EP0249141A2 - Röntgenröhren-Treffplatte - Google Patents

Röntgenröhren-Treffplatte Download PDF

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Publication number
EP0249141A2
EP0249141A2 EP87108040A EP87108040A EP0249141A2 EP 0249141 A2 EP0249141 A2 EP 0249141A2 EP 87108040 A EP87108040 A EP 87108040A EP 87108040 A EP87108040 A EP 87108040A EP 0249141 A2 EP0249141 A2 EP 0249141A2
Authority
EP
European Patent Office
Prior art keywords
graphite
target
platinum
layer
tantalum
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP87108040A
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English (en)
French (fr)
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EP0249141A3 (de
Inventor
Andrew Leslie Lux
Robert Michael Guezuraga
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co
Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by General Electric Co filed Critical General Electric Co
Publication of EP0249141A2 publication Critical patent/EP0249141A2/de
Publication of EP0249141A3 publication Critical patent/EP0249141A3/de
Withdrawn legal-status Critical Current

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    • 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
    • H01J35/108—Substrates for and bonding of emissive target, e.g. composite structures

Definitions

  • This invention relates generally to x-ray tube anode targets and, more particularly, to composite structures for x-ray tube rotating anode targets.
  • a known approach for obtaining the advantages of each of the commonly used materials, i.e., refractory metal and graphite, is to use a combination of the two in a so-called composite substrate structure.
  • This structure is commonly characterized by the use of a refractory metal disc which is attached to the stem and which has affixed to its front side an annular focal track. Attached to its rear side, in concentric relationship to the stem, is a graphite disc which is, in effect, piggybacked to the refractory metal disc.
  • Such a combination provides for (a) an easy attachment of the metal disc to the stem, (b) a satisfactory heat flow path from the focal track to the metal disc and then to the graphite disc, and (c) the increased heat storage capacity along with the low density characteristics of the graphite disc.
  • a common method for joining the graphite portion to the metal portion is that of furnace or induction brazing with the use of an intermediate metal.
  • Zirconium has been commonly used for that purpose because of its excellent flow and wetting characteristics.
  • a problem that arises with the use of zirconium, however, is the formation of carbides at the interface between the zirconium and the graphite. Since the carbides tend to embrittle the joint, the strength of a joint is inversely related to both the amount of carbide formed and the thickness of the carbide layer. The amount of the carbide formed depends on the thermal history of the component during both the manufacturing and the operational phases thereof, neither of which can be adequately controlled so as to ensure that the undesirable carbides are not formed.
  • the metal portion is generally formed of a molybdenum alloy commonly known as TZM. While TZM is the preferred material in this application, MT104 can be substituted for TZM. This alloy, in addition to molybdenum, contains about 0.5% titanium, 0.07% zirconium and 0.05% carbon.
  • M 02 C molybdenum carbide
  • Another object of the present invention is to provide a method and brazing material for minimizing carbide formations in braze joints between a graphite element and a metal element.
  • a relatively thin layer of tantalum is applied to the metal element to form a shield.
  • a disc of platinum is then applied to the tantalum, and the graphite portion is placed over the platinum disc.
  • the combination is thereafter heated to cause a brazing together of the materials.
  • the platinum becomes the primary binding material, while the thin layer of tantalum functions to isolate the metal portion from direct contact with the graphite, a combination which would tend to form carbides.
  • the tantalum is applied in the form of a film of a few microns thick by using tantalum inks, screen printed on the metal, with the resulting wet film being dried and fired to anneal the tantalum to the metal portion.
  • the platinum layer and graphite substrate is then applied and the combination is heated to effect a brazing action.
  • the tantalum coat could be applied by plasma spraying using the same firing and annealing steps.
  • the assembly includes a metal disc 11 having a focal track 12 applied to a forward face thereof for producing x-rays when bombarded by the electrons from a cathode in a conventional manner.
  • the disc 11 is composed of a suitable refractory metal such as molybdenum or molybdenum alloy (TZM or MT104).
  • the conventional focal track 12 disposed thereon is composed of a tungsten or a tungsten/rhenium alloy material.
  • the disc 11 is attached to the stem 13 by a conventional method, such as by brazing, diffusion bonding, or mechanical attachment.
  • a graphite disc 14 Attached to a rear face of the metal disc 11 is a graphite disc 14, the attachment being made by the interspersing of adjacent layers of platinum and tantalum, indicated generally by the numerals 16 and 17, respectively, in a manner to be described hereinafter.
  • the primary purpose of the graphite disc 14 is to provide a heat sink for the heat which is transferred through the metal disc 11 from the focal track 11, without contributing significantly to the mass of the target assembly.
  • FIG. 2 A method for fabricating the anode assembly is shown in FIG. 2.
  • the metal disc element 11 and graphite disc element 14 have been formed by conventional methods with each having a central bore 18 for receiving in close-fit relationship the stem 13 of the x-ray tube.
