EP2451986B2 - Nickel base superalloy - Google Patents

Description

Technical area

The invention relates to the field of materials technology. It relates to a nickel-base superalloy, in particular for the production of single-crystal components (SX alloy) or components with directionally solidified structure (DS alloy), such as blades for gas turbines. However, the alloy according to the invention can also be used for conventionally cast components.

State of the art

Such nickel-base superalloys are known. Single crystal components of these alloys have a very good material strength at high temperatures. As a result, z. B. the inlet temperature of gas turbines are increased, whereby the efficiency of the gas turbine increases. Nickel-based superalloys for single crystal components, as they are made US 4,643,782 . EP 0 208 645 and US 5,270,123 For this purpose, mixed-crystal-hardening alloying elements, for example Re, W, Mo, Co, Cr, and γ'-phase-forming elements, for example Al, Ta, and Ti, are included. The content of high-melting alloying elements (W, Mo, Re) in the basic matrix (Austenitic γ-phase) increases continuously with the increase of the stress temperature of the alloy. To contain z. B. common nickel-based superalloys for single crystals 6-8% W, about 3-6% Re and up to 2% Mo (in wt .-%). The alloys disclosed in the above references have high creep strength, good LCF (low duty cycle fatigue) and HCF (high cycle fatigue) properties, and high oxidation resistance.

These known alloys have been developed for aircraft turbines and therefore optimized for short and medium time use, i. the load duration is designed for up to 20,000 hours. In contrast, industrial gas turbine components have to be designed for a load duration of up to 75,000 hours, ie for long-term use.

After a period of use of 300 hours z. For example, the alloy CMSX-4 US 4,643,782 when used experimentally in a gas turbine at a temperature above 1000 ° C, a strong coarsening of the γ'-phase, which is associated with an increase in the creeping speed of the alloy adversely.

Due to the long-term stress of gas turbines, it is thus necessary to improve the oxidation resistance of the known alloys at very high temperatures.

Out GB 2 234 521 A It is known that the enrichment of nickel-based superalloys with boron or carbon in a directional solidification produces microstructures which have an equiaxial or prismatic grain structure. Carbon and boron strengthen the grain boundaries because C and B cause the precipitation of carbides and borides at the grain boundaries, which are stable at high temperatures. Moreover, the presence of these elements in and along the grain boundaries delays the diffusion process, which is a major cause of grain boundary weakness. It is therefore possible to increase the disorientations (usually 6 °) to 10 ° to 12 ° and still achieve good properties of the material at high temperatures.

Out EP 1 359 231 B1 is a nickel-based superalloy is known, which has an improved castability and a higher oxidation resistance compared to known nickel-based superalloys and also z. B. is particularly suitable for large gas turbine single crystal components with a length of> 80 mm. The nickel-base superalloy disclosed therein is characterized by the following chemical composition (in% by weight): 7.7-8.3 Cr, 5.0-5.25 Co, 2.0-2.1 Mo, 7.8-8.3 W, 5.8-6.1 Ta, 4.9 -5.1 Al, 1.3-1.4 Ti, 0.11-0.15 Si, 0.11-0.15 Hf, 200-750 ppm C, 50-400 ppm B, remainder nickel and production-related impurities. A preferred alloy having the composition (in% by weight): 7.7-8.3 Cr, 5.0-5.25 Co, 2.0-2.1 Mo, 7.8-8.3 W, 5.8-6.1 Ta, 4.9-5.1 Al, 1.3-1.4 Ti " 0.11-0.15 Si, 0.11-0.15 Hf, 200-300 ppm C, 50-100 ppm B, remainder nickel and production-related impurities is outstandingly suitable for the production of large single-crystal components, for example blades for gas turbines.

Presentation of the invention

The aim of the invention is to develop an alloy which, compared to the alloys known from the prior art, is characterized by a further property optimization with regard to use as a gas turbine component. The invention is based on the object to develop a nickel-based superalloy, which has a high oxidation resistance and at the same time a high corrosion resistance (with different fuel properties) and to which is advantageously less expensive compared to known such nickel-based superalloys.

