Patent Application
20190366441
The present invention relates to a composite material for an application in a turbo machine, such as a gas turbine. Particularly, the composite material may be envisaged for heat shields applied in the turbine technology, e.g. in the hot gas path, and/or blade technology. Further, a method to manufacture the composite material making use of additive manufacturing technology, is presented.
Additive manufacturing techniques comprise e.g. powder bed methods, such as selective laser melting (SLM) or selective laser sintering (SLS) or electron beam melting (EBM).
Additive manufacturing methods have particularly proven to be useful and advantageous in the fabrication of prototypes or complex and filigree components of lightweight design or cooling components e.g. comprising mazelike internal structures.
Further, additive manufacture stands out for its short chain of process steps, as a manufacturing step can be carried out directly based on corresponding CAD/CAM and/or construction data.
Powder bed manufacturing methods such as selective laser melting or selective laser sintering are relatively well known methods for fabricating, prototyping or manufacturing parts or components from a powder material, for instance. Conventional apparatuses or setups for such methods usually comprise a manufacturing or build platform on which the component is built layer-by-layer after the feeding of a layer of base material which may then be melted, e.g. by the energy of a laser beam and subsequently solidified. The layer thickness is determined by a wiper that moves, e.g. automatically, over the powder bed and removes excess material. Typical layer thicknesses amount to 20 μm or 40 μm. During the manufacture, said laser beam scans over the surface and melts the powder in selected areas which may be predetermined by a CAD-file according to the geometry of the component to be manufactured.
A heat shield for a turbine is e.g. described in EP 2 883 003 B1.
Currently produced ceramic heat-shields (CHSs) used in gas turbines tend to cause failure or form cracks and break into pieces after a certain operating period. This can cause significant damage e.g. to the turbine blades and vanes. Said failure or damage happens due various reasons, i.e. thermal shock and acoustic vibrations or combinations thereof.
Currently, there are two main types of heat-shields used, namely heat shields which are either fully ceramic or fully metallic, e.g. coated with a so-called TBC (“thermal barrier coating”). However, until today, attempts to reinforce a heat shield, such as a CHS with a metallic scaffold, in order to overcome the described drawbacks of delamination, failed. This may be due to the difficulty of adapting thermal expansion coefficients of the dissimilar materials involved.
It is thus an object of the present invention to provide means, by which the mentioned drawbacks can be overcome. Particularly, a novel composite material and an according manufacturing method for the composite material is provided, particularly a material, which does—in a turbine application in a hot gas environment—not break our tend to fall into pieces, e.g. when or after the ceramic material of the respective component or heat shield shows cracks.
The mentioned object is achieved by the subject-matters of the independent claims. Advantageous embodiments are subject-matter of the dependent claims.
An aspect of the present invention relates to a composite material for an application in a turbo machine, such as a gas turbine. The composite material comprises a metallic lattice and a ceramic matrix, wherein the metallic lattice pervades the ceramic metrics, thereby mechanically reinforcing or supporting the ceramic matrix against thermal and/or mechanical loads or impacts in an application of the composite material, e.g. in during an operation a respective turbo machine. Particularly, the composite material shall withstand peeling of or delamination of parts of e.g. the ceramic, during operation, e.g. under thermal loads of up to 1500° C. or even more.
Another aspect of the present invention relates to a method to manufacture said composite material comprising additively manufacturing the metallic lattice, e.g. by powder bed based selective laser melting or electron beam melting, infiltrating the metallic lattice by a ceramic base material, such as a powder or slurry, such that an inside of the metallic lattice is at least partly filled or pervaded, such as coated, and sintering the infiltrated metallic lattice, wherein the ceramic powder is solidified and the composite material is formed.
By these means, it may—with the aid of additive manufacturing technology—be achieved that particularly the metallic lattice holds together the whole composite material e.g. composed of the lattice and the matrix. This is e.g. achieved in a way such that a delamination, breakage or cracking of ceramic parts off the composite material is avoided. As a consequence, secondary damage of the turbine may be also prevented, e.g. damage of heat shields of the gas turbine.
In an embodiment, the metallic lattice is or comprises a regular mesh-like structure which is configured such that it avoids peeling of parts from the composite material during thermal and/or mechanical loads in an operation of the composite material. This embodiment may be advantageous for expediently and reliably holding together the ceramic matrix.
The term “regular” shall denote that a long-range order shall prevail or be present, over roughly the whole extension of the respective component.
In an embodiment, the metallic lattice is or comprises an irregular mesh-like structure which is configured such that it avoids peeling of parts from the composite material during thermal and/or mechanical loads in an operation of the composite material.
The term “irregular” shall denote solely a short-range order of the lattice, wherein the lattice may be densified or particular regions of the respective heat shield material, e.g. according to an (expectedly) increased thermal and/or mechanical load. In other regions of the respective component, e.g. where the described load is expected to be smaller, the lattice may be configured less densified, e.g. with larger lattice constants.
In an embodiment the coefficient of thermal expansion of the material of the metallic lattice and that one of the ceramic matrix is chosen to be similar, advantageously approximately equal. A difference in thermal expansion coefficients of the metallic lattice on one side and the ceramic on the other side shall at least be comparably small. This embodiment allows for a design of the composite material, wherein the ceramic as well as the metallic lattice are awarded with similar thermal expansion behaviour.
In an embodiment the metallic lattice and a ceramic matrix are joined by positive locking to one another. This embodiment may ease to achieve the purpose of the present invention.
