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
  • C22C19/03—Alloys based on nickel or cobalt based on nickel
  • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
  • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
  • C22C19/056—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 10% but less than 20%

Definitions

• the present invention is directed to a nickel-base casting alloy which develops high strength at elevated temperatures and is characterized by improved corrosion resistance and good castability, and, more particularly, to a nickel-base casting alloy especially useful for the production of vacuum melted and vacuum cast aircraft gas turbine blades for use in engines wherein corrosive attack due to oxidation and sulfidation is encountered.
• the gas turbine industry has now become firmly established and is capable of producing gas turbine engines for use in aircraft, automotive, marine and stationary applications which are characterized by long life and reliability.
• the requirements imposed upon gas turbine engines by actual and prospective users has placed greater and greater demands upon the builders of gas turbines.
• the requirements for parts to be used in gas turbine engines has continually been based upon higher and higher performance standards.
• a particularly sensitive part in the gas turbine mechanical structure is the turbine blading. It has been found that the temperature requirements imposed upon turbine blading materials is always being raised to a higher level.
• performance standards imposed upon the gas turbine engine and the constituent parts thereof are raised to higher levels, it is found that other problems are encountered which must be solved.
• nickel-base casting alloy having substantial rupture strength at temperatures of the order of up to about 1 800 F. and having improved corrosion resistance, e.g., sulfidation resistance, as compared to prior nickel-base alloys employed for the production of cast gas turbine blades.
• the present invention comprises a nickelbase alloy having high stress-rupture properties and having improved corrosion resistance, e.g., sulfidation resistance, at elevated temperatures, when produced as castings in the vacuum melted and vacuum cast form which contains about 15%, e.g., 15.5% or 16%, to about 18% chromium, about 0.5% to about 2.5% molybdenum, about 0.5% to about 2% columbium, about 1% to about 3% tungsten, about 1% to about 3% tantalum, about 6% or 6.5 to about 7.5% or about 8% of aluminum plus titanium, up to about 10% or cobalt, about 0.025% to about 0.25% carbon, about 0.01% to about 0.04% or 0.05 boron, about 0.01% to about 0.2%; zirconium, and the balance essentially nickel.
• corrosion resistance e.g., sulfidation resistance
• An essentially cobalt-free alloy contains, by weight, about 16% or 16.5% to about 17.5% chromium, about 1% to about 2% molybdenum, about 0.75% to about 1.25% columbium, about 1.5% to about 2.5% tungsten, about 1.5% to about 2.5% tantalum, about 5.5% or 6% to about 6.5% aluminum, up to about 0.5% titanium, about 0.03% to about 0.07% or 0.08% carbon, about 0.015% to about 0.025% boron, about 0.05% to about 0.15% zirconium, up to about 1% cobalt, and the balance essentially nickel.
• Such alloys are characterized by a rupture life at 1800 F. and 22,000 p.s.i. of at least about 30 hours or more in combination with improved corrosion resistance, e.g., sulfidation resistance, at elevated temperatures.
• the alloys provided in accordance with the invention be produced using the purest materials commensurate with reasonable cost.
• the contents of subversive impurities such as lead, bismuth, tellurium, sulfur, selenium, phosphorus, oxygen, nitrogen, hydrogen, arsenic, antimony, tin and thallium should be as low as possible.
• Cobalt may be present in the alloy in amounts up to about 10% or about 15%, e.g., about 4% to 12%, as this element appears to contribute to the sulfidation resistance of the alloy, although cobalt increases cost.
• Iron may be present in impurity amounts, e.g., up to about 1%, as iron decreases the ability of the alloy to resist microstructural changes after long exposure to elevated temperature. Silicon and manganese are detrimental elements and should not be present in amounts exceeding about 0.3% or, more advantageously, about 0.2% or about 0.1%, of each.
• cobalt-containing alloys i.e., alloys containing about 4% to about 12% cobalt
• These alloys more advantageously contain reduced proportions of aluminum, e.g., 3% or 3.5% or more of aluminum, increased proportions of carbon, e.g., up to about 0.25% carbon, and increased proportions of titanium such that the titanium content is at least about six times the carbon content and is up to about 4% or 4.5%.
