Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C19/00—Alloys based on nickel or cobalt
  • C22C19/07—Alloys based on nickel or cobalt based on cobalt
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K6/00—Preparations for dentistry
  • A61K6/80—Preparations for artificial teeth, for filling teeth or for capping teeth
  • A61K6/84—Preparations for artificial teeth, for filling teeth or for capping teeth comprising metals or alloys

Definitions

• This invention concerns a chromium-cobalt alloy having high strength, high ductility, and an improved balance of elongation and toughness, which, owing to these properties, is particularly adapted for the production of cast partial denture appliances.
• Chromium-cobalt alloys having come into wide use in the production of castings for partial or complete denture appliances, must meet certain physical properties requirements, e.g., adequate elongation and toughness and the right degree of hardness, to permit the dentist or dental technical to make minor but necessary adjustments at the time of delivery to the patient.
• the technician or dentist must be able to bend the clasp attachment to more than a ten degree angle without breakage occurring. Counterbalancing such good flexibility, however, the clasp must have suflicient rigidity to retain the shape and position to which it has been adjusted and to resist distortion by' the biting forces.
• the present composition consisting essentially of an alloy composed of chromium, cobalt, nickel and tantalum in specific proportions, gets its strength through a precipitation hardening mechanism, rather than by the formation of carbides.
• carbides since there is no carbide precipitation, the foregoing manipulative conditions during casting of the alloy and other processing do not cause a variation in mechanical properties and strength.
• Remelting of the new alloy, including the recasting of scraps thereof, and variations in casting temperatures do not cause variations in the physical properties of the alloy.
• loss of ductility as the alloy is strengthened by the precipitation hardening mechanism is kept to a minimum.
• Tantalum has previously been disclosed as an additive to chromium-cobalt alloys to improve certain properties (but not in the unique proportions embodied in the present invention which unexpectedly provide a special combination of strength, toughness, and ductility to the alloy making it particularly useful in dental appliance manufacture).
• Canadian Pat. 238,742, Mar. 18, 1924 discloses a chromium-cobalt alloy for cutting tools, containing not more than about 5% tantalum. In the only specific example cited in this Canadian specification, the alloy also contains about 15% tungsten and 2% carbon. Michael et al., 11.8. 3,085,005, Apr.
• the alloy of the present invention consists essentially of 18% to 28% chromium (preferably 23 to 26% Cr), 25% to 50% cobalt (preferably 33 to 36% Co), 18% to 40% nickel (preferably 24 to 30% Ni), and from 12.3% to 13.5% tantalum (preferably about 13%), such amounts of Ta being critical to obtain the properties hereinafter described. (All amounts of constituents of alloys described herein are given in percents by weight.)
• the alloys of this invention which are essentially free of carbon to avoid undesired carbide precipitation, have an elongation of at least 10% and a toughness factor of at least about 8000.
• the yield point of the alloy is greater than about 80,000 p.s.i. and its hardness is not greater than about 330 KHN units.
• the percentage of elongation is a measure of the extent an alloy will increase in length as it is drawn from a zero load to the breaking point. Percentage of elongation has a direct relationship to cold shaping of an alloy as in the use of pliers to shape wire into clasps.
• the yield point (Y.S.) is an indication of the behavior of a clasp, as Well as the entire denture frame, under biting forces, which forces can easily produce stresses above the yield strength of an alloy deficient in that property, causing the denture to shift out of the proper occlusal relationship to which it was originally designed.
• Toughness is the ability of an alloy to withstand sudden shocks and blows that stress the alloy beyond its yield point but within its breaking point.
• the toughness factor is defined as the product obtained by multiplying the percentage of elongation (as a decimal fraction) by the ultimate tensile strength of the alloy in pounds per square inch. Ultimate tensile strength (U.T.S.) is the greatest unit stress an alloy will stand in tension to the point of breaking. Hardness is the resistance of an alloy to surface penetration, and is a measure of surface wear etfects. Extreme hardness is undesirable because of the wear a hard denture causes to opposing teeth in contact therewith.
• the physical and mechanical properties of alloys described herein were determined using an Instron Universal Testing Machine and a strain gauge estensometer.
• the microhardness was determined using a Tukon Microhardness Tester and a Knoop indenter with a 500 gram load. Specimens for microhardness testing were longitudinal sections from test bars polished with conventional metallurgical procedures.
• the representative alloys described below were prepared under argon atmosphere using induction type heating units. After melting together the chromium, cobalt and nickel, the measured amount of tantalum was added and blended into the molten alloy. It was observed that the tantalum actually dissolves in the ternary alloy of chromium of Cr-Co-Ni.
• the alloying temperatures ranged from 2800 F. to 2850 F.
• the quaternary alloy was remelted under argon for homogenization in the same temperature range, and then cast at 2750 to 2800" F. using a centrifugal induction unit.
• Wax patterns were prepared using a modified split brass mold into which molten wax was injected, and the wax patterns were sprued horizontally.
• the mold supplied the tensile specimen, feeding sprue and venting sprue, all in one piece.
• the dimensions of the Wax patterns to produce tensile specimens were the same as those specified by the American Dental Association Specification No. 14 for dental chromium-cobalt casting alloys.
• the wax patterns were then invested using a phosphate-bonded investment. The investment was then heated to 1800 F. and heat soaked for one and one-half hours before the castings were made.
• the constituents of representative alloy compositions are shown in Table 1 below, and the physical properties of these alloys are set forth in Table 2.
• TAB LE 1 Representative Alloy Compositions, Constituents in Percent by Weight Cr Co Ni Ta Example number:
• An alloy consisting essentially of 18%, to 28% chromium, 25% to 50% cobalt, 18% to 40% nickel, and 12.3% to 13.5% tantalum.

Landscapes

• Health & Medical Sciences (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Chemical & Material Sciences (AREA)
• Veterinary Medicine (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Epidemiology (AREA)
• Plastic & Reconstructive Surgery (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Dental Preparations (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22940921

Family Applications (1)

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Cited By (4)

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• 1972
  • 1972-05-01 US US00248843A patent/US3756809A/en not_active Expired - Lifetime
• 1973
  • 1973-04-04 CA CA167,923A patent/CA975998A/en not_active Expired
  • 1973-04-09 GB GB1697073A patent/GB1423901A/en not_active Expired
  • 1973-04-19 DE DE2320016A patent/DE2320016A1/de active Pending
  • 1973-04-20 IT IT23278/73A patent/IT984037B/it active
  • 1973-04-27 FR FR7315340A patent/FR2183059B1/fr not_active Expired
  • 1973-05-01 JP JP48047692A patent/JPS4966526A/ja active Pending

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