• 7.7-8.3 Cr
• 5.0-5.25 Co
• 2.0-2.1 Mo
• 7.8-8.3 W
• 5.8-6.1 Ta
• 4.9-5.1 Al
• 1.0-1.5 Ti
• 1.0-2.0 Re
• 0.1-0.2 Nb
• 0.11-0.15 Si
• 0.1-0.7 Hf
• 0,02-0.17 C
• 50-400 ppm B

Rest Nickel und herstellungsbedingte Verunreinigungen.According to the invention, this object is achieved in that the inventive nickel-based superalloy characterized by the following chemical composition (in% by weight):

• 7.7-8.3 Cr
• 5.0-5.25 Co
• 2.0-2.1 Mo
• 7.8-8.3 W
• 5.8-6.1 Ta
• 4.9-5.1 Al
• 1.0-1.5 Ti
• 1.0-2.0 Re
• 0.1-0.2 Nb
• 0.11-0.15 Si
• 0.1-0.7 Hf
• 0.02-0.17 C
• 50-400 ppm B

Remaining nickel and manufacturing-related impurities.

The advantages of the invention are that the alloy has a very high oxidation resistance and at the same time a high corrosion resistance at high temperatures. This is achieved in a surprising manner, especially by the relatively low Re addition.

Of particular advantage is when the alloy 1.0-1.5. preferably has 1.5% by weight of Re. If the C content is only about 200-300 ppm and the boron content is 50-100 ppm, preferably 90 ppm, then these alloys according to the invention are particularly suitable for producing single-crystal components. The alloy according to the invention has 0.1-0.2% by weight of Nb

• 8.2 Cr
• 5.2 Co
• 2.1 Mo
• 8.1 W
• 6.1 Ta
• 5.0 Al
• 1.4 Ti
• 1.5 Re
• 0.1-0.2 Nb
• 0.12 Si
• 0.1-0.6 Hf
• 0.095-0.17 C
• 240-290 ppm B

A particularly preferred nickel-base superalloy has the following composition (in% by weight):

• 8.2 Cr
• 5.2 Co
• 2.1 Mo
• 8.1 W
• 6.1 Ta
• 5.0 al
• 1.4 Ti
• 1.5 Re
• 0.1-0.2 Nb
• 0.12 Si
• 0.1-0.6 Hf
• 0.095-0.17 C
• 240-290 ppm B

Remaining nickel and manufacturing-related impurities. This alloy has excellent properties at high temperatures and is also not too expensive due to the relatively low Re content.

• 8.2 Cr
• 5.2 Co
• 2.1 Mo
• 8.1 W
• 6.1 Ta
• 5.0 Al
• 1.4 Ti
• 1.5 Re
• 0.1 Nb
• 0.12 Si
• 0.1 Hf
• 200 ppm C
• 90 ppm B

A further advantageous alloy composition is mentioned below (in% by weight):

• 8.2 Cr
• 5.2 Co
• 2.1 Mo
• 8.1 W
• 6.1 Ta
• 5.0 al
• 1.4 Ti
• 1.5 Re
• 0.1 Nb
• 0.12 Si
• 0.1 Hf
• 200 ppm C
• 90 ppm B

Remaining nickel and manufacturing-related impurities. This latter alloy is particularly suitable for the production of single crystal components.

Further advantageous variants are described in the subclaims.

Brief description of the drawings

Fig. 1

die Ergebnisse von Zugversuchen (Streckgrenze, Zugfestigkeit, Dehnung) bei Raumtemperatur für eine aus dem Stand der Technik bekannte Vergleichslegierung und eine erfindungsgemässe Legierung;

Fig. 2

die Abhängigkeit der spezifischen Massenänderung von der Zeit bei einer Temperatur von 950 °C für die gleichen Legierungen wie in Fig. 1 und

Fig. 3

die Abhängigkeit der Kriechfestigkeit vom Larson-Miller Parameter für die gleichen Legierungen wie in Fig. 1.

In the drawings, an embodiment of the invention is shown. Show it:

Fig. 1

the results of tensile tests (yield strength, tensile strength, elongation) at room temperature for a comparison alloy known from the prior art and an alloy according to the invention;

Fig. 2

the dependence of the specific mass change of the time at a temperature of 950 ° C for the same alloys as in Fig. 1 and

Fig. 3

the creep resistance dependence of the Larson-Miller parameter for the same alloys as in Fig. 1 ,

Ways to carry out the invention

Hereinafter, the invention with reference to an embodiment and the Fig. 1 to 3 explained in more detail.

