Tungsten diamond composite and method for producing same

Abstract

The present invention relates to composite materials made from tungsten and diamond (tungsten diamond) and methods for producing same. The invention also relates to the use of such materials for manufacturing parts intended for high-temperature fields such as aviation, aerospace and nuclear energy. The invention further relates to parts comprising a material according to the invention that are intended for the fields of aviation, aerospace and nuclear energy.

Description

[0001] DESCRIPTION

[0002] TITLE: TUNGSTEN-DIAMOND COMPOSITE AND ITS PROCESS OF

[0003] MANUFACTURING

[0004] Technical field of the invention

[0005] The present invention relates to tungsten-diamond composite materials and their manufacturing processes.

[0006] The invention also relates to the use of such materials for the manufacture of parts intended for high heat fluxes in fields such as aviation, aerospace and nuclear energy.

[0007] Parts intended for the fields of aviation, aerospace and nuclear energy, comprising a material according to the invention, constitute another object of the invention.

[0008] These parts can, for example, be or form part of the internal lining of a rocket engine, an aircraft engine, or a nuclear fusion or fission reactor.

[0009] Technical background

[0010] Materials used in aerospace applications are subjected to extreme environmental conditions. They are exposed to extreme temperatures, high heat fluxes, and must be able to withstand and absorb high-intensity shocks and vibrations.

[0011] Tokamaks, like rocket engines, use carbon (particularly carbon fibers or graphite) or tungsten as materials under high heat flux. Carbon has the disadvantage of eroding rapidly, which is not the case with tungsten.

[0012] Indeed, tungsten is a refractory material with low reactivity and is widely used in high-temperature applications such as aviation, aerospace, and nuclear energy. However, tungsten degrades rapidly under thermal shock due to its modest thermal conductivity (<100 W / m²). -1 .K' 1 ).

[0013] C. Rustet et al. (Fusion Engineering and Design, vol. 86, no. 9, 2011, pages 1677-1680) investigate the characteristics and performance of tungsten (W) coatings deposited on carbon materials (carbon fiber composites - CFCs and fine-grained graphite - FGGs). To improve coating adhesion to the CFC and reduce overall material stress, this paper describes the introduction of an intermediate Mo layer (2-3 µm thick) between the CFC and the W coating. High heat flux (HHF) tests show that nanoscopic porous structures appear at the carbon-Mo and Mo-W interfaces and contribute to the degradation of the W coating.

[0014] E. Fortuna-Zalesna et al. (Nuclear Materials and Energy, vol. 9, 2016, pages 128-131) describe a graphite tile coated with a 12 µm layer of tungsten. An intermediate 2-3 µm thick layer of molybdenum (Mo) is deposited between the tungsten layer and the graphite substrate to improve the layer's adhesion. Walnut (W) carbides are observed at the Mo-W interface and are thought to contribute to the degradation of the Walnut coating by delamination.

[0015] Qin Shiying et al. (A Novel Tungsten-Coated Diamond Composite Design for Nuclear Fusion Applications, February 26, 2024, pages 1-14) describe the fabrication of diamond coated with a layer of approximately 1.8 µm of tungsten (W) with an intermediate layer of tungsten carbide approximately 80 nm thick. This paper is silent regarding the ability of their material to withstand extreme operating conditions such as high heat flux testing.

[0016] Therefore, there is a real need for a material that combines a low level of erosion with good thermal conductivity (>400 W / m²). -1 .K' 1 ) under high continuous power density (~0.1 - 100 MW.nr 2 ) and transient (>20 MW.m- 2 .s 0 5 ).

[0017] Summary of the invention

[0018] The present invention is specifically designed to meet these needs by providing a composite material comprising tungsten and diamond (tungsten-diamond), characterized in that it comprises a diamond substrate having a thickness of 0.1 to 1 mm, a density greater than 99% and which can be either of a purity greater than 99.95%, or doped with boron at an atomic percentage of 0.05 to 0.5%, said diamond substrate being coated - on one of its faces, with a layer of molybdenum having a density greater than 99% having a thickness of 1 to 100 pm (Mo-1 layer),

[0019] - possibly, on the other face located opposite the Mo-1 layer, a molybdenum layer with a density greater than 99% and a thickness of 0.5 to 5 pm (Mo-2 layer),

[0020] - a tungsten layer with a density greater than 99% and a thickness of 10 to 100 pm, on

[0021] • the uncoated face of the substrate, located opposite the Mo-1 layer, or

[0022] • the side of the substrate containing the Mo-2 layer, located opposite the Mo-1 layer.

