HYBRID BLADE FOR TURBOMACHINES

Abstract

Disclosed is a blade for a turbomachine, comprising an outer shell and an inner core which is at least partially enclosed by the outer shell and has a higher porosity than the outer shell. The outer shell is formed by a ceramic body or a body made of a ceramic matrix composite material, and the inner core is formed by a fiber-reinforced ceramic or a fiber-reinforced ceramic matrix composite material.

Claims

1. A blade for a turbomachine, wherein the blade comprises an outer shell and an inner core which is at least partially enclosed by the outer shell and has a higher porosity than the outer shell, the outer shell being formed by a ceramic body or a body of a ceramic matrix composite material and the inner core being formed by a fiber-reinforced ceramic or a fiber-reinforced ceramic matrix composite material.

2. The blade of claim 1, wherein the outer shell is formed by a compact ceramic body and the inner core is formed by a porous fiber-reinforced ceramic.

3. The blade of claim 1, wherein the ceramic matrix composite material is a ceramic/ceramic composite material or a composite of a ceramic and one or more intermetallic compounds.

4. The blade of claim 1, wherein the porosity of the outer shell is not higher than 5 vol %, and/or the porosity of the inner core ranges from 10 to 30 vol %.

5. The blade of claim 4, wherein the porosity of the outer shell is not higher than 1 vol %, and/or the porosity of the inner core ranges from 15 to 23 vol %.

6. The blade of claim 1, wherein the ceramic material by which the ceramic body of the outer shell or the body of the ceramic matrix composite material of the outer shell is formed comprises at least one material which is selected from HfB.sub.2, ZrB.sub.2, HfN, ZrN, TiC, TiN, ThO.sub.2, TaC and mixtures of at least one of the aforementioned materials with SiC.

7. The blade of claim 1, wherein the ceramic material by which the ceramic of the core or the ceramic matrix composite material of the core is formed comprises at least one material which is selected from HfB.sub.2, ZrB.sub.2, HfN, ZrN, TiC, TiN, ThO.sub.2, TaC and mixtures of at least one of the aforementioned materials with SiC.

8. The blade of claim 1, wherein the fibers of the fiber-reinforced ceramic or of the fiber-reinforced matrix composite material comprise at least one material which is selected from HfB.sub.2, ZrB.sub.2, HfN, ZrN, TiC, TiN, ThO.sub.2, TaC and mixtures of at least one of the aforementioned materials with SiC.

9. A method for producing a blade of a turbomachine, wherein the method comprises forming an outer shell of the blade from a ceramic body or from a body of ceramic matrix composite material and subsequently using the outer shell thus formed as a mold for an inner core, the inner core being formed by introducing a flowable mixture into the outer shell, and forming the flowable mixture and the outer shell into the blade by a heat treatment.

10. The method of claim 9, wherein the outer shell is produced by a generative method.

11. The method of claim 10, wherein the outer shell is produced by a three-dimensional printing method.

12. The method of claim 9, wherein the outer shell is produced by a wax or plastic melting method.

13. The method of claim 9, wherein a ceramic slurry, which is formed into a green body, is used for producing the outer shell, the green body being used directly or after a heat treatment as a mold for the inner core.

14. The method of claim 9, wherein the flowable mixture comprises a starting material comprising from 10 to 30 vol % of fibers and from 20 to 30 vol % of one or more pore-forming agents, the remainder being ceramic material and/or one or more intermetallic compounds.

15. The method of claim 14, wherein the flowable mixture comprises a starting material comprising from 15 to 25 vol % of fibers.

16. The method of claim 14, wherein the starting material is mixed with a solvent to form the flowable mixture.

17. The method of claim 16, wherein the solvent comprises hexane and/or distilled water.

18. The method of claim 9, wherein the flowable mixture is homogenized before introduction into the outer shell.

19. The method of claim 9, wherein the ceramic material for at least one constituent from a group that comprises the ceramic slurry and the ceramic material of the flowable mixture and the fibers of the flowable mixture, is selected from at least one material selected from HfB.sub.2, ZrB.sub.2, HfN, ZrN, TiC, TiN, ThO.sub.2, TaC and mixtures of at least one of the aforementioned materials with SiC.

20. The method of claim 9, wherein the outer shell and the flowable mixture in the outer shell are aged at a temperature ranging from about 1300° C. to about 1700° C. for at least about 2 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In the appended drawings, purely schematically,

[0037] FIG. 1 shows a side view of a turbine blade according to the invention with a core indicated by dashes,

[0038] FIG. 2 shows a side view of the turbine blade of FIG. 1 with a core, indicated by dashes, rotated by 90°, and

[0039] FIG. 3 shows a cross-sectional view of the turbine blade of FIG. 1 with a core indicated by dashes.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0040] 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.

