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

• Titanium alloys for use in the present generation of advanced aircraft engines now have to meet a creep property requirement of less than 0.1% total plastic strain during 100 hours exposure to a stress of 31 hbar. (20 tonf./in. at a temperature of 520 C. At the same time these alloys must possess adequate room temperature tensile strength, i.e. at least 100 hbar. (65 tout/in?) combined with ductility of at least 15% reduction of area and 8% elongation measured on a gauge length of D where D is the diameter of the test specimen. Furthermore, these values must be retained after exposure to service temperatures, since in practice alloys used in aircraft engine components are subjected to thermal cycles between normal atmospheric temperature and service temperatures of at least 500 C.
• IMI Titanium 685 which has the nominal composition 6% aluminum, 5% zirconium, 0.5% molybdenum, 0.25%
• the above-mentioned alloy was itself an improvement on another earlier alloy IMI Titanium 684 which advanced the utility of titanium by raising the service temperature to about 520 C. and had a composition of 6% aluminium, 5% zirconium, 1% tungsten, 0.3% silicon. Whilst this alloy possessed excellent high temperature properties, it was found that it was not always sufficiently resistant to embrittlement on exposure to high temperatures. Embrittlement in this context means loss of ductility measured at room temperature before and after exposure to high temperatures.
• a titanium-base alloy consists of one or both of the alpha stabilisers aluminium and tin in an amount equal to an aluminium equivalent of 4.5-6.5% by weight, aluminium being present in an amount not less than 2.5% and tin, when present, not exceeding 12%; zirconium, 27%, silicon ODS-0.5%, hafnium 0.55.0%, balance titanium apart from impurities.
• the alloy may also contain 0-2% molybdenum.
• aluminium equivalent refers to the wellknown replacement of aluminium by tin in the proportion of 3% tin for each 1% of aluminium replaced wherein the mechanical properties remain substantially unaffected by such replacement.
• the alloys of the invention are based on the discovery that a small addition of hafnium in the presence of silicon improves creep resistance and stability Without detriment to the other properties necessary in an aircraft engine a1- loy. Moreover, the improvement in creep resistance and stability enables the alloy to be used in service up to 540 C., an increase of 20 C. on the temperature hitherto regarded as the upper limit of service temperatures of the present titanium alloys available to the aircraft engine industry.
• hafnium has the effect of strengthening the alpha phase at elevated temperatures.
• hafnium ' is added 'to' alloys lacking silicon, such as titanium, 5% aluminium, 3% tin and 2% zirconium or titanium, 3% aluminium, 6% tin and 2% zirconium, there is little improvement in tensile properties with hafnium contents up to 5% but such alloys have been found to possess a high degree of metallurgical stability. Instability resulting resulting from metallurigcal changes occurring during such exposure is usually monitored by changes in room temperature tensile properties measured before and after exposure.
• Hafnium is a dense metal and when the intended use of the alloy is in aircraft, the strength/Weight ratio is particularly important. Having regard to this ratio and to the optimum combination of tensile and creep properties, the preferred range is 0.5-3% hafnium.
• Molybdenum is beneficial in producing a worthwhile increase in tensile strength without adversely aifecting creep properties.
• the preferred amount is 0.5% and examples of the improvement in strength are shown in Tables I and II.
• the preferred range of molybdenum is 0.25-0.75
• a further increase in tensile strength without detriment to creep properties for applications in which weldability is not important can be obtained with molybdenum contents up to 2%.
• the heat-treated alloys of the invention have better creep resistance at a temperature of 540 C. than the previously known alloys and the properties of these alloys are compared in Table II.
• Tensile properties before and after creep testing are similar in the alloys of the invention and the prior art alloys indicating that all are of similar strength and are thermally stable, the alloys of the invention being superior in this respect.
• the diiference in properties is to be seen in the total plastic strain at 540 C. in which the prior art alloys have a much greater strain than the alloys of the invention and are, in fact, considerably in 4 excess of the maximum permitted strain of 0.1% in 100 hours;
• alpha stabilising elements aluminium, tin and zirconium
• the functions of these are well known having been the basic constituents for many known alloys.
• the limits specified are dictated by the need to provide a strong, ductile alloy which is resistant to embrittlement by hydrogen pick-up, is readily forgeable and weldable without loss of ductility.
• tin is a preferred constituent, it can be omitted, provided that the aluminium content is increased by 1% for each 3% tin.
• the tin-free alloy has the advantage of lower density.
• NorE.-Post creep duetilitles determined without further surface preparation of test piece. All material beta heat-treated 1 h. 1050" 0., air cooled, aged 24 h. 550 C. (12 mm. square bar).
• a titanium-base alloy consisting of one or both of the alpha stabilisers aluminium and tin in an amount equal to an aluminium equivalent of 4.56.5% by Weight, aluminium being present in an amount not less than 2.5% and tin when present, not exceeding 12%; zirconium 2- 7%, silicon ODS-0.5%, hafnium 0.55.0%, and option ally, 02% molybdenum, balance titanium apart from impurities.
• a titanium base alloy as claimed in claim 1 containing 0.25-0.75% molybdenum.
• a titanium-base alloy as claimed in claim 2 containing 0.5% molybdenum.
• a titanium-base alloy as claimed in claim 1 containing 0.5-3.0% hafnium.
• a titanium-base alloy consisting of 4% aluminium, 6% tin, 3% zirconium, 2% hafnium, 0.25% silicon, balance titanium, apart from impurities.
• a titanium-base alloy consisting of 5% aluminium, 3% tin, 3% zirconium, 2% hafnium, 0.25% silicon, balance titanium, apart from impurities.
• a titanium-base alloy consisting of 5% aluminium, 3% tin, 3% zirconium, 2% hafnium, 0.5% molybdenum, 0.25 silicon, balance titanium, apart from impurities.
• a titanium-base alloy consisting of 4% aluminium
• An aircraft engine component made from a titanium-base alloy consisting of one or both of the alpha stabilisers aluminium and tin in an amount equal to an aluminium equivalent of 4.5-6.5 -by weight, aluminium being present in an amount not less than 2.5% and tin when present, not exceeding 12%; zirconium 2-7%, silicon 0.050.5%, hafnium 0.55.0%, and optionally, 0-2% molybdenum, balance titanium, apart from impurities.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Laminated Bodies (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)
• Silicon Compounds (AREA)

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Cited By (6)

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• 1969
  • 1969-09-24 GB GB4704969A patent/GB1297152A/en not_active Expired
• 1970
  • 1970-09-11 US US71331A patent/US3666453A/en not_active Expired - Lifetime
  • 1970-09-16 DE DE19702045816 patent/DE2045816A1/de active Pending
  • 1970-09-23 FR FR7034425A patent/FR2062537A5/fr not_active Expired
  • 1970-09-24 JP JP45083060A patent/JPS4941246B1/ja active Pending

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