• the chromium content may be reduced to as low as about 15% with concomitant increase in high temperature properties.
• Such alloys are strong at 1800 F., have improved stress-rupture strength at lower temperatures, e.g., 1350 F.
• the alloys retain the long-time structural stability which characterizes the aforementioned essentially cobalt-free alloys.
• alloys accordingly contain about 15% to about 18% chromium, about 4% to about 12% cobalt, about 0.75% to about 2.2% molybdenum, about 1% to about 3% tungsten, about 0.5% to about 2% columbium, about 1% to about 3% tantalum, about 3% to about 6% or 7% aluminum, titanium in amounts at least six times the carbon content up to about 4%, about 0.1% to about 0.2% carbon, about 0.01% ⁇ to about 0.04% or 0.05% boron, about 0.01% to about 0.2% zirconium, and the balance essentially nickel.
• the total content of aluminum and titanium in the alloys does not exceed about 7% or 7.5
• a preferred range comprises about 15.5 to about 17% chromium, about 8% to about 11% cobalt, about 0.75% to about 2.2% molybdenum, about 1.8% to about 3% tungsten, about 0.75% to about 1.25% columbium, about 1% to abo t a a m,
• a preferred range comprises about 15.5% to about 17% chromium, about 4% to about 6% cobalt, about 0.75 to about 2.2% molybdenum, about 1.8% to about 3% tungsten, about 0.75% to about 1.25% columbium, about 1% to about 2% tantalum, about 3% to about 4% aluminum, about 3% to about 4% titanium, about 0.14%; to about 0.2% carbon, about 0.01 to about 0.03% boron, about 0.05 to about 0.15% zirconium, and the balance essentially nickel.
• the aforementioned cobalt-containing alloys when properly heat treated, will have a stress-rupture life of at least about 30 hours at 1800 F. and 22,000 p.s.i. stress and of at least about hours at 1350 F. and 90,000 p.s.i. stress. More advantageous alloys containing nominally 4% aluminum and 3% titanium will have stressrupture lives of at least about 50 hours and at least about 200 hours under the respective test conditions.
• chromium and molybdenum are carefully controlled in amount to enable obtaining improved corrosion resistance at temperature and satisfactory stress-rupture properties as contemplated in accordance With the invention.
• chromium is desirably about 16% to about 18% and molybdenum is about 1% but does not exceed about 2.5
• chromium may be increased up to about 19% or 20% with improvement in corrosion resistance, e.g., sulfidation resistance, in instances wherein microstructural stability during long periods of exposure to elevated temperatures are of reduced importance.
• an essentially cobalt-free alloy otherwise in accordance with the invention but containing ony 0.01% carbon developed an unacceptable stress-rupture life of only 10 hours at 1800 F. and 22,000 p.s.i. whereas a similar essentially cobalt-free alloy containing 0.03% carbon developed a satisfactory stress-rupture life of 40 hours at 1800 F. and 22,000 p.s.i.
• carbon exceeds about 0.08% the stress-rupture properties of the alloys are again detrimentally affected, unless the appropriate adjustments in composition, particularly with regard to cobalt, aluminum and titanium noted hereinbefore, are made.
• Titanium may be employed in amounts not exceeding about 0.75 or, more advantageously, not more than 0.5% or even 0.25%, in the special essentially cobaltfree alloys which contain not more than about 0.08% carbon described hereinbefore.
• the aforementioned cobalt-containing alloys also having increased contents of titanium, e.g., up to about 3.5% or 4% titanium, with reduced aluminum contents such that the total content of aluminum plus titanium is about 6.5 to about 7.5 advantageously contain substantially increased carbon contents, e.g., about 0.14% to about 0.18% or about 0.2%.
• Such alloys also advantageously contain about 2% molybdenum for increased strength, particularly at 1350 F., while maintaining freedom from the formation of brittle phases, e.g., sigma phase, on long-time heating.
• h lo g a e 1 i c udes the composition of
• the tensile tests conducted upon cast-to-size test bars at room temperature have indicated a yield strength (0.2% offset) of about 120,000 p.s.i. along with TABLE I Percent Mo Cb eighteen alloys produced in accordance with the invention by vacuum melting and vacuum casting. The balance of the alloy in each case is essentially nickel.
• Alloy No. 18 still showed no evidence of corrosion after 200 hours in the test.
• This alloy was strong in all conditions of testing as shown in Table III and was microstructurally stable after long-time elevated temperature exposure, i.e., the alloy did not develop a brittle phase such as sigma phase.
