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
  • C22C19/057—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being less 10%

Definitions

• the invention deals with the field of materials science. It relates to a nickel-base superalloy, in particular for the production of single-crystal components (SX alloy) or components with a directionally solidified microstructure (DS alloy), such as for example blades or vanes for gas turbines.
• SX alloy single-crystal components
• DS alloy directionally solidified microstructure
• the alloy according to the invention can also be used for conventionally cast components.
• Nickel-base superalloys of this type are known. Single-crystal components produced from these alloys have a very good material strength at high temperatures. This makes it possible, for example, to increase the inlet temperature of gas turbines, which boosts the efficiency of the gas turbine.
• Nickel-base superalloys for single-crystal components as are known from U.S. Pat. No. 4,643,782, EP 0 208 645 and U.S. Pat. No. 5,270,123, for this purpose contain alloying elements which strengthen the solid solution, for example Re, W, Mo, Co, Cr, as well as elements which form ⁇ ′ phases, for example Al, Ta, and Ti.
• the level of high-melting alloying elements (W, Mo, Re) in the base matrix (austenitic ⁇ phase) increases continuously with the increase in the temperature to which the alloy is exposed.
• standard nickel-base superalloys for single crystals contain 6-8% of W, up to 6% of Re and up to 2% of Mo (details in % by weight).
• the alloys disclosed in the abovementioned documents have a high creep strength, good LCF (low cycle fatigue) and HCF (high cycle fatigue) properties and a high resistance to oxidation.
• the alloy CMSX-4 from U.S. Pat. No. 4,643,782 when tested for use in a gas turbine at a temperature of over 1000° C., has a considerably coarsened ⁇ ′ phase after a load time of 300 hours, and this phenomenon is disadvantageously associated with an increase in the creep rate of the alloy.
• a further problem of the known nickel-base superalloys is that in the case of large components, e.g., gas turbine blades or vanes with a length of more than 80 mm, the casting properties leave something to be desired.
• the casting of a perfect, relatively large directionally solidified single-crystal component from a nickel-base superalloy is extremely difficult, since most of these components have defects, e.g., small-angle grain boundaries, freckles, i.e., defects caused by a series of identically directed grains with a high eutectic content, equiaxed limits of variation, microporosity, etc.
• grain boundaries are particularly harmful to the high-temperature properties of the single-crystal items.
• small-angle grain boundaries in relative terms have only a minor influence on the properties, they are highly relevant to the casting properties and oxidation properties of large SX or DS components at high temperatures.
• Grain boundaries are regions with a high local disorder of the crystal lattice, since the neighboring grains collide in these regions, and therefore there is a certain misorientation between the crystal lattices.
• Patent EP 1 359 231 A1 describes a nickel-base superalloy which has improved casting properties and a higher resistance to oxidation than known nickel-base superalloys. Moreover, this alloy is, for example, particularly suitable for large gas turbine single-crystal components with a length of >80 mm. It has the following chemical composition (details in % by weight):
• TBC thermal barrier coating
• One of numerous aspects of the present invention includes avoiding the abovementioned drawbacks of the prior art.
• Another aspect includes further improving the nickel-base superalloy which is known from EP 1 359 231 A1, in particular with a view to achieving better compatibility with TBC layers to be applied to this superalloy combined with equally good casting properties and a high resistance to oxidation compared to the nickel-base superalloy which is known from EP 1 359 231 A1.
• a nickel-base superalloy embodying principles of the present invention is characterized by the following chemical composition (details in % by weight):
• the alloy has very good casting properties, a high resistance to oxidation at high temperatures, and is very compatible with TBC layers that are to be applied.
• the alloy has the following composition (details in % by weight):
• An advantageous alloy according to the invention has the following chemical composition (details in % by weight):