Exemplary Embodiment

[0041] FIG. 1 shows a side view of a high-pressure turbine blade 1 according to the present invention. The high-pressure turbine blade 1 comprises a blade span (airfoil) region 2 and a root region 3, with which the turbine blade 1 can be fitted into a turbine disk. Provided between the blade span region 2 and the root region 3, there is an inner cover strip (shroud) 4.

[0042] According to the invention, the high-pressure turbine blade 1 shown in FIG. 1 to FIG. 3 comprises an outer shell 5 and an inner core 6. The outer shell 5 may be formed from a dense, compact ceramic, for example hafnium diboride, zirconium diboride, hafnium nitride, zirconium nitride, titanium carbide, titanium nitride, thorium dioxide, tantalum carbide and/or combinations of one or more of the aforementioned ceramics with admixtures of silicon carbide.

[0043] The inner core 6, which is enclosed by the outer shell 5 except for the casting openings 7 and 8 and the vent opening 9 (see FIG. 3), is formed in the exemplary embodiment shown by a porous fiber-reinforced ceramic body, in which case both the fibers and the ceramic matrix in which the fibers are incorporated may be formed from the same ceramic material as the outer shell 5. In particular, the fiber and matrix materials may also be the same. The fibers, which are incorporated in the ceramic matrix of the inner core 6, may be in the form of chopped ceramic fibers or so-called whiskers (needle crystals). The porosity of the inner core 6 may, for example, be 20 vol %.

[0044] The production of the blade 1 is carried out by first manufacturing the outer shell 5, in which case a 3D printing method, in which the shell 5 can be printed layer-by-layer with a ceramic slurry in order to fowl a green body, may be used as the manufacturing method. Furthermore, other methods may also be used as an alternative, for example wax melting or plastic melting methods in which a wax or plastic model of the inner core 6 is coated with a ceramic slurry, for example by repeated immersion, so that an outer shell is formed around the wax or plastic core. The outer core may then additionally be shaped according to the outer contour of the blade be produced, and the wax or plastic model may be melted after burning, or simultaneously with the burning of the ceramic slurry or of the green body resulting therefrom, so that a cavity is produced in the shape of the outer shell 5.

[0045] The corresponding ceramic body in the shape of the outer shell 5, or a green body after production by 3D printing, is then used as a mold for the inner core 6. To this end, a flowable mixture, which forms the inner core 6, is poured into the outer shell 5 through the casting openings 7 and 8, in which case air in the cavity can escape from the outer shell 5 through the vent opening 9.

[0046] The flowable mixture comprises a starting material with which the desired inner core 6 of the blade 1 can be produced. In the present exemplary embodiment, the starting material comprises about 20 vol % of chopped ceramic fibers and about 25 vol % of pore-forming agents for producing the pores, as well as corresponding ceramic material in the form of ceramic powder as the remainder. The pore-forming agents may be formed by organic substances, for example nylon, polyester, acrylic compounds or epoxy resins.

[0047] The flowable mixture may furthermore be formed with or without liquid components. Preferably, the flowable mixture comprises a solvent, for example an organic solvent such as hexane, or water, in particular distilled water.

[0048] Before introduction of the flowable mixture into the cavity of the outer shell, the flowable mixture may be mixed in a mixer, for example in a rotary mixer with a rotational speed of from about 15,000 to 20,000 revolutions per minute for a time of a few minutes, for example about 2 minutes. After the mixing, the flowable mixture may be put into an ultrasound homogenizer in order to obtain a mixture which is as homogeneous as possible. This mixture may then be introduced into the outer shell 5, or the cavity of the outer shell 5.

[0049] By a heat treatment of the outer shell 5 filled with the flowable mixture at a temperature of from about 1300° C. to about 1700° C. for a time of about 2 or more hours, the pore-forming agents are converted into the gas phase in order to form the desired pores in the inner core 6. At the same time, the ceramic material is sintered to form a ceramic body, the inner core 6 and the outer shell 5 simultaneously being bonded to one another.

[0050] A blade 1 is thus formed which has a porous inner core 6 with a compact, dense outer shell 5, and in which the inner core 6 additionally comprises ceramic fibers. Because of its structure, such a blade 1 has an improved fracture toughness, a low density simultaneously being achieved. The tensile strength of the blade is improved by the incorporation of chopped ceramic fibers or needle crystals into the inner core, while the shear strength and the elasticity are improved by the porosity of the inner core.

[0051] Although the present invention has been described in detail with the aid of the exemplary embodiment, it is clear to a person skilled in the art that the invention is not restricted by this exemplary embodiment, but rather that variants are possible in that individual features may be omitted or other types of combinations of features may be implemented, without departing from the protective scope of the appended claims. The present disclosure also includes all combinations of the individual features proposed.

LIST OF REFERENCE NUMBERS

[0052] 1 blade, high-pressure turbine blade

[0053] 2 blade span region

[0054] 3 root region

[0055] 4 cover strip

[0056] 5 outer shell

[0057] 6 inner core

[0058] 7 casting opening

[0059] 8 casting opening

[0060] 9 vent opening