Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C14/00—Alloys based on titanium

Definitions

• This invention relates to titanium base alloys which contain tungsten as an essential component, and which are characterized by high elevated temperature strength, thermal stress stability, good notch properties and good creep resistance. These properties are particularly desirable in the construction of modern high speed jet engine parts.
• the invention also relates to the processing of these alloys in a manner which serves to maximize their desired characteristics.
• Titanium because of its low density and high melting point is well adapted to high temperature structural applications in aircraft and the like.
• the pure metal alone does not possess suflicient strength for most applications; and it must be alloyed with other metals in order to overcome this deficiency.
• Aluminum can be alloyed with titanium to provide increased strength; however the amount of aluminum must be kept below about 8% in order to preserve the ductility of the material.
• Tin, zirconium and molybdenum also add to the strength of Patented Dec. 9, 1969 temperatures, it does present other problems.
• the element silicon has a tendency to segregate during melting. Also, even small amounts of this element produce severe embrittlement of the titanium base alloy.
• the present invention makes use of the discovery that silicon may be omitted entirely in titanium base alloys through the substitution of tungsten for molybdenum. It has been discovered that by virtue of this substitution, it becomes possible to fabricate a titanium base alloy which has high temperature creep resistance, strength and ductility.
• the present invention makes possible the elimination of silicon in titanium base alloys without the attendant loss of creep resistance at high temperatures. Moreover, ductility and strength are preserved and have been found to be at least equal to any known titanium alloy. These advantages are achieved through the substitution of tungsten for molybdenum and the elimination of silicon.
• the alloy of the present invention consists essentially of about 5 to 7% aluminum, 1 to 4% tin, 2 to 5% zirconium, 1 to 4% tungsten, up to 0.5% in total amount of carbon, oxygen and nitrogen, but preferably not to exceed 0.1% nitrogen and 0.2% carbon, balance titanium, apart from impurities within commercial tolerances.
• a preferred alloy according to the invention is Ti-6Al-2Sn-4Zr-2W. Another preferred alloy is For purposes of comparing properties of alloys according to the invention with closely related compositions containing silicon, compositions were melted in accordance with the following Table I, forged specimens of which were tested in various heat treated conditions and with results and as shown in the succeeding table hereof. Table I gives both the nominal and actual composition of the various alloys melted and tested.
• the beta transus of Ti-6Al-2S-n-4Zr-2W is about 1885 F. NASA sharp notch properties of this alloy (Le. Ingot No. 3428) after being processed and solution treated below the beta transus, are shown in Table V.
• Table V demonstrates that the sharp notch values decrease with increase in aging time at 1100" F.
• Table V also shows that increasing the solution temperature tends to raise NASA sharp notch values for each aging time.
• increasing the solution temperature from 1675 F. to 1775 F., and then to 1825 F., raised the sharp notch values from 113 to 115, and then to 118.
• This demonstrates that employment of higher solution temperatures may be expected to improve the NASA sharp notch performance of Ti-6ALZSn-4Zr-2W.
• Ti-6Al-2Sn-4Zr-2W i.e. Ingots Nos. V-3072 and V-3428
• Table VI The creep stability properties of Ti-6Al-2Sn-4Zr-2W (i.e. Ingots Nos. V-3072 and V-3428) processed and solution treated below the beta transus
• the amount of deformation was also about 0.1%
• the elastic modulus of the samples has a creep resi d by the beta treatment to the range of 17.5-
• M W HT meet DA MW wenwemwwemmnnmhn gamma .1 :m eA awn o e 1 1 e mn m 1 LLLLLLLLLLLLLLLLLLLLLLLLLL 0F Yi 6 e 2 e f b P P DR81NNI 0 beta processing the yield strengths are in the range of -150K p.s
• Heat treatment Table IX shows that at room temperature the 0.2% offset yield strength of the alloy of the present invention is somewhat greater than that of the silicon con taining alloys. However, at increased temperatures, the alloy of the present invention exhibited much greater yield strengths than the silicon containing alloy which also contained tungsten; and while at the higher temperatures its yield strength was slightly below the other silicon containing alloy, its notch strength and creep resistance very greatly exceeded that of both silicon containing alloys.
• the NASA Sharp Notch Values for the silicon free alloy of the present invention ranged between 110 and 102 when aged for dilferent lengths of time at 1100 F.
• the NASA Sharp Notch Values for the silicon containing alloys ranged between 71 and 100 for corresponding aging times and temperatures.
• the creep resistance of the alloy of the present invention at elevated temperatures was far superior to the silicon containing alloys; and at 1100 F. the alloy of the present invention exhibited less than half the creep undergone by the silicon containing alloys under the same loads and durations.
• the alloy of the present invention provides a combination of tensile strength, creep resistance, toughness and ductility at elevated temperatures which is unmatched by any other previously known alloy. Moreover, the improved mechanical properties of the alloy of the present invention are sharply enhanced when the alloy is either processed or annealed above its beta transus temperature.
• An age hardenable titanium base alloy consisting essentially of about: 57% aluminum, 14% tin, 2-5% zirconium, 1-4% tungsten, up to 0.5% in total amount of carbon, oxygen and nitrogen, balance titanium apart from impurities within commercial tolerances, characterized by high strength and ductility at room and elevated temperatures and high creep strength at elevated temperatures up to about 1100 F.
• An age hardened alloy according to claim 1 having an ultimate strength of at least 150K p.s.i. and a tensile elongation of at least 10%.
• An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 2 to 4% tungsten.
• An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 2% tungsten.
• An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 4% tungsten.

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Citations (4)

• 1967
  • 1967-08-08 US US659027A patent/US3482968A/en not_active Expired - Lifetime
• 1968
  • 1968-07-11 SE SE09558/68A patent/SE339876B/xx unknown
  • 1968-08-06 DE DE19681758778 patent/DE1758778B1/de active Pending
  • 1968-08-06 GB GB37535/68A patent/GB1169867A/en not_active Expired
• 1969
  • 1969-11-12 FR FR1584373D patent/FR1584373A/fr not_active Expired

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