  • the graphite element 14 is first cleaned, with particular care being given to the flat surface 19 to which the flat surface 21 of the metal element 11 is to be attached.
  • the surfaces of the graphite disc 14 are preferably treated by ultrasonic cleaning or other suitable surface treatment processes to prevent the release of graphite particles (dusting) during operation of the tube.
  • the preferred process for treating the graphite element 14 actually begins in the machine process when the graphite element is formed from a billet of raw graphite.
  • a pryolytic carbon coating is applied to the surface of the machined graphite in order to minimize dust production during machining.
  • the pyrolitic carbon coating is generally applied by a chemical vapored deposition process well known in the art.
  • the element 14 is processed further by outgassing the graphite by placing it in an oven or furnace at 1900°C for approximately one hour. If it is preferred that a skin cut over the graphite surface be made using a dry lathe process to establish a smooth outer surface, that process is normally completed before the graphite is outgassed.
  • a thermal shock process is also applied in order to clean pores in the surface of the graphite to enhance the bonding.
  • Thermal shock is performed by heating the graphite in air to a temperature of about 250°C to 300°C and then quickly submerging the heated graphite in de-ionized water at room temperature. After thermal shocking, the graphite is again outgassed by heating to the elevated temperature of 1900°C for about one hour. The processed graphite is then ready for brazing to a metal element.
  • the metal portion of the anode target is preferably formed of TZM or MT104.
  • the TZM is vacuum fired to 1900°C for about one hour for outgassing.
  • the TZM face which is to be attached to the graphite surface is finish machined to true up the flatness of the surface since outgassing at the elevated temperature tends to cause the metal element to warp.
  • the TZM metal element is cleaned, typically by using an ultrasonic methanol bath. If necessary, the surface to be bonded may also be shot peened. After drying from the ultrasonic cleaning, the TZM or MT104 metal element is then ready to be bonded to the graphite element.
  • a preferred method of preparing the TZM or MT104 element for bonding to the graphite element is to coat the TZM or MT104 surface with a slurry of tantalum.
  • the tantalum layer is then formed by firing the cap element to cause the tantalum to bond to the TZM material.
  • a composite structure is thereafter formed by placing the TZM or M T 104 element face downward, placing a washer or foil layer of platinum over the exposed tantalum layer, and then positioning the graphite material over the platinum washer or foil.
  • several assemblies typically three or four, may be formed concurrently by stacking one on top of the other.
  • the second composite structure would be arranged such that its graphite element is positioned adjacent the graphite element in the first target structure.
  • the final target structure would then be inverted so that its metal element is placed adjacent the metal element in the second target structure.
  • a weight preferably about 16 pounds, is placed on top of the three stacked structures, and the stack structure is placed into a vacuum chamber furnace.
  • the furnace is typically pulled to a vacuum of about 10 -5 torr.
  • the first step in the process is to heat the furnace to about 1800°C and to hold that temperature for approximately five minutes to allow the platinum to melt.
  • the oven temperature is then allowed to cool in vacuum backdown to approximately 450° C.
  • the oven is filled with argon gas to force a rapid cooling to about 100°C. At that point the oven is opened to allow removal of the bonded anode target structures.
  • This particular process has been found to provide the best bonds without forming carbide layers which tend to be brittle and weaken the bonding between the platinum and graphite.
  • carbide forming elements may be used in place of the platinum in the manner described above.
  • any of the elements, rhodium, osbium, rethinium, palladium, or a platinum chromium alloy may be used as the bonding material.
  • the required characteristics are, first of all, that the material be essentially non-carbide forming, and secondly, that it be susceptible to the spreading of a relatively thin layer. For example, layers varying between 1.5 and 2.5 mils have been used successfully. Optimum firing conditions using such layers produce a 1 to 10 micron thick "getter" zone which is a multi-element system comprised of the titanium, platinum, molybdenum and carbon. The structure tends to be free of the cracked intermediate zones characteristic of platinum-zirconium bonding.
  • the platinum layer tends to work best when prepared in a thickness of 1 to 3 mils thick and brazed at a temperature of 10 C to 25 0 C above the liquidous temperature of the filler material.
  • Pure platinum has relatively low high temperature properties. At least a 25% increase in elevated temperature properties, i.e., tensile strength, can be achieved by using platinum alloys such as 95% platinum 5% nickel, or 90% platinum 10% rhodium, or 95% platinum 5% zirconium, or 95% platinum 5% tungsten.
  • the utilization of platinum as a filler metal can be economized by plating an area less than 1 mil thick onto and within the graphite bulk by PVD technology. PVD technology involves placing platinum into a specially designed carrier and placing the to be brazed area of the graphite above the carrier. The platinum is then heated up to its liquidous point and held for periods up to 5 hours. This causes the platinum to diffuse into the graphite material.
  • tantalum has been found to be the preferred form of material for bonding to the TZM or MT104 surface to prevent formation of molybdenum carbide layers, some success has also been achieved by using platinum in combination with tungsten, rhodium, and nickel.