Nickel-based superalloys having the chemical composition given in Table 1 were investigated (in% by weight): Table 1: Chemical composition of the investigated alloys IN738LC (DS) comparative alloy KNX1 (CC) KNX2 (CC) KNX3 (CC) KNX4 (CC) KNX0 (CC) comparative alloy Ni rest rest rest rest rest rest Cr 16 8.2 8.2 8.2 8.2 8.2 Co 8.5 5.2 5.2 5.2 5.2 5.2 Not a word 1.7 2.1 2.1 2.1 2.1 2.1 W 2.6 8.1 8.1 8.1 8.1 8.1 Ta 1.7 6.1 6.1 6.1 6.1 6.1 al 3.4 5 5 5 5 5 Ti 3.4 1.4 1.4 1.4 1.4 1.4 Hf - 0.6 0.1 0.1 0.1 12:11 C - 12:17 12:02 0095 12:17 12:02 B 12:01 0029 0009 0024 0029 0009 Si - 12:12 12:12 12:12 12:12 12:12 Nb 0.9 - 0.1 - 0.2 - Zr 0.1 - - - re - 1.5 1.5 1.5 1.5 -

The alloy IN738LC is a comparative alloy known from the prior art, KNX0 is also a comparative alloy (according to EP 1 359 231 B1 ), while the alloys KNX2 and KNX4 are alloys according to the invention and the alloys KNX1 and KNX3 are not inventive alloys. The suffix CC stands in each case as an abbreviation for "conventionally cast", ie conventionally cast alloys with conventional polygonal structure and the addition DS as an abbreviation for "directionally solidified", ie for directionally solidified microstructure.

The alloys according to the invention and the comparative alloy differ, for example, in that the comparative alloy is not alloyed with C, Si, Hf and Re in contrast to the alloys according to the invention.

Carbon strengthens, especially with the presence of boron, the grain boundaries, in particular also in the <001> direction in SX or DS gas turbine blades made of nickel-based superalloys occurring small angle grain boundaries, since these elements to the precipitation of carbides / borides cause the grain boundaries, which at high Temperatures are stable. In addition, the presence of C in and along the grain boundaries reduces the diffusion process, which is a major cause of grain boundary weakness. As a result, the castability of long single-crystal components, for example, gas turbine blades with a length of about 200 to 230 mm, significantly improved.

If nickel-base superalloys with low C and B contents (maximum 200-300 ppm C and 50-100 ppm B) are chosen according to claim 1 of the invention, these are useful as single crystal alloys, with higher contents of these elements ( maximum limits see claim 1), the components produced from corresponding alloys can also be cast conventionally.

The addition of 0.11 to 0.15% by weight of Si, especially in combination with Hf in the specified order of magnitude, achieves a substantial improvement in the oxidation resistance at high temperatures compared with the nickel-base superalloy known from the prior art (see, for example, US Pat Fig. 2 ).

Also Al and Cr cause in the specified amounts a good oxidation resistance for the novel nickel-based superalloy. Cr also has a positive effect on improving the corrosion resistance in combination with the Si.

Re, W, Mo, Co, and Cr are alloy-strengthening alloying elements, and Al, Ta, and Ti are γ'-phase-forming elements, all of which improve material strength at high temperatures. Since, in this regard, the content of high-melting alloying elements (W, Mo, Re) in the basic matrix is regarded as decisive for the increase in the maximum possible stress temperature of the alloy, these alloying elements, especially the Re, have hitherto been added in relatively large amounts.

The moderate rhenium content of the nickel-based superalloy according to the invention of preferably 1.5% by weight advantageously increases the creep resistance of the alloy on the one hand, and on the other hand does not cause such extremely high costs by this alloying element as is the case, for example, with the nickel known from the prior art Second and third generation base single crystal superalloys which have relatively high rhenium levels (about 3 to 6 wt% Re).

In Fig. 1 are the results of tensile tests (yield strength, tensile strength, elongation) at room temperature for an alloy known from the prior art (DS IN738LC) and the alloy CC KNX1 The respective chemical composition of the alloys is given in Tab.

Before making the tensile specimens, the material was subjected to the following heat treatment: 1. IN738LC: 1120 ° C / 2h / Fan cooling (GFC) + 845 ° C / 24h / air cooling 2. KNX1: 1260 ° C / 2.5 h / air cooling + 1080 OC / 5h / air cooling + 870 ° C / 16h / air cooling

In Fig. 1 It can be clearly seen that the alloy KNX1 (conventionally cast) has a significantly increased yield strength σ _0.2 compared to the known (directionally solidified) IN738LC. However, the tensile strength σ _UTS and the elongation at break ε are lower than in the case of the comparative alloy, which, however, has little significance in view of the intended use (gas turbine components).

