US3218154A - Metal processing method - Google Patents

Metal processing method Download PDF

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Publication number
US3218154A
US3218154A US242781A US24278162A US3218154A US 3218154 A US3218154 A US 3218154A US 242781 A US242781 A US 242781A US 24278162 A US24278162 A US 24278162A US 3218154 A US3218154 A US 3218154A
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Prior art keywords
mass
metal
electron beam
compact
melted
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Expired - Lifetime
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US242781A
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English (en)
Inventor
Heinz G Sell
Mcfall Thomas
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Westinghouse Electric Corp
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Westinghouse Electric Corp
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Priority to NL301308D priority Critical patent/NL301308A/xx
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Priority to US242781A priority patent/US3218154A/en
Priority to CH1468663A priority patent/CH434585A/de
Priority to GB47858/63A priority patent/GB999226A/en
Priority to FR956345A priority patent/FR1435759A/fr
Application granted granted Critical
Publication of US3218154A publication Critical patent/US3218154A/en
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/16—Heating of the molten zone
    • C30B13/22—Heating of the molten zone by irradiation or electric discharge

Definitions

  • FIG. 5 is a diagrammatic representation of FIG. 5.
  • Electron-beam, zone-refining of refractory metals, such as tungsten or molybdenum is generally described in US. Patent No. 2,809,905, granted Oct. 15, 1957 to Davis et al.
  • a substantially solid bar of the metal to be refined is first prepared. This bar is then placed into an evacuated enclosure and the zone-refining process is carried out by sequentially melting zones of the bar with an electron beam.
  • the resulting metal is limited in diameter (0.125 inch or less) but is quite pure and, in some cases, single crystals of the refined metal can be produced.
  • the refractory metal such as tungsten or molybdenum for example
  • the metal powder is compacted into an ingot, the ingot presintered, and then self-resistance sintered or otherwise heated to a very high temperature, in order to cause the finely divided particles to coalesce into a unitary mass. Thereafter the resulting ingot is swaged and centerless ground to a bar of the desired dimensions, then surface cleaned for electron-beam, zone-refining purification.
  • the finely divided refractory metal into a self-sustaining, elongated compact or mass.
  • This compact is supported in a vacuum and a limited length portion of the supported compact is bombarded with an electron beam which has sufficient energy to melt such bombarded portion. Since only a limited length portion of the compact is bombarded, the surface tension of the melted material prevents it from running.
  • the bombarding electron beam is moved along the length of the elongated compact at such rate of speed as to sequentially melt adjacent limited length portions of the compact with melted portions of the compact solidifying after bombardment.
  • the resulting solidified material has a bulk density which is substantially equal to the theoretical density of the metal.
  • This melting and solidifying procedure is continued until a predetermined, desired length of the compact has been melted and then solidified.
  • the resulting material will frequently have a single crystal structure and single crystal alloys of refractory metal can also be produced by this method.
  • FIG. 1 is a schematic view of an electron-beam, zonerefining furnace
  • FIG. 2 is a perspective view of a porous, self-sustaining compact of compacted refractory metal powder
  • FIG. 3 is a perspective view of the compact as shown in FIG. 2, but with end supports added, preparatory to refining;
  • FIG. 4 is a perspective view of the finished metal bar after refining in accordance with the present method.
  • FIG. 5 is a flow chart which sets forth the essential steps of the present method.
  • the electron-beam, zone-refining furnace 10 as shown in FIG. 1 generally comprises a shell 12 which is hermetically closed at both ends by flanges 14 and 16.
  • a threaded spindle 18 extends into the furnace 10 through a vacuum-tight bushing 20.
  • a frame 22 is slidably mounted within the furnace shell 12 on a pair of vertical guide rods 24-, and the upper end of the sliding frame 22 is affixed to the threaded spindle 18.
  • a pair of brackets 26 are affixed to the upper and lower ends of the sliding frame 24, in order to support the metal compact 28 which is being treated.
  • a worm wheel and worm drive 30 connects to the threaded spindle 18 and is driven at a uniform speed by a motor drive (not shown) to reciprocate the threaded spindle 18 at a predetermined, uniform rate, with the frame 22 moving up and down on the guide rods 24.
  • the volume enclosed by the furnace is adapted to be evacuated by a conventional vacuum system.
  • the electron gun comprises a circular cathode 32, which is formed of tungsten, and is adapted to encircle the compact 28 which is to be sintered.
  • the circular cathode 32 is electrically connected to a power pack 34 and the compact 28 comprises the anode or target for the electron beam.
  • the compact 28 is moved relative to the fixed gun 32.
  • the uppermost and lowermost positions of the movable compact 28 are shown in dotted lines in FIG. 1.
  • the compact has already moved the distance a and will move the distance :1 before completing one pass through the electron gun 32.
  • the power pack 34 has been shown only in block form, a power pack suitable for operation with the present invention is disclosed in copending application Ser. No. 118,389, filed June 20, 1961, and owned by the present assignee.
  • Finely divided tungsten metal powder is first refined from the ore in accordance with conventional practices to as pure a state as possible. This finely divided metal powder is then placed into a mold and formed into a compact 28 of such finely divided material, as shown in FIG. 2.
  • the dimensions of the compart are A inch square and twelve inches long, and the compacting pressure which is used in forming the compact is about 20,000 p.s.i.
  • the bulk density of the formed compact is about 60% of the theoretical density of tungsten, which is 19.3.
  • the formed compact is self-sustaining in nature in that it can be handled without breakage and the pressed compact could be zone refined without any preliminary sintering.
  • the formed compact is heated to a temperature of 1000 C. for a period of 30 minutes in a hydrogen atmosphere, or in vacuum in the case of alloys.
  • small holes 36 are drilled into the ends of the compact 28 and metal support rods 38 inserted therein, as is shown in FIG. 3.
  • the compact 28 is then placed into the electron beam furnace 10, as shown in FIG. 1, and the compact is supported proximate to its ends by inserting the metal bars 38 into the retaining brackets 26.
  • the furnace 10 is then evacuated to a pressure of l mm. Hg or less, for example.
  • the compact is mounted vertically in the furnace since there is less tendency for the metal comprising the melted zone to run.
