Patent Description:
Composite compressor blades for gas turbines are known; for example these compressor blades are made out of carbon fibres impregnated with an epoxy resin. In addition, in order to withstand erosion caused by water droplets or other elements that could pass through the filter at the entrance of the gas turbine inlet, these blades can be provided with an erosion protection layer at selected portions thereof. In particular, it is known to provide erosion protection layers made out of titanium or titanium alloys or nickel or nickel alloys, in order to guarantee the required reliability for the blade. For example, <CIT> discloses the use of such materials.

Titanium and titanium alloys are expensive and difficult to apply, e.g. because titanium components are difficult to machine and shape. In addition, titanium, nickel and alloys thereof have proved to provide only partially satisfying erosion protection.

<CIT> discloses a blade for use in a gas turbine comprising at least a composite material part and at least an insert at least partially covering the composite material part, wherein the insert is made out of steel, and the insert is coated with an erosion protection layer. Other examples of known blades are disclosed in <CIT>, <CIT>, <CIT>, <CIT> and in <CIT>.

The invention includes providing a blade and a method for manufacturing these blades, which allow an improved erosion protection of the blades compared to existing blades.

These and further aspects are attained by providing a blade and a method in accordance with the accompanying claims.

The inventors have surprisingly discovered that the use of steel, in particular high chromium (Cr) content steel, together with a specific erosion protection layer, can guarantee a better erosion protection than the known solutions.

Further characteristics and advantages will be more apparent from the description of nonexclusive embodiments of the blade and method, illustrated by way of non-limiting example in the accompanying drawings, in which:.

Embodiments and/or examples are only according to the invention if they fall within the scope of the accompanying claims.

With reference to the figures, these show a blade <NUM> (stator or rotor blade) such as a compressor blade of a gas turbine; preferably the blade <NUM> is part of the first and/or second and/or third and/or fourth stage of a compressor of a gas turbine, but it can also be used for other stages.

The blade <NUM> generally has a root <NUM> and an airfoil <NUM>.

The blade <NUM> comprises one or more composite material parts; e.g. the blade <NUM> is made out of a composite material (i.e. the root <NUM> and the airfoil <NUM> are both made out of a composite material), or only a part of the blade <NUM> can be made out of a composite material, in this case preferably the airfoil <NUM> or a part of the airfoil <NUM> is made out of a composite material and the rest of the blade can be made out of metal, such as known nickel steel alloys. For example, <FIG> shows a blade defined by the composite material part and <FIG> show blades having metal parts <NUM> and provided with composite material parts <NUM>, as better described in the following.

In different examples, the composite material can comprise carbon fibres impregnated with an epoxy resin or polybenzoxazine or cyanate or polyimide such as a bisMaleimide (BMI) resin (BMI resin allows a higher operating temperature than epoxy resin).

The carbon fibres can be T700S and/or T800S and/or T1000G and/or M50J and/or M60J manufactured by Toray.

The resin can be epoxy RTM6 manufactured by Hexcel or BMI-RTM651 manufactured by Hexcel or araldite MT 35710FST manufactured by Huntsman Corporation.

Impregnation can be carried out by epoxy resin infiltration process for carbon fibres (Carbon Fibres Reinforced Plastic).

Machining after infiltration is possible and final erosion protection coating is possible as well.

Blades made this way can be operated up to a temperature of <NUM>-<NUM>.

Alternatively, the composite material can comprise ceramic fibres impregnated with a molten metal.

The ceramic fibres can e.g. be: Nextel <NUM>, Nextel <NUM>, Nextel <NUM>, Nextel <NUM> manufactured by <NUM>.

The molten metal can be aluminium, aluminium alloys, magnesium, magnesium alloys, copper, copper alloys, steel, steel alloys; as an example pure aluminium (e.g. aluminium having an Al content of <NUM>% by weight or higher) can be used as the molten metal.

The infiltration method can be melt infiltration using a pressureless, pressure assisted, vacuum assisted infiltration technique. the infiltration method can be a molten metal infiltration process for ceramic fibres (Metal Matrix Composite).

