TURBOMACH IN E, COMPONENT OF A TURBOMACH IN E AND

TURBOMACH INE

DESCRIPTION TECHN ICAL FIELD

Embodiments of the subject matter disclosed herein relate to methods of manufacturing a component of a turbomachine, components of a turbomachine and turbomachines.

More particularly, the applications of the present invention are in the field of seal systems for turbomachines.

BACKGROUND ART

There are many types of known seal systems for turbomachines; one of these types is commonly called "abradable seal" and comprises an abradable part and an abrading part; in general, the abradable part is provided on a stationary component of the turbomachine (for example the inner surface of a casing of a turbine, i.e. the shroud surface) and the abrading part is provided on a rotatable component of the turbomachine (for example the airfoil tips of the blades of a bucket assembly of a turbine). During start-up of the turbomachine, when the turbomachine rotor starts rotating and consequently the rotatable component rotates, the abrading part abrades (slightly) the abradable part; subsequently, the abrading part and the abradable part define a clearance therebetween . Advantageously, the abradable part has patterned protrusions made of ceramic material ; the material used for the abradable part is a very hard, typically more than 90 HR1 5Y, but less hard than the material used for the abrading part.

In order to realize such ceramic patterned protrusions, first a flat surface and smoothed of the body of the component where they are desired is covered with a ceramic layer and then the ceramic layer is machined so to form protrusions.

Machining a ceramic layer is lengthy and expensive; furthermore, the machining tool dimension limits the size of the machining of the layer (for example, the distance between adjacent protrusions is not less that some mill imeters).

SUMMARY

Therefore, there is a need for an improved way of real izing patterned protrusions, in particular on a component of a turbomachine, in particular to be used in abradable seals.

The present inventors have also considered that due to the complications of the process used till now for realizing such patterned protrusions, the shape (both the transversal shape and the longitudinal shape) and size (both the transversal size and the longitudinal size) of such patterned protrusions were, in practice, restricted, i.e. could not be chosen according to their best performances.

The present inventors have thought of forming the protrusions directly in the body of the component and then coat it through one or more layers of ceramic material or materials. The body of the component is made of metal material and therefore can be machined relatively easily; the overlying ceramic layer or layers does not need to be machined .

Furthermore, thanks to the above improved manufacturing of the protrusions, the present inventors have thought of shaping and sizing them at best. A first aspect of the present invention is a method of manufacturing a component of a turbomachine. The method comprises the steps of :

A) providing a body of the component having a base surface, B) covering the base surface with a bond layer,

C) covering the bond layer with a top layer made of abradable ceramic material creating a top surface of the component; the base surface has patterned protrusions and, through the two covering steps, also the top surface of the component has patterned protrusions.

In this way, the shapes of the patterned protrusions of the top surface are similar to the shapes of patterned protrusions of the base surface.

A second aspect of the present invention is a component of a turbomachine. The component comprises :

- a body of the component,

- a bond layer covering a base surface of the body,

- a top layer covering the bond layer and being made of abradable ceramic material; both the base surface and the top surface of the component has patterned protrusions.

A third aspect of the present invention is a turbomachine.

The turbomachine comprises at least one component as set out above.

BRIEF DESCRIPTION OF DRAWINGS The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the present invention and, together with the detailed description, explain these embodiments. In the drawings: Fig .1 shows schematically a turbine stage of a turbine section of a combustion gas turbine engine according to an exemplary embodiment of the present invention,

Fig .2 shows schematically an exemplary portion of the inner surface of the turbine casing of the turbine section of F ig .1 ,

Fig .3 shows a partial cross-section (transversal view) of a ridge of the exemplary embodiment of Fig .2,

Fig .4 shows schematically a partial cross-section (transversal view) of "ridges" and "lowlands" of a patterned abradable part, this view being used for explaining several exemplary embodiments of the present invention,

Fig .5 shows schematically a partial longitudinal view (including "ridges" and "lowlands") of a patterned abradable part, this view being used for explaining several exemplary embodiments of the present invention, and

Fig .6 shows schematically three possible longitudinal shapes of ridges of three patterned abradable parts according to exemplary embodiments of the present invention . DETAILED DESCRIPTION

The following description of exemplary embodiments refers to the accompanying drawings.

