NL2018995B1

NL2018995B1 - Self-healing particles for high temperature ceramics

Info

Publication number: NL2018995B1
Application number: NL2018995A
Authority: NL
Inventors: Gerrit Sloof Willem; Lucia Carabat Alexandra
Original assignee: Univ Delft Tech
Priority date: 2017-05-30
Filing date: 2017-05-30
Publication date: 2018-12-07
Also published as: WO2018222036A1

Abstract

22 ABSTRACT: The invention provides a particulate material (1) comprising particles 5 (100), wherein the particles (100) comprise molybdenum silicide (MoSi2), boron and aluminum, wherein the particles (100) comprise molybdenum silicide (MoSi2) having a hexagonal structure, wherein boron in the particles (100) is available in an amount selected from the range of 0.5-3 wt% and wherein aluminum in the particles (100) is available in an amount selected from the range of 5-20 wt% relative to the total weight 10 of the particles (100), and wherein the particles (100) have weight average particle sizes selected from the range of 5-50 µm. 15

Description

SELF-HEALING PARTICLES FOR HIGH TEMPERATURE CERAMICS

FIELD OF THE INVENTION

The invention relates to a particulate material as well as a method for providing such particulate material. The invention also relates to a method for providing a high temperature ceramic coating on a substrate, such substrate, as well as a device comprising such substrate.

BACKGROUND OF THE INVENTION

Gas turbine engine component coatings with self-healing barrier layers are known in the art. WO2015080839, for instance, describes that many gas turbine engine components are subject to temperatures in excess of the melting temperature of the component substrate, which may be constructed from a nickel super alloy or non-oxide ceramic, for example. Cooling features and thermal barrier or environmental coatings are used to protect the substrate from these extreme temperatures. Further, W02015080839 describes that thermal barrier coatings (TBC) or environmental barrier coating (EBC) made from yttria- stabilized zirconia (YSZ) and gadolinium zirconium oxide are typically used to reduce the temperature of cooled turbine and combustor components. Additionally, these materials may also be used as abradable seal materials on cooled turbine blade outer air seals (BOAS) as well as other components. In these applications, there are several degradation and failure modes. During engine operation, thermal barrier coatings may become spalled, delaminated, chipped or eroded, for example, due to debris or environmental degradation. According to WO2015080839, bond coats for thermal barrier coatings as well as environmental barrier coatings for high temperature composite materials rely on an oxygen diffusion barrier layer that is often alpha alumina. Alpha alumina is an excellent barrier to oxygen diffusion and naturally forms at elevated temperature on aluminum rich alloys. This layer is often referred to as a thermally grown oxide (TGO). As this TGO layer grows with time and temperature it typically buckles and spalls off at which time it must regenerate, drawing further from the aluminum reserves of the host material by diffusion. As the aluminum gets depleted, non-ideal oxides begin to form which make the TGO less effective at preventing further oxidation. Making TGO adhesion more difficult is the coefficient of thermal expansion (CTE) mismatch between the metallic aluminum donor and alumina layers during the thermal cycling present in most applications. W02015080839 proposes a component for high temperature applications, comprising: a substrate; and a layer of an aluminum-containing MAX phase material and another material applied to the substrate. A MAX phase material is a group of ternary carbides with the formula Mn+iAX„ (where n=l-3, M is an early transition metal, A is an A-group element and X is carbon and/or nitrogen). According to W02015080839, desired MAX phase materials for the bond coat include aluminum as the A-group element, which provides an aluminum rich source for thermally grown oxides having a high aluminum diffusion rate. Example MAX phase materials include Cr2AlC, Ti2AlC, EffiAlN and T13AIC7. According to WO2015080839, niobium-, tantalum- and vanadium-based MAX phase materials may also be used.

SUMMARY OF THE INVENTION

According to W.G. Sloof et al., in “Crack healing in yttria stabilized zirconia thermal barrier coatings”, published in Self Healing Materials - Pioneering Research in the Netherlands, Publisher: IOS Press under the imprint Delft University Press, 2015, Editors: S. Van der Zwaag, E. Brinkman, pp. 219-227, the field of (intentionally engineered) self-healing materials has a long history, but gained widespread attention with the publication of the work of White et al. in 2001 (S.R. White, N.R. Sottos, P.H. Geubelle, J.S. Moore, M.R. Kessler, S.R. Sriram, E.N. Brown, S. Viswanathan, Nature, 409 794-797). The White-Sottos-Moore concept showed that autonomous recovery of mechanical properties in a thermoset polymer could be obtained by incorporating capsules containing a liquid healing agent as well as catalytic particles into the epoxy prior to curing. When fracturing such a composite, the following chain of reactions take place: i) the crack formed penetrates the matrix as well as the capsules containing the healing agent, ii) the healing agent flows out of the capsules due to capillary forces and fills the crack, iii) the healing agent comes into contact with the catalytic particles, cross links and thereby turns into a well-bonded solid with load bearing capabilities. The sequence of these three reactions upon the formation of a crack and in the absence of an additional force or trigger, creates an autonomously self-healing material. While the materials used in this landmark publication can only be used at room or slightly elevated temperatures, the concept is very versatile and, once properly modified, can in principle also be used to create autonomous crack healing at (very) high temperatures. A high-temperature application where autonomous crack healing is highly desirable can be found in thermal barrier coatings (TBCs) that are applied on components in the hot section of turbine engines. These components can be exposed to working temperatures over 1000 °C. The TBC is applied to allow a higher working temperature in the turbine without raising the temperature of the metallic components (made of nickel based super alloys) such as blades so that they maintain their strength and creep resistance. High temperature ceramics with a low thermal conductivity are the preferred materials as TBCs as they retain their properties under harsh thermal and thermomechanical conditions. Ceramic coatings, in conjunction with an internal cooling system in the component, create the desired temperature gradient. The most common TBCs are based on Yttria Stabilized Zirconia (YSZ), as this ceramic has both excellent thermo-mechanical properties and can be bonded well via an intermediate MCrAlY or Pt-aluminide coating to the super alloy turbine component. However, the lifetime of TBC is limited to 2000-4000 thermal cycles (around 30000 hours of flying time) due to the difference in thermal expansion coefficients (CTEs) of the metal substrate and ceramic coating. During thermal cycling, the CTE differences lead to the formation and growth of micro cracks, which eventually turn into larger cracks and ultimately lead to TBC delamination. The periodic replacement of (slightly damaged) TBCs generates high maintenance costs. So far, attempts to increase the lifetime of TBC have mainly focused on routes to reduce the likelihood of crack formation by CTE mismatch. Such an improvement may be realized by applying another coating layer on top of TBC, which has better thermal properties than the base TBC material. Pyrochlore zirconates (Ln2Zr2O-) are an interesting example of such an approach as they have an even lower thermal conductivity and excellent thermal stability at high temperatures. Doping pyrochlore zirconates with rare earth elements has also been researched due to the enhancement of thermo-physical properties. Another method to improve the durability of the coatings is by using hexaaluminates ((La,Nd)MAlnOi9) as the base coating material. Functionally graded hexaaluminate composites, with a gradient concentration of A12O?, can also be applied.

