EP3091095B1 - Low density rhenium-free nickel base superalloy - Google Patents

Description

The present invention relates to a nickel-base alloy which is substantially free of rhenium but at the same time achieves the creep resistance properties of the second-generation nickel-based superalloys and has a reduced density compared to comparable alloys.

In gas turbines, such as stationary gas turbines or aircraft engines, nickel-base superalloys are used for example as blade materials, since these materials still have sufficient strength for the high mechanical loads even at high operating temperatures. For example, turbine blades are exposed in stationary gas turbines or jet engines in commercial aircraft exhaust gas flow at temperatures of up to 1500 ° C and are subject to very high mechanical loads due to centrifugal forces. Under these conditions, it is particularly important that the creep resistance of the material used meets the requirements. In order to increase creep resistance, turbine blades have also been produced monocrystalline for several decades in order to further improve creep resistance by avoiding grain boundaries.

In the nickel-base superalloys of the so-called second and third generation currently in use, the alloys usually have the chemical element rhenium in a proportion of three or six percent by weight, since rhenium further improves the creep resistance.

However, the low availability of rhenium, the addition of rhenium is very expensive. Accordingly, efforts are already being made in the prior art to reduce the proportion of rhenium or to completely dispense with the alloying of rhenium, at the same time preserving the mechanical properties, in particular with regard to creep resistance. Examinations are available from A. Heckl, S. Neumeier, M. Goken, RF Singer, "The Effect of Re and Ru on y / microstructure, γ-solid solution strengthening and creep strength in nickel-base superalloys", in Material Science and Engineering A 528 (2011) 3435-3444 and Paul J. Fink, Joshua L. Miller, Douglas G. Konitzer, "Rhenium Reduction - Alloy Design Using an Economically Strategic Element", JOM, 62 (2010), 55-57 , In addition, corresponding alloys are also subject matter patent applications and patents, such as EP 2 725 110 A1 . DE 102010037046 . US 2011/0076180 A1 . EP 2 314 727 A1 . EP 2 305 847 A1 . EP 2 305 848 A1 . US 2013/0129522 A1 . WO 2013/083101 A1 . EP 2 576 853 B1 . WO 2009/032578 A1 . WO 2009/032579 A1 . EP 0 962 542 A1 . US 6,054,096 . US 2013/0230405 A1 and US 2010/0135846 A1 ,

For example, the EP 2 725 110 A1 a nickel-based alloy which is substantially free of rhenium and has a solidus temperature of higher than 1320 ° C, wherein at temperatures of 1050 ° C to 1100 ° C excretions of a y 'phase in a γ matrix in a proportion of 40 to 50 Vol .-% are present, the γ / γ 'mismatch at temperatures of 1050 ° C to 1100 ° C in the range of -0.15% to -0.25% and the tungsten content in the γ-matrix is greater than in the excreted y'-phases. The alloy has the following chemical composition: aluminum of 11 to 13 at.%, Cobalt of 4 to 14 at.%, Chromium of 6 to 12 at.%, Molybdenum of 0.1 to 2 at.%, Tantalum from 0.1 to 3.5 at .-%, titanium from 0.1 to 3.5 at .-%, tungsten from 0.1 to 3 at .-%, and the balance nickel and unavoidable impurities.

Although there are already some proposed solutions for rhenium reduction or rhenium-free nickel-base superalloys, there is a continuing need to develop rhenium-reduced or rhenium-free nickel-based superalloys whose mechanical properties, in particular high-temperature properties such as creep resistance, are in the range of rhenium-containing and rhenium-free nickel base currently used Super alloys and compared to these alloys have further improved properties, such as a lower density.

It is therefore an object of the present invention to provide a nickel-based superalloy which has comparable mechanical properties, in particular high temperature properties, such as creep resistance, such as currently used nickel-base superalloys of the second and third generation, but contains substantially no rhenium. In addition, the alloy should have the lowest possible density and good solution heatability, be economical and efficient to produce and monocrystalline or directionally solidified and compared to the in EP 2 725 110 A1 Reinforced rhenium-free nickel-based alloy improved with comparable creep resistance Have properties, in particular a lower density, a lower proportion of Resteutikikum and improved Lösungsglühbarkeit.

TECHNICAL SOLUTION

This object is achieved by an alloy having the features of claim 1 and a corresponding object, in particular a component of a stationary gas turbine or aircraft gas turbine with the features of claim 12. Advantageous embodiments are the subject of the dependent claims.