  • the end portions of the compact 28 desirably are heated by the electron beam to a temperature slightly below the melting temperature of the metal, in order to effect a sintering between the metal support rods 38 and the compact 28.
  • the compact 28 is then moved in a first pass through the electron gun 32 at a rate of approximately five millimeters per minute, but with a power input level lower than that required for melting.
  • the power input used during this first pass is approximately 90% of that power as is required for melting the metal. This first pass facilitates outgassing the pourous compact and also effects some sintering.
  • the power level is then raised to a predetermined input, as is required for melting, and a molten zone is formed at one end of the compact.
  • This molten zone is caused to travel the length of the compact 28 by moving the compact through the electron gun 28, with the rate of movement being about five millimeters per minute.
  • the power input which is required to melt a limited section of the foregoing specific compact requires a potential of approximately 2500 volts and a current of 0.5 ampere.
  • the square cross section of the compact changes to a circular cross section having an average diameter of about 0.22 inch, and a variation in diameter of about 0.01 inch can be expected.
  • the section of the compact which is molten at any one time has a length of about 0.25 inch.
  • the finished processed bar or rod 40 is shown in FIG. 4.
  • the ends or end which contain the impurities are removed.
  • the resulting metal has an exextremely high degree of purity and a bulk density which is about 99.99% that of the theoretical density of tungsten.
  • the resulting formed material is one continuous crystal with the same crystallographic orientation throughout. The essential steps of the foregoing method are outlined in the flow chart as shown in FIG. 5.
  • tungsten has been considered in detail in the foregoing example, other metals which have melting points greater than 1100 C. can also be processed in accordance with this method.
  • other metals are molybdenum, niobium, tantalum, rhenium, osmium, ru-
  • the extreme purity of the metal which has been processed in accordance with the present method is best illustrated by the residual resistance ratio of the resulting metal.
  • the residual resistance ratio is the ratio of the electrical resistance at room temperature divided by the electrical resistance at liquid helium temperature. The higher this ratio, the purer the metal.
  • the residual resistance ratios obtained are in excess of 35,000.
  • the residual resistance ratio for tungsten purified by electronbeam, zone-refining a sintered and swaged tungsten rod can vary from 5,600 to a maximum of 14,000.
  • the residual resistance ratio obtained with tungsten prepared in accordance with conventional powder metallurgy techniques is about 200.
  • the residual resistance ratio for molybdenum processed in accordance with the present method is about 4200.
  • the residual resistance ratio for molybdenum which is processed in accordance with usual powder metallurgy techniques is from about 50 to 80.
  • the present method also permits a better control of the melted section of the elongated mass being processed.
  • a porous compact which has a density of approximately 60% that of theoretical, is a relatively poor conductor of heat. Thus there is less heat conducted from the zone which is being melted and this makes the melted zone more stable and more readily controlled. This is in addition to the other advantages of refining a porous compact rather than a bar of solid metal.
  • the first pass which is made with a power input less than that required to melt the compact, is very effective in causing the volatile impurities to evaporate. If only one pass was used, the material would be densified more rapid- 1y, thereby eliminating substantially all voids in a fairly rapid fashion. This would limit the volatilization of some of the impurities. It should be understood, however, that only one pass can be used if desired, in which case the very porous compact would be melted and converted to solidified material during only one pass.
  • the present method is extremely useful for making alloys of refractory metals, and with this method it is possible to produce alloys which heretofore have not been practical to produce because of swaging or other difliculties.
  • alloys of tungsten-niobium, tungsten-tantalum, tungsten-molybdenum, tungsten-rhenium, molybdenum-rhenium and molybdenum-niobium can readily be produced by the present process.
  • the elongated mass or compact of refractory metal is supported at longitudinally spaced locations in a vertical position. Such an orientation is preferred since the melted zone or length portion of the compact has less tendency to run.
  • the compact could be suspended in a horizontal position with both ends firmly fixed and the melted zone limited in size so that its surface tension would prevent the melted metal from running.
  • Alloying materials which are present in the concentration range of solid solubility, and most single metals, can be readily formed into single crystals when they are processed in accordance with the present method. In the case of metal such as iron which undergoes phase transformations, however, some difiiculties in producing single crystals are encountered. Dispersed second phase alloys can be produced when the second phase is stable at the melting temperature of the alloy.
  • a pressure-compacting technique when preparing the elongated mass.
  • the compact can be otherwise fabricated, however, such as by using'a slipcasting technique.
  • a suitable slip-casting medium is isobutyl acetate or o-xylene.
  • the finely divided metal to be refined is first formed in a self-sustaining, elongated mass, which has a substantial degree of porosity.
  • This mass is supported in a vacuum at longitudinally spaced locations and a limited length portion of the mass is bombarded with an electron beam which has such predetermined energy as required to melt a limited length portion of the mass.
  • the surface tension of the melted metal keeps the melt from running from the mass.
  • the elongated mass and bombarding electron beam are moved relative to one another between the supported locations on the mass and at a predetermined rate of speed to sequentially melt adjacent limited length portions of the mass, with melted portions solidifying after bombardment. This sequential bombardment, melting and cooling of limited length portions of the mass is continued until a predetermined length of the mass has been melted and then solidified.
  • the method of consolidating finely divided refractory metal into a unitary mass having a high bulk density substantially corresponding to the theoretical density of such refractory metal comprises:
  • said refractory metal is one metal of the group consisting of tungsten and molybdenum.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)
US242781A 1962-12-06 1962-12-06 Metal processing method Expired - Lifetime US3218154A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
NL301308D NL301308A (enrdf_load_stackoverflow) 1962-12-06
US242781A US3218154A (en) 1962-12-06 1962-12-06 Metal processing method
CH1468663A CH434585A (de) 1962-12-06 1963-12-02 Verfahren zum Herstellen von Metallstäben
GB47858/63A GB999226A (en) 1962-12-06 1963-12-04 Processing refractory metals
FR956345A FR1435759A (fr) 1962-12-06 1963-12-06 Procédé de traitement des métaux

