Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper

Definitions

• the invention relates generally to copper alloys, and more specifically, to copper- bismuth alloys having high strength, ductility, and lubricity.
• Copper alloys containing 20-30 wt.% lead also known as highly-leaded bronze, are commonly used due to benefits such as high strength, high ductility, high melting temperature, and high lubricity.
• Highly-leaded bronze is often used in rotating shaft bearings such as plain journal bearings or sleeve bearings, where the presence of adequate additional lubrication fluid is uncertain or periodically interrupted.
• the lubricity in highly-leaded bronze is provided by a lead-based second phase which forms during solidification. The lubricity is at least partially proportionate to the volume fraction of this lead-based second phase, which in turn is proportionate to the amount of lead in the alloy.
• aspects of the invention relate to a lead-free copper alloy that includes, in combination by weight, about 10.0% to about 20.0% bismuth, about 0.05% to about 0.3% phosphorous, about 2.2% to about 10.0% tin, up to about 5.0% antimony, and up to about 0.02% boron, the balance essentially copper and incidental elements and impurities.
• the alloy contains no more than about 0.10 wt.% lead.
• the alloy contains less than 0.05 wt.% lead.
• the alloy contains about 12.0 wt.% bismuth, about 2.4 wt.% to 3.1 wt.% tin, about 1.0 wt.% antimony, about 0.1 wt.% phosphorous, and about 0.01 wt.% boron, or the alloy contains about 12.0 wt.% bismuth, about 5.5 to about 6.2 wt.% tin, about 0.1 wt.% phosphorous, up to about 0.05 wt.% lead, and up to about 0.01 wt.% boron.
• the alloy has a phase fraction Of Cu 3 Sn of below about 0.15 (i.e. 15 vol.%), a phase fraction of CuSb of below about 0.15 (i.e. 15 vol.%), and a phase fraction Of Cu 3 P of below about 0.01 (i.e. 1 vol.%).
• the alloy has an ultimate tensile strength (UTS) in the range of about 90-210 MPa (13-31 ksi), a yield strength in the range of about 80-120 MPa (12- 17 ksi), and an elongation in the range of about 1-20%.
• UTS ultimate tensile strength
• the alloy further contains at least one rare earth element in a form selected from a group consisting of: elemental lanthanum, elemental cerium, and mischmetal, and any combination thereof.
• Additional aspects of the invention relate to a lead- free copper alloy that includes, in combination by weight, about 10.0% to about 20.0% bismuth, about 0.05% to about 0.3% phosphorous, about 2.2% to about 10.0% tin, up to about 5.0% antimony, up to about 0.02% boron, and at least one rare earth element in a form selected from a group consisting of: elemental lanthanum, elemental cerium, and mischmetal, and any combination thereof, with the balance essentially copper and incidental elements and impurities.
• the alloy contains up to about 0.10 wt.% lead. Additionally, the alloy contains a volume fraction of a bismuth-based phase of at least 0.04.
• Further aspects of the invention relate to a method that includes casting billet formed of an alloy composed of about 10.0% to about 20.0% bismuth, about 0.05% to about 0.3% phosphorous, about 2.2% to about 10.0% tin, up to about 5.0% antimony, and up to about 0.02% boron, the balance essentially copper and incidental elements and impurities, with no more than about 0.10 wt.% lead.
• the billet is then cooled to room temperature and solidified.
• the billet is cast by centrifugal casting, to near net shape.
• the billet is cooled to room temperature at a rate of about 100 0 C per minute.
• the billet is cast by direct-chill casting and cooled with water.
• FIG. 1 is an optical micrograph showing one embodiment of the present invention.
• the present invention relates to ductile lead-free Cu-Bi alloys which contain more than 10 wt.% Bi.
• Prior efforts to increase the bismuth content of copper alloys to above 10 wt.% resulted in the bismuth-based second phase segregating to the grain-boundary region, which in turn decreased the ductility of the alloys.
• the Cu-Bi alloys disclosed herein employ alloying additions of tin, antimony, and/or phosphorus, which can assist in avoiding this problem.
• a Cu-Bi alloy contains about 10.0 wt.% to about 20.0 wt.% bismuth, about 2.2 wt.% to about 10 wt.% tin, up to about 5.0 wt.% antimony, about 0.05 wt.% to about 0.3 wt.% phosphorous, and up to about 0.02 wt.% boron, the balance essentially copper and incidental elements and impurities.
• the alloy is "lead-free", which signifies that the alloy contains less than 0.10 wt.% lead, or in another embodiment, less than 0.05 wt.% lead.
• the alloy may contain a small but effective amount of rare-earth elements to help getter some impurities.