• höchstmöglicher gewichteter Mischkristallhärtungsindex I_SSS in der Matrix
• optimale γ-Morphologie:
  • o γ/γ'-Fehlpassung bei 1100 °C von -0,1 bis -0,5 %
  • o y'-Anteil bei 1100 °C von 44 bis 48 mol-%
• Solidustemperatur > 1320 °C.

The present invention relates to a nickel-base superalloy containing at least the elements Al, Cr, Mo and Ta, which has been optimized with the following objectives:

• highest possible weighted solid solution hardening index I _SSS in the matrix
• optimal γ-morphology:
  • o γ / γ 'mismatch at 1100 ° C from -0.1 to -0.5%
  • o y'-content at 1100 ° C from 44 to 48 mol%
• Solidus temperature> 1320 ° C.

Here, I _SSS = 2.44 × ^γ _Re + 1.22 × ^γ _W + x ^γ M _o (x ^γ _i = concentration in at .-% of the respective element in the matrix) and the γ / γ 'mismatch is defined as the normalized difference of the lattice constants of the two phases γ and γ ': $$\frac{{\mathrm{a}}_{\gamma \text{'}}-{\mathrm{a}}_{\gamma }}{1/2*\left({\mathrm{a}}_{\gamma \text{'}}-{\mathrm{a}}_{\gamma }\right)}$$

According to the above optimization, a nickel-base alloy may have the following chemical composition: aluminum of 4.1 to 7.7 wt%, cobalt of 0 to 16.8 wt%, chromium of 6 to 11.8 wt% , Molybdenum from 3.6 to 11.3 wt%, tantalum from 0 to 3.9 wt%, titanium from 0 to 3.6 wt%, tungsten from 0 to 11.3 wt% , Carbon of 0 to 0.05 wt.%, Phosphorus of 0 to 0.015 wt.%, Copper of 0 to 0.05 wt.%, Zirconium of 0 to 0.015 wt.%, Silicon of 0 to 0 , 01% by weight, sulfur from 0 to 0.001% by weight, iron from 0 to 0.15% by weight, manganese from 0 to 0.05% by weight, boron from 0 to 0.003% by weight , Hafnium from 0 to 0.15 wt .-%, yttrium from 0 to 0.002 wt .-%, and balance nickel and unavoidable impurities. As can be seen, the alloy is essentially free of rhenium, ie contains rhenium, if at all Trace amount range (eg not more than 0.001% by weight). The alloy may also be substantially free of tantalum.

In a preferred embodiment, a nickel-based alloy according to the present invention may have the following chemical composition: aluminum of 4.7 to 5.7% by weight, cobalt of 2.6 to 13.6% by weight, chromium of 6.3 to 7.3% by weight, molybdenum from 3.7 to 4.7% by weight, tantalum from 0 to 0.5% by weight, titanium from 2.8 to 3.6% by weight, tungsten from 7.4 to 8.4 wt .-%, carbon from 0 to 0.05 wt .-%, phosphorus from 0 to 0.015 wt .-%, copper from 0 to 0.05 wt .-%, zirconium from 0 to 0.015% by weight, silicon from 0 to 0.01% by weight, sulfur from 0 to 0.001% by weight, iron from 0 to 0.15% by weight, manganese from 0 to 0.05% by weight. %, Boron from 0 to 0.003% by weight, hafnium from 0 to 0.15% by weight, yttrium from 0 to 0.002% by weight, as well as the balance nickel and unavoidable impurities.

In a further preferred embodiment, a nickel-based alloy according to the present invention may have the following chemical composition: aluminum of 5.0 to 5.4 wt .-%, cobalt of 2.9 to 13.3 wt .-%, chromium of 6.6 to 7% by weight, molybdenum from 4 to 4.4% by weight, tantalum from 0 to 0.2% by weight, titanium from 3.1 to 3.5% by weight, tungsten from 7.7 to 8.1% by weight, carbon from 0 to 0.05% by weight, phosphorus from 0 to 0.015% by weight, copper from 0 to 0.05% by weight, zirconium from 0 to 0.015% by weight. %, Silicon from 0 to 0.01% by weight, sulfur from 0 to 0.001% by weight, iron from 0 to 0.15% by weight, manganese from 0 to 0.05% by weight, boron from 0 to 0.003% by weight, hafnium from 0 to 0.15% by weight, yttrium from 0 to 0.002% by weight, as well as the balance nickel and unavoidable impurities.