The blade also has one or more inserts for protecting the composite material part from erosion. <FIG> shows an insert 4a at the leading edge <NUM>, an insert 5a at the trailing edge <NUM> and an insert 6a at the tip <NUM> of the blade <NUM>. It is clear that even if <FIG> shows one insert for the leading edge, one for the trailing edge and one for the tip of the blade <NUM>, inserts need not be provided at all the indicated positions and in addition inserts could also be provided at different positions of the blade. In addition one insert can cover multiple positions among those indicated above or multiple inserts can be provided at the shown positions. Likewise the composite material parts <NUM> of <FIG> can be provided with an insert 7a.

According to the invention, the insert or the inserts are made out of steel, preferably a high content chromium steel; advantageously the steel of the insert has a chromium content between <NUM>-<NUM>% by weight and preferably between <NUM>-<NUM>% by weight. For example the following steel can be used <NUM>-<NUM> PH steel.

In a first example the inserts 4a, 5a, 6a of the embodiments of <FIG> comprise a foil; in the figure the foil covers the leading edge <NUM>, trailing edge <NUM>, tip <NUM>. The insert 7a of the embodiments of <FIG> is preferably a foil as well.

Alternatively, the inserts 4a, 5a, 6a comprise one or more solid elements that constitute the leading edge <NUM>, trailing edge <NUM>, tip <NUM>. The insert of the embodiment of <FIG> can be a solid element as well, but this embodiment is not preferred.

Naturally also a combination of insert being foils and solid elements is possible.

According to the invention, the insert or the inserts are advantageously coated with an erosion protection layer <NUM>. The coating is preferably applied onto the inserts before the same inserts are connected to the composite material part.

Different techniques for coating the inserts are available, but the following have proven to be particularly advantageous.

In a first example which is an example according to the invention, the.

erosion protection layer has a dual layer structure with a Nickel-Phosphor (NiP) layer and a Nickel-Phosphor/Silicon Carbide (NiP/SiC) layer above it or a multi-layer structure with multiple couples of NiP layer and a NiP/SiC layers one above the other. The dual layer structure proved to give better results.

The inserts can be coated by electroless nickel plating (in a bath). In this case the thickness of the erosion protection layer <NUM> is between greater than <NUM> to <NUM> micron, preferably between <NUM>-<NUM> micron, more preferably between <NUM>-<NUM> micron and even more preferably it is about <NUM> micron.

In addition, a nickel interlayer having a thickness of <NUM>-<NUM> micron and e.g. made by an electrolytic process can be provided to promote adhesion of the NiP-NiP/SiC layers to the insert.

In a second example which is not according to the invention, the inserts are coated by chemical vapour deposition of Tungsten/Tungsten Carbide (W/WC); preferably the chemical vapour deposition is carried out at a temperature less than or equal to <NUM> such that the properties of the material of the insert are not negatively affected. In this case the thickness of the erosion protection layer <NUM> is between greater than <NUM> to <NUM> micron, preferably between <NUM>-<NUM> micron, more preferably between <NUM>-<NUM> micron and even more preferably it is about <NUM> micron.

The structure of this erosion protection layer <NUM> preferably has a single or multiple W/WC layers.

Also in this case, a nickel interlayer having a thickness of <NUM>-<NUM> and preferably about <NUM> micron and e.g. made by an electrolytic process can be provided to promote adhesion of the W/WC layer to the insert.

With reference to <FIG>, the advantageous selection of the processes above is explained.

<FIG> is representative of the erosion resistance of the inserts covered or not with an erosion protection layer.

Samples were made out of steel (e.g. <NUM>-<NUM> PH steel, this material can be used for manufacturing the inserts) and had a rectangular shape with a size of 25x8x3 mm.

The erosion protection layer was made by different techniques and different materials.

The samples (a side thereof provided with the erosion protection layer, when required) were perpendicularly impinged by water droplets having a diameter of <NUM> micron at a speed of <NUM>/s.

<FIG> shows the relationship between the mass loss -number of impacts for these samples. In particular, in this figure "M" represents the mass of the sample that was lost (i.e. eroded) because of the impacts of the water droplets and "I" represents the number of impacts.