An alternative concept to increase the lifetime of TBCs is based on modifying the density of the TBC by doping the YSZ coating material with trivalent transition metal oxides such as La2CT, Nd2O?„ etc. Such modifications introduce atomic level defects and decrease the radiative transport (by decreasing the Debye temperature) through the coating. The reduction in internal heat transport can be realized during coating application or by a post-deposition laser heat treatment. The main reason for failure in TBCs is the accumulation of interfacial stress in the structure upon thermal cycling. Heating the metallic substrate before the coating application is also a method to reduce the stress on the coating, which helps to increase the lifetime. Essentially, all these routes aim at reducing the occurrence of cracks, but, once formed, all such cracks will always grow and unavoidably lead to coating delamination and spallation. The application of the White-Sottos-Moore concept of autonomously self-healing polymers to high temperature ceramics for TBCs operating at 1000 °C or above, requires a few modifications of the base material selection criteria, namely: i) the healing agent to be embedded in the TBC should be a solid at the operating temperature, as liquids generally have an unacceptably large CTE as well as a large thermal conductivity; ii) the healing agent should turn into a (flowing) liquid which will fdl the crack and wet the TBC crack surfaces, iii) the liquid or viscous medium flown into the crack should turn into a solid by a subsequent solid state chemical reaction with the TBC material in order to create a solid, i.e. load bearing material. The final outcome of all these reactions should be a crack filled with a well-bonded crystalline material of low thermal conductivity. Additional design criteria, such as particle size, volume fraction and effective ‘shelf life’, also come into play in actual applications and they should be calibrated to the to the volumetric dimensions of the crack.

As indicated above, failure by cracking and delamination of ceramics for high temperature applications limiting the lifetime of components is a problem of solutions proposed in the prior art.

Hence, it is an aspect of the invention to provide an alternative particulate material, a coated substrate (especially for a high temperature application), as well as a device with such coated substrate, which preferably further at least partly obviates one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

In a first aspect, the invention provides a particulate material comprising particles, wherein the particles comprise molybdenum silicide (MoSi2). Further, the particles comprise boron and aluminum. Especially, in specific embodiments the particles comprise molybdenum silicide (MoSi2) having a hexagonal structure due to alloying with aluminum. In embodiments, boron in the particles is available in an amount selected from the range of 0.5-3 wt% relative to the total weight of the particles. In embodiments, aluminum in the particles is available in an amount selected from the range of 5-20 wt% relative to the total weight of the particles, such as 5-15 wt%. Especially, the particles have weight average particle sizes selected from the range of 5-50 pm, especially 10-40 pm.

It appears that such particles have surprising self-healing properties, better than those with only an alumina coating, and better than those without boron. Further, it appears surprising that the less stable hexagonal phase provides better results than the more stable tetragonal structure of molybdenum silicide. Hence, with such material high-temperature applications can be effected, such as self-healing particles in high-temperature ceramics, such as zirconia based high-temperature ceramics. Hence, high-temperature engines with a longer lifetime can be made when the particulate material of the invention is used as basis for self-healing particles in such high-temperature ceramic.

As indicated above, the invention provides a particulate material comprising molybdenum silicide (MoSi2) particles. Such material may heal by the formation of silica while molybdenum may evaporate as a molybdenum oxide. Such healing may occur during a high temperature application; see further also below.

The particles also comprise boron. It appears that a small amount of boron improves healing. Therefore, boron in the particles is available in an amount selected from the range of 0.5-3 wt%. Especially, boron in the particles is available in an amount selected from the range of 1-2 wt%; this may give the best results. Note that the weight of boron is evaluated on an elementary basis.

Further, the particles comprise aluminum. The aluminum and boron are distributed over the particles in a relatively even way. Hence, boron in the particles may homogeneously be distributed. Boron may be available as another phase, such as MoB2, which may essentially be homogeneously available in the particles. Aluminum may be available as dopant in the MoSi2 material. Also aluminum in the particles may homogeneously be distributed. The distribution of A1 (and B) may be evaluated with e.g. X-ray microanalysis.