[0023] The densities of molybdenum, tungsten, or diamond can be measured by scanning electron microscopy with image processing of a sliced ​​sample, or by weighing. For example, in the case of a sliced ​​sample, the percentage of porous areas is measured in the slice image, and the density is expressed as a percentage (100 minus porosity).

[0024] Porosity is a physical quantity defined as the ratio between the volume of voids and the total volume of a material (i.e. the sum of the volume of solid and the volume of pores), its value being between 0 and 1 (or, as a percentage, between 0 and 100%).

[0025] The materials according to the invention combine a low level of erosion thanks to the tungsten layer with good thermal conductivity (>400 W.rrr) 1 .K' 1 ) thanks to the diamond substrate under high continuous power density (~0.1 - 100 MW.m 2 ) and transient (>20 MW.m -2 .s 0 5 ).

[0026] The invention also relates to the manufacturing processes of these materials as detailed below.

[0027] The invention also relates to the use of such materials for the manufacture of parts intended for high heat fluxes in fields such as aviation, aerospace and nuclear energy.

[0028] Components intended for the aviation, aerospace, and nuclear energy sectors, comprising a material according to the invention, constitute another object of the invention. These components may, for example, be or form part of the internal cladding of a rocket engine, an aircraft engine, or a nuclear fusion or fission reactor.

[0029] Brief description of the figures

[0030] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for which reference should be made to the attached figure in which:

[0031] [Fig. 1] represents an embodiment in which the tungsten-diamond composite material according to the invention comprises an intermediate layer of molybdenum (Mo-2) deposited by physical vapor deposition (PVD).

[0032] [Fig. 2] represents an embodiment in which the tungsten-diamond composite material is made by physical vapor deposition (PVD) of tungsten directly onto diamond without an intermediate layer of molybdenum (Mo-2).

[0033] [Fig. 3] represents the diagram of the optical adjustment system allowing the incident power density to be varied.

[0034] [Fig. 4] represents W-diamond samples after exposure to repetitive fast transients of 1 ms at deposited power densities ranging from 1 to 3 GW.m -2 in zones 1 to 6 (identical from one sample to another).

[0035] [Fig. 5] represents examples of scanning electron microscopy and IB smear analysis of intact and damaged samples after testing.

[0036] [Fig. 6] represents an example of scanning electron microscopy and IB-F1 analysis of a sample after 20 cycles of 1 s at 100 MW.m -2

[0037] Detailed description of the invention

[0038] The present invention relates to a composite material comprising tungsten and diamond (tungsten-diamond), characterized in that it comprises a diamond substrate having a thickness of 0.1 to 1 mm, a density greater than 99% and which can be either of a purity greater than 99.95%, or doped with boron at an atomic percentage of 0.05 to 0.5%, said diamond substrate being coated - on one of its faces, with a layer of molybdenum having a density greater than 99% having a thickness of 1 to 100 pm (Mo-1 layer),

[0039] - possibly, on the other face located opposite the Mo-1 layer, a molybdenum layer with a density greater than 99% and a thickness of 0.5 to 5 pm (Mo-2 layer),

[0040] - a tungsten layer with a density greater than 99% and a thickness of 10 to 100 pm, on

[0041] • the uncoated face of the substrate, located opposite the Mo-1 layer, or

[0042] • the side of the substrate containing the Mo-2 layer, located opposite the Mo-1 layer.

[0043] It should be noted that for diamond, purity and density are important parameters. Boron doping makes diamond conductive, thus preventing electrical arcing problems when exposed to plasma.

[0044] The presence of the tungsten layer on the surface of the diamond substrate protects the diamond from erosion and the excellent thermal conductivity of the diamond allows good heat diffusion during thermal shocks.

