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 relates to a nickel-based alloy hardening by precipitation of a gamma-prime phase.
• Cobalt is one of the typical elements of superalloys. It has been and still is of great importance for producers of superalloys and is moreover considered as a strategic element whose supply has been difficult and could very well become it again. It was and still is an addition to super alloys for many reasons such as: solid solution hardening properties of phase stability, increased ductility and resistance to hot corrosion.
• the present invention relates to a nickel-based superalloy with a lower cobalt content than that usually encountered in superalloys.
• a very elaborate selection and a rigorous balance between the various elements allowed the realization of an alloy with low cobalt content, presenting a judicious distribution of the contents of chromium, molybdenum, tungsten, vanadium, aluminum, titanium, carbon and boron.
• the alloy is characterized by the highly sought-after combination of property of resistance to creep rupture, resistance to corrosion, to oxidation, phase stability and ductility. It is particularly suitable for molding articles such as rotor blades and turbine stators.
• the object of the present invention relates to the development of a nickel-based alloy, hardening by precipitation of gamma prime phase and low in cobalt content.
• the alloy is characterized by the following composition in weight proportions: from 14 to 18% of chromium, from 0.3 to 3% of molybdenum, from 4 to 8% of tungsten, from 0.01 to 1 , 0% vanadium, up to 0.05% tantalum, up to 0.05% niobium, 3.5 to 5.5% aluminum, 1 to 4% titanium, 3 to 7% cobalt, up to 2% iron, 0.01-0.05% carbon, 0.035-0.1 boron, up to 0.1% zirconium, up to 0.01 % nitrogen, up to 0.5% copper, up to 0.12% manganese, up to 3% elements of the rhenium-ruthenium group, up to 0.2% elements rare earth not lowering the starting melting temperature below the gamma-prime phase solvus temperature in the alloy, up to 0.15% of elements of the magnesium-calcium-strontium-barium group, up to 0.1% hafnium and the complement to 100 being essentially nickel, said boron content
• the components of the alloy must balance so as to give a stable alloy, in particular free of sigma phase and other topologically compact phases.
• a weight percentage of chromium of 14 to 18% is provided in the alloy.
• a content of at least 14% is necessary to ensure protection against corrosion.
• the alloy becomes unstable at contents higher than 18%.
• the preferred content is within a range of 15 to 17%.
• a molybdenum weight percentage of 0.3 to 3.0% is provided in the alloy, with a preferred range of 0.8 to 1.8%. Molybdenum is added to harden the solid solution. An excess of molybdenum is detrimental because it tends to prevent the formation of a well adherent oxide layer and as a result it will decrease the corrosion resistance. It is however beneficial to corrosion resistance in a content of less than 3%.
• a weight percentage of tungsten of 4 to 8% is provided in the alloy. Like molybdenum, it contributes to the hardening of the solid solution. Excess tungsten can be detrimental for the same reasons as excess molybdenum. Additions of tungsten, however, are advantageous in that they tend to give the alloy more homogeneous properties. Tungsten tends to segregate in the areas of dendritic nuclei while molybdenum tends to segregate in the interdendritic areas of the alloy. A preferred content of tungsten is between 5 and 7%.
• a weight percentage of vanadium of 0.01 to 1.0% is provided in the alloy, with a preferred content of 0.3 to 0.7%. Vanadium improves the resistance to creep rupture of the alloy, but can be detrimental, in case of excess, resistance to hot corrosion and oxidation, as well as to the stability of the alloy.
• tantalum and niobium there is a maximum limit of 0.05% tantalum and niobium. Higher amounts of tantalum and niobium tend to cause detrimental formation of topologically compact phases. These elements also form large, stable carbides which cannot be dissolved during heat treatments. These large carbides are the sites of initiation of fatigue cracks.
• An aluminum weight percentage of 3.5 to 5.5% is provided in the alloy. It forms the gamma prime phase, the basic mechanism for hardening the alloy and is also necessary to ensure correct resistance to oxidation. Too much aluminum causes excess gamma prime eutectic phase detrimental to the strength of the alloy.
• the preferred aluminum content is between 4 and 5%.
• titanium forms the gamma prime phase. Titanium also increases the hot corrosion resistance of the alloy; its usual proportion is 1.3 to 3.7%. With an excess of titanium, an eta phase (Ni 3 Ti) tends to form. The eta phase lowers the ductility of the alloy.
• the preferred content of titanium is between 1.5 and 2.5%.
• a weight percentage of cobalt of 3 to 7% is provided in the alloy.
• a minimum of 3% is essential for the hardening effect.
• the alloy tends to become structurally unstable when the content becomes greater than 7%.
• the preferred cobalt content is between 4 and 6%.
• a maximum limit of 2% iron is tolerated. Iron tends to alter the mechanical properties of the alloy at high temperatures. The maximum preferred content is 0.5%.