In a further preferred embodiment, a nickel-based alloy according to the present invention may have a cobalt content of less than 5% by weight, preferably less than 4% by weight. Since cobalt has a lower molar mass than nickel, a relatively low cobalt content has an advantageous effect on the overall density of the nickel-based alloy, and thus also on the total weight of the target component produced from this alloy.

Alternatively, however, the nickel-based alloy according to the invention may also have a cobalt content of greater than 11% by weight, preferably greater than 13% by weight. A correspondingly high cobalt content has a positive effect on the segregation during solidification and the microstructural stability against the undesired formation of TCP phases.

It is also preferred that the nickel-based alloy according to the present invention contains at least 67 at.%, In particular at least 68 at.%, Nickel.

• Dichte von nicht höher als 8,5 g/cm³, vorzugsweise nicht höher als 8,4 g/cm³;
• Solidustemperatur von höher als 1320°C;
• 44 bis 48 Vol.-% Ausscheidungen einer y'-Phase in einer γ-Matrix bei einer Temperatur von 1100°C;
• γ/γ'-Fehlpassung im Bereich von -0,1 % bis -0,5 % bei einer Temperatur von 1100°C;
• Resteutektikum von nicht mehr als 4 %, vorzugsweise nicht mehr als 3 %.

It is further preferred that the nickel-based alloy according to the present invention has one or more (and preferably all) of the following properties:

• Density of not higher than 8.5 g / cm ³ , preferably not higher than 8.4 g / cm ³ ;
• Solidus temperature of higher than 1320 ° C;
• 44 to 48% by volume precipitates of a y'-phase in a γ-matrix at a temperature of 1100 ° C;
• γ / γ 'mismatch ranging from -0.1% to -0.5% at a temperature of 1100 ° C;
• Resteutikumikum of not more than 4%, preferably not more than 3%.

As "unavoidable impurities" in the alloy elements are to be understood, the addition of which is not intended, but which can not be prevented for technical reasons or only with extremely great effort. For example, in the alloy according to the invention the following elements may still be present in the form of trace elements, the content of which is limited to the following ranges: bismuth from 0 to 0.00003% by weight, selenium from 0 to 0.0001% by weight, Thallium from 0 to 0.00005 wt%, lead from 0 to 0.0005 wt%, and tellurium from 0 to 0.0001 wt%.

With the alloy according to the invention in particular articles such as components of gas turbines, preferably turbine blades, and the like can be prepared, which may be monocrystalline or directionally solidified.

The attached figure shows a Larson-Miller plot to illustrate the creep resistance of the alloy according to the invention compared to known alloys.

An alloy according to the invention was produced, the composition of which can be taken from the table below (alloy 1). Alloys 2 and 3 were chosen as comparison alloys, with the alloy 3 in the chemical composition essentially corresponding to that of the rhenium-containing material CMSX-4, and the alloy 2 corresponding to that in EP 2 725 110 A1 disclosed rhenium-free nickel base superalloy is. The components of the alloys are given in the table in weight percent (balance nickel and unavoidable impurities). Alloy no. al Co Cr Not a word re Ta Ti W 1 5.2 3.1 6.8 4.2 - - 3.3 7.9 2 4.8 8.6 5.0 1.4 - 10.1 1.3 8.8 3 5.6 9.0 6.5 0.6 3.0 6.5 1.0 6.0

The alloy 1 according to the invention was produced in a columnar crystal structure on a laboratory Bridgman casting installation in a three-bar geometry. The rods had a diameter of 12 mm each and a length of 180 mm each and showed a typical dendritic microstructure with a dendrite spacing of about 230 μm. The proportion of residual eutectic is very low at 2.8% (alloys 2 and 3 have a residual eutectic of 6.5% and 9.0%, respectively). With suitable heat treatment (see below), alloy 1 has a typical fully cubic y'-phase morphology.

In addition, pressure creep tests were performed on cylinders made of the finished heat-treated alloys 1 to 3 (diameter 4.0 mm, height 6.4 mm). The faces were turned off to ensure their parallelism. All creep tests were carried out at constant voltages and with the following parameters: 1100 ° C / 137 MPa, 1050 ° C / 200 MPa, 950 ° C / 300 MPa, 950 ° C / 400 MPa. The corresponding creep curves are shown in the figure (1% plastic strain, DB material, λ = 220 μm).