In <FIG> curve A refers to a sample without an erosion protection layer; curve B refers to a sample with an erosion protection layer made by titanium nitride applied by PVD (physical vapour deposition) with a thickness of <NUM> micron, other technologies for making the erosion protection layer, such as polyurethane coating with a thickness of <NUM> - <NUM> micron applied by HVLP (high volume low pressure), airless spraying or brushing, provided similar results; curve C refers to a sample covered by an erosion protection layer made by electroless nickel plating (in a bath) with a thickness of <NUM> micron; curve D refers to a sample with an erosion protection layer made by chemical vapour deposition of W/WC at a temperature less than or equal to <NUM> and a thickness of <NUM> micron.

The thickness of the coating is optimized to get adhesion/mechanical properties/chemical properties/erosion resistance.

This figure shows that uncoated samples have poor erosion resistance, because droplet impacts make them lose a large amount of material (curve A).

The behaviour improves by providing an erosion protection layers (curve B).

Curves C and D show a dramatic erosion resistance improvement that is obtained by providing an erosion protection layer made by electroless nickel plating or chemical vapour deposition. In addition, between these two techniques, the chemical vapour deposition carried out at low temperature, such as at a temperature equal to or less than <NUM> has shown the best results.

The present disclosure also refers to a method for manufacturing a blade.

The method comprises providing one or more fibre preforms <NUM>; the fibre preforms can have the shape of the final blade part to be manufactured or can be deformed in order to have such a final shape. The fibre preforms are realized in different examples by stitching, braiding, knitting, weaving, uniaxial/multiaxial non crimp weaving of fibres, or through fabric lay-up.

According to the invention, the method then comprises providing one or more inserts 4a, 5a, 6a, 7a; the inserts can be used for the leading edge and/or trailing edge and/or tip or for a different part of the blade; the inserts are made out of steel. The inserts are advantageously of the kind addressed above, such as foils and/or solid elements.

Thus, the method comprises impregnating the fibre preforms <NUM> and joining the impregnated fibre preforms <NUM> to the inserts 4a, 5a, 6a, 7a.

According to the methods, the insert is coated with an erosion protection layer preferably before joining. As explained above, coating advantageously comprises electroless nickel plating or chemical vapour deposition, that is preferably carried out at a temperature less than or equal to <NUM>.

Impregnating and joining can be carried out in different ways, namely in one step or in multiple steps.

When the method is carried out is one step (<FIG>), impregnating and joining comprise placing fibre preforms <NUM> (<FIG>) and the inserts 4a, 5a, 6a (<FIG>) in a mould <NUM>, providing an impregnant <NUM> (<FIG>) such as an epoxy resin or polybenzoxazine or cyanate or polyimide resin such as BMI resin in the mould <NUM>; the impregnant is thus solidified (i.e. the resin is cured), to impregnate the fibre preforms <NUM> joining the impregnated fibre preforms <NUM> and the inserts 4a, 5a, 6a and define the blade <NUM> in one step.

In a preferred embodiment impregnating (and joining) is carried out by resin transfer moulding process (RTM process).

After impregnation the blade <NUM> is removed from the mould <NUM> (<FIG>).

When the method is carried out in multiple steps (<FIG>), impregnating comprises placing the fibre preforms <NUM> in a mould <NUM> (<FIG>), providing an impregnant <NUM> such as epoxy or polybenzoxazine or cyanate or polyimide such as BMI or molten metal (<FIG>), solidifying the impregnant <NUM> to form one or more composite material parts <NUM>.

Then joining comprises bonding or mechanically interlocking the composite material parts <NUM> and the inserts 4a, 5a, 6a, 7a and possibly a metal blade part <NUM>, to define the blade <NUM> (<FIG>).

For example, the method for realizing a blade in multiple steps can comprise manufacturing a composite material part that has all the geometrical features of the blade and then apply the coated inserts on it, e.g. at the leading edge and/or trailing edge and/or tip thereof, resulting in the blade of <FIG>.

Alternatively, the method for realizing a blade in multiple steps can comprise manufacturing one or more composite material parts <NUM>, providing a metal blade part <NUM> provided with one or more seats, providing the composite material parts <NUM> and the inserts 7a (preferably coated inserts) into the seats, resulting in the blade of <FIG>. In this case, preferably the insert 7a and preferably also the erosion protection layer thereof are housed within the seat, i.e. as shown in <FIG> the surface of the insert 7a (an preferably also of the erosion protection layer) facing outwards is flush with the external surface of the metal part <NUM> of the blade <NUM>.

