GAS TURBINE PART AND METHOD FOR MANUFACTURING SUCH GAS

Abstract

The present disclosure relates to building very large gas turbines without changing rotor materials. The gas turbine part can include a structure composed of a metal and a ternary ceramic called MAX phase, having a formula Mn+1AXn, where n=1, 2, or 3, M is an early transition metal such as Ti, V, Cr, Zr, Nb, Mo, Hf, Sc, Ta, and A is an A-group element such as Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb, and X is C and/or N.

Claims

1. Gas turbine part configured for exposure to heat and centrifugal forces when installed within a gas turbine, wherein said gas turbine part has comprises: a structure, which is composed of a metal and a ternary ceramic called MAX phase, having a formula M.sub.n+1AX.sub.n, where n=1, 2, or 3, M is an early transition metal selected from a group which includes Ti, V, Cr, Zr, Nb, Mo, Hf, Sc, Ta, and A is an A-group element selected from a group which includes Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb, and X is C and/or N, whereby M is in a range of 40-60 at-%, A is in a range of 10-30 at-% and X is in a range of 20-40 at-%, and whereby M+A+X is in a range of 80-100% with 0-20% being elements other than those already listed and are a result of impurities or oxidation.

2. Gas turbine part as claimed in claim 1, wherein said MAX phase is single phase Ti.sub.2AlC or a composition of two phases, Ti.sub.2AlC and Ti.sub.3AlC.sub.2, where the range of a Ti.sub.2AlC phase is 60-95%.

3. Gas turbine part as claimed in claim 1, wherein said MAX phase is single phase Ti.sub.3SiC.sub.2 or a composition of two phases, Ti.sub.3SiC.sub.2 and Ti.sub.4SiC.sub.3, where the a range of the Ti.sub.3SiC.sub.2 phase is 60-95%.

4. Gas turbine part as claimed in claim 1, wherein said MAX phase is a mixture of two main phases Ti.sub.3SiC.sub.2 and Ti.sub.2AlC, where a range of the Ti.sub.3SiC.sub.2 phase is 40-90%, and whereby two MAX phases are in the-a range of 50-100% with 0-20% being other MAX phases or elements.

5. Gas turbine part as claimed in claim 1, wherein said metal is an Ni or Co based super alloy, or is of the composition MCrAlYX, where M represents Ni, Co or Fe, and X represents other elements with less than 20%.

6. Gas turbine part as claimed in claim 1, wherein said gas turbine part has a hollow metal structure comprising: one or more cavities, which are filled with said MAX phase material.

7. Gas turbine part as claimed in claim 1, wherein said gas turbine part comprises: a bulk MAX phase, which is coated with said metal.

8. Method for manufacturing a gas turbine part as claimed in claim 1, comprising: a) providing a metal suitable for being used in a gas turbine environment; b) providing a ternary ceramic called MAX phase, having the formula M.sub.n+1AX.sub.n, where n=1, 2, or 3, M is an early transition metal selected from a group which includes Ti, V, Cr, Zr, Nb, Mo, Hf, Sc, Ta, and A is an A-group element selected from a group which includes Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb, and X is C and/or N, whereby M is in a range of 40-60 at-%, A is in the range of 10-30 at-% and X is in a range of 20-40 at-%, and whereby M+A+X is in a range of 80-100% with 0-20% being elements other than those already listed and area result of impurities or oxidation; and c) combining said metal and said MAX phase by powder technology processes and/or spray methods to build said gas turbine part up.

9. Method as claimed in claim 8, wherein said metal is Ni or Co based super alloys or MCrAlYX where M represents Ni, Co or Fe and X represents other elements less than 20%.

10. Method as claimed in claim 8, wherein said gas turbine part is subjected to a heat treatment or Hot Isostatic Pressing (HIP) process after step c).

11. Method as claimed in claim 10, wherein said HIP or heat treatment process is done at a temperature less than a melting point of said metal and MAX phase for densification and/or stress relaxation at high temperature.

12. Method as claimed in claim 8, wherein in step c) a metal hollow metal structure of said metal is filled with said MAX phase.

13. Method as claimed in claim 8, characterized in that wherein in step c) a bulk MAX phase is coated with said metal using a spraying process.

14. Method as claimed in claim 13, wherein spraying process comprises: one of cold plasma spraying and High Velocity Oxygen Fuel spraying (HVOF).

15. Method as claimed in claim 13, wherein said MAX phase is pre-oxidized to form a thin TGO (Thermally Grown Oxide) to avoid oxidation and inter-diffusion with said metal.

16. Method as claimed in claim 12, wherein said metal hollow structure is pre-oxidized to form a thin TGO (Thermally Grown Oxide) to avoid oxidation and inter-diffusion with said MAX phase.

17. Method as claimed in claim 8, wherein in step c) a metal hollow metal structure of said metal is filled with a mixture of MAX phase and metallic powder, where said MAX phase is 50-100% wt. and said metal powder has a lower melting point than said MAX phase and the metal hollow structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

[0036] FIG. 1 shows an embodiment of a gas turbine part according to the invention;

[0037] FIG. 2 shows the main steps of the process for manufacturing the gas turbine part of FIG. 1;

[0038] FIG. 3 shows an example of a heat treatment process, which is used to generate compressive stress in the MAX phase;

[0039] FIG. 4 shows a rotor heat shield with separate parts (fins) on the top of the heat shield, which are made of Max phases, and are inserted into a recess on top of the heat shield;

[0040] FIG. 5 shows a further embodiment of a gas turbine part according to the invention; and

[0041] FIG. 6 shows the main steps of the process for manufacturing the gas turbine part of FIG. 5.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

[0042] The invention is about producing a gas turbine part, especially rotor heat shield of gas turbine using new materials, design and processing where new materials provides low density and therefore reduce centrifugal force on rotor and new design and processing method facilitate fabrication of the parts.