Before an annealing of the particles, the particle may thus be particles without having a core-shell structure. After annealing, especially in an oxidizing atmosphere, the aluminum in the particle may form an alumina coating or shell, whereby a core-shell particle is formed.

Core-shell particles are desired in view of the formation of the high temperature coating. With the alumina shell, the molybdenum silicide is protected. The molybdenum silicide may become available in the high temperature coating upon formation of cracks (see also below).

Hence, the presence of aluminum in the particles (before annealing) is desirable. Therefore, aluminum in the particles is available in an amount selected from the range of 5-20 wt% relative to the total weight of the particles. Note that the weight of aluminum is evaluated on an elementary basis. Especially, at least 7.5 wt%, such as even more especially at least 10 wt% A1 is available.

Not being bound by theory, it may be that when cracks are formed the particles may also be broken or damaged, by which oxygen may have access to the molybdenum silicide. In this way, silica may be formed that may fill the cracks.

As indicated above, the particles comprise molybdenum silicide (MoSi2) having a hexagonal structure when alloyed with aluminum. It appears that best results are obtained with the hexagonal structure, and not with the more stable tetragonal structure without aluminum (see also above). A good distribution of the aluminum and boron in the particles with the tetragonal structure appeared to be very difficult, whereas surprisingly this appeared to be much easier when using the less stable hexagonal structure. Hence, in specific embodiments at least 60 wt%, such as at least 80 wt%, even more especially at least 90 wt% of the molybdenum silicide (MoSi2) (in the particles) has the hexagonal structure. Even more especially, at least 95 wt% of the molybdenum silicide (MoSi2) has the hexagonal staicture. The structure of the molybdenum silicide can be evaluated with XRD. Note that the weight of MoSi2 is evaluated on a molecular weight basis.

Further, best results are obtained with particles having weight average particle sizes selected from the range of 10-40 pm, especially having weight average particle sizes selected from the range of 20-35 pm, such as especially 20-30 pm.

In embodiments, a dso of 10-50 μιη, such as 10-40 μιη, is chosen, especially 20-35 μιη, such as more especially 20-30 μιη. The right particle size may e.g. be obtained via wind sifting, such as with an air classifier, to provide the desired particle size (range). Too large particles, such as larger than 50 pm, may not easily be used for plasma spraying, further, too small particles, such as smaller than 5 pm, may not include enough Al for a good coating. Hence, a desired particle distribution may be obtained with sieving and/or wind sifting. The particle size (distribution) may be evaluated with laser diffraction.

It is not excluded that in addition to aluminum, boron, and molybdenum silicide, the particles may also comprise other materials. In specific embodiments, at least 65 wt% of the particles consist of molybdenum silicide, even more especially at least 85 wt%, such as at least 87 wt%. Even more especially, molybdenum silicide in the particles is available in an amount selected from the range of 87-94.5 wt%. The remainder may thus at least comprise boron and aluminum. In further specific embodiments, molybdenum silicide in the particles is available in an amount selected from the range of at least 90 wt%.

The particles with the hexagonal molybdenum silicide with boron and aluminum embedded therein can be made via e.g. mixing powders of Mo, Si, Al , B, or compounds like: M0S12, SiBö, MoxAly, MoAlB, etc., in the desired ratio. Then, densification with spark plasma sintering (homogeneous alloy (bulk)) may be applied, for instance at pressure above 25 MPa, such as at least 30 MPa, and temperatures of at least 1400 °C. Next, pulverizing and milling to obtain particles. Finally, sieving and/or wind sifting to remove fines and obtain the desired range of particle sizes. An alternative may be to prepare a ‘rod’ of the MoSiAlB alloy to make spherical particles by gas atomization (very good, but difficult, low yield, expensive).

Hence, in yet a further aspect the invention also provides a method of providing particulate material, the method comprising: combining 1) one or more of Mo and a Mo comprising compound, 2) one or more of Al and an Al comprising compound, and 3) one or more of B and a boron comprising compound, to provide a composition comprising M0S12 and 1) one or more of boron and a boron comprising compound, and 2) one or more of Al and an Al comprising compound; optionally densifying of the thus obtained composition; and processing the (thus obtained (optionally densified)) composition into particulate material, with the particulate material having the characteristics as defined herein.

In specific embodiments, the method may comprise combining a boron compound, an aluminum compound, and a molybdenum compound and heating the composition to a temperature of at least 1400 °C in an inert atmosphere, especially in argon, and processing the composition into particulate material

The (thus obtained) particulate material may, also indicated elsewhere herein, be used in the production of a ceramic material.

The particulate material may be used for creating high temperature coatings (HTC), such as thermal barrier coatings (TBC), more especially as healing agent for such coatings. Other applications of the particulate material may e.g. be structural high temperature ceramics, like zirconia, yttria stabilized zirconia, alumina, Mullite, etc..

For the use as healing agent, it is desirable that the particles have a protective shell. Therefore, in specific embodiments a method for providing a material including the particulate material may include a heating stage (herein also indicated as “annealing”), especially a heating stage in a (slightly) oxidizing atmosphere.

Therefore, in yet a further aspect the invention also provides a method of providing a coating (herein also indicated as “high temperature ceramic coating”) on a substrate, the method comprising providing high temperature stable material and the particulate material according to any one of the preceding claims on the substrate, and annealing the thus obtained deposited material in the presence of an oxidizing gas.