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CH (1) CH434585A (enrdf_load_stackoverflow)
GB (1) GB999226A (enrdf_load_stackoverflow)
NL (1) NL301308A (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3338706A (en) * 1965-03-11 1967-08-29 Westinghouse Electric Corp Metal processing method and resulting product
US3372024A (en) * 1966-11-10 1968-03-05 Army Usa Zone refinement of liquid-phase sintered tungsten alloys
US3382114A (en) * 1964-01-07 1968-05-07 Philips Corp Method of manufacturing semiconductor plate using molten zone on powder support
US3425826A (en) * 1966-03-21 1969-02-04 Atomic Energy Commission Purification of vanadium and columbium (niobium)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2743199A (en) * 1955-03-30 1956-04-24 Westinghouse Electric Corp Process of zone refining an elongated body of metal
US2809905A (en) * 1955-12-20 1957-10-15 Nat Res Dev Melting and refining metals
US2904411A (en) * 1955-06-17 1959-09-15 Bell Telephone Labor Inc Suspension of liquid material
US3163523A (en) * 1962-06-27 1964-12-29 Sylvania Electric Prod Method of purifying germanium

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2743199A (en) * 1955-03-30 1956-04-24 Westinghouse Electric Corp Process of zone refining an elongated body of metal
US2904411A (en) * 1955-06-17 1959-09-15 Bell Telephone Labor Inc Suspension of liquid material
US2809905A (en) * 1955-12-20 1957-10-15 Nat Res Dev Melting and refining metals
US3163523A (en) * 1962-06-27 1964-12-29 Sylvania Electric Prod Method of purifying germanium

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3382114A (en) * 1964-01-07 1968-05-07 Philips Corp Method of manufacturing semiconductor plate using molten zone on powder support
US3338706A (en) * 1965-03-11 1967-08-29 Westinghouse Electric Corp Metal processing method and resulting product
US3425826A (en) * 1966-03-21 1969-02-04 Atomic Energy Commission Purification of vanadium and columbium (niobium)
US3372024A (en) * 1966-11-10 1968-03-05 Army Usa Zone refinement of liquid-phase sintered tungsten alloys

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GB999226A (en) 1965-07-21
CH434585A (de) 1967-04-30
NL301308A (enrdf_load_stackoverflow)

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