Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/04—Alloys based on tungsten or molybdenum
• • 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
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/045—Alloys based on refractory metals

Definitions

• This invention relates to tungsten alloys. More particularly it relates to tungsten alloys with a tungsten content of from about 70% to about 98% by weight of tungsten having improved properties as a result of different nickel to iron ratios than in prior art materials.
• Tungsten heavy alloys generally contain from about 88% to about 98% by weight of tungsten, balance iron and nickel. It is commonly believed that a 7:3 nickel to iron ratio gives the optimum properties for the tungsten-nickel-iron system.
• a juxtaposdated tungsten base alloy body consisting essentially of from about 70% to about 98% by weight of tungsten, balance nickel and iron in essentially an 8:2 weight ratio.
• a tungsten alloy containing from about 70% to about 90% by weight of tungsten is prepared by following essentially the same procedure as with the alloys having higher amounts of tungsten except that only solid state sintering is used , thus, sintering temperatures of less than about 1450°C are used.
• a relatively uniform blend of the elemental metal powders is preferably prepared. While the elemental metal powders are preferred as the initial starting material, metallic salts having a fugitive nonmetallic components can be used as long as the proper amount of metallic elements are present in the blend.
• the relative uniform blend is made by using conventional blending equipment such as a V blender, the material is heated to remove the volatile component if any are present. Time and temperatures will depend upon the materials that are used and will be known to those skilled in the art of powder metallurgy.
• a typical consolidation technique for producing green bodies is an isostatic press using pressures of from about 30 psi to about 50 psi.
• the green body is solid state sintered at a temperature below the melting point of any of the elements for a period of time sufficient to remove any binders used to aid in the pressing to form a green body and to achieve a density sufficient to enable handling which is generally greater than about 80% of theoretical.
• nickel is the lowest melting element utilized in the practice of this invention, the initial temperature will be below about 1425°C and preferably about 1400°C.
• the time required for sintering at about 1400°C is about 4 hours. Longer times are required for lower temperatures while shorter times are required at temperatures approaching the melting point of nickel.
• the material is then sintered to full density by liquid phase sintering above the melting point of both iron and nickel to achieve full density and the desired microstructure, that is, rounded tungsten grains in a continuous second phase containing the iron and nickel.
• the actual sintering temperature will vary depending upon the tungsten content, for example, for 93% tungsten about 1540-1545°C for about 45 minutes is sufficient to achieve full density which is about 10 to about 15°C higher than required for a 7:3 nickel to iron ratio material.
• Alloys containing from about 70% to about 90% by weight of tungsten can be prepared by following essentially the same procedure as with the alloys having from about 88% or above of tungsten except that solid state sintering only is used, thus, sintering temperatures of less than about 1450°C are used. Sintering is carried out in a reducing atmosphere which includes hydrogen, hydrogen-nitrogen mixtures and dissassociated ammonia.
• Alloys are prepared by blending elemental metal powders of the metals for about 90 minutes in a V-blender. Bars are made from the powder blends by isostatically pressing the blends at about 35 ksi. The bars are presintered in wet hydrogen for about 4 hours at about 1400°C which produces a 90% dense material. The partially densified bars are sintered in a wet hydrogen atmosphere at temperatures ranging from 1510 °C to about 1540°C for the 90% tungsten and the 93% tungsten alloys respectively.
• An alloy containing 90% tungsten with an Ni:Fe weight ratio of 8:2 has an impact strength of over 50 ft-lbs as compared to 28 ft-lbs for a similar alloy having a 7:3 Ni:Fe weight ratio.
• the tensile elongation is increased from an average of about 35% to an average of 41%.
• the impact strength is increased from 18 ft-lbs to 32 ft-lbs and the tensile elongation improved from an average of 33% to an average of 38%.
• Alloys each containing about 70% tungsten are prepared by solid state sintering at from about 1400°C to about 1420°C for about 4 hours in wet hydrogen. Rolled sheets of tunsten prepared as above are compared. The material having the 7:3 Ni:Fe ratio has a tensile elongation of about 15% while the material having the 8:2 Ni:Fe ratio has a tensile elongation of about 25%.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)

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Cited By (4)

Citations (5)

• 1988
  • 1988-12-29 EP EP88121867A patent/EP0326713A1/de not_active Withdrawn

Patent Citations (5)

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