RHENIUM-FREE NICKEL BASE SUPERALLOY OF LOW DENSITY

Abstract

The invention relates to a substantially rhenium-free nickel base alloy showing a high creep resistance and relatively low density which comprises in % by weight: aluminum from 3.0 to 7.7, cobalt from 0 to 16.8, chromium from 3 to 11.8, molybendum from 3.1 to 11.3, tantalum from 0 to 3.9. In addition to nickel and unavoidable impurities this alloy may further comprise one or more of titanium, tungsten, carbon, phosphorus, copper, zirconium, silicon, hafnium, yttrium, niobium, and germanium.

Claims

1. A nickel base alloy exhibiting high creep resistance and being substantially free of rhenium, wherein the alloy comprises the following elements in % by weight relative to the total weight of the alloy: aluminum from 3.0 to 7.7 cobalt from 0 to 16.8 chromium from 3 to 11.8 molybendum from 3.1 to 11.3 tantalum from 0 to 3.9.

2. The alloy of claim 1, wherein the alloy comprises: aluminum from 3.4 to 7.7 cobalt from 0 to 16.8 chromium from 4 to 11.8 molybendum from 3.3 to 11.3 tantalum from 0 to 3.9.

3. The alloy of claim 1, wherein the alloy comprises: aluminum from 3.8 to 7.7 cobalt from 0 to 16.8 chromium from 5 to 11.8 molybendum from 3.4 to 11.3 tantalum from 0 to 3.9.

4. The alloy of claim 1, wherein the alloy comprises: aluminum from 4.1 to 7.7 cobalt from 0 to 16.8 chromium from 6 to 11.8 molybendum from 3.6 to 11.3 tantalum from 0 to 3.9.

5. The alloy of claim 1, wherein the alloy comprises: aluminum from 4.7 to 7.7 cobalt from 2.6 to 13.6 chromium from 6.3 to 7.3 molybendum from 3.7 to 4.7 tantalum from 0 to 0.5 titanium from 2.8 to 3.6 tungsten from 7.4 to 8.4.

6. The alloy of claim 1, wherein the alloy comprises: aluminum from 5.0 to 5.4 cobalt from 2.9 to 13.3 chromium from 6.6 to 7 molybendum from 4 to 4.4 tantalum from 0 to 0.2 titanium from 3.1 to 3.5 tungsten from 7.7 to 8.1.

7. The alloy of claim 1, wherein the alloy further comprises: titanium from 0 to 6.0 tungsten from 0 to 11.3 carbon from 0 to 0.05 phosphorus from 0 to 0.015 copper from 0 to 0.05 zirconium from 0 to 0.015 silicon from 0 to 6.0 sulfur from 0 to 0.001 iron from 0 to 0.15 manganese from 0 to 0.05 boron from 0 to 6.0 hafnium from 0 to 4.0 yttrium from 0 to 0.002 niobium from 0 to 8.0 germanium from 0 to 8.0, remainder nickel and unavoidable impurities.

8. The alloy of claim 7, wherein the alloy comprises: titanium from 0 to 5 silicon from 0 to 5.0 boron from 0 to 5.0 hafnium from 0 to 3.0 niobium from 0 to 6.0 germanium from 0 to 6.0.

9. The alloy of claim 8, wherein the alloy comprises: titanium from 0 to 4 silicon from 0 to 4.0 boron from 0 to 4.0 hafnium from 0 to 3.0 niobium from 0 to 4.0 germanium from 0 to 4.0.

10. The alloy of claim 9, wherein the alloy comprises: titanium from 0 to 4 silicon from 0 to 4.0 boron from 0 to 4.0 hafnium from 0 to 3.0 niobium from 0 to 4.0 germanium from 0 to 4.0.

11. The alloy of claim 10, wherein the alloy comprises: titanium from 0 to 3.6 silicon from 0 to 2.0 boron from 0 to 2.0 hafnium from 0 to 1.0 niobium from 0 to 1.0. germanium from 0 to 1.0.

12. The alloy of claim 1, wherein the alloy comprises less than 5% by weight cobalt.

13. The alloy of claim 1, wherein the alloy comprises more than 11% by weight cobalt.

14. The alloy of claim 1, wherein the alloy has a density of not higher than 8.5 g/cm.sup.3.

15. The alloy of claim 1, wherein the alloy has a solidus temperature of higher than 1320 C.

16. The alloy of claim 1, wherein the alloy has a residual eutecticum of not more than 4%.

17. An article made of the alloy of claim 1.

18. The article of claim 17, wherein the article is monocrystalline or directionally solidified.

19. The article of claim 21, wherein the article is a component of a gas turbine or an aircraft engine.

20. A method of making a nickel base alloy, wherein the method comprises melting together metals in proportions which result in the alloy of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0062] The attached FIGURE shows a Larson-Miller plot for illustrating the creep resistance of the alloy of the present invention compared to that of known alloys.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0063] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description in combination with the drawings making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

EXAMPLE

[0064] An alloy according to the present invention whose composition can be taken from the following table was prepared (Alloy 1). Alloys 2 and 3 were chosen as comparative alloys, Alloy 3 corresponding in its chemical composition essentially to that of the rhenium containing material CMSX-4 and Alloy 2 being the rhenium-free nickel base superalloy disclosed in EP 2 725 110 A1. The components of the alloys are indicated in wt. % (remainder Ni and unavoidable impurities).

