cause anode melting.
• the thermal conductivity that is so important for the resilience of X-ray tubes decreases about with the square of the porosity.
• Porosity of the focal track surface causes increased surface roughness and reduces the X-ray yield due to self-absorption.
• a porous surface also means the risk of particle breakouts from the surface, which significantly increases the negative effects of gas leaks.
• the mechanical bonding of the individual crystallites in the structure depends on the porosity, but also on the metallurgical conditions at the grain boundaries, in particular on impurities at the grain boundaries. In the course of powder metallurgical manufacturing processes, however, a concentration of impurities that are insoluble in the metal at the grain boundaries is unavoidable; this means another disruptive factor when operating X-ray rotary anodes.
• Focal path linings produced by sinter metallurgical processes in particular made of tungsten-rhenium, occasionally show a brittle, intermetallic tungsten-rhenium phase, the so-called sigma phase, which is due to inhomogeneities due to inadequate mixing of the individual alloy components in the powder batch.
• the inevitable thermal shock loading of rotating anodes during operation then leads, particularly in these and in the areas emanating from them, to highly undesirable crack formation, with a reduction in the X-ray yield in the focal path area as a result.
• the object of the present invention is then the elimination, or at least a substantial reduction of the aforementioned disadvantages.
• the task is to reduce the porosity and impurities, especially at the grain boundaries in the focal path area.
• the previous manufacturing processes prowder metallurgy and CVD or PVD processes
• the object is achieved according to the invention by a method according to which the focal path region of an X-ray rotary anode is aftertreated at a depth of less than 1.5 mm by means of local, superficial melting.
• the inventive aftertreatment by means of superficial melting is carried out in accordance with a method which has been tried and tested in practice by the action of focused beams of high-energy electrons or photons on the surface of the focal path area of X-ray rotary anodes down to a certain depth of action.
• a changed metallic structure is formed in this area, the porosity and the proportion of impurities, in particular in the grain boundary area, are significantly reduced.
• the grain structure remains comparatively fine in contrast to conventional melt metallurgical processes.
• the grain size that can be achieved corresponds to that which is customary in powder metallurgy or by means of application methods of the focal track areas.
• the melting can be carried out once or several times in succession and influences the metallic structure of the focal track area that can be achieved in the final state. With the removal of the residual porosity, the disturbances in the operation of x-ray rotary anodes shown at the beginning also disappear.
• Suitable focusable energy sources for the melting process are the laser, devices for generating particle beams, in particular electron beams, and highly focusable high-power lamps.
• the material-related degree of conversion of radiated energy / heat is important for the energy source selected in the individual case.
• the equipment complexity and the processing e.g. B. Treatment under protective gas or in a high vacuum, a role. Due to the high reflectivity of refractory metals for electromagnetic waves in the spectral range 0.3 - 20 ⁇ m (> 80%), the use of electron beams with an efficiency of ⁇ 60% usually offers advantages.
• the desired melting depth according to the inventive method is to be dimensioned to match the thermomechanical loads to be expected in the combustion path area during operation.
• a melting depth between 0.05 and 1.5 mm has proven to be useful. In the majority of applications, a melting depth between 0.5 and 0.8 mm offers the best cost-benefit ratio.
• the process of melting and rapid cooling results in the structure states being amorphous, very fine-grained isotropic, finely grained or coarse-crystalline.
• the resulting stresses in the structure can be reduced by a subsequent vacuum annealing in the range 900 - 1600 o C.
• the melting process leads to a very smooth surface with a low surface roughness in the focal path area. Nevertheless, due to the extremely high demands on the surface smoothness of X-ray rotary anodes in the focal path area, it is generally unavoidable to grind the surface after the melting process.
• a rotating anode base body with a tungsten / rhenium focal track area which is manufactured in the usual powder metallurgical way, is - like later in operation - mounted on a rotating holding shaft and inserted into a piston that can be evacuated to high vacuum.
• the rotating anode focal path area is arranged opposite a focussing glow emission cathode.
• the slowly rotating rotating anode is brought uniformly to approx. 800 o C by means of a defocused electron beam.
• the rotating anode is degassed, which means that foreign atoms and insufficiently adhering material particles are removed from the surface.
• the electron beam is then brought to a line focus of 20 mm in length and 2 mm in width and to a power of 6 kW, and the rotating anode rotating at 3-6 revolutions per minute is melted on the surface in three successive revolutions.
• the melt which is horizontal due to the arrangement, solidifies during the subsequent cooling process so smoothly that even with subsequent removal of 0.2-0.3 mm a smooth burn sheet surface that meets the requirements is achieved by grinding.
• the structure of a focal path region melted in this way has directionally solidified crystallites with an average diameter of 150 ⁇ m. It shows no pores and provides reliable information for an excellent bond between the individual grains or crystallites.
• An X-ray rotary anode manufactured according to the present invention was compared with a rotary anode manufactured according to the prior art.
• a so-called tube test bench in which the load on the X-ray rotating anode can be simulated completely identically to that in later operation, both comparison rotating anodes were tested with the following loading cycles: Electron beam power 60 kW, focus 12 x 1.8 mm2, irradiation cycle 7 x 0.1 S with 0.1 S pause each (corresponds to an X-ray image) and 59 S cooling, total number of images 1200.
• the two comparative rotating anodes were checked for their superficial structural changes both under a scanning electron microscope and measured for surface roughness using the stylus.
• the roughening of the rotating anode according to the present invention as a result of material fatigue was not only less, but, based on the entire surface area of the focal path, was more uniform than with the rotating anode according to the prior art. Accordingly, the x-ray rotating anode according to the invention showed a more uniform and less dense crack network with smaller crack widths than the comparison anode according to the prior art.
• the rotating anode according to the invention has a very high vacuum stability.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• X-Ray Techniques (AREA)
• Powder Metallurgy (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Light Receiving Elements (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=3503501

Family Applications (1)

Country Status (4)

Cited By (3)

Citations (2)

• 1991
  • 1991-05-07 AT AT0094791A patent/AT397005B/de not_active IP Right Cessation
• 1992
  • 1992-05-01 JP JP13969692A patent/JP3345439B2/ja not_active Ceased
  • 1992-05-04 EP EP92201234A patent/EP0512633B1/fr not_active Expired - Lifetime
  • 1992-05-04 DE DE59200292T patent/DE59200292D1/de not_active Expired - Fee Related
  • 1992-05-04 AT AT92201234T patent/ATE108948T1/de not_active IP Right Cessation

Patent Citations (2)

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