AU2007237291A1

AU2007237291A1 - Low-density directionally solidified single-crystal superalloys

Info

Publication number: AU2007237291A1
Application number: AU2007237291A
Authority: AU
Inventors: Inigo Hernandez Aguirre; Amaia Subinas Rapp; Inaki Madariaga Rodriguez; Koldo Estolaza Zamora
Original assignee: Industria de Turbo Propulsores SA
Current assignee: Industria de Turbo Propulsores SA
Priority date: 2006-12-01
Filing date: 2007-11-30
Publication date: 2008-06-19
Also published as: EP1927669A1; ES2269013A1; ES2269013B2; ES2524249T3; EP1927669B1; US20080240972A1; CA2612815A1

Description

S&F Ref: 836235

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Industria De Turbo Propulsores, of Parque Tecnol6gico, Edificio 300, 48170, Zamudio, Vizcaya, Spain Ifiaki Madariaga Rodriguez, Iiigo Hernndez Aguirre, Amaia Subinas Rapp, Koldo Estolaza Zamora Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Low-density directionally solidified single-crystal superalloys The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c(10460O)4 I) LOW-DENSITY DIRECTIONALLY SOLIDIFIED SINGLE-CRYSTAL SUPERALLOYS z Field of the Invention The present invention relates to nickel-base superalloys used to manufacture gas turbine blades or vanes by means of directional solidification or in the form of single crystals. The present invention particularly relates to low-density alloys which can work under high temperature and high load conditions.

State of the Art 17-Nickel-base superalloys are widely used in the manufacture of components for CK1 10 gas turbines. In the particular field of gas turbines for aircraft, apart from the high Srequirements from the stress and temperature point of view, it is also important to rl' develop low-density alloys. A precursor of low-density alloys is the In100O alloy (density 7.76 gr/cm3) developed at that beginning of the 60s by The International Nickel Company (INCO) and covered by patent US 3,061,426. This alloy is still used today to manufacture equiaxed turbine blades although it is admitted that it has low castability and low corrosion resistance.

In100O has been used as the basis for developing many alloys. Among others, In6212 (density 8.02 gr/cm3) covered by patent US 4,358,318 was also developed by INCO as a low-density material with better corrosion resistance and castability than those of In100O at the expense of a slight increase of density.

These two equiaxed materials, In100O and In 6212, have been used as the basis for developing several single-crystal alloys. In100O was used as a reference for developing the RR2000 alloy, covered by patent GB 2105369A in 1983 whereas In6212 was used as the basis for developing the CMSX-6 alloy, covered by patent US 4,721,540.

Both single-crystal alloys were developed according to a similar strategy. In both cases, the amount of grain boundary hardening elements such as carbon, boron and zirconium was eliminated to increase the melting point of the alloy. It was thus possible to carry out a solution heat treatment of the hardening gamma prime phase dissolving the microstructure obtained directly after the casting and achieving a fine and homogeneous distribution of precipitates in the subsequent heat treatments.

There is therefore a need to develop alternative alloys to those used currently.

Description of the Invention The present invention provides a low-density superalloy (7.867 g/cm 3 useful for manufacturing components by means of directional solidification or single-crystal O components with a relaxed grain structure specification.

A first aspect of the invention relates to a nickel-base superalloy comprising the O following elements (percent by weight): z 7-13% Chromium, 0-16% Cobalt, Titanium, 4.5-7% Aluminium, 0-5% Tantalum, S0-2% Hafnium, 0-3% Tungsten 0-2% Vanadium r 0-5% Molybdenum 0.06-0.12% Carbon, 0.01-0.03% Boron, 0.005-0.02% Zirconium, Nickel and residual impurities In a particular embodiment the present invention relates to a nickel-base superalloy comprising: 0.07% carbon, 10% chromium, 15% cobalt, 3% molybdenum, aluminium, 4% titanium, 1% vanadium, 1.4% hafnium, 0.015% boron and 0.01% zirconium.

In a particular embodiment the present invention relates to a nickel-base superalloy comprising: 0.07% carbon, 10% chromium, 5% cobalt, 3% molybdenum, 2% tantalum, 4.8% aluminium, 4.7% titanium, 1.4% hafnium, 0.015% boron and 0.01% zirconium.

A second aspect of the present invention relates to the use of a nickel-base superalloy described above for obtaining a directionally solidified casting or a casting in single-crystal form.

A third aspect of the present invention relates to a process for obtaining a superalloy as described above, comprising.the following steps: a) Solution heat treatment at a temperature comprised between 1190-1250 OC for 1 to 5 hours b) Intermediate heat treatment at a temperature comprised between 1000-1100 OC for 1 to 5 hours c) Precipitation heat treatment at a temperature comprised between 850-900 OC for 1 to 16 hours

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O A fourth aspect of the present invention relates to a gas turbine comprising components manufactured with a superalloy as described above, or from alloys O obtained by means of a process comprising the following steps: a) Solution heat treatment at a temperature comprised between 1190- 1250 °C for 1 to 5 hours b) intermediate heat treatment at a temperature comprised between 1000-1100 °C for 1 to 5 hours c) precipitation heat treatment at a temperature comprised between 850-900 OC for 1 to 16 hours SBrief Description of Drawings Figure 1: Low-cycle fatigue of composition E compared to commercial composition A.

Detailed Description of an Embodiment The present invention provides a low-density superalloy useful for manufacturing components by means of directional solidification or single-crystal components with a relaxed grain structure specification. The alloy of the present invention was developed taking two single-crystal alloys, RR2000 and CMSX-6, as a reference.

The following table shows examples of alloys according to this invention, alloys E to G, inclusive. Alloys A and B are commercial alloys for directional solidification whereas C and D are commercial alloys for manufacturing low-density single-crystal components. The latter alloys are only set forth as a comparison and are not included within the scope of this invention.