Due to the presence of the self-healing material in the form of the particulate material, the lifetime of the temperature stabile material may be enhanced. Even though cracks may be formed, the self-healing particles may at least fill part of the cracks, thereby increasing lifetime, and thus decreasing material costs, and also increasing safety.

The temperature stable material may be stable up to temperatures of at least 1000 °C. Examples of temperature stable materials include one or more of high temperature ceramics, like zirconia, yttria stabilized zirconia, alumina, Mullite, etc., such as especially yttrium stabilized zirconia. Therefore, in specific embodiments the high temperature stable material comprises yttria stabilized zirconia, and the method comprises depositing yttria stabilized zirconia particles. Instead of or in addition to yttrium stabilization, also other elements may be used to stabilize, such as Nd. Instead of in addition to stabilization with yttria (Υ2Ο2ι), one or more of MgO, CaO, and CeO2 may (also) be applied.

Silica and zirconia may form ZrSiCfl (zirconium orthosilicate) which may further increase stability in the crack, and thus of the material.

Different methods may be used to create the high temperature ceramic coating. In a specific embodiment, the method comprises using a plasma spray process. Additionally or alternatively, one or more of high velocity oxygen fuel (HVOF), sol-gel deposition. Especially, plasma spraying may be applied, such as APS (atmospheric pressure plasma spraying), VPS (vacuum pressure plasma spraying), LPPS (low-pressure plasma spraying), even more especially APS.

The plasma spray process is basically the spraying of molten or heat softened material onto a surface to provide a coating. Material in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity. The hot material impacts on the substrate surface and rapidly cools forming a coating. This plasma spray process carried out correctly is called a "cold process" (relative to the substrate material being coated) as the substrate temperature can be kept low during processing avoiding damage, metallurgical changes and distortion to the substrate material.

The plasma spray gun may comprise a copper anode and tungsten cathode, both of which are water cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows around the cathode and through the anode which is shaped as a constricting nozzle. The plasma is initiated by a high voltage discharge which causes localized ionization and a conductive path for a DC arc to form between cathode and anode. The resistance heating from the arc causes the gas to reach extreme temperatures, dissociate and ionize to form a plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma which does not carry electric current) which is quite different to the plasma transferred arc coating process where the arc extends to the surface to be coated. When the plasma is stabilized ready for spraying the electric arc extends down the nozzle, instead of shorting out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal pinch effect. Cold gas around the surface of the water cooled anode nozzle being electrically non-conductive constricts the plasma arc, raising its temperature and velocity. Powder is fed into the plasma flame most commonly via an external powder port mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that spray distances can be in the order of 25 to 150 mm.

The plasma spray process is most commonly used in normal atmospheric conditions and referred as APS. Some plasma spraying is conducted in protective environments using vacuum chambers normally back filled with a protective gas at low pressure, this is referred as VPS or LPPS. Plasma spraying has the advantage that it can spray very high melting point materials such as refractory metals like tungsten and ceramics like zirconia unlike combustion processes. Plasma sprayed coatings are generally much denser, stronger and cleaner than the other thermal spray processes.

In the present invention, both the high temperature stable material and the particulate material may be plasma sprayed, such as for instance described in DE 102016007231.8, which is herein incorporated by reference. Therefore, in embodiments the substrate is configured at a first position (Pl), wherein at an upstream position (P2) at a first temperature, particulate high temperature stable material, especially yttrium stabilized zirconia particles, is provided, and wherein at a downstream position (P3) at a second temperature the particulate material is provided, wherein the substrate is configured at the first position (Pl) downstream of the upstream position (P2) and the downstream position (P3), wherein the substrate is maintained at a third temperature.

Hence, the high temperature material in the form or particles, especially yttrium stabilized zirconia particles, are provided at the highest temperature, upstream of a position where at a lower temperature the particulate material with the MoSii particles is provided.

In specific embodiments, the first temperature is selected from the range of 2800-3200 °C, wherein the second temperature is selected from the range of 2050-2200 °C, and wherein the third temperature is selected from the range of 200-500 °C.

The plasma spray process is essentially executed in an oxygen free atmosphere, such as in a noble gas atmosphere, such as argon and/or helium.

As indicated above, especially the particles are provided with essentially no alumina coating, but upon deposition or after deposition, at least part of the available aluminum is oxidized to alumina. This leads to a migration of the aluminum to the exterior of the particles and a formation of an alumina shell, which may have a protective function.

The annealing may e.g. be executed after formation of essentially the entire coating (by APS). Therefore, in specific embodiments after deposition of at least part of the yttrium stabilized zirconia and the particulate material, even more especially after deposition of (essentially all) the yttrium stabilized zirconia and the particulate material the thus obtained deposited material is annealed, especially to a temperature of at least 1000 °C. More especially, after deposition of at least part of the high temperature stable material and the particulate material, the thus obtained deposited material is annealed in the presence of the oxidizing gas at an oxygen partial pressure below 1.1 O'10 Pa, such as even more especially the thus obtained deposited material is annealed in the presence of the oxidizing gas at an oxygen partial pressure below 1.10’14 Pa. The oxidizing gas may comprise one or more of O2, CO2, H2O, etc.. For control of the desired O2 partial pressure, it may be desirable to add CO to CO2. For control of the desired O2 partial pressure, it may be desirable to add H2 to H2O.

The high temperature stable material is in the plasma spray process also provided as particles. Characteristic particle sizes may e.g. be selected from the range of 10-40 pm. The coating thickness may e.g. be selected from the range of 100 - 1000 pm.

During annealing, the aluminum may migrate to the particle surface and form the alumina shell. Further, the MoSi2 core may change from a hexagonal structure to a tetragonal structure.