• Carbon and boron are present in the alloy in the respective weight proportions of 0.01 to 0.05% and 0.035 to 0.1%. They together form carbo-borides and borides. In the best conditions of rupture creep resistance and ductility, the alloys have indicated contents of boron and carbon, the content of boron being greater than the carbon content. The resistance drops to 900 ° C with an excess of carbon. It also results from an excess of boron the formation of too many borides at the grain boundaries which adversely affect the ductility and the strength.
• the preferred carbon content is between 0.02 and 0.04%, the preferred boron content is between 0.06 and 0.09%.
• zirconium Up to 0.1% zirconium can be added to the alloy since the zirconium strengthens the grain boundaries and counteracts the influence of sulfur. Higher quantities of zirconium would tend to form a harmful Ni 5Zr phase at the grain boundaries which would contribute to the embrittlement of the alloy. In general, zirconium is present in the alloy, with a minimum content of 0.015%.
• the maximum percentages of the elements of the magnesium-calcium-strontium-barium group is usually 0.05%.
• the presence of hafnium is usually tolerated in an amount equal to or less than 0.05%.
• Hafnium tends to form carbides insensitive to heat treatments.
• Alloy B contains vanadium under the conditions defined for the present invention while alloy A does not contain it. Alloy A is free of vanadium.
• the Md values of alloys A and B are respectively 0.961 and 0.968. A study of the microstructures of the two alloys, however, revealed their instability although alloys whose Md value is less than or equal to 0.97 generally fall within the present invention.
• the value Md of the alloy A is incompatible with the value of the data, that of B is located in a poorly defined zone.
• the value of Md should preferably be equal to or less than 0.967 for the invention.
• alloys A and B demonstrate the effects of vanadium.
• Alloy B which contains vanadium has a higher Md value than alloy A which does not contain it. Therefore, the vanadium content must be carefully controlled so as to comply with the maximum value of 1.0% of the invention and, preferably, a maximum value of 0.7%.
• Alloy D has a cobalt content within the range of the invention, while alloy C does not contain it.
• the respective values Md of the alloys C and D are 0.966 and 0.963. A study of the microstructures of these alloys revealed their stability. In the present invention, the Md value of the alloys is less than or equal to 0.970.
• alloys H and I in carbon and boron remain within the limits of the present invention.
• the carbon contents of alloys E and G are excessive; (> 0.05% carbon).
• the boron contents of E and F are too low (less than 0.035% boron).
• the boron content of F is not greater than the carbon content.
• the study of the microstructures of each of these alloys has shown their stability.
• the alloys according to the present invention have a value of Md less than or equal to 0.970.
• Table IX very clearly shows that the alloy of the present invention has advantageous and combined characteristics of breaking strength and ductility.
• Alloy J was subjected to an oxidation test lasting 500 hours at a temperature of 1000 ° C. This test was carried out in one hour cycles at the end of which the samples are cooled to room temperature and then reheated to 1000 ° C. The results were very positive, no change in weight was observed. Oxidation only occurred at a depth of 50 mm on a first test piece and 80 / mm on a second.
• Alloy K is in accordance with the present invention while alloy L is not because it comprises tantalum.
• the alloys M and N agree with the data of the present invention.
• the study of their microstructure has demonstrated their stability and their respective Md values are 0.963 and 0.969.
• Alloy specimens M and N were heated to the temperature of 850 ° C. under an atmosphere resulting from the combustion of kerosene loaded with sulfur and air loaded with sodium chloride. This ambient environment is analogous to that encountered in gas turbines. Three times a day the test pieces are cooled to room temperature and then reheated to 850 ° C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Materials For Medical Uses (AREA)
• Laminated Bodies (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Powder Metallurgy (AREA)

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• 1984
  • 1984-12-10 US US06/679,725 patent/US4629521A/en not_active Expired - Fee Related
• 1985
  • 1985-10-22 ZA ZA858123A patent/ZA858123B/xx unknown
  • 1985-11-11 BR BR8505667A patent/BR8505667A/pt not_active IP Right Cessation
  • 1985-11-22 CA CA000495994A patent/CA1255518A/en not_active Expired
  • 1985-11-25 JP JP60264721A patent/JPS61139633A/ja active Pending
  • 1985-11-25 IL IL77135A patent/IL77135A/xx not_active IP Right Cessation
  • 1985-11-27 AU AU50416/85A patent/AU574538B2/en not_active Ceased
  • 1985-12-04 EP EP85402397A patent/EP0187573B1/de not_active Expired
  • 1985-12-04 DE DE8585402397T patent/DE3563984D1/de not_active Expired
  • 1985-12-04 AT AT85402397T patent/ATE36009T1/de not_active IP Right Cessation

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