The following description does not l imit the present invention that, in particular, is not limited to combustion gas turbine engines but may be applied to other kinds of turbomachines. Instead, the scope of the present invention is defined by the appended claims. Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed . Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. Fig .1 refers to a combustion gas turbine engine 1 00; the basic sections of a gas turbine engine are the compressor section, the combustors section and the turbine section; Fig .1 shows schematically a turbine stage 140 of the turbine section 1 08. The turbine section 1 08 is enclosed within a turbine casing 109. The turbine section comprises a rotor assembly and a stator assembly; the rotor assembly comprises a turbine shaft 1 1 5 and one or more bucket assemblies coupled to the turbine shaft 1 1 5, each bucket assembly comprising a plurality of turbine blades (or buckets) 1 60; the stator assembly comprises the turbine casing 1 09 and one or more nozzle assemblies coupled to the turbine casing 1 09, each nozzle assembly comprising a plurality of turbine vanes (or nozzles) 1 25. Each combination of a turbine bucket assembly and an adjacent nozzle assembly defines a turbine stage 140.

In Fig .1 , there is shown a schematic view of an exemplary seal system 200 that may be used with the combustion gas turbine engine 1 00, in particular with its turbine section 1 08. Each turbine blade 1 60 comprises an airfoil tip 1 84, the blades 1 60 projecting outwardly from the turbine shaft 1 15. The turbine casing 1 09 comprises an inner surface 1 88, the vanes 1 25 projecting inwardly from the turbine casing 1 09. In this exemplary embodiment, seal system 200 comprises an abradable part 202 located over the inner surface 1 88, i .e. the "shroud surface", and an abrading part 204 located over the airfoil tip 1 84. The abradable part 202 has a first hardness value and the abrading part 204 has a second hardness value that is greater than the first hardness value. In operation of the combustion gas turbine engine 1 00 (at start- up), a rotational motion 206 is induced in the turbine shaft 1 1 5 such that the abrading part 204 rubs against the abradable part 202 and a clearance gap 208 is defined between the abrading part 204 located at the airfoil tip 1 84 and the abradable part 202 formed at the turbine casing 1 09; the clearance gap 208 has a predetermined range of values that facilitates reducing a flow of working fluid (not shown in Fig .1 ) between the turbine blades 1 60 and the turbine casing 1 09, thereby increasing the efficiency of the combustion gas turbine eng ine, while also reducing the rubbing of the turbine blades with the turbine casing, thereby increasing a useful life expectancy of the turbine blades.

Fig .2 shows schematically an exemplary portion of the inner surface 1 88 in Fig .1 , i.e. the "shroud surface", partially covered with an abradable part 202. The abradable part 202 has a top surface with patterned protrusions in the form of a plurality of parallel (or substantially parallel) shaped "ridges" 210; each couple of adjacent "ridges" 21 0 is separated by a "lowland" 21 2. In this embodiment, each shaped ridge comprises: a first initial straight section (beginning at the BEGIN side of the seal), a second intermediate curved section contiguous with the first straight section, a third final straight section (longer that the first section) (ending at the END side of the seal) contiguous with the second curved section .

Fig .3 shows a partial cross-section of a ridge 210 of the exemplary embodiment of Fig .2; Fig .3 shows a "peak" of a "mound"; this "peak" is pointed but, alternatively, it may correspond for example to a "plateau". In Fig .3, there may be seen : a portion 306 of the body of the turbine casing 1 09, a bond layer 304 covering a base surface of the body (i.e. a portion of the inner surface 1 88 of the turbine casing 1 09), and a top layer 302 covering the bond layer 304 and made of abradable ceramic material .

The structure of Fig .3 is obtained through the step of: A) providing the body 306 having a base surface that is not flat, then

B) covering this base surface with the bond layer (304), then

C) covering the bond layer 304 with the top layer 302 of abradable ceramic material thus creating the top surface of said component (see

Fig .2).