The invention also provides the thus obtained substrate, such as a wall of a turbine, or a rotor of a turbine, a wall of a combustion chamber, or other parts of a combustion chamber or turbine, such as a blade, a vane, a shroud, etc. Therefore, in yet a further aspect, the invention also provides a substrate comprising a high temperature ceramic coating, the high temperature ceramic coating comprising high temperature stable material with particulate material embedded therein, wherein the particulate material comprises particles, wherein the particles comprise molybdenum silicide (MoSi2), boron and aluminum, wherein the particles comprise molybdenum silicide (MoSi2) (which may have the tetragonal structure), wherein the particles have a coreshell sttucture, with the core comprising molybdenum silicide (MoSi2) and boron (especially a molybdenum boron compound), and the shell comprising aluminum.

Especially, wherein the particles have weight average particle sizes selected from the range of 10-40 μιη (see also above).

Further, especially the boron in the particles is available in an amount selected from the range of 0.5-3 wt% relative to the total weight of the particles (including the shell) (see also above). Further, especially aluminum is available in an amount selected from the range of 5-20 wt% relative to the total weight of the particles (including the shell) (see also above). The aluminum is available in the alumina coating and part of the aluminum may also be available in the core of the particle. Note that the weight of boron and/or aluminum are evaluated on an elementary basis. Further, as also indicated above, in specific embodiments at least 65 wt% of the particles consist of molybdenum silicide. The weight of M0S12 is evaluated on a molecular weight basis.

As indicated above, the high temperature stable material may especially comprise zirconia, even more especially stabilized zirconia, such as in specific embodiments yttria stabilized zirconia (in the art also indicated as yttrium stabilized zirconia).

In yet a further aspect, the invention also provides a device, comprising the substrate as defined herein, such as especially the substrate is obtainable with the method as defined herein. In embodiments, the device is a turbine, and wherein the substrate is part of a combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. 1 schematically depicts a crack-healing mechanism in a thermal barrier coating (TBC) with encapsulated Mo-Si based particles. The TBC system comprises a super alloy substrate with a bond coating (BC), which produces a thermally grown oxide (TGO) during service, and the modified yttria-stabilized zirconia (TBC). Upon oxidation of a cracked Mo-Si-based particle, silica (S1O2) fills the crack over a long distance; and

Fig. 2 schematically depicts embodiments of a plasma spray apparatus and the plasma spray process.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 schematically depicts a possible crack healing mechanism involving Mo-Si-based dispersed particles acting as the healing agent in the ceramic matrix of a TBC. As indicated above, boron alloyed MoSi2 was chosen as the healing particle. Addition of MoSi2 particles in an yttria stabilized zirconia (YSZ) structure will not generate extra stresses during thermal cycling because of their compatible CTEs and the fact that MoSi2 remains in its solid state at 1100 °C in the absence of an oxidative atmosphere. Upon exposure to a gaseous environment with sufficiently high oxygen potential, the MoSi2 particle decomposes under the formation of gaseous Mo-oxides and SiO2. Alloying the MoSi2 with B is expected to increase the fluidity of the SiO2 at the intended operating temperature in order to facilitate the filling of cracks. Finally, SiO2 is expected to react with the ZrO2 in the TBC to form a solid reaction product such as ZrSiO4.

Reference 200 indicates a substrate, which may consist of an element 201 such as a (nickel or cobalt based) super alloy, or an inner blade cooling system. Reference 202 indicates a bond coating (BC), which produces a thermally grown oxide (TGO) during service. Thereon, a TGO (thermally grown oxide) layer may be available, such as alpha alumina (α-alumina). Thereon, the actual coating 210, here a thermal barrier coating may be available. This figure shows an example of a substrate 200. However, other substrates may also be possible.

Fig. 1 schematically depicts an embodiment of a substrate 200 comprising a high temperature ceramic coating 210. The high temperature ceramic coating 210 comprises high temperature stable material 150 with particulate material 1 embedded therein. The particulate material 1 comprises particles 100, wherein the particles 100 comprise molybdenum silicide MoSi2 and boron and aluminum, wherein the particles 100 comprise molybdenum silicide MoSi2 having a hexagonal staicture. The particles 100 have a core-shell structure 140, with the core 141 comprising molybdenum silicide MoSi2 and boron, and the shell 142 comprising alumina. The high temperature stable material 150 may comprise ((yttrium) stabilized) zirconia. Reference 211 indicates the surface of the coated substrate 200. This surface 211 may be subjected to high temperatures, such as over 1000 °C.

The crack formation is explained above. Fig. 1 shows with reference C a crack, and with reference F the fdling of the crack with healing material, such as SiCb or ZrSiCfi when S1O2 reacts with zirconia.

Fig. 2 schematically depicts a plasma spray apparatus 1000, comprising a nozzle 1010 from which a plasma may escape during operation of the apparatus. The apparatus 1000 comprises a cathode 1030 and an anode 1020, here the latter being annularly configured. A plasma gas 1040, such as a mixture of argon and helium may be provided. A voltage difference over the cathode 1030 and anode 1020 may e.g. be in the order of about 100 V and a current of about 400 to 500 A.

Further, especially the apparatus 1000 comprises two injectors 1050, a first injector 1051 configured upstream of a second injector 1052, with both being configured of the substrate 200 during operation of the apparatus.