• Such rare-earth elements may be added by mischmetal (which may contain a mix of cerium and/or lanthanum, as well as possibly other elements), or elemental cerium or lanthanum, or a combination of such forms.
• the alloy contains an aggregate content of such rare earth elements of about 0.02 wt.%.
• a Cu-Bi alloy contains about 12.0 wt.% bismuth, about 2.4 wt.% to 3.1 wt.% tin, about 1.0 wt.% antimony, about 0.1 wt.% phosphorous, and about 0.01 wt.% boron, the balance essentially copper and incidental elements and impurities.
• the alloy is "lead- free," which signifies that the alloy contains less than 0.10 wt.% lead.
• this nominal composition may incorporate a variation of 5% or 10% of each stated weight percentage.
• Fig. 1 is an optical micrograph showing this embodiment.
• a Cu-Bi alloy contains about 12.0 wt.% bismuth, about 5.5 to about 6.2 wt.% tin, about 0.1 wt.% phosphorous, up to about 0.05 wt.% lead, and up to about 0.01 wt.% boron, the balance essentially copper and incidental elements and impurities.
• this nominal composition may incorporate a variation of 5% or 10% of each stated weight percentage.
• Alloys according to various embodiments may have advantageous physical properties and characteristics, including high strength, high ductility, high melting temperature, and high lubricity.
• the alloy may have an ultimate tensile strength (UTS) in the range of about 90-210 MPa (13-31 ksi), a yield strength in the range of about 80-120 MPa (12-17 ksi), and an elongation in the range of about 1-20%.
• the alloy may have a UTS in the range of about 140-210 MPa (21-31 ksi), a yield strength in the range of about 80-120 MPa (12-17 ksi), and an elongation in the range of about 7-20%.
• the alloy may have a melting temperature of about 1000 0 C.
• the lubricity of the alloy may be comparable to that of lead-containing copper alloys, such as highly-leaded bronze.
• the alloy has a higher volume fraction of a bismuth-based second phase, as compared to existing Cu-Bi alloys. This can increase the lubricity of the alloy, as the bismuth-based second phase has high lubricity.
• the volume fraction of the bismuth-based second phase in the alloy is at least 0.04 (i.e. 4 vol.%) in one embodiment.
• Cu-Bi alloys disclosed herein promote liquid immiscibility.
• the liquid with a lower solidification temperature i.e. Bi
• the grain boundaries of the solid formed from the other liquid i.e. Cu.
• some embodiments of the disclosed alloys contain appropriate alloying additions of tin, antimony, and phosphorus.
• Cu-Bi alloys disclosed herein can also limit the formation of detrimental phases, such as Cu 3 Sn, CuSb, and/or Cu 3 P.
• the phase fraction of Cu 3 Sn is limited to below about 0.15 (i.e. 15 vol.%)
• the phase fraction of CuSb limited to below about 0.15 (i.e. 15 vol.%)
• the phase fraction of Cu 3 P limited to below about 0.01 (i.e. 1 vol.%).
• This can be achieved by limiting the additions of tin to below about 10.0 wt.%, antimony to below about 5.0 wt.%, and phosphorus to below about 0.3 wt.%. It is noted that at least some of these intermetallic phases are present in the sample shown in FIG. 1, but these phases are not revealed by the etching technique used.
• the alloy of the present invention can be manufactured by casting in a steel mold, without vacuum melting.
• the alloys can be centrifugally cast to near-net shape parts. The casting is then cooled to room temperature at a rate of about 100 0 C per minute. Higher cooling rates are desirable to eliminate as-cast segregation. The higher cooling rates are accessible through direct-chill casting where the billet is cooled, for example, with water during solidification.
• the alloy may consist of, or consist essentially of, the elemental compositions disclosed herein. It is also understood that aspects of the invention may also be embodied in a product, such as a cast product, that is formed wholly or partially of an alloy according to one or more of the embodiments described above. [26] Several examples of specific embodiments that were created and tested are explained in detail below, including the details of processing the embodiments and the resultant physical properties and characteristics. The prototypes evaluated in the examples below are summarized in the following table, with the balance of each alloy being copper:

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• 2010
  • 2010-03-02 US US13/202,805 patent/US8518192B2/en active Active
  • 2010-03-02 WO PCT/US2010/025893 patent/WO2010101899A1/en not_active Ceased
  • 2010-03-02 EP EP10706465.1A patent/EP2403966B1/en active Active
  • 2010-03-02 CN CN2010800105198A patent/CN102341513A/zh active Pending
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