As can be seen from the figure, Alloy 1 (L1) according to the present invention has a creep resistance substantially equal to that of rhenium-free alloy 2 (L2), the creep resistances of these alloys being similar to the creep resistance of Alloy 3 (L3) corresponds to a second generation nickel base superalloy. In comparison to the alloys 2 and 3, however, the alloy 1 in particular has a lower density. Analysis of the microstructure of the inventive alloy 1 after creep revealed no TCP phase formation.

Thus, it is clear that nickel-based superalloys can be provided by the teachings of the present invention which can dispense with the hard-to-obtain element rhenium but nevertheless provide high temperature mechanical properties such as creep resistance, such as known rhenium containing alloys, and also have lower density than known rhenium-containing and rhenium-free alloys.

The following table compares some properties of alloys 1-3. property Alloy 1 calculated Alloy 1 measured Alloy 2 measured Alloy 3 is calculated Density, g / cm ³ 8.3 8.4 9.0 8.7 Liquidus temp., ° C 1373 1371 1371 1381 Solidus, ° C 1348 1302 * 1316 * 1338 γ '- Solvustemp. ° C 1232 1255 1242 1257 γ / γ 'mismatch, 1100 ° C,% -0.5 -0.45 ** -0.02 ** -0.17 γ 'content, 1100 ° C, mol% 44.0 - - 44.9 * Cast state ** room temperature

Particularly noteworthy is the relatively low density of the inventive alloy 1. The γ / γ 'mismatch could only be measured at room temperature; Usually the values are higher at higher temperatures.

• Erwärmung der Legierung um 4 K/min bis auf 1285 °C,
• 2 h Halten bei 1285°C,
• Erwärmung der Legierung um 1 K/min bis auf 1300 °C,
• 6,5 h Halten bei 1300 °C,
• anschließend Schnellabkühlung.

The solution annealing of alloy 1 can be carried out, for example, in two stages as follows:

• Heating the alloy by 4 K / min up to 1285 ° C,
• 2 h hold at 1285 ° C,
• Heating the alloy by 1 K / min up to 1300 ° C,
• 6.5 hours hold at 1300 ° C,
• then rapid cooling.

In addition, alloy 1 may undergo one or both of the following precipitation heat treatments after solution annealing:
Excretion heat treatment 1: temperature heating rate hold time 1000 ° C 4 K / min 1050 ° C 1K / min 1050 ° C 1 h 20 ° C rapid cooling
Excretion heat treatment 2: temperature heating rate hold time 840 ° C 4 K / min 870 ° C 1K / min 870 ° C 24 hours 20 ° C rapid cooling

Longer annealing times than 2 hours at 1050 ° C or higher temperatures lead to an aging of the microstructure.

• Kriechbeständigkeit nahe derjenigen von CSMX-4
• niedrige Dichte von 8,4 g/cm³ (Vergleich: CSMX-4: 8,7 g/cm³)
• geringes Resteutektikum von 2,8 % (Vergleich: CSMX-4: 9,0 %)
• gute Lösungsglühbarkeit (8,5 Stunden Halten bei 1285 °C/ 1300 °C).
• geringe TCP-Phasenneigung.

Obwohl die vorliegende Erfindung anhand des Ausführungsbeispiels detailliert beschrieben worden ist, ist für den Fachmann selbstverständlich, dass die Erfindung nicht auf dieses Ausführungsbeispiel beschränkt ist, sondern dass vielmehr Abwandlungen in der Weise möglich sind, dass einzelne Merkmale weggelassen oder Merkmale andersartig kombiniert werden können, solange der Schutzbereich der beigefügten Anspruche nicht verlassen wird. Die vorliegende Offenbarung offenbart sämtliche Kombinationen aller vorgestellter Einzelmerkmale.In summary, it can be stated that the above-described alloy according to the invention has in particular the following properties:

• Creep resistance close to that of CSMX-4
• low density of 8.4 g / cm ³ (comparison: CSMX-4: 8.7 g / cm ³ )
• low residual eutectic of 2.8% (comparison: CSMX-4: 9.0%)
• good solution heatability (8.5 hours hold at 1285 ° C / 1300 ° C).
• low TCP phase slope.

Although the present invention has been described in detail with reference to the embodiment, it will be understood by those skilled in the art that the invention is not limited to this embodiment, but rather modifications in the manner it is possible that individual features may be omitted or features otherwise combined, as long as the scope of protection of the appended claims is not abandoned. The present disclosure discloses all combinations of all presented individual features.