[0045] Furthermore, the inventors observed that the presence of the intermediate Mo-2 layer between the tungsten and the diamond, and, where applicable, Mo-1 between a metallic bonding surface and the diamond, improves the mechanical and thermal bond between the diamond, the tungsten, and, where applicable, a metallic bonding surface. This effectively enhances the performance of the composite material under high continuous and / or transient power density in components intended for the aviation, aerospace, and nuclear energy sectors. Power density refers to the power passing through a surface during heat transfer; that is, the thermal energy transferred per unit of time and area. It is expressed in watts per square meter (Wm²). -2 ).

[0046] In the context of the invention, density refers to the percentage of the material's volume that is not empty. In practice, it is measured by scanning electron microscopy with image processing of a slice of a sample after cutting, or by weighing.

[0047] The diamond substrate, with a purity greater than 99.95% or doped with boron at an atomic percentage of 0.05 to 0.5%, can be monocrystalline or polycrystalline, has a density greater than 99%, and a thermal conductivity >1000 W / m². -1 .K -1 at 20°C. It can be produced using the chemical vapor deposition (CVD) technique, which allows for precise control of the impurity levels in the crystals by controlling the purity of the gas phase. This method is well known to those skilled in the art.

[0048] One can also use one of the CVD variants known to the person skilled in the art, such as plasma-assisted processes like MPCVD (or Microwave plasma-assisted); PECVD (or Plasma Enhanced CVD); RPECVD (or Remote plasma-enhanced); ALCVD (or Atomic layer CVD); HWCVD (or Hot wire CVD); or MOCVD (from the English Metalorganic chemical vapor deposition).

[0049] The diamond substrate can be a plate or a surface of any geometry.

[0050] Tungsten and molybdenum can be pure or in the form of alloys. Preferably, these metals are pure with a purity greater than 99.9% and a density greater than 99%.

[0051] Another object of the invention is a method for manufacturing a composite material comprising tungsten and diamond (tungsten-diamond) as described above, comprising the following steps:

[0052] A) We have a diamond substrate with a purity greater than 99.95% or doped with boron at an atomic percentage of 0.05 to 0.5%, which can be monocrystalline or polycrystalline, has a density greater than 99% and a thermal conductivity >1000 W / m². -1 .K -1 at 20°C obtained by chemical vapor deposition (CVD), with a thickness of 0.1 to 1 mm,

[0053] B) One face of this substrate is coated with a layer of molybdenum, having a thickness of 1 to 100 pm (Mo-1 layer), by physical vapor deposition (PVD); C) Alternatively to A) and B) the diamond substrate can also be grown by chemical vapor deposition (CVD) with a thickness of 1 to 100 pm of molybdenum (Mo-1 layer) which will have been obtained beforehand by physical vapor deposition (PVD) or by any other method.

[0054] D) Optionally, the other face of the diamond substrate obtained in B) or C), located opposite the Mo-1 layer, is coated with a molybdenum layer, with a thickness of 0.5 to 5 pm (Mo-2 layer), by physical vapor deposition (PVD),

[0055] E) we put on

[0056] • the uncoated face of the diamond substrate obtained in step B) or C), located opposite the Mo-1 layer, or

[0057] • the face of the diamond substrate containing the Mo-2 layer obtained in step D), located opposite the Mo-1 layer, of a tungsten layer with a thickness ranging from 10 to 100 pm, by physical vapor deposition (PVD).

[0058] In the materials of the invention, tungsten and molybdenum are deposited on the diamond substrate by the physical vapor deposition (PVD) method.

[0059] Physical vapor deposition can be carried out by all methods known to those skilled in the art, including

[0060] - vacuum evaporation,

[0061] - electron beam evaporation (or electron beam evaporation in English),

[0062] - sputtering, where metal particles are separated from their substrate by ion bombardment,

[0063] - pulsed laser ablation (or pulsed laser deposition or pulsed laser ablation in English) where atoms and ions are vaporized under the action of intense laser radiation,

[0064] - molecular jet epitaxy, and

[0065] - Arc vapor deposition (or arc PVD) involves vaporizing atoms and ions under the influence of a strong current, generated by an electrical discharge between two electrodes with a high potential difference. This discharge detaches metal particles and causes them to transition to a gaseous phase. Preferably, the tungsten and molybdenum layers are deposited using the physical vapor deposition method by sputtering. In this method, an argon plasma (typically) sprays a tungsten or molybdenum target, and the ejected atoms are deposited onto the surface to be coated.

