Method for joining an anode target comprising tungsten to a graphite substrate

Abstract

Tungsten anode targets are joined to graphite substrates by a brazing method employing a .[.controlled.]. .Iadd.hydrogen .Iaddend.atmosphere and a suitable braze material such as platinum and an alloy of platinum and chromium.

I claim as my invention: 
     
       1. A method for joining an anode target to a graphite substrate of a disc for use in a rotating x-ray anode tube comprising the process steps of a. preparing a graphite substrate for assembling an anode target to a preselected surface area thereof;   b. disposing a layer of a metal .[.of a predetermined thickness.]. on .[.the.]. .Iadd.said .Iaddend.preselected surface area of .[.the.]. .Iadd.said .Iaddend.substrate, .[.the.]. .Iadd.said .Iaddend.layer of metal having a .[.predetermined.]. thickness .Iadd.of at least 1/4 mil .Iaddend.and .[.comprising a.]. .Iadd.consisting of at least one .Iaddend.metal selected from the group consisting of .[.rhodium, osmium, ruthenium,.]. platinum.[., palladium.]. and an alloy of platinum and .[.chronmium.]. .Iadd.chromium.Iaddend., wherein chromium is present in amounts up to about 1 percent by weight;   c. disposing .[.an.]. anode target .Iadd.material .Iaddend.on .[.the.]. .Iadd.said .Iaddend.layer of metal, .[.the.]. .Iadd.said .Iaddend.anode target .Iadd.material .Iaddend.comprising a metal selected from the group consisting of tungsten and a tungsten-rhenium alloy wherein rhenium is present in amounts up to about 25 percent by weight;   d. preheating .[.the.]. .Iadd.said .Iaddend.substrate, layer of metal and anode target .Iadd.material .Iaddend.in a .[.controlled.]. .Iadd.hydrogen .Iaddend.atmosphere at a first elevated temperature of from about 600° to about 900° C. for a predetermined period of time;   e. heating .[.the.]. .Iadd.said .Iaddend.substrate, .[.the.]. .Iadd.said layer of .Iaddend.metal .[.layer.]. and .[.the.]. .Iadd.said .Iaddend.anode target .Iadd.material .Iaddend.to a second elevated temperature of from about 1770° to 1830° C. for a predetermined period of time up to 5 minutes in a .[.controlled.]. .Iadd.hydrogen .Iaddend.atmosphere to braze the anode target .Iadd.material .Iaddend.to .[.the.]. .Iadd.said .Iaddend.preselected surface area of .[.the.]. .Iadd.said .Iaddend.substrate, and   f. cooling .[.the.]. .Iadd.said .Iaddend.substrate, .Iadd.layer of .Iaddend.metal .[.layer.]. and .Iadd.resulting .Iaddend.anode target in a .[.controlled.]. .Iadd.hydrogen .Iaddend.atmosphere to a low enough temperature to permit exposure to the atmosphere.   
     
     
       2. The method of claim 1 wherein the thickness of the metal layer is at least 0.5 mil. 
     
     
       3. The method of claim 2 wherein the thickness of the metal layer is no greater than about 1 mil. 
     
     
       4. The method of claim 3 wherein the metal of the metal layer is platinum. .[.5. The method of claim 4 wherein the controlled atmosphere is hydrogen 
     
     
        gas..]. 6. The method of claim 3 wherein the metal of the .Iadd.layer of .Iaddend.metal .[.layer.]. is an alloy of platinum and chromium. .[.7. The method of claim 6 wherein the controlled atmosphere is hydrogen gas..]. 
     
     
           The method of claim 1 wherein the layer of metal is plated onto the preselected surface area of the graphite substrate by electrodeposition means, and including practicing the additional process step prior to disposing the anode target .Iadd.material .Iaddend.thereon of degassing .[.the.]. .Iadd.said .Iaddend.plated substrate at a predetermined elevated 
     
     
        temperature for a predetermined period of time. 9. The method of claim 8 
     
     
        wherein the plated layer is at least 0.5 mil in thickness. 10. The method of claim 9 wherein the metal of the plated layer is platinum. .[.11. The method of claim 10 wherein the controlled atmosphere is hydrogen gas..]. 
     
     
          . The method of claim 8 wherein a second layer of metal is disposed on the plated surface of the substrate and the anode target .Iadd.material .Iaddend.is disposed on .[.the.]. .Iadd.said .Iaddend.second layer, the metal of .[.the.]. .Iadd.said .Iaddend.second layer is one selected from the group consisting of .[.rhodium, osmium, ruthenium,.]. platinum.[.,.]. .Iadd.and .Iaddend.an alloy of platinum and chromium, wherein chromium is present in amounts up to about 1 percent by weight.[., and palladium.].. 
     
     
          . The method of claim 12 wherein the plated layer of metal and the 
     
     
        second metal layer are each at least 0.5 mil in thickness. 14. The method of claim 13 wherein the metal of the plated layer is platinum, and the metal of the second metal layer is platinum. .[.15. The method of claim 14 
     
     
        wherein the controlled atmosphere is hydrogen gas..]. 16. The method of claim 14 wherein the thickness of the second metal layer is about 1 mil. .[.17. The method of claim 16 wherein the controlled atmosphere is 
     
     
        hydrogen gas..]. 18. The method of claim 13 wherein the metal of the plated layer is platinum, and the metal of the second layer is an alloy of platinum and chromium wherein chromium is present in amounts up to about 1 percent by weight. .[.19. The method of claim 18 wherein the controlled 
     
     
        atmosphere is hydrogen gas..]. 20. The method of claim 18 wherein the thickness of the second metal layer is about 1 mil. .[.21. The method of claim 20 wherein the controlled atmosphere is hydrogen gas..].