Claims (12)

1. A nickel base alloy that exhibits high creep resistance, is free of rhenium or contains no more than 0.001 wt% rhenium, and has the following chemical composition:

   aluminum from 4.1 to 7.7 wt%,

   cobalt from 0 to 16.8 wt%,

   chromium from 6 to 11.8 wt%,

   molybdenum from 3.6 to 11.3 wt%,

   tantalum from 0 to 3.9 wt%,

   titanium from 0 to 3.6 wt%,

   tungsten from 0 to 11.3 wt%,

   carbon from 0 to 0.05 wt%,

   phosphorus from 0 to 0.015 wt%,

   copper from 0 to 0.05 wt%,

   zirconium from 0 to 0.015 wt%,

   silicon from 0 to 0.01 wt%,

   sulfur from 0 to 0.001 wt%,

   iron from 0 to 0.15 wt%,

   manganese from 0 to 0.05 wt%,

   boron from 0 to 0.003 wt%,

   hafnium from 0 to 0.15 wt%,

   yttrium from 0 to 0.002 wt%,

   and a remainder of nickel and unavoidable impurities.
2. The nickel base alloy according to claim 1,
   characterized in that
   the alloy has the following chemical composition:

   aluminum from 4.7 to 5.7 wt%,

   cobalt from 2.6 to 13.6 wt%,

   chromium from 6.3 to 7.3 wt%,

   molybdenum from 3.7 to 4.7 wt%,

   tantalum from 0 to 0.5 wt%,

   titanium from 2.8 to 3.6 wt%,

   tungsten from 7.4 to 8.4 wt%,

   carbon from 0 to 0.05 wt%,

   phosphorus from 0 to 0.015 wt%,

   copper from 0 to 0.05 wt%,

   zirconium from 0 to 0.015 wt%,

   silicon from 0 to 0.01 wt%,

   sulfur from 0 to 0.001 wt%,

   iron from 0 to 0.15 wt%,

   manganese from 0 to 0.05 wt%,

   boron from 0 to 0.003 wt%,

   hafnium from 0 to 0.15 wt%,

   yttrium from 0 to 0.002 wt%,

   and a remainder of nickel and unavoidable impurities.
3. The nickel base alloy according to claim 2,
   characterized in that
   the alloy has the following chemical composition:

   aluminum from 5.0 to 5.4 wt%,

   cobalt from 2.9 to 13.3 wt%,

   chromium from 6.6 to 7 wt%,

   molybdenum from 4 to 4.4 wt%,

   tantalum from 0 to 0.2 wt%,

   titanium from 3.1 to 3.5 wt%,

   tungsten from 7.7 to 8.1 wt%,

   carbon from 0 to 0.05 wt%,

   phosphorus from 0 to 0.015 wt%,

   copper from 0 to 0.05 wt%,

   zirconium from 0 to 0.015 wt%,

   silicon from 0 to 0.01 wt%,

   sulfur from 0 to 0.001 wt%,

   iron from 0 to 0.15 wt%,

   manganese from 0 to 0.05 wt%,

   boron from 0 to 0.003 wt%,

   hafnium from 0 to 0.15 wt%,

   yttrium from 0 to 0.002 wt%,

   and a remainder of nickel and unavoidable impurities.
4. The nickel base alloy according to any of the preceding claims,
   characterized in that
   the alloy has a cobalt content of less than 5 wt%, preferably less than 4 wt%.
5. The nickel base alloy according to any of claims 1-3,
   characterized in that
   the alloy has a cobalt content of greater than 1 wt%, preferably greater than 13 wt%.
6. The nickel base alloy according to any of the preceding claims,
   characterized by
   having a density of not higher than 8.5 g/cm³, preferably not higher than 8.4 g/cm³.
7. The nickel base alloy according to any of the preceding claims,
   characterized by
   having a solidus temperature of higher than 1320°C.
8. The nickel base alloy according to any of the preceding claims,
   characterized by
   having a residual eutectic of not more than 4%, preferably not more than 3%.
9. An article produced from the nickel base alloy according to any of the preceding claims.
10. The article according to claim 9,
    characterized in that
    the article is monocrystalline or directionally solidified.
11. The article according to claim 9 or 10,
    characterized in that
    the article is a component of a stationary gas turbine or an aircraft engine, in particular, a turbine blade.
12. A method for producing a nickel base alloy,
    characterized in that
    the method comprises combining and melting together metals in ratios that result in the alloy according to any of claims 1 to 8.

Images