[0066] The invention relates to the use of a material according to the invention, for the manufacture of parts intended for the fields of aviation, aerospace and nuclear energy.

[0067] Another object of the invention relates to parts intended for the fields of aviation, aerospace and nuclear energy, comprising a material according to the invention.

[0068] EXAMPLES:

[0069] Example 1: Preparation of a composite material comprising tunasten, molybdenum and diamond according to the invention

[0070] The various materials in solid or gaseous form used in the process of the invention and in the examples are, in general, commercial compounds or can be prepared by any process known to those skilled in the art. All metals used have a minimum purity of 99.9%.

[0071] The CVD filament furnace for manufacturing diamond substrates and the PVD cavity for all metal deposits are commercial technologies accessible to those skilled in the art.

[0072] 1.1. Implementation of the embodiment according to [Fig. 1]:

[0073] A polycrystalline diamond substrate, with a purity greater than 99.95%, a density greater than 99%, a thickness of 0.5 mm, and a rectangular surface area of ​​20 x 30 mm, is produced by the CVD method in a hot filament furnace. This substrate is grown at ~800–900°C on a 50 µm thick molybdenum film with a density greater than 99% in a low-pressure atmosphere (~0.1 bar) of hydrogen and methane heated by filaments at ~2000°C. This substrate is then coated by PVD (powder deposition of the target material with an argon plasma) with a 2 µm thick molybdenum layer with a density greater than 99% on the side opposite the 50 µm molybdenum coating. The 2 pm layer of Mo is then covered with a 10 pm layer of tungsten with a density greater than 99%, again using the PVD method.

[0074] 1.2. Implementation of the embodiment according to [Fig. 2]:

[0075] A polycrystalline diamond substrate, with a purity greater than 99.95%, a density greater than 99%, a thickness of 0.5 mm, and a rectangular surface area of ​​20 x 30 mm, is produced by the CVD method in a hot filament furnace. This substrate is grown at ~800–900°C on a 50 µm thick molybdenum film with a density greater than 99% in a low-pressure atmosphere (-0.1 bar) of hydrogen and methane heated by filaments at -2000°C. This substrate is then coated by PVD (powder deposition of the target material with an argon plasma) with a 10 µm thick tungsten layer with a density greater than 99% on the side opposite the 50 µm molybdenum coating.

[0076] Example 2: Extreme thermal shock tests of W-diamond samples with and without an intermediate Mo layer

[0077] Monocrystalline and polycrystalline diamond samples, 0.5 mm thick and with a square (10 x 10 mm) surface, coated with 12 µm of tungsten (W) or 10 µm of W with a 2 µm intermediate layer of molybdenum (Mo), were tested under thermal shock at the Laser Controlled Heating (CHAUCOLASE) facility at the Fresnel Institute of the University of Marseille [M. Minissale et al., Rev. Sci. Instrum. 91 (2020) 035102]. This involves a 1350 W infrared laser (1 µm) that can be focused to achieve maximum incident power densities of 14 GW. 2Power deposition takes place in a vacuum chamber where tungsten-diamond samples are held on an actively cooled copper support by an aluminum component. A sheet of Papyex (a commercially available, flexible, heat-conducting carbon fiber approximately 0.5–1 mm thick) is placed between the copper water circuit and the back of the sample to ensure good thermal contact.

[0078] The choice of incident power density is made using an adjustable converging lens, which allows the heat deposition area on the sample to be increased or decreased (see Fig. 3 below). These adjustments must take into account the power to be deposited on the sample and therefore its reflectivity at the considered wavelength. In our case, the W surfaces have a reflectivity of -60% at 1 pm [ED Palik, Handbook of Optical Constants of Solids, Academic Press, Orlando, FL, 1985].