Hence, Fig. 2 also schematically depicts an embodiment of a method of providing a high temperature ceramic coating 210 on a substrate 200, the method comprising providing high temperature stable material 150 and the particulate material 1. The high temperature stable material 150 may especially comprises yttrium stabilized zirconia. Here, the method comprises depositing yttrium stabilized zirconia particles 150. Further, here the method comprising using a plasma spray process. Especially, the substrate 200 is here configured at a first position Pl. At an upstream position P2 at a first temperature, particulate high temperature stable material 150, especially yttrium stabilized zirconia particles, is provided. At a downstream position P3 at a second temperature the particulate material 1 is provided. The substrate 200 is configured at the first position Pl downstream of the upstream position P2 and the downstream position P3, wherein the substrate 200 is maintained at a third temperature. The apparatus in this way provides a spray stream of molten particles.

The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the propagation of a spray from a spray generating means (here the especially the plasma spray apparatus 1000), wherein relative to a first position within a beam of spray from the spray generating means, a second position in the beam of spray closer to the spray generating means is “upstream”, and a third position within the beam of spray further away from the spray generating means is “downstream”.

The distance between the nozzle 1010 and the substrate 200 may be selected from the range of about 100 - 200 mm. Further, the distance from the nozzle 1010 and the first injector 1051 at the upstream position P2 may be selected from the range of about 10 - 30 mm. The distance from the nozzle 1010 and the second injector downstream position P3 may be selected from the range of about 40- 100 mm.

Optionally, two different nozzles may be applied. Further, more than two injectors may be applied.

In an experiment, powders in desired ratios (Mo, Si, Al, B or compounds) were weighed, mixed, sintered (e.g. spark plasma sintering at 1500 °C for 1 hour with 35 MPa), crushed, milled, sieved (to remove particle larger than 50 pm), and wind sifted (to remove fines smaller than 10 pm). MoSi2 particles with 2 wt% B and 2 wt% Al, or 6 wt% Al or 12 wt% Al were made.

Amongst others, a particle size with dso of about 14-18 pm is obtained, which is - upon (multiple) wind sifting - increased to a dso of about 33 pm, with a FWHM of about 15 pm. Further, after multiple wind-sifting ,the Dw was about 16-17 pm and the Dy0 was about 58-59 pm. X-ray diffraction of MoSi2 and MoSi2 with B and Al showed that the MoSi2 structure was essentially available. Only a small fraction of Mo2B4 and/or Si was available. Further, according to X-ray diffraction it appeared that the 6% Al sample consists for about 20 wt% of the C l lb tetragonal MoSi2 phase and for about 80 wt% of the C40 hexagonal phase. It further appeared that the 12 wt% Al sample consists for about 3 wt% of the Cl lb tetragonal MoSi2 phase and for about 97 wt% of the C40 hexagonal phase.

After wind-sifting, the composition of the particles was evaluated, see the table below wherein the compositions in weight fractions

(wt%) are indicated:

It appears that with the method as described herein, especially including SPS (spark plasma sintering) all particles essentially have the same Al content and/or B content.

After annealing at low partial pressure of O2 of the particles it appeared

that the high A1 content sample showed the best shell formation. After high temperature exposure in laboratory air, the high A1 content sample also appeared to maintain best the core-shell structure. Further, based on thermos gravimetric experiments on the particles, all Al-containing samples appeared to be much more stable than the sample with only boron (MoSi2 with only boron, and no Al). Further, it appeared that the presence of boron promotes the formation of SiO2, which is used for the healing effect.

It was experimentally shown that an α-alumina shell was created. This has as advantage that a good shell is formed. Upon crack formation, the core may come available for healing.

With atmospheric pressure plasma spraying a thermal barrier coating with the 12 wt% containing particles was generated. Based on confocal microscopy images, the particles are well embedded in the yttria stabilized zirconia TBC. With SEM it was also shown that the particles have a healing effect.

The term “substantially” herein, such as in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of’. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an embodiment refer to "consisting of' but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The term “plurality” refers to two or more.

The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

Claims

1. Een deeltjesvormig materiaal (1) omvattende deeltjes (100), waarbij de deeltjes (100) molybdeen silicide (MoSij), boor en aluminium omvatten, waarbij de deeltjes (100) molybdeen silicide (MoSi,;) met een hexagonale structuur omvatten, waarbij boor in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 0,5-3 gew,% en waarbij aluminium in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 5-20 gew.% ten opzichte van het totale gewicht van de deeltjes (100), en waarbij de deeltjes (100) gewichtsgemiddelde deeltjesgroottes hebben gekozen uit het bereik van 5-50 p.m.A particulate material (1) comprising particles (100), wherein the particles (100) comprise molybdenum silicide (MoSi), boron and aluminum, wherein the particles (100) comprise molybdenum silicide (MoSi ,;) with a hexagonal structure, wherein boron in the particles (100) is available in an amount selected from the range of 0.5-3% by weight and wherein aluminum in the particles (100) is available in an amount selected from the range of 5-20% by weight. % relative to the total weight of the particles (100), and wherein the particles (100) have weight average particle sizes selected from the range of 5-50 µm

2. Het deeitjesvormig materiaal (1) volgens conclusie 1, waarbij de deeltjes (100) gewichtsgemiddelde deeltjesgroottes hebben gekozen uit het bereik van 20-30 pm, en waarbij aluminium in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 10-15 gew.%.The particulate material (1) according to claim 1, wherein the particles (100) have weight average particle sizes selected from the range of 20-30 µm, and wherein aluminum in the particles (100) is available in an amount selected from the range of 10-15% by weight.

3. Het deeitjesvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij ten minste 60 gew.% van het molybdeen silicide (MoSij) de hexagonale structuur heeft.The particulate material (1) according to any of the preceding claims, wherein at least 60% by weight of the molybdenum silicide (MoSij) has the hexagonal structure.

