Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting

Definitions

• United States Patent U.S. Cl. 75-135 8 Claims ABSTRACT OF THE DISCLOSURE Methods for forming and treating titanium-nickel alloys which include preparing the alloys by induction melting the nickel, adding the titanium to the molten nickel, contacting the resulting alloy with carbon while under vacuum. The alloys are further cast in suitable graphite molds with the solidification process proceeding from the bottom toward the top of the mold.
• This invention pertains to the formation and treatment of alloys and more particularly to the formation and treatment of alloys comprising a highly reactive metal and a relatively unreactive metal.
• the alloys of highly reactive metals are generally prepared by arcmelting techniques, e.g., titanium-nickel alloys have been formed by both consumable and non-consumable methods, employing a water-cooled copper crucible.
• the method of this invention for forming the alloy generally comprises melting the relatively unreactive component of the alloy in a container formed from a stable material, adding to and melting in the container the reactive metal component and pouring the resulting alloy into a suitable mold for solidification.
• the melting operation is performed in an inert atmosphere, i.e., any atmosphere that excludes atmospheric contaminants including, for example, a vacuum; a rare gas such as argon, helium, etc., and the like, with the use of a rare gas at atmospheric pressure or higher being preferred since it prevents the leakage of air into the system.
• the container is generally formed from either thoria or magnesia with magnesia being preferred due to its lower cost and less toxic nature. It is to be understood, however, that the term container formed from a stable material is not limited to containers wholly made from such materials but also includes containers made from other materials that have their inner surfaces coated with stable materials.
• the stable material used for forming the container generally has a purity of at least about 97%, with at least about 99% being preferred, in order to lessen the possibilities of oxygen impurities resulting from the interaction of the reactive metal component with the oxide impurities generally found in such materials.
• the relatively unreactive material is melted in the container first since it has been found that the molten unreactive component has a moderating effect upon the reactive metal component which reduces metal-container interaction. Since this moderating effect is considerably reduced when the atomic ratio of reactive component to unreactive component exceeds about 2 to 1, the method of this invention is most effective on alloys that fall within this ratio.
• the components are generally melted in a low frequency induction furnace since such an operation has a good mixing effect which promotes chemical homogeneity.
• low frequency induction melting techniques are preferred because they produce superior alloys at a lower cost, it is to be understood that other melting techniques may be employed so long as they are utilized in an inert atmosphere and the relatively unreactive component is melted first in a container formed from a stable material such as magnesia or thoria.
• the method of this invention is generally performed, using a nickel-titanium alloy as a representative example, by first placing a dry clean magnesia or thoria crucible containing the desired weight of nickel into a low frequency induction furnace having an inert atmosphere. The nickel is melted and the amount of titanium necessary to give the desired nickel-titanium ratio is charged from a charging chute into the molten nickel. The molten titanium and nickel are intimately mixed in the crucible by the low frequency of the furnace and when alloying is complete, the molten alloy is charged into a suitable mold for solidification.
• the method of this invention for removing oxygen impurities generally comprises contacting the molten alloy with carbon under vacuum. More particularly, the alloy may be purified either by induction melting the alloy under a vacuum of at least about 10' mm. in a carbon container, preferably in the form of high density graphite or by induction melting the alloy under a vacuum of at least mm. in any suitable container followed by the addition of carbon.
• the invention is not to be limited or bound by any theoretical reactions or equations, it is believed that the removal of oxygen impurities is effected, using a nickel-titanium alloy as a representative example, by the following reaction:
• the purification effect of the carbon may be enhanced by adding to the molten alloy a metal that both forms an oxide having a high heat of formation and does not alloy with the metals present in the molten alloy.
• a metal that both forms an oxide having a high heat of formation and does not alloy with the metals present in the molten alloy For example, an excess of calcium or magnesium metal (based on the amount necessary to combine with the oxygen impurities present) is placed beneath the surface of the molten alloy in the graphite container, said metal and oxygen combining to form an oxide which is raked off as a slag.
• the purification may be promoted by bubbling hydrogen into the molten alloy in the carbon crucible, said hydrogen combining with the oxygen imuprity to form water vapor.
• the alloy forming and purification techniques described herein may be performed on any alloy comprising highly reactive and relatively unreactive metal components.
• highly reactive metal components there may be mentioned Group IV metals such as hafnium, zirconium, titanium, etc., rare earth metals such as cerium, etc., and the like.
• relatively unreactive metal components there may be mentioned iron, cobalt, copper, indium, aluminum, nickel, gold, lead, and the like.
• the methods of this invention are particularly applicable to the 50 to 70 weight percent nickel, remainder essentially titanium alloys, especialy the stoichiometric nickel-titanium alloy (53.5 to 56.5 weight percent nickel, the remainder essentially titanium) which are described in more detail in US. Patent No. 3,174,851, granted Mar. 23, 1965, which is hereby incorporated by reference.
• One such embodiment comprises forming the alloy by the method of this invention, pouring the molten alloy before solidification into a carbon crucible, said alloy being kept molten under vacuum to effect purification and pouring the molten alloy into a suitable mold for solidification.
• any suitable crucible may be used followed by the addition of carbon to elfect purification.
• Another embodiment comprises placing an ingot prepared by either the method of this invention or any other method into a graphite crucible, induction melting the alloy under vacuum to effect purification and pouring the molten alloy into a suitable mold for solidification.
• any suitable crucible may be employed followed by the addition of carbon to the molten alloy.
• a further embodiment comprises pouring the molten alloy prepared by the method of this invention before solidification through a carbon lined funnel into a suitable mold for solidification, said operation being performed under vacuum.
• Still another embodiment for providing intricate cast shapes while effecting purification comprises delivering under vacuum the alloy formed by the method of this invention in either liquid or solid form to a specially designed mold made of high purity dense dried graphite.
• the mold has a suitably matched induction coil around it and the induction coil is equipped with taps to regulate heating specific sections of the mold. If the charge to the mold is molten, the mold may be preheated to a ternperature in excess of the melting point of the alloy concerned. Once the mold is filled (including the filling of generous, hot top”), the induction coil is gradually closed off starting at the bottom of the mold. By solidifying the casting from the bottom of the mold to the top it is possible to produce a minimum shrinkage pipe, and it will be in the hot top section.
• the solid alloy is placed in a graphite hopper attached to the top of the mold, said induction coils being wound well up on the hopper.
• the mold and hopper is heated by induction causing the alloy concerned to melt in the hopper and run into the mold.
• the solidification is then performed as mentioned above placing the shrinkage pipe in the hopper.
• a 55 weight percent nickel, remainder essentially titanium alloy may be prepared in the following manner.
• a nickel-titanium alloy (55 weight percent nickel, remainder essentially titanium) is purified by placing the alloy in a high density graphite crucible which is then placed into an induction furnace. A vacuum of 10* millimeters is pulled and the induction input to the furnace is approximately 3,000 cycles. The alloy is held at about 1500 C. to effect purification and is then poured into a mold for solidification.
• a method for forming and purifying a metal alloy comprising, said method comprising:
• the method of claim 2 further comprising promoting the purification by placing a metal selected from the group consisting of calcium and magnesium beneath the surface of the molten alloy during the contacting.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Mold Materials And Core Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