• This alloy is eminently suitable for the production of large single-crystal components, for example blades or vanes for gas turbines.
• Nickel-base superalloys which are known from the prior art (comparison alloys CA1 to CA5) and the alloy according to the invention A1, having the chemical composition listed in Table 1, were tested (details in % by weight): TABLE 1 chemical composition of the alloys tested CA5 (in accordance CA1 CA2 CA3 CA4 with (CMSX-11B) (CMSX-6) (CMSX-2) (René N5) EP 1359231A) Ni Remainder Remainder Remainder Remainder Remainder A1 Remainder Cr 12.4 9.7 7.9 7.12 7.7 7.7 Co 5.7 5.0 4.6 7.4 5.1 5.1 Mo 0.5 3.0 0.6 1.4 2.0 2.0 W 5.1 — 8.0 4.9 7.8 7.8 Ta 5.18 2.0 6.0 6.5 5.84 5.8 Al 3.59 4.81 5.58 6.07 5.0 5.0 Ti 4.18 4.71 0.99 0.03 1.4 1.4 Hf 0.04 0.05 — 0.17 0.12 0.12 C — — — 0.02 0.02 B — — —
• the alloy A1 is a nickel-base superalloy for single-crystal components, the composition of which is described herein.
• the alloys CA1, CA2, CA3, CA4 are comparison alloys which are prior art known under the designations CMSX-11B, CMSX-6, CMSX-2 and René N5. Inter alia, they differ from the alloy according to the invention primarily by virtue of the fact that they are not alloyed with C, B, Si, and Y and/or La.
• the comparison alloy CA5 is known from EP 1 359 231 A1 and differs from the alloy according to the invention in terms of the S, Y, and/or La content.
• Restricting the composition according to the invention to a sulfur content of ⁇ 5 ppm produces very good properties, in particular good bonding of the TBC layer which has been applied to the surface of the superalloy, for example by thermal spraying. If the sulfur content is >5 ppm, this has an adverse effect on the TBC bonding, and the layer quickly flakes off in the event of fluctuating thermal stresses.
• Y and/or La in the specified range in each case 5 to 100 ppm, i.e., in total, that is to say Y+La, 10 to 200 ppm, if both elements are present produces very good bonding of the ceramic thermal barrier coating (TBC layer) which is to be applied.
• the Y content of 50 ppm and the La content of 10 ppm specified for the alloy A1 is particularly advantageous, since A1 is particularly compatible with the TBC layers to be applied. Moreover, these two elements also increase the resistance to environmental influences. The addition of these elements in these low ranges stabilizes the aluminum/chromium oxide scale layer on the alloy surface and produces a significant resistance to oxidation. Y and La are oxygen-active elements which improve the bonding strength of the scale layer on the base material. The resistance to spalling during cyclic oxidation is the key factor for the stability of the TBC layer.
• Table 2 in each case lists the number of cycles which it takes for the Al 2 O 3 and other oxide layers formed to flake off under cyclic oxidation at 1050° C./1 h/air cooling to room temperature for the alloys listed in Table 1: TABLE 2 number of cycles until spalling occurs Alloy Number of cycles until spalling occurs CA1 ⁇ 30 CA2 200 CA3 80 CA4 230 CA5 1500 A1 2500
• the alloy according to the invention A1 compared to the alloys which are known from the prior art, has by far the highest number of cycles before the oxide layer flakes off. This implies a high stability of a TBC layer which is to be applied to the surface of the superalloy, for example by thermal spraying.
• nickel-base superalloys with higher C and B contents at most 750 ppm of C and at most 400 ppm of B
• the components produced from these alloys it is also possible for the components produced from these alloys to be cast conventionally, i.e., without them producing single crystals.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Turbine Rotor Nozzle Sealing (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Physical Vapour Deposition (AREA)
• Laminated Bodies (AREA)

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• 2005
  • 2005-11-01 CA CA2586974A patent/CA2586974C/en not_active Expired - Fee Related
  • 2005-11-01 JP JP2007541905A patent/JP5186215B2/ja not_active Expired - Fee Related
  • 2005-11-01 EP EP05815708A patent/EP1815035A2/de not_active Withdrawn
  • 2005-11-01 CN CN2005800393705A patent/CN101061244B/zh not_active Expired - Fee Related
  • 2005-11-01 WO PCT/EP2005/055676 patent/WO2006053826A2/de active Application Filing
  • 2005-11-11 AR ARP050104755A patent/AR051423A1/es not_active Application Discontinuation
• 2007
  • 2007-05-02 US US11/743,218 patent/US20070199628A1/en not_active Abandoned

Patent Citations (9)

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