[0043] This allows building very large gas turbines without changing rotor materials. This can be done by application of new materials and processing to manufacture components with reduced specific density and robust mechanical strength.

[0044] In this connection, so-called MAX phases, ternary ceramics, are extremely interesting candidates that can fulfill this request, with density of about 4-4.5 g/cm.sup.3, thermal expansion coefficient >810.sup.6 K.sup.1, thermal conductivity >50 W/mK at 700 C., fracture toughness >5 MPa.Math.m.sup.1/2, and high oxidation resistance.

[0045] The proposed solution of using MAX phases with will solve the oxidation problem especially on fins on top of a heat shield (see FIG. 4).

[0046] The MAX phases, which are used to produce hot turbine parts by powder metallurgy processes, are a family of ceramics having M.sub.n+1AX.sub.n formula, where n=1, 2, or 3, M is an early transition metal such as Ti, V, Cr, Zr, Nb, Mo, Hf, Sc, Ta and A is an A-group element such as Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Tl, Pb and X is C and/or N. M is in the range of 40-60 at-%, A in the range of 10-30 at-% and X in the range of 20-40 at-%. And M+A+X is in the range of 80-100% and 0-20% elements, which are not listed above and are result of impurities or oxidation.

[0047] One preferred composition of MAX phase is single phase Ti.sub.2AlC, or two phases, Ti.sub.2AlC and Ti.sub.3AlC.sub.2 (211 and 312), where the range of the 211 phase is 60-95%.

[0048] Another preferred composition of MAX phase is single phase Ti.sub.3SiC.sub.2, or two phases, Ti.sub.3SiC.sub.2 and Ti.sub.4SiC.sub.3 (312 and 413), where the range of the 312 phase is 60-95%.

[0049] Another preferred composition of MAX phase is a mixture of two main phases Ti.sub.3SiC.sub.2 and Ti.sub.2AlC, where the range of the Ti.sub.3SiC.sub.2 phase is 40-90%, and whereby two MAX phases are in the range of 50-100% with 0-20% being other MAX phases or elements.

[0050] When the gas turbine part is especially a rotor heat shield of a gas turbine, it is produced from a MAX phase and metal by powder technology processes and/or spray methods, and the metal is Ni or Co based super alloys or MCrAlYX where M represents Ni, Co or Fe and X represents other elements less than 20%.

[0051] As shown in FIG. 1 and FIG. 2, a gas turbine part 10a, which has for example a T-like cross section, is produced from a hollow metal structure 11, whose cavities 12 are filled with MAX phase and will be subjected to a heat treatment and/or Hot Isostatic Pressing (HIP) process. The current method to avoid cracking of parts is inducing compressive stress using methods such as shot peening.

[0052] The present invention proposes a different solution to induce compressive stress. It combines materials such as MAX phase and metals with specific heat treatment methods (see FIG. 3). MAX phase has lower thermal expansion coefficient compared to said metal. By applying a certain heat treatment as shown in an example in FIG. 3 compressive stress is generated in the bulk at operational temperature. The heat treatment process will be done at temperature higher than operational temperature in order to generate compressive stress in the MAX phase. MAX phase will be stress-free at heat treatment temperature and under compressive stress in the range from room temperature to operational temperature.

[0053] The metal hollow structure 11 filled with MAX phase contributes to reduce weight compared to a bulk metal part and to increase strength compared to a hollow metal part.

[0054] The metal hollow structure 11 filled with a mixture of MAX phase and metallic powder, where MAX phase is 50-100% wt. and metal powder, has lower melting point than MAX phase and the metal hollow structure 11.

[0055] HIP or heat treatment is done at temperature less than the melting point of the metal and MAX phase for densification and/or stress relaxation at high temperature. Operational temperatures less than HIP or heat treatment temperature put MAX phase under compression and increase the tensile loading capability of the part.

[0056] As shown in FIG. 5 and FIG. 6, a gas turbine part 10b is produced from bulk MAX phase 15, which is coated with metal (metal coating 16) using spraying methods (e.g. cold plasma spray, HVOF) and then whole part is heat treated or subjected to HIP. HIP or heat treatment is done at temperature less than the melting point of the metal and MAX phase for densification and/or stress relaxation at high temperature (at room temperature MAX phase is under compression due to lower coefficient of thermal expansion). Operational temperatures less than HIP or heat treatment temperature; MAX phase 15 remains under compression which in turn increases the tensile loading capability of the part 10b. The weight of the part 10b is decreased by using MAX phase and the machinability is improved with external metallic layer (metal coating 16).

[0057] The MAX phase 15 can be pre-oxidized to form a thin TGO (Thermally Grown Oxide) to avoid oxidation and inter-diffusion with said metal.

[0058] The metal hollow structure 11 can be pre-oxidized to form a thin TGO (Thermally Grown Oxide) to avoid oxidation and inter-diffusion with MAX phase.

[0059] In addition, according to another embodiment of the invention, as shown in FIG. 4, separate parts (fins 14) on the top of a rotor heat shield 13 may be made of such MAX phases, which fins 14 could be inserted into respective recesses on top of the heat shield 13.

LIST OF REFERENCE NUMERALS

[0060] 10a,b gas turbine part [0061] 11 hollow metal structure [0062] 12 cavity [0063] 13 rotor heat shield [0064] 14 fin [0065] 15 bulk MAX phase [0066] 16 metal coating