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Family Applications (1)

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Cited By (3)

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Citations (14)

• 1965
  • 1965-10-07 US US493940A patent/US3508914A/en not_active Expired - Lifetime
• 1966
  • 1966-09-23 DK DK493366AA patent/DK124342B/da unknown
  • 1966-09-28 GB GB43411/66A patent/GB1167543A/en not_active Expired
  • 1966-09-28 GB GB31035/67A patent/GB1167544A/en not_active Expired
  • 1966-09-29 DE DE19661533187 patent/DE1533187A1/de active Pending
  • 1966-10-03 CH CH1423666A patent/CH492790A/de not_active IP Right Cessation
  • 1966-10-03 BE BE687749D patent/BE687749A/xx unknown
  • 1966-10-05 NL NL6614026A patent/NL6614026A/xx unknown
  • 1966-10-06 AT AT1006269A patent/AT298085B/de active
  • 1966-10-06 ES ES0331999A patent/ES331999A1/es not_active Expired
  • 1966-10-06 SE SE13490/66A patent/SE333643B/xx unknown
  • 1966-10-06 AT AT937366A patent/AT284476B/de active
  • 1966-10-07 NO NO165043A patent/NO115500B/no unknown
  • 1966-10-07 JP JP41065771A patent/JPS5017935B1/ja active Pending
• 1967
  • 1967-03-29 ES ES338606A patent/ES338606A1/es not_active Expired

Patent Citations (14)

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