TABLE-US-00001 Alloy No. Al Co Cr Mo 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

[0065] Alloy 1 according to the present invention was prepared in a Labor-Bridgman casting apparatus in three-bar geometry. Each of the bars had a diameter of 12 mm and a length of 180 mm and exhibited a typical dendritic microstructure with a dendrite distance of about 230 m. The proportion of residual eutectic of 2.8% is very low (Alloy 2 and Alloy 3 showed a residual eutectic of 6.5% and 9.0% respectively). If suitably heat-treated (see below), Alloy 1 has a typical, completely cubic y-phase morphology.

[0066] Additionally, push-pull experiments were conducted on cylinders (diameter 4.0 mm, height 6.4 mm) made from the completely heat-treated Alloy 1 to 3. The front faces of the cylinders were finished to ensure they were parallel. All creep experiments were conducted at constant stress with the following parameters: 1100 C./1137 MPa, 1050 C./200 MPa, 950 C./1300 MPa, 950 C./1400 MPa. Die corresponding creep curves are shown in the FIGURE (1% plastic deformation, DB material, =220 m).

[0067] As can be seen from the FIGURE, Alloy 1 according to the invention (L1) shows a creep resistance which is substantially the same as that of the rhenium-free Alloy 2 (L2), the creep resistances of these alloys being similar to the creep resistance of Alloy 3 which corresponds to a nickel base superalloy of the second generation. However, compared to Alloy 1 and Alloy 2, Alloy 1 particularly shows a lower density Analysis of the microstructure of Alloy 1 according to the invention after creep does not reveal any TCP phase formation.

[0068] This shows that the present invention can provide nickel base alloys which do not depend on the presence of the not readily available element rhenium but nevertheless can exhibit high temperature mechanical properties such as creep resistance similar to those of known rhenium-containing alloys and additionally have a lower density than known rhenium-containing and rhenium-free alloys.

[0069] In the following table the properties of Alloys 1-3 are compared to each other.

TABLE-US-00002 Alloy 1 Alloy 3 as Alloy 1 Alloy 2 as Property calculated as measured as measured measured Density, g/cm.sup.3 8.3 8.4 9.0 8.7 Cost, Euro/kg 81 103 207 As of 2012 Liquidus temp., C. 1373 1371 1371 1381 Solidus temp., C. 1348 1302* 1316* 1338 -Solvus temp. C. 1232 1255 1242 1257 /-Mismatch, 0.5 0.45** 0.02** 0.17 1100 C., % Proportion, 44.0 44.9 1100 C., mol-% *as cast **room temperature

[0070] To be particularly emphasized is the relatively low density of Alloy 1 according to the invention. Further, the raw material costs as of 2012 are only about 40% of those for Alloy 3 (CMSX-4). The /-mismatch values could be measured only at room temperature; usually the values are higher at higher temperatures.

[0071] Annealing of Alloy 1 may for example be carried out in two stages as follows: [0072] Heating the alloy at 4 K/min up to 1285 C., [0073] Holding for 2 h at 1285 C., [0074] Heating the alloy at 1 K/min up to 1300 C.; [0075] Subsequent rapid cooling.

[0076] Additionally, following solution annealing, Alloy 1 may be subjected to one or both of the following precipitation hardening treatments:

[0077] Precipitation hardening treatment 1:

TABLE-US-00003 Temperature Heating rate Hold time 1000 C. 4 K/min 1050 C. 1 K/min 1050 C. 1 h 20 C. Rapid cooling

[0078] Precipitation hardening treatment 2:

TABLE-US-00004 Temperature Heating rate Hold time 840 C. 4 K/min 870 C. 1 K/min 870 C. 24 h 20 C. Rapid cooling

[0079] Annealing times of more than 2 hours at 1050 C. or higher temperatures result in an excessive aging of the microstructure.

[0080] In summary, it can be stated that the above-described alloy according to the invention shows the following properties in particular:

[0081] Creep resistance close to that of CSMX-4

[0082] Low density of 8.4 g/cm.sup.3 (comparison: CSM X-4: 8.7 g/cm.sup.3)

[0083] Low residual eutectic of 2.8% (comparison: CSMX-4: 9.0%)

[0084] Good annealability (holding for 8.5 hours at 1285 C./1300 C.).

[0085] Low tendency for TCP phase formation

[0086] Very low cost compared to CSMX-4.

[0087] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.