<FIG> show different examples of inserts bounded or mechanically interlocked to the composite material part of the blade. In particular, <FIG> refer to mechanical interlocking and <FIG> refer to bonding. In addition, mechanical interlocking and bonding can be simultaneously applied. Moreover, <FIG> refer to foils as inserts, and <FIG> refer to solid elements as inserts.

In the following there are described some embodiments of the blade.

The blade is made out of composite material and the inserts are defined by foils or solid elements made out of high chromium steel coated by an erosion protection layer.

The composite material comprises or consists of carbon fibres impregnated with epoxy resin, alternatively the composite material comprises or consists of ceramic fibres impregnated with molten metal.

The erosion protection layer has a single layer structure or dual layer structure or multi-layer structure.

The erosion protection layer is realized by electroless nickel plating and has a thickness greater than <NUM> and smaller or equal to <NUM> micron, preferably between <NUM>-<NUM> micron, more preferably between <NUM>-<NUM> micron and even more preferably it is about <NUM> micron.

The insert further comprises a nickel interlayer to promote adhesion of the erosion protection layer; preferably the nickel interlayer has a thickness of <NUM>-<NUM> micron.

Alternatively the erosion protection layer is realized by chemical vapour deposition and comprises one or more (preferably only one) layer of W/WC. In this case, the erosion protection layer has a thickness between greater than <NUM> to <NUM> micron, preferably between <NUM>-<NUM> micron, more preferably between <NUM>-<NUM> micron and even more preferably it is about <NUM> micron.

Advantageously the chemical vapour deposition is carried out at a temperature less than or equal to <NUM>.

When the insert is a foil, it has a thickness of <NUM>-<NUM> and preferably it is pre-shaped or moulded to the desired shape.

The steel of the insert has a chromium content between <NUM>-<NUM>% by weight and preferably between <NUM>-<NUM>% by weight.

For example, the insert (either the foil or solid insert) can be done out of <NUM>-<NUM> PH steel.

Preferably, the composite material part is made out of a ceramic fibre preform impregnated with the molten metal.

The ceramic fibres can e.g. be: Nextel <NUM>, Nextel <NUM>, Nextel <NUM>, Nextel <NUM> manufactured by <NUM>. The preform can be prepared by stitching, braiding, knitting, weaving, uniaxial/multiaxial non crimp weaving of fibres, fabric, spread tow. The molten metal can be aluminium, aluminium alloys, magnesium, magnesium alloys, copper, copper alloys. For example pure aluminium (Al content <NUM>% by weight or higher) can be used as molten metal. The infiltration method can be melt infiltration using a pressureless, pressure assisted, vacuum assisted infiltration technique. Machining after infiltration is possible and final erosion protection coating is possible as well.

Coating can be made by electroless nickel plating or chemical vapour deposition of W/WC, preferably carried out at a temperature less than or equal to <NUM>.

When the insert is a foil, the foil has a thickness of preferably <NUM>-<NUM> and is pre-shaped or moulded to the desired shape. The steel of the insert has a chromium content between <NUM>-<NUM>% by weight and preferably between <NUM>-<NUM>% by weight.

Naturally the features described may be independently provided from one another. For example, the features of each of the attached claims can be applied independently of the features of the other claims. In addition reference to nickel or nickel alloys in the above description has to be understood to refer to nickel or nickel alloys used in the field.

In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art.

Claim 1:
A blade (<NUM>) for use in a gas turbine comprising at least a composite material part (<NUM>, <NUM>) and at least an insert (4a, 5a, 6a, 7a) at least partially covering the composite material part (<NUM>, <NUM>), wherein the insert (4a, 5a, 6a, 7a) is made out of steel, and the insert (4a, 5a, 6a, 7a) is coated with an erosion protection layer (<NUM>), characterised in that the erosion protection layer (<NUM>) has one of a dual layer structure with a Nickel-Phosphor layer and a Nickel-Phosphor/Silicon Carbide layer above the Nickel-Phosphor layer or a multi-layer structure with multiple couples of Nickel-Phosphor layers and Nickel-Phosphor/Silicon Carbide layers one above the other.