4. Het deeitjesvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij ten minste 95 gew.% van het molybdeen silicide (MoSi?) de hexagonale structuur heeft.The particulate material (1) according to any of the preceding claims, wherein at least 95% by weight of the molybdenum silicide (MoSi) has the hexagonal structure.

5. Het deeitjesvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij boor m de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 1-3 gew.% en waarbij aluminium in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 5-20 gew.% ten opzichte van het totale gewicht van de deeltjes (100).The particulate material (1) according to any of the preceding claims, wherein boron m the particles (100) is available in an amount selected from the range of 1-3 wt% and wherein aluminum is available in the particles (100) in an amount selected from the range of 5-20% by weight relative to the total weight of the particles (100).

6. Het deeltj esvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij molybdeen silicide (M0S12) in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit bet bereik van 87-94,5 gew.%.The particulate material (1) according to any of the preceding claims, wherein molybdenum silicide (MOS12) is available in the particles (100) in an amount selected from the range of 87-94.5% by weight.

7. Het deeitjesvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij molybdeen silicide (MoSii) in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van ten minste 90 gew.%.The particulate material (1) according to any of the preceding claims, wherein molybdenum silicide (MoSii) in the particles (100) is available in an amount selected from the range of at least 90% by weight.

8. Het deeltjesvormig materiaal (1) volgens één van de voorgaande conclusies, waarbij boor en aluminium in de deeltjes (100) homogeen verdeeld zijn.The particulate material (1) according to any of the preceding claims, wherein boron and aluminum are homogeneously distributed in the particles (100).

9. Een werkwijze voor het verschaffen van een deeltjesvormig materiaal (1), waarbij de werkwijze omvat: het combineren van 1) één of meer van Mo en een Mo-omvattende verbinding, 2) één of meer van Al en een Al-omvattende verbinding, 3) één of meer van B en een boor-omvattende verbinding, voor het verschaffen van een verbinding omvattende MoSii en 1) één of meer van boor en een boor-omvattende verbinding en 2) één of meer van Al en een Al-omvattende verbinding; optioneel het verdichten van de aldus verkregen verbinding; en het verwerken van de verbinding in een deeltjesvormig materiaal.A method for providing a particulate material (1), the method comprising: combining 1) one or more of Mo and an Mo-containing compound, 2) one or more of Al and an Al-comprising compound , 3) one or more of B and a boron-containing compound, to provide a compound comprising MoSii and 1) one or more of boron and a boron-containing compound and 2) one or more of Al and an Al-comprising link; optionally compacting the compound thus obtained; and processing the compound into a particulate material.

10. De werkwijze volgens conclusie 9, omvattende het combineren van een boor-verbinding, een aluminium-verbinding en een molybdeen-verbinding, en het opwarmen van de verbinding tot een temperatuur van ten minste 1400 °C in een inerte argon atmosfeer, en het verwerken van de verbinding in een deeltjesvormig materiaal.The method of claim 9, comprising combining a boron compound, an aluminum compound and a molybdenum compound, and heating the compound to a temperature of at least 1400 ° C in an inert argon atmosphere, and processing the compound in a particulate material.

11. Een werkwijze voor het verschaffen van een hoge-temperatuur keramische coating (210) op een substraat (200), de werkwijze omvattende het verschaffen van hoge-temperatuur stabiel materiaal (150) en een deeltjesvormig materiaal (1) volgens één van de voorgaande conclusies op het substraat (200), en het temperen van het aldus verkregen afgezette materiaal in de aanwezigheid van een oxiderend gas.A method of providing a high-temperature ceramic coating (210) on a substrate (200), the method comprising providing high-temperature stable material (150) and a particulate material (1) according to any of the preceding claims on the substrate (200), and annealing the deposited material thus obtained in the presence of an oxidizing gas.

12. De werkwijze volgens conclusie 11, waarbij het hoge-temperatuur stabiel materiaal (150) yttrium gestabiliseerd zirkonia omvat, en waarbij de werkwijze het afzetten van yttrium gestabiliseerd zirkonia deeltjes (150) omvat.The method of claim 11, wherein the high temperature stable material (150) comprises yttrium stabilized zirconia, and wherein the method comprises depositing yttrium stabilized zirconia particles (150).

13. De werkwijze volgens conclusies 11-12, waarbij de werkwijze het gebruik van een plasmaspuitproces omvat.The method of claims 11-12, wherein the method comprises the use of a plasma spray process.

14. De werkwijze volgens conclusie 13, waarbij het substraat is geconfigureerd op een eerste positie (PI), waarbij op een bovenstroomse positie (P2) bij een eerste temperatuur, deeltjesvormig hoge-temperatuur stabiel materiaal (150), in het bijzonder yttrium gestabiliseerd zirkonia deeltjes, wordt verschaft, en waarbij op een benedenstroomse positie (P3) bij een tweede temperatuur het deeltjesvormige materiaal (1) wordt verschaft, waarbij het substraat (200) is geconfigureerd op de eerste positie (PI) benedenstrooms van de bovenstroomse positie (P2) en de benedenstroomse positie (P3), waarbij het substraat (200) op een derde temperatuur wordt gehouden.The method of claim 13, wherein the substrate is configured at a first position (P1), wherein at an upstream position (P2) at a first temperature, particulate high-temperature stable material (150), in particular yttrium-stabilized zirconia particles, and providing the particulate material (1) at a downstream position (P3) at a second temperature, the substrate (200) being configured at the first position (P1) downstream of the upstream position (P2) and the downstream position (P3), wherein the substrate (200) is kept at a third temperature.

