Metal fusion bonding – Process – Repairing – restoring – or renewing product for reuse
Reexamination Certificate
1999-08-30
2001-03-13
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Repairing, restoring, or renewing product for reuse
C228S248100, C228S262800, C228S194000, C228S119000
Reexamination Certificate
active
06199747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and novel composition for use in joining refractory metal structures, and, more particularly, to the transient liquid phase bonding of such refractory metal structures.
2. Description of Related Art
Refractory metal structures may be employed as support structures in high temperature sintering furnaces known as sintering furniture or hardware. Oftentimes, the sintering furniture is made from molybdenum to withstand operating temperatures of up to 1700° C. Occasionally, the sintering furniture breaks and must be repaired or discarded. Attempts at cost containment have led to methods of repairing the sintering furniture. Most preferably, repairing the sintering furniture achieves a defect free bond joint having a strength comparable to that of the sintering furniture itself.
Typically, repairs have been made by mechanically joining the broken pieces together. The mechanical joining process may comprise forming nubs on the one surface of the broken piece of sintering furniture and press fitting the nub into a drilled hole of the corresponding piece of furniture. However, due to the expansion and contraction of the pieces during thermal cycling of the furnace, the mechanical joint would fail. Thus, it would be desirable to join the broken pieces in a manner which is capable of sustaining the repeated thermal cycling of the furnace. A preferred manner of joining the structures would be a sintered joint which can withstand the thermal cycling and does not re-soften at the operating temperature of the furnace.
Transient liquid phase bonding has proven to be a very useful method in producing high quality bonds in high temperature metals. In transient liquid phase bonding, different metals of a eutectic system are deposited on the surfaces of the article to be bonded. It is desirable to find the system which produces a high quality joint while excluding from the interlayer alloy those elements which may adversely effect the bonding process or the quality of the resulting joint.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for joining refractory metal structures which provides a joint capable of withstanding repeated thermal cycling at extreme temperatures.
It is another object of the present invention to provide a method for joining molybdenum sintering furniture which provides a sintered joint capable of withstanding the repeated thermal cycling at extreme temperatures while not prone to re-melting or re-softening.
A further object of the invention is to provide a novel eutectic system for transient liquid phase bonding of refractory metal structures wherein the resulting joint does not contain elements which would substantially affect the bonding process or the quality of the joint.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method of joining refractory metal components comprising the steps of: (a) providing a first refractory metal component and a second refractory metal component, the first and second refractory metal components having corresponding surfaces in need of joining; (b) providing a joining paste mixture comprising a binder mixture, a refractory material, and a material having a lower melting point than the refractory material; (c) applying the paste mixture to the surface in need of joining on the first refractory metal component and to the surface in need of joining on the second refractory metal component; (d) contacting the first refractory metal component to the second refractory metal component at the surfaces in need of joining to form a joined structure; (e) heating the joined structure to a eutectic point of the paste mixture; and (f) forming a substantially refractory joint between the first and second refractory metal components.
Preferably, step (b) comprises providing a joining paste mixture comprising a binder mixture, a refractory material, the refractory material present in an amount of about 95.0 to about 99.8 wt. %, and a material having a lower melting point than the refractory material present in an amount of about 0.2 to about 5.0 wt. % based on a total weight of the refractory material and the material having a lower melting point than the refractory material.
Preferably, during step (e) the material having a lower melting point than the refractory material forms a localized liquid region with the refractory material at the surfaces in need of joining wherein the material having a lower melting point than the refractory material diffuses into the refractory metal components and into the refractory material of the paste. Preferably, during step (f) the material having a lower melting point than the refractory material diffuses into the refractory metal components forming a solid joint as the localized liquid region decreases its concentration of the material having a lower melting point than the refractory material thereby becoming more refractory.
In another aspect, the present invention is directed to a method of repairing molybdenum sintering furniture comprising the steps of: (a) providing a first piece of sintering furniture and a second piece of sintering furniture having corresponding surfaces in need of joining; (b) providing a metal paste mixture comprising an organic binder mixture, about 80.0 to about 85.0 wt. % molybdenum and about 0.5 to about 5 wt. % iron based on a total weight of the paste mixture; (c) applying a layer of the paste mixture to the surfaces in need of joining on the first and second pieces of the sintering furniture; (d) contacting the pieces to be joined at its surfaces having the paste mixture to form a joined piece; (e) heating the joined piece; and (f) forming a substantially refractory joint between the first and second pieces of sintering furniture.
In yet another aspect, the present invention is directed to a method of repairing tungsten sintering furniture comprising the steps of: (a) providing a first piece of sintering furniture and a second piece of sintering furniture having corresponding surfaces in need of joining; (b) providing a metal paste mixture comprising an organic binder mixture, about 95.0 to about 99.8 wt. % tungsten, and about 0.2 to about 5.0 wt. % of a material selected from the group consisting of iron, nickel and cobalt based on a total weight of the tungsten and the material selected from the group consisting of iron, nickel and cobalt, and; (c) applying a layer of the paste mixture to the surfaces in need of joining on the first and second pieces of the sintering furniture; (d) contacting the pieces to be joined at its surfaces having the paste mixture to form a joined piece; (e) heating the joined piece; and (f) forming a substantially refractory joint between the first and second pieces of sintering furniture.
In still yet another aspect, the present invention is directed to a paste mixture for joining of refractory materials comprising a first component comprising a refractory material having a particle size of about 1.5 to about 3.0 &mgr;m; a second component having a lower melting point than the first component and a particle size wherein at least about 50% of a total number of particles are less than about 3 to about 6 &mgr;m; and an organic binder mixture. Preferably, the first component is present in an amount of about 80 to about 85 wt. % of a total weight of the paste. Preferably, the second component is present in an amount of about 0.2 to about 5 wt. % of a total weight of the first and second components. Preferably, the first component comprises molybdenum or tungsten, and the second component is selected from the group consisting of iron, nickel, and cobalt.
In a further aspect, the present invention is directed to
Cohn Michael A.
DeGeorge Joseph P.
Vallabhaneni Rao V.
Blecker Ira D.
DeLio & Peterson LLC
International Business Machines - Corporation
Johnson Jonathan
Peterson Peter W.
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