As partially shown in Fig .2, the base surface to be covered is a portion of the inner surface 1 88 and is preliminarily prepared before being coated, i.e. patterned protrusions are provided in the body 306 (see Fig .2 and Fig .3); after the two covering steps, also the top surface of the component has patterned protrusions (in this exemplary embodiment the protrusions correspond to the "ridges" 21 0).

Fig .4 also shows "ridges" and "lowlands" in cross-section . The protrusions of the base surface is labeled 414 and the protrusions of the top surface is labeled 41 0; more specifically, the "ridges" of the base surface is labeled 414 and the "lowlands" of the base surface is labeled 41 6 (these elements can not be seen after the end of manufacturing as they are concealed behind the bond layer and the top layer) while the "ridges" of the top surface is labeled 41 0 (similar to "ridges" 21 0 in Fig .2) and the "lowlands" of the top surface is labeled 41 2 (similar to "lowlands" 21 2 in Fig .2). The patterned protrusions (414 in Fig .4) of the base surface of the body (406 in Fig .4) may be obtained for example by casting, mill ing, grinding, electric discharge machining or additive manufacturing .

The body (406 in Fig .4) is made of a metal material and may be made for example of a stainless steel of the AISI 300 series, a nickel base superalloy, "inconel 738", "hastelloy x", "rene 1 08" or "rene 1 25". Metal materials can be easily and quickly shaped, for example machined.

The bond layer (404 in Fig .4) may be made for example of MCrAlY (where M = Co, Ni or Co/Ni - d ); alternatively, it may be made of N i ₃ AI (nickel aluminide). This layer may be obtained by spraying, for example Physical Vapor Deposition (PVD), Low Pressure Plasma Spraying (LPPS), Vacuum Plasma Spraying (VPS), Air Plasma Spraying (APS), or High Velocity OxyFuel (HVOF) spraying; alternatively, it may be obtained by diffusion, for example sol id state diffusion, liquid state diffusion or chemical vapor diffusion; MCrAlY is more tyipically obtained by spraying and Ni ₃ AI is more typically obtained by diffusion .

The thickness tk (see Fig .4) of the bond layer (404 in Fig .4) is substantially uniform; the thickness tk may be in the range 0.01 -1 .0 mm, more preferably in the range 0.05-0.3 mm.

The top layer (402 in Fig .4) is made of a ceramic material and may be made for example of DVC YSZ (dense vertically-cracked yttria- stabil ized zirconia) or DVC DySZ (dense vertically-cracked dysprosia- stabil ized zirconia) and may be obtained by spraying, for example Physical Vapor Deposition (PVD), Low Pressure Plasma Spraying (LPPS), Vacuum Plasma Spraying (VPS) Air Plasma Spraying (APS), or High Velocity OxyFuel (HVOF) spraying).

The thickness of the top layer may be uniform or variable. According to a typical embodiment, there is a first thickness h i (see Fig .4) at the "lowlands" of the base surface and a second thickness h2 (see Fig .4) at the "peaks" of the "ridges" of the base surface, the first thickness h i being greater than the second thickness h2; the th icknesses h i and h2 may be in the range 0.6-6.0 mm; the thickness h2 is preferably in the range 0.6-3.0 mm.

The structures of Fig.2 and Fig.4 (it corresponds to a large set of similar structures) may be obtained through the method set out above and may be realized on a statoric shroud .

According to a typical embodiment, the "ridges" are parallel to each other and arranged at a uniform distance or pitch P (see Fig .4); the pitch P may be in the range 2.5-1 5.0 mm; it is to be noted that the pitch of the protrusions of the top surface (41 0 in Fig . 4) is equal to the pitch of the protrusions of the base surface (414 in Fig .4).

The "ridges" according to the present invention may have different shapes and sizes (both transversally and longitudinally); with reference to Fig .4, it is to be noted that the shapes and sizes primarily important for the sealing function of the abradable seal is the shapes and sizes of the protrusions 41 0; anyway, the shapes and sizes of the protrusions 41 0 derive from the shapes and sizes of the protrusions 414 through two covering steps; therefore, all these shapes and sizes are linked together.