Alloy Co Cr Mo W Al Ta V Ti Re Hf C B Zr A 9,2 8,1 0,5 9,5 5,6 3,2 0,7 1,4 0,07 0,015 0,007 B 9,3 6 0,5 8,4 5,7 3,4 0,7 3 1,4 0,07 0,015 0,005 C 15 10 3 5,5 1 4 D 5 10 3 4,8 2 4,7 0,1 E 15 10 3 5,5 1 4 1,4 0,07 0,015 0,005 F 6 12 3 2 4,5 4,7 1,4 0,07 0,015 0,005 G 5 10 3 4,8 2 4,7 1,4 0,07 0,015 0,005 Carbon, boron and zirconium were added to the base composition of RR2000 and CMSX-6 but without reaching the high levels of these elements in the compositions

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O In100 or of In6212. The C, B and Zr of the alloy of this invention were maintained at the same levels as other commercial allows that are usually used for manufacturing 0 directionally solidified components such as alloy A and B of the previous table. The maximum carbon content was limited to 0.12%, the maximum boron content to 0.03% 5 and the maximum zirconium content to 0.02%, while these limits are 0.1% and 0.25% respectively in In100O. Hafnium was added to the composition to favor carbide formation in the grain boundary.

The introduction of these elements involved a reduction in the melting Stemperature of the alloy. Such that the maximum temperature at which the CK 10 supersolution heat treatment can be carried out is limited, and therefore it is not Spossible to reach the high temperatures that are used in the supersolution treatments of single-crystal materials. The gamma prime dissolution that was achieved with the supersolution treatments was thus not as effective as that achieved with the high temperature treatments used in single-crystals. Nevertheless, there are commercial alloys which can be used to manufacture components by means of directional solidification with and without supersolution heat treatment. The absence of supersolution heat treatment gave rise to a drop in the alloy temperature capacity of about 30 0

C.

Even with this reduction, the benefit obtained with the low density of the alloy of this invention makes it a suitable option for manufacturing gas turbine blades or vanes.

The absence of supersolution heat treatment can also give rise to a loss of the resistance to low-cycle fatigue of the alloy with respect to the commercial RR2000 alloy from which it has been developed. However, as can be seen in Figure 1, composition E of Table 1 has fatigue properties that are greater than those of commercial alloy A.

The introduction or grain boundary hardening elements allowed the use of this alloy for manufacturing directionally solidified components, which is not possible with most single-crystal alloys. The fact of using an alloy in directional solidification form instead of in single-crystal form gave rise to reduction in the creep rupture of the alloy.

Nevertheless, this decrease was considered very small and therefore the alloy of this invention is sufficiently attractive for a wide range of applications.

Finally, it must be mentioned that the main purpose of this alloy is to offer a lowdensity alternative to alloys that are currently used in gas turbines. The presence of elements such as C, B, Zr and Hf improved the tolerance of the alloy to the presence of grain boundaries at the expense of a small reduction in properties such as fatigue or creep rupture. But having been designed from low-density single-crystal alloys, even r O with this decrease of properties, the alloy of the present invention offers a clear improvement with respect to the alloys that are currently used for manufacturing z directionally solidified materials. This benefit will be even greater in the design of advanced gas turbines in which the rotational speed is higher and therefore the centrifugal forces are greater, and the use of a low-density material is a clear advantage.

Likewise, it must also be mentioned that the use of this material in gas turbines for aircraft involves a clear improvement with respect to current alloys because it can Sgive rise to lighter components and therefore to a lower specific turbine consumption.

Claims

1. A nickel-base superalloy comprising the following elements (percent by z weight)

7-13% Chromium, 0-16% Cobalt, Titanium, S4.5-7% Aluminium, 0-5% Tantalum, C 0-2% Hafnium, 0 o 0-3% Tungsten, CI 0-2% Vanadium, Molybdenum, 0.06-0.12% Carbon, 0.01-0.03% Boron, 0.005-0.02% Zirconium, Nickel and residual impurities. 2. A superalloy according to claim 1, comprising: 0.07% carbon, chromium, 15% cobalt, 3% molybdenum, 5.5% aluminium, 4% titanium, 1% vanadium, 1.4% hafnium, 0.015% boron and 0.01% zirconium. 3. A superalloy according to any one of the previous claims, comprising: 0.07% carbon, 10% chromium, 5% cobalt, 3% molybdenum, 2% tantalum, 4.8% aluminium, 4.7% titanium, 1.4% hafnium, 0.015% boron and 0.01% zirconium. 4. A superalloy as claimed in claim 1, substantially as hereinbefore described with reference to any one of the examples and/or the accompanying drawing. 5. The use of a nickel-base superalloy according to any one of the previous claims for obtaining a directionally solidified casting or a casting in single-crystal form. 6. A process for obtaining a superalloy described in any one of claims 1 to 3, comprising the following steps: a) solution heat treatment at a temperature comprised between 1190-1250 0 C for 1 to 5 hours; b) intermediate heat treatment at a temperature comprised between 1000-1100°C for 1 to 5 hours; c) precipitation heat treatment at a temperature comprised between 850-900°C for 1 to 16 hours.

1042461-11-HJG O 7. A process for obtaining a superalloy, said process as claimed in claim 6 and substantially as hereinbefore described with reference to any one of the examples and/or O z the accompanying drawing. 8. A superalloy obtained by the process of claim 6 or 7. 9. A gas turbine comprising components manufactured with a superalloy Saccording to any one of claims 1 to 4 or 8. Dated 30 November, 2007 SIndustria De Turbo Propulsores, S.A. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 1042461- HJG