In an embodiment the metallic lattice is—at least to a predetermined or certain extent—(freely) movable or slidable within the ceramic matrix, thus allowing some mutual movement, slide of freedom between the metallic lattice and the ceramic matrix, which may be necessary to compensate for different thermal expansion behavior of the mentioned materials. Said movement may relate to one, two or three independent spatial dimensions. This embodiment advantageously allows to provide a play of free spaces in which parts of the composite material may expand. This may, in turn, prevent the whole composite material from breakage or cracking, as stresses in the material may systematically be reduced.
The composite material comprises internal cavities. These internal cavities may function as spaces into which parts of the composite material may expand, as described herein.
A further aspect of the present invention relates to a heat shield for a turbo machine, such as a gas turbine. According to this embodiment, the heat shield comprises the composite material as described and is or is applied as a part of a combustion chamber of the gas turbine or any other part of the respective gas flow path hardware.
In an embodiment, the metallic lattice is only partly filled, coated or infiltrated with the ceramic powder, such that cavities in the composite material remain which may—in an application or operation of the composite material—receive or adopt thermal expansion of the lattice material and/or the ceramic material (matrix), as described above.
In an embodiment the metallic lattice is designed such that, the additive manufacturing is carried out such that, the infiltrating is carried out such that and/or the sintering is carried out such that shrinkage of the material of the ceramic matrix during sintering establishes the described cavities. Thereby, the known adverse effect of shrinkage during sintering may be exploited by the presented method for an adoption of thermal expansion and/or stresses originating from dissimilar thermal expansion coefficients of the respective metallic and the ceramic.
A further aspect of the present invention relates to a computer program or computer program product and/or a, advantageously non-volatile, computer readable medium comprising executable program instructions which are suitable to effect a data processing unit or an additive manufacturing device to design the geometry of the metallic lattice e.g. by computerised topology optimisation means, wherein thermal expansion coefficients of the metallic lattice and the ceramic matrix are considered and/or taken into account.
Advantages relating to the described material or component may as well pertain to the method and vice versa.
Further features, expediencies and advantageous refinements become apparent from the following description of the exemplary embodiment in connection with the Figures.
Like elements, elements of the same kind and identically acting elements may be provided with the same reference numerals in the figures.
Although the metallic lattice is shown in
Indicated by numeral 4, the composite material 10 may comprise cavities. The cavities may particularly serve for providing spaces or play which may account for or receive a thermal expansion of parts of the composite material 10, advantageously the ceramic matrix. In other words, the cavities may adopt or receive material (thermally) expanding into these spaces as a consequence of a hot ambient, such as 1500° C., of a turbine gas flow.
Cavity 4a is particularly arranged in an area of an elongated part, such as a strut 11 or truss, of the metallic lattice 1.
Cavity 4b is shown arranged in an area of a cross-over 12 or intersection of struts of the metallic lattice 1.
Additionally or alternatively, cavity 4c may be provided in an area only taken by the ceramic lattice material 2. However, it is advantageous that the spaces or volume of the cavities contacts the metallic material.
Even though this is not explicitly indicated in
In general, the component or composite material described herein as well as the described method (see below) stabilise or reinforce the described composite material in a way that a component comprising said material is less prone to cracking such that parts of the ceramic peel off or break or fall apart. This effect is particularly achieved by the described metallic lattice which—in other words—mechanically holds the ceramic material (matrix) together.
The length of the struts 11 may define the size of an according lattice cell of the metallic lattice 1.
Deviating from the indication of
Although this is also not explicitly indicated, the metallic lattice 1 may comprise or constitute a regular or irregular mesh of any perceivable lattice geometry, e.g. chosen from face-centred cubic (FCC), body-centred cubic (BCC), rhombic, and tetragonal, hexagonal, prism-like of further morphologies.
For instance, in an application of gas turbine, tiles of the combustion chamber constitute heat shields in order to withstand the harsh temperature environment during operation. As a consequence of the high temperatures, conventional tiles are prone to break or tend to deteriorate and crack or fall apart over time which may cause serious secondary damage to the turbine.
According to the present invention, the described composite material is applied for said heat shield tiles. Thereby, the probability of cracking, breaking or e.g. peeling off of parts of the ceramic can be significantly reduced, as compared to prior art heat shields.
Particularly reference numeral a) indicates additively manufacturing the metallic lattice 1, e.g. by selective laser melting or electron beam melting, advantageously a powder bed-based manufacturing technique.
Further, reference numeral b) indicates an, e.g. computerized, topology optimization step, wherein thermal expansion coefficients of e.g. the metallic lattice 1 and the ceramic matrix 2 are considered, e.g. edited by a user of a corresponding data processing system (not explicitly indicated) or computer program.
Reference numeral c) indicates infiltrating the metallic lattice 1 by a ceramic powder such that an inside of the metallic lattice 1 is at least partly filled with the ceramic.
Still further, reference numeral d) indicates sintering the infiltrated metallic lattice 1, wherein the ceramic powder is solidified and the composite material 10 is formed.
By means of the provided cavities or spaces as described above, according to the design of the metallic lattice and with the aid of additive manufacturing as well as topology optimisation technology (see below), it may be achieved that differences in thermal expansion coefficients of the metallic lattice on one side and a ceramic material (matrix) on the other side may be compensated for such that stresses or tensions are advantageously not established in the composite material but e.g. balanced out.
The scope of protection of the invention is not limited to the examples given hereinabove. The invention is embodied in each novel characteristic and each combination of characteristics, which particularly includes every combination of any features which are stated in the claims, even if this feature or this combination of features is not explicitly stated in the claims or in the examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17157621.8 | Feb 2017 | EP | regional |
This application is the US National Stage of International Application No. PCT/EP2018/052476 filed Feb. 1, 2018, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP17157621 filed Feb. 23, 2017. All of the applications are incorporated by reference herein in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/052476 | 2/1/2018 | WO | 00 |
