Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
  • B22F7/06—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools
  • B22F7/08—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of composite workpieces or articles from parts, e.g. to form tipped tools with one or more parts not made from powder
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B37/00—Joining burned ceramic articles with other burned ceramic articles or other articles by heating
  • C04B37/02—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles
  • C04B37/023—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles characterised by the interlayer used
  • C04B37/025—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles characterised by the interlayer used consisting of glass or ceramic material
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
  • C04B2237/02—Aspects relating to interlayers, e.g. used to join ceramic articles with other articles by heating
  • C04B2237/04—Ceramic interlayers
  • C04B2237/08—Non-oxidic interlayers
  • C04B2237/083—Carbide interlayers, e.g. silicon carbide interlayers
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
  • C04B2237/02—Aspects relating to interlayers, e.g. used to join ceramic articles with other articles by heating
  • C04B2237/04—Ceramic interlayers
  • C04B2237/09—Ceramic interlayers wherein the active component for bonding is not the largest fraction of the interlayer
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
  • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
  • C04B2237/32—Ceramic
  • C04B2237/36—Non-oxidic
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
  • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
  • C04B2237/40—Metallic
  • C04B2237/403—Refractory metals

Definitions

• Thepresent invention relates to methods for joining refractory compounds to metallic bases, and in particular deals with the joining of metallic carbides to such bases.
• thermoelectric transducers and vacuum tubes utilizing carbide emitters it has frequently become necessary to join a refractory carbide to a solid metallic base.
• Examples of such joints appear in the co-pending application of Grover et al., S.N. 821,339, wherein are described structures utilizing emitter electrodes of UC, ZrC and solid solutions of UC and ZrC. These electrodes are joined to a base of tantalum or niobium, and it is the primary purpose of the present invention to furnish methods whereby such joints are made.
• the present inventors have conceived and reduced to pnactice a technique for achieving strong solid joints between such refractory carbides and refractory base metals which avoids the ditliculties experienced by prior workers in the art in liberating uranium, such joints having none of the brittleness characteristic of the prior art brazed joints.
• the methods of the present inventors are based on sound thermodynamic and kinematic considerations, and should be applicable to all cases where it is sought to join a refractory metal compound to a refractory base metal, including in such refractory metal compounds not only carbides but nitrides, borides and silicides.
• the technique of the present inventors involves first of all the consideration of whether or not the base metal forms carbides which are thermodynamically more stable than the carbide which is to be joined to it. If the carbide of the base metal is the more stable, and additional step is necessary before the joint can be made. If this step is not taken, the base metal will replace the metal in the carbide to be joined and will liberate such metal. Thus tantalum and niobium displace uranium from UC. While the reaction proceeds rather slowly at low temperatures, it is fast enough to prevent the obtaining of sound joints at the temperatures of joining and will proceed even more rapidly if the joint is exposed to temperatures exceeding 1800 C. in the course of operation. a
• the method of the present inventors may or may not be necessary, depending on the solubility of such base'metal in the carbide to which it is joined.
• TaC is less stable than ZrC and the tantalum will not displacezirconium from ZrC.
• ZrC and tantalum form a low melting eutectic, having a melting point of 2500x200 C. While the joint can be satisfactorily made, it would dissolve at the operating temperatures employed in such devices as thermoelectric transducers.
• the method of the present inventors is essential, but it may be omitted in those cases where the base metal and carbide joined to it form no such low melting eutectic.
• the second consideration is Whether or not the base metal forms carbides which are sufliciently soluble in the carbide to be joined that a solid solution may readily be formed.
• TaC and NbC form acontinuous series of solid solutions with UC, ZrC, and solid solutions of UC and ZrC.
• base metal carbides it is a simple matter to form a solid solution joint with the other carbides mentioned.
• base metals whose carbides have limited solubilities in UC or ZrC, and joints therebetween are much more dilficult to achieve.
• the third consideration is the ease with which a carbide layer may be formed on the base metal, and the tenacity of such layer to the base metal.
• taut-alum and niobium may be readily carburized by heating them in contact with graphite powder in a vacuum or inert atmosphere.
• the resulting carbide surfaces are extremely thin and tenacious, and are apparently impervious to migration of the underlying base metal.
• tantalum there is an inner layer adjacent to the tantalum consisting of Ta C.
• the outer f layer usually thinner, is a TaC phase.
• Suchcarburizing may also be accomplished by heating .thebase metal in gas mixtures containing hydrocarbons.
• the method of the present invention' consists essentially of heating the out-gassed metal base in contact with out-gassed graphite powder to a temperature of about 2000-2200 C. for a period of about .15 minutes in a non-oxidizing atmosphere (vacuum or inert gas) and UC, or the carbide to be joined may be sintered to the carburized base at a somewhat lower temperature.
• a non-oxidizing atmosphere vacuum or inert gas
• UC non-oxidizing atmosphere
• the carbide to be joined may be sintered to the carburized base at a somewhat lower temperature.
• the latter alternative may be employed in any event, and may be a sintering of an already compacted carbide to the carbide surface of the base metal or may be a simultaneous compacting of a mass of carbide powder and a sintering of such compact to the carburized base metal.
• a refinement which reduces the necessary sintering temperature somewhat includes the use of sintering aids such as iron, cobalt, or nickel in the carbide to be joined. Such a sintering aid may of course be left in place in the final product, in those instances where it does no harm, or it may be removed by heating to 2000-2200 C. in vacuum. It has been found that less than about 5 weight percent of the sintering aid is all that can be profitably used, and that larger amounts are likely to promote crack formation in such carbides as UC.
• Example 2 The solid solution was then powdered in a diamend mortar and pestle to to +200 mesh. The powdering was done in an inert atmosphere dry box.
• nickel was added as both a binder and sintering aid.
• the system was evacuated to about mm. Hg
• the temperature was 2000 C. i200 C. and the pressure 4000-6000 psi. Both the temperature and pressure were maintained until the pres? sure dropped extremely slowly on release of the press handle.
• nickel powder with the carbide mixture is not essential, as similar joints have been made at a slightly higher temperature without such a binder;
• the pressurizing step is also unnecessary, but it does shorten the time neces sary to form the joint.
• formed strong joints As previously noted, the use of the selected from the class consisting of uranium carbide and zirconium carbide to a surface of, a refractory metal base selected from the class consisting of tantalum and niobium comprising carburizing the surface of said. metal base and 'sinteringsaid mass and said base at a tempera ture in the rangeof 1700? C.-2200 C. in a non-oxidizing atmosphere while said base is held in contact with said carbide during the sintering step.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Composite Materials (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Ceramic Engineering (AREA)
• Structural Engineering (AREA)
• Organic Chemistry (AREA)
• Ceramic Products (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

Country Status (4)

Cited By (4)

Citations (2)

• 1959
  • 1959-11-12 US US852585A patent/US3020632A/en not_active Expired - Lifetime
• 1960
  • 1960-06-30 ES ES0259308A patent/ES259308A1/es not_active Expired
  • 1960-07-18 CH CH814860A patent/CH405871A/de unknown
  • 1960-07-19 BE BE593149A patent/BE593149A/fr unknown

Patent Citations (2)

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