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  • Physical Vapour Deposition (AREA)
  • Ceramic Products (AREA)
EP87108040A 1986-06-13 1987-06-03 Röntgenröhren-Treffplatte Withdrawn EP0249141A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US874230 1978-02-01
US87423086A 1986-06-13 1986-06-13

Publications (2)

Publication Number Publication Date
EP0249141A2 true EP0249141A2 (de) 1987-12-16
EP0249141A3 EP0249141A3 (de) 1988-07-13

Family

ID=25363268

Family Applications (1)

Application Number Title Priority Date Filing Date
EP87108040A Withdrawn EP0249141A3 (de) 1986-06-13 1987-06-03 Röntgenröhren-Treffplatte

Country Status (2)

Country Link
EP (1) EP0249141A3 (de)
JP (1) JPS6324533A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0428347A2 (de) * 1989-11-13 1991-05-22 General Electric Company Röntgenröhren-Treffplatte
EP0464916A2 (de) * 1990-06-28 1992-01-08 PLANSEE Aktiengesellschaft Hochtemperaturbeständiger Verbundkörper
US8165269B2 (en) * 2008-09-26 2012-04-24 Varian Medical Systems, Inc. X-ray target with high strength bond
US10804063B2 (en) 2016-09-15 2020-10-13 Baker Hughes, A Ge Company, Llc Multi-layer X-ray source fabrication

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3122424A (en) * 1961-12-13 1964-02-25 King L D Percival Graphite bonding method
US3890521A (en) * 1971-12-31 1975-06-17 Thomson Csf X-ray tube target and X-ray tubes utilising such a target
EP0037956A1 (de) * 1980-04-11 1981-10-21 Kabushiki Kaisha Toshiba Eine Drehanode für eine Röntgenstrahlröhre und Verfahren zu ihrer Herstellung
USRE31568E (en) * 1977-04-18 1984-04-24 General Electric Company Composite substrate for rotating x-ray anode tube

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3122424A (en) * 1961-12-13 1964-02-25 King L D Percival Graphite bonding method
US3890521A (en) * 1971-12-31 1975-06-17 Thomson Csf X-ray tube target and X-ray tubes utilising such a target
USRE31568E (en) * 1977-04-18 1984-04-24 General Electric Company Composite substrate for rotating x-ray anode tube
EP0037956A1 (de) * 1980-04-11 1981-10-21 Kabushiki Kaisha Toshiba Eine Drehanode für eine Röntgenstrahlröhre und Verfahren zu ihrer Herstellung

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0428347A2 (de) * 1989-11-13 1991-05-22 General Electric Company Röntgenröhren-Treffplatte
EP0428347A3 (en) * 1989-11-13 1991-08-28 General Electric Company X-ray tube target
EP0464916A2 (de) * 1990-06-28 1992-01-08 PLANSEE Aktiengesellschaft Hochtemperaturbeständiger Verbundkörper
EP0464916A3 (en) * 1990-06-28 1992-09-02 Metallwerk Plansee Gesellschaft M.B.H. High-temperature-resistant composite body
US8165269B2 (en) * 2008-09-26 2012-04-24 Varian Medical Systems, Inc. X-ray target with high strength bond
US10804063B2 (en) 2016-09-15 2020-10-13 Baker Hughes, A Ge Company, Llc Multi-layer X-ray source fabrication

Also Published As

Publication number Publication date
EP0249141A3 (de) 1988-07-13
JPS6324533A (ja) 1988-02-01

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