[0079] Using this setup, tungsten-diamond samples were subjected to repetitive rapid thermal shocks of 1 ms at deposited power densities ranging from 1 to 3 GW.m -2 to simulate the effect of possible instabilities in a fusion reactor. Power densities were deposited in different areas (see Fig. 3 below) according to the following protocol:

[0080] • Zone 1: 100 cycles from 1 ms to 1 GW.m -2 at 50 Hz,

[0081] • Zone 2: 100 cycles from 1 ms to 1.5 GW.m -2 at 50 Hz,

[0082] • Zone 3: 100 cycles from 1 ms to 2 GW.m -2 at 50 Hz,

[0083] • Zone 4: 100 cycles from 1 ms to 2.5 GW.m -2 at 50 Hz,

[0084] • Zone 5: 100 cycles from 1 ms to 3 GW.m -2 at 50 Hz,

[0085] • Zone 6: 10,000 cycles of 1 ms at 20 Hz at power density - 15% lower (typically 1.7-2 GW.m 2) at the highest power density without observable damage after 100 cycles.

[0086] On the tungsten-diamond samples shown in [Fig. 4], the tested areas with traces of coating melting from W to 3 GW.m can be seen quite clearly. -2 and sometimes 2.5 GW.m -2 A scanning electron microscopy analysis of the exposed surfaces and their cross-sections using the Focused Ion Beam (FIB) method (well known to those skilled in the art) revealed that the tungsten-only coatings and the tungsten-with-molybdenum-intermediate coatings are intact both on the surface and throughout their thickness after 100 cycles from 1 ms to 2 GW.m -2 for all samples and up to 2.5 GW.m -2 In the case of tungsten and an intermediate molybdenum layer on single-crystal diamond, tests at 10,000 cycles demonstrate good coating resistance to successive thermal shocks from 1 ms to 1.7 GW.m -2for all samples with tungsten and molybdenum intermediate layer on single-crystal diamond up to 10,000 cycles from 1 ms to 2 GW.m -2 The following table is a summary of the thermal shock tests.

[0087] In light of these results, it can be seen that with a single-crystal substrate, the molybdenum interlayer between the tungsten and the diamond appears to provide an advantage in resistance to such thermal shocks. It is worth recalling that single-crystal CVD diamond is a material of interest for the applications envisaged by the patent due to its superior thermal conductivity properties (-2300-2400 W / m²). -1 .K -1 ) to those of polycrystalline diamond (- 1800-1900 Wm -1 .K -1). These excellent thermal properties also have the advantage of being isotropic and its tritium retention level (for fusion applications) is extremely low due to the absence of boundaries in the single crystal.

[0088] It should also be mentioned that similar samples have been subjected to up to 20 cycles of 1 second at 100 MW. 2 as shown in [Fig. 6], to simulate the ignition of a rocket engine as well as certain transient conditions that may exist in a fusion reactor. The same scanning electron microscopy and FIB analyses revealed no surface or deep damage to the tungsten and tungsten-molybdenum interlayer coatings on mono- and polycrystalline diamond substrates.

[0089] Discussion on the formation of tungsten carbide and the potential role of a molybdenum interlayer

[0090] Although the affinity of molybdenum for diamond and tungsten is known to those skilled in the art, it was not initially obvious that these properties would be preserved in an interlayer (rather than alone with tungsten or diamond) under such extreme conditions as those described above and which correspond to the applications targeted by the invention.

[0091] Indeed, thermal shock experiments on a similar tungsten coating (10-20 pm thick) and molybdenum coating (2-3 pm thick) carried out on carbon fiber composite (CFC) elements for applications similar to those described in C. Rustet et al. (Fusion Engineering and Design, vol. 86, no.9, 2011, pages 1677-1680) and in E. Fortuna-Zalesna et al. (Nuclear Materials and Energy, vol. 9, 2016, pages 128-131), show that nanoscopic porous structures appear at the carbon-molybdenum and molybdenum-tungsten interfaces and would participate in the degradation of the tungsten coating as described in the last sentence of the conclusion in C.Ruset et al. (Fusion Engineering and Design 88 (2013) 1690-1693).This study also mentions that despite the presence of a molybdenum interlayer between carbon and tungsten, tungsten carbides are observed at the molybdenum-tungsten interface in the damaged samples. This means that, contrary to what was previously thought, molybdenum is not, or ceases to be (at high temperatures), a diffusion barrier from carbon to tungsten, leading to the formation of carbides.