The "ridges" 510 in the exemplary embodiment of Fig.5, that are separated by "lowlands" 51 2, comprise :

- a first initial straight section 514 (beginning at the BEGIN side of the seal),

- a second intermediate curved section 51 6 contiguous with the section 514, - a third final straight section 518 contiguous with the section 51 6 (ending at the END side of the seal); in this exemplary embodiment sections 514 and 51 8 have different lengths, in particular section 514 is longer than section 51 8. The angle λ (522 in Fig .5) between the section 514 and a circumferential line (specifically lying in a plane transversal to the rotation axis of the turbomachine and corresponding to the BEGIN of the seal) may be in the range 25°-85°. The angle μ (524 in Fig .5) between the section 518 and a circumferential line (specifically lying in a plane transversal to the rotation axis of the turbomachine and corresponding to the END of the seal) may be in the range 25°-85°. The angles λ and μ may be equal or different; in the exemplary embodiment of Fig .5, they are different.

Differently from Fig .5, the "ridges" 602, 604 and 606 in the exemplary embodiments of Fig .6 comprise respectively one, two and three curved sections without straight sections.

Fig .4 may be used for understanding many possible transversal shapes of the protrusions, in particular the "ridges"; as already said the shapes and sizes of the protrusions (414 in Fig .4) of the base surface are similar, even if not identical, to the shapes and sizes of the protrusions (41 0 in Fig .4) of the top surface.

The cross-section shape of the protrusions (414 in Fig .4) of the base surface may be a triangle, for example with rounded corners (more particularly with rounded "peak" of e.g . 0.5 mm radius), or a trapezium (i.e. a quadrilateral with one pair of parallel sides). The cross-section shape of the protrusions (41 0 in Fig .4) of the top surface may be a triangle, for example with rounded corners (more particularly with rounded "peak" of e.g . 0.5 mm radius), or a trapezium (i.e. a quadrilateral with one pair of parallel sides). One possibility is that the element 414 is a triangle and that element 41 0 is a trapezium. It is to be noted that the initial shape of the element 41 0 may be a triangle and that, after rubbing, the final shape of the element 41 0 is a trapezium.

The angle a (see Fig .4) on one side of the trapezium of the base surface may be in the range 25°-90°, preferably in the range of 30-75°, more preferable about 45°. The angle β (see Fig .4) on the other side of the trapezium of the base surface may be in the range 25°-90°, preferably in the range of 30-75°, more preferable about 45°. The angles a and β may be equal or different; in the exemplary embodiment of Fig .4, they are equal ; possible exemplary combinations are: 45° and 45° , 30° and 30°, 60° and 60° , 30° and 60° , 60° and 30°.

The angle γ (see Fig .4) on one side of the trapezium of the top surface may be in the range 25°-90°, preferably in the range of 30-75°, more preferable about 45°. The angle δ (see Fig .4) on the other side of the trapezium of the top surface may be in the range 25°-90°, preferably in the range of 30-75°, more preferable about 45°. The angles γ and δ may be equal or different; in the exemplary embodiment of Fig .4, they are equal ; possible exemplary combinations are: 45° and 45° , 30° and 30°, 60° and 60° , 30° and 60° , 60° and 30°. It is to be expected that angle γ is typically less (only a bit less, e.g . 5° to 1 0°) than angle a and that angle δ is typically less (only a bit less) than angle β.

As far as the trapezium of the base surface is concerned, its height H 1 (see Fig .4) may be in the range 0.5-5.0 mm, and its upper base L1 (see Fig .4) may be in the range 0.0-5.0 mm; if the upper base is in the range of 0.0-0.5 mm, the trapezium may be considered a triangle. As far as the trapezium of the top surface is concerned, its height H2 (see Fig .4) may be in the range 0.5-5.0 mm, and its upper base L2 (see Fig .4) may be in the range 0.0-5.0 mm; if the upper base is in the range of 0.0-0.5 mm, the trapezium may be considered a triangle. It is to be expected that height H2 is typically less (only a bit less) than height H 1 and that upper base L2 is typically more (only a bit more) than angle L1 .