In Fig. 2 is a quasi-isothermal oxidation diagram shown. The specific mass change Δm / A (given in mg / cm ² ) at a temperature of T = 950 ° C. and a time t in the range from 0 to 720 h is shown for the aforementioned alloys DS IN738LC and CC KNX1. If one compares the two curves, a superiority of the alloy CC KNX1 is shown in the entire range examined. From an aging time of about 5 h and longer, the mass change in the investigated sample of the alloy is only about 60% of the weight change in the sample investigated from the comparative alloy.

Fig. 3 shows, on the one hand, the dependence of creep resistance on the Larson-Miller parameter for the same alloys as in Fig. 1 and 2 , The values of these two investigated alloys can be assigned to a single curve, ie they are comparable. But taking into account the fact that DS (or SX) alloys usually due to their microstructure have improved creep resistance over conventional non-directionally solidified multi-crystalline structures of alloys with comparable chemical composition, so significantly improved creep properties for inventive alloys with DS- or To expect SX structures.

On the other hand goes out Fig. 3 also shows that the creep strength at high temperatures with the inventive alloy CC KNX2 over the known comparative alloy CC KNX0 is enormously improved. It was found that at a stress of T = 950 ° C and σ = 140 MPa, the comparative alloy CC KNX0 already broke after 17.2 hours, while the inventive alloy CC KNX2 more than 3.5 times longer withstand the stress. Since the chemical composition of these two alloys essentially differs only in the Re content (the inventive CC KNX2 contains 1.5% by weight of Re, while CC KNX0 contains no Re), this is mainly due to the favorable influence of this element in the specified relatively moderate amount.

Of course, the invention is not limited to the described embodiments.

Claims (10)

1. Nickel-based super-alloy, characterised by the following chemical composition (data in w.%):

   7.7 - 8.3 Cr,

   5.0 - 5.25 Co,

   2.0 - 2.1 Mo,

   7.8 - 8.3 W,

   5.8 - 6.1 Ta,

   4.9 - 5.1 Al,

   1.0 - 1.5 Ti,

   1.0 - 2.0 Re,

   0.1 - 0.2 Nb,

   0.11 - 0.15 Si,

   0.1 - 0.7 Hf,

   0.02 - 0.17 C,

   50 - 400 ppm B,

   remainder nickel and impurities unavoidably caused in production.
2. Nickel-based super-alloy according to claim 1, characterised by 1.0 - 1.5 w.% Re.
3. Nickel-based super-alloy according to claim 2, characterised by 1.5 w.% Re.
4. Nickel-based super-alloy according to claim 1, characterised by 0.1 w.% Nb.
5. Nickel-based super-alloy according to any of claims 1 to 4, characterised by 0.1 - 0.6 w.% Hf.
6. Nickel-based super-alloy according to claim 5, characterised by 0.1 w.% Hf.
7. Nickel-based super-alloy according to any of claims 1 to 6, characterised by 0.02-0.095, preferably 0.02 - 0.03 w.% C.
8. Nickel-based super-alloy according to any of claims 1 to 7, characterised by 50 - 100 ppm, preferably 90 ppm B.
9. Nickel-based super-alloy according to claim 1, characterised by the following chemical composition (data in w.%):

   8.2 Cr,

   5.2 Co,

   2.1 Mo,

   8.1 W,

   6.1 Ta,

   5.0 Al,

   1.4 Ti,

   1.5 Re,

   0.1 - 0.2 Nb,

   0.12 Si,

   0.1 - 0.6 Hf,

   0.095 - 0.17 C,

   240 - 290 ppm B,

   remainder nickel and impurities unavoidably caused in production.
10. Nickel-based super-alloy according to claim 1, characterised by the following chemical composition (data in w.%):

    8.2 Cr,

    5.2 Co,

    2.1 Mo,

    8.1 W,

    6.1 Ta,

    5.0 Al,

    1.4 Ti,

    1.5 Re,

    0.1 Nb,

    0.12 Si,

    0.1 Hf,

    200 ppm C,

    90 ppm B,

    remainder nickel and impurities unavoidably caused in production.

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