[0092] Tungsten carbide is known to be a brittle material and therefore a priori unlikely to survive the significant thermomechanical stresses that can be expected during a thermal shock, which is confirmed in H. Maier et al. (Journal of Nuclear Materials 415 (2011) S310-S312).

[0093] In this work, the intentional creation of a W carbide layer at the molybdenum-tungsten interface leads to delamination of the tungsten coating. Therefore, it is not clear that an intermediate tungsten carbide layer would have a beneficial effect on maintaining a tungsten coating on diamond during thermal shock. It should be noted that Qin Shiying et al. (A Novel Tungsten-Coated Diamond Composite Design for Nuclear Fusion Applications, February 26, 2024, pages 1-14) only covers the fabrication of a sample with a thin tungsten layer (1.8 µm), which is certainly insufficient for the applications targeted by the present invention, which require a significant lifespan under erosion. Furthermore, it is shown in C. Rustet et al. (Fusion Engineering and Design 88 (2013) 1 690- 1693) that the thinner the tungsten thickness, the more difficult its delamination.It is therefore possible that this parameter aided the adhesion of tungsten to diamond, which is not affected by thermal shocks as described in the present invention. Qin Shiying et al. provide no information on the ability of their material to withstand the operating conditions of the applications targeted by the present invention. In the case of the materials according to the invention involving diamond instead of carbon fiber composite (CFC), FIB analysis did not reveal any tungsten carbide between the tungsten and diamond or between the molybdenum and tungsten. None of the work cited in the prior art mentioned above guarantees this property under thermal shock.

Claims

DEMANDS 1. A composite material comprising tungsten and diamond (tungsten-diamond), characterized in that it comprises a diamond substrate having a thickness of 0.1 to 1 mm, a density greater than 99%, and a thermal conductivity >1000 W / m². -1 .K -1 at 20°C, and which is either of a purity greater than 99.95%, or doped with boron at an atomic percentage of 0.05 to 0.5%, said diamond substrate being coated - on one of its faces, a layer of molybdenum with a density greater than 99% and a thickness of 1 to 100 pm (Mo-1 layer), - possibly, on the other face located opposite the Mo- layer 1, of a molybdenum layer with a density greater than 99% and a thickness of 0.5 to 5 pm (Mo-2 layer), - a tungsten layer with a density greater than 99% and a thickness of 10 to 100 pm, on • the uncoated face of the substrate, located opposite the Mo-1 layer, or • the side of the substrate containing the Mo-2 layer, located opposite the Mo-1 layer; the density being measured by scanning electron microscopy with image processing of the slice of a sample after cutting or also by weighing.

2. A method for manufacturing a composite material comprising tungsten and diamond (tungsten-diamond) according to claim 1, characterized in that it comprises the following steps: A) We have a diamond substrate with a purity greater than 99.95% or doped with boron at an atomic percentage of 0.05 to 0.5%, which is monocrystalline or polycrystalline, has a density greater than 99%, and a thermal conductivity >1000 W / m². -1 .K -1 at 20°C obtained by chemical vapor deposition (CVD), with a thickness of 0.1 to 5 mm, B) One face of this substrate is coated with a layer of molybdenum, with a thickness of 1 to 100 pm (Mo-1 layer), by physical vapor deposition (PVD), C) Alternatively to A) and B), the diamond substrate can also be grown by chemical vapor deposition (CVD) over a thickness of 1 to 100 pm of molybdenum (Mo-1 layer) which will have been obtained beforehand by physical vapor deposition (PVD) or by any other method, D) Optionally, the other face of the substrate obtained in B) or C), located opposite the Mo-1 layer, is coated with a molybdenum layer, with a thickness of 0.5 to 5 pm (Mo-2 layer), by physical vapor deposition (PVD), E) we put on • the uncoated face of the substrate obtained in step B) or C), located opposite the Mo-1 layer, or • the face of the substrate containing the Mo-2 layer obtained in step D), located opposite the Mo-1 layer, of a tungsten layer with a thickness ranging from 10 to 100 pm, by physical vapor deposition (PVD).

3. Use of a material according to claim 1, for the manufacture of parts intended for the fields of aviation, aerospace and nuclear energy.

4. Parts intended for the fields of aviation, aerospace and nuclear energy, characterized in that they comprise a material according to claim 1.

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