15. De werkwijze volgens conclusie 14, waarbij de eerste temperatuur wordt gekozen uit het bereik van 2800-3200 °C, waarbij de tweede temperatuur wordt gekozen uit het bereik van 2050-2200 °C, en waarbij de derde temperatuur wordt gekozen uit het bereik van 200-500 °C.The method of claim 14, wherein the first temperature is selected from the range of 2800-3200 ° C, the second temperature is selected from the range of 2050-2200 ° C, and wherein the third temperature is selected from the range from 200-500 ° C.

16. De werkwijze volgens één van de voorgaande conclusies 11-15, waarbij na het afzetten van ten minste een deel van het yttrium gestabiliseerd zirkonia en het deeltjesvormige materiaal (1), het aldus verkregen afgezette materiaal getemperd wordt naar een temperatuur van ten minste 1000 °C,The method according to any of the preceding claims 11-15, wherein after depositing at least a portion of the yttrium stabilized zirconia and the particulate material (1), the deposited material thus obtained is tempered to a temperature of at least 1000 ° C

17. De werkwijze volgens één van de voorgaande conclusies 11-16, waarbij na afzetting van ten minste een deel van het hoge-temperatuur stabiel materiaal (150) en het deeltjesvormige materiaal (1), het aldus verkregen afgezette materiaal wordt getemperd in de aanwezigheid van het oxiderende gas bij een zuurstof partieeldruk onder 1· 10'10 Pa.The method of any one of the preceding claims 11-16, wherein after depositing at least a portion of the high-temperature stable material (150) and the particulate material (1), the deposited material thus obtained is tempered in the presence of the oxidizing gas at an oxygen partial pressure below 1 · 10 · 10 Pa.

18. De werkwijze volgens één van de voorgaande conclusies 11-17, waarbij het aldus verkregen afgezette materiaal wordt getemperd in de aanwezigheid van het oxiderende gas bij een zuurstof partieeldruk onder 1 · 10‘14 Pa.The method according to any of the preceding claims 11-17, wherein the deposited material thus obtained is tempered in the presence of the oxidizing gas at an oxygen partial pressure below 1 · 10–14 Pa.

19. Gebruik van het deeltjesvormige materiaal (1) volgens één van de voorgaande conclusies 1-8, bij de productie van een keramisch materiaal.Use of the particulate material (1) according to one of the preceding claims 1-8, in the production of a ceramic material.

20. Een substraat (200) omvattende een hoge-temperatuur keramische coating (210), waarbij de hoge-temperatuur keramische coating (210) hoge-temperatuur stabiel materiaal (150) met daarin ingebed deeitjesvormig materiaal (1) omvat, waarbij het deeitj esvormig materiaal (!) deeltjes (100) omvat, waarbij de deeltjes (100) moiybdeen silicide (MoSii) en boor en aluminium omvatten, waarbij de deeltjes (100) moiybdeen silicide (MoSis) omvatten, waarbij boor in de deeltjes (100) beschikbaar is in een hoeveelheid gekozen uit het bereik van 0,5-3 gew.%, waarbij de deeltjes (100) een kern-schil structuur hebben, met de kern (141) omvattende moiybdeen si heide (MoSi?) en boor, en de schil (141) omvattende aluminiumoxide en waarbij aluminium beschikbaar is in een hoeveelheid gekozen uit het bereik van 5-20 gew.% ten opzichte van het totale gewicht van de deeltjes (100), en waarbij de deeltjes (100) gewichtsgemiddelde deeltjesgroottes hebben gekozen uit het bereik van 5-50 pm.A substrate (200) comprising a high-temperature ceramic coating (210), wherein the high-temperature ceramic coating (210) comprises high-temperature stable material (150) with embedded particle-shaped material (1) embedded therein, the particle-shaped material material (!) comprises particles (100), wherein the particles (100) comprise moiybdenum silicide (MoSii) and boron and aluminum, wherein the particles (100) comprise moiybdenum silicide (MoSis), where boron is available in the particles (100) in an amount selected from the range of 0.5-3% by weight, the particles (100) having a core-shell structure, with the core (141) comprising moibdenum silicon (MoSi) and boron, and the shell (141) comprising alumina and wherein aluminum is available in an amount selected from the range of 5-20 wt% relative to the total weight of the particles (100), and wherein the particles (100) have weight average particle sizes selected from the range of 5-50 pm.

21. Het substraat (200) volgens conclusie 20, waarbij het hoge-temperatuur stabiel materiaal (150) yttrium gestabiliseerd zirkonia omvat.The substrate (200) of claim 20, wherein the high temperature stable material (150) comprises yttrium stabilized zirconia.

22. Een inrichting, omvattende het substraat (200) volgens één van de voorgaande conclusies 20-21.A device comprising the substrate (200) according to any of the preceding claims 20-21.

23. De inrichting (300) volgens conclusie 22, waarbij het substraat (200) verkrijgbaar is met de werkwijze volgens één van de voorgaande conclusies 11-18.The device (300) of claim 22, wherein the substrate (200) is obtainable by the method of any one of the preceding claims 11-18.

24. De inrichting (300) volgens één van de voorgaande conclusies 22-23, waarbij de inrichting een turbine is, en waarbij het substraat (200) onderdeel is van een verbrandingskamer (310).The device (300) of any one of the preceding claims 22-23, wherein the device is a turbine, and wherein the substrate (200) is part of a combustion chamber (310).