• the corrosion resistance of the alloys provided in accordance with the invention was on the order of ten to fifty times better than that of the AMS 5391 alloy.
• the alloys also exhibit improved elevated temperature sulfidation resistance under alternating reducing and oxidizing conditions.
• Castings produced in accordance with the invention may be employed in the as-cast condition with good results.
• Heat treatment of the castings may be employed for the purpose of improving certain properties.
• the castings may be subjected to a solution heat treatment comprising a heating at about 2100 F. to about 2200 F., e.g., 2150 F., for a time of about one to about ten hours, e.g., about two hours.
• the solution heat treatment may be followed by an aging treatment at about 1600 F. to about 1700 F., e.g., about 1650 F., for about ten hours to about fifty hours, e.g., twenty-four hours.
• the aforementioned cobalt-containing alloys are heat treated by solution heating in the temperature range of about 1925 F. to about 2075 F., e.g., about 1975 F. to about 2050 F., for a time of about one to about ten hours, e.g., about two to about six hours.
• the solution treatment may be followed by an aging treatment at about 1500 F. or 1550 F. to about 1650 F. for about 24 to about 16 hours.
• An advantageous heat treatment comprises two beatings within 75 the temperature range of about 1925 F.
• Castings produced from the alloys provided in accordance with the invention may be employed not only in cast aircraft, industrial, marine and automotive gas turbine blades but also in cast stationary gas turbine components such as guide vanes, nozzle partitions and other cast gas turbine components which are subjected to corrosive environments at elevated temperatures. Sulfur compounds are normally present in fuels used for gas turbines. It is found that when gas turbine engines also ingest salt, as is the case in marine service of various types, that attack upon the hot surfaces of the engines is vastly accelerated. The invention is particularly useful for the production of parts which must operate in the presence of salt, e.g., sodium chloride, as encountered in gas turbines operated at sea, including marine and aircraft gas turbines.
• salt e.g., sodium chloride
• Castings may be produced from the alloys provided in accordance with the invention using commercial vacuum melting and vacuum casting equipment and employing investment molds, static casting, etc.
• the alloys should be prepared by vacuum melting. It is also desirable to vacuum cast the alloys. In commercial practice, it is permissible to prepare remelt stock by vacuum melting and then remelt and cast under an argon atmosphere.
• An alloy having an improved combination of elevated temperature stress-rupture strength and corrosion resistance consisting essentially of about 15% to about 18% chromium, about 8% to about 11% cobalt, about 0.75% to about 2.2% molybdenum, about 1.8% to about 3% tungsten, about 0.5% to about 2% columbium, about 1% to about 3% tantalum, about 3% to about 4% aluminum, about 0.1% to about 0.2% carbon, about 3% to about 4% titanium with the total content of aluminum and titanium not exceeding about 7.5%, about 0.01% to about 0.05% boron, about 0.01% to about 0.2% zirconium, and the balance essentially nickel.
• a corrosion resistant alloy having high elevated temperature rupture strength consisting essentially of about 16% chromium, about 10% cobalt, about 2% molybdenum, about 2.5% tungsten, about 1% columbium, about 1.25% tantalum, about 4% aluminum, about 3% titanium, about 0.18% carbon, about 0.02% boron, about 01% zirconium, and the balance essentially nickel.
• a corrosion resistant alloy having high elevated temperature rupture strength consisting essentially of about 16% chromium, about 10% cobalt, about 2% molybdenum, about 2.5% tungsten, about 1% columbium, about 1.25% tantalum, about 3% aluminum,

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Chemically Coating (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Battery Electrode And Active Subsutance (AREA)

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Citations (4)

• 1967
  • 1967-02-20 US US617071A patent/US3459545A/en not_active Expired - Lifetime
• 1968
  • 1968-01-29 GB GB4562/68A patent/GB1144622A/en not_active Expired
  • 1968-02-09 NL NL6801847A patent/NL6801847A/xx unknown
  • 1968-02-12 AT AT127768A patent/AT275886B/de active
  • 1968-02-16 DE DE19681608185 patent/DE1608185A1/de active Pending
  • 1968-02-19 ES ES350629A patent/ES350629A2/es not_active Expired
  • 1968-02-19 CH CH233468A patent/CH501058A/fr not_active IP Right Cessation
  • 1968-02-20 BE BE711015D patent/BE711015A/xx unknown

Patent Citations (4)

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