Water droplet erosion resistant coating for turbine blades and other components

Abstract

A material for water droplet erosion and corrosion resistant coatings comprising metallic tungsten alloyed with substantially uniform nanostructured carbon that is substantially oxygen-free except at surface portions exposed to air or moisture. The disclosed coatings may be particularly resistant to water droplet erosion when applied to gas or steam turbine blades.

Description

[Technical Field]

[0001] This disclosure relates to coated turbine blades or vanes, more specifically to turbine blades or vanes for steam turbines and gas turbines used in power generation, and to blades and vanes used in cryogenic compressor sections of aircraft engines. Certain embodiments also relate to coated pump impellers, valves, and other components that may be subject to cavitation erosion in liquids.

[0002] This disclosure further relates to a coating applied to the airfoil portion of a turbine blade to enhance its surface resistance to erosion, including erosion by high-speed water droplet impact and erosion by ingested solid particles such as sand, dust, and scale. The proposed coating is intended to protect the blade against corrosion and / or the combined effect of erosion along with corrosion. The proposed coating may also provide resistance to cavitation to components such as pump impellers and valves that are exposed to liquid flow.

[0003] This disclosure also relates to a chemical vapor deposition (CVD) process developed to manufacture the above coating. [Background technology]

[0004] Turbine blades are essential components of steam and gas turbines, widely used in power generation, and also crucial components of aircraft turbine engines. They are highly engineered components, often constructed using advanced materials. To achieve optimal aerodynamic performance, turbines typically have an airfoil shape and an optimal surface finish. During turbine operation, blades often move at speeds close to or exceeding the speed of sound, exposing them to erosion from high-speed water droplet and solid particle impacts. As a result, the turbine blade surface becomes rough, leading to a significant increase in drag and a loss of turbine efficiency.

[0005] Some gas turbine operating systems use water introduced into the gas flow at the turbine inlet to increase mass flow rate and improve turbine efficiency. Water mist may be used to clean deposits accumulated on the blades. Water droplets from the mist strike the leading edges of the first four to five rows of turbine blades, causing water droplet erosion (WDE) mainly on the leading edges of the blades, which can roughen the blade surface and increase blade friction and drag.

[0006] In steam turbines, the rapid expansion of steam causes water to condense towards the last row of the turbine. These condensed water droplets accumulate on the stationary turbine vane surface, forming larger droplets that can impact the leading edge of the rotating blades, thus potentially causing WDE (Wall Deposition Emission). This is particularly problematic near the tip of the rotating blades where the impact velocity is highest. WDE is considered unavoidable under wet steam operating conditions for steam turbines.

[0007] The WDE mechanism is not fully understood and involves multiple factors, namely, high-speed droplet impact, high-speed water jets, shock waves in liquids and stress waves in metals, cavitation bubbles in liquids, and hydraulic penetration, all of which lead to deformation of the blade material. Depending on the turbine operating conditions, these mechanical factors may also be accelerated by chemical and corrosive effects. Due to the discrete nature of impact, the metal surface is exposed to fatigue conditions, resulting in the initiation, propagation, and crossing of fatigue cracks, which can lead to the gradual loss of blade material. The solid surface response to droplet impact has an impact nature and is determined by dynamic mechanical properties rather than static mechanical properties. Starting from an initial latent phase when the metal surface undergoes deformation, work hardening, introduction of defects such as dislocations, twinning, crack initiation, and surface roughening without material loss, the metal surface's response to WDE changes over time. This typically affects the top 30-50 μm layer of the metal. This is followed by an erosion acceleration phase in which material removal is accelerated by the propagation of cracks and intersections below the surface, resulting in the loss of material particles, lateral water jets with speeds many times greater than the droplet impact velocity, and tearing action that removes asperities and deformed material. A distinct feature of WDE is that the eroded metal surface becomes extremely rough. High-speed water droplets impacting pre-existing cracks or pits can enlarge the cracks or pits, potentially leading to metal surface tunneling and bulging through water jets and hydrostatic penetration. After a while, the erosion rate reaches its maximum, and the WDE rate begins to decrease in a deceleration / attenuation phase, which is likely due to the attenuation effect of water cushions held in deep pits or cavities formed on the metal surface, although erosion continues at a lower rate even in this phase. Some brittle materials or coatings do not exhibit this WDE deceleration / attenuation phase, but instead, through an increase in erosion rate, reach a so-called catastrophic phase in which the material or coating is completely destroyed.

[0008] Different materials are affected by WDE to different degrees and in different ways. For example, the surface of a ductile material may be plastically deformed by an impact that forms a depression, and the raised edges and asperities around it may be removed by the shearing action of a high-speed lateral water jet. On the other hand, harder and more brittle materials tend to form cracks and fatigue cracks after repeated impacts. Materials with heterogeneous structures, such as thermal spray coatings consisting of tungsten carbide particles in a cobalt metal matrix, tend to have damage initiated in weak spots or weaker components. Porosity, mechanically weak inclusions, and defects in the surface layer of a material can become stress concentrators where subsurface cracks can be initiated. Higher concentrations of porosity, inclusions, and defects in the surface layer of a material can accelerate the onset of the latency phase and material loss, making such materials less resistant to WDE. It is thought that WDE degradation of a material at different stages may include all or most of the mechanisms described above. Due to the complexity of the WDE process, there is no unified theory of WDE development, nor is there a general approach to predicting material resistance to WDE or developing materials that can protect against WDE. Despite extensive research in this field, it is considered impossible to develop a universal approach to protection against WDE. There are only a few empirical rules that work for some types of materials but not for others. There is no single material parameter that can reliably characterize the ability of a material to resist WDE.

[0009] One of the most frequently considered important factors is hardness. Material hardness is generally thought to have a strong influence on WDE erosion resistance: for similar materials, erosion resistance is expected to be proportional to the square or 2.5th power of the Vickers hardness (Heymann, F. J.; "Toward Quantitative Prediction of Liquid Impact Erosion"; STP 474; ASTM; 1970; pp.212-248).

[0010] The alloying elements and other metals in steel, as well as the microstructure of the alloy, are considered important factors influencing their resistance to WDE. Cobalt-chromium-tungsten alloys such as Stellite® are known to have high resistance to WDE, which is generally thought to be due to their microstructure.

[0011] Corrosion can affect the turbine blade surface, and when combined with WDE and / or solid particle erosion, corrosion and erosion may have some synergistic effect, as erosion can cause the loss of the passive surface oxide layer present on many alloys, thus accelerating corrosion. Corrosion can be a problem for turbines installed near coastal areas where salt particles and / or saltwater droplets are present in the air. Additives or impurities from feedwater can concentrate into so-called "premature condensates," leading to significant corrosive damage and stress corrosion cracking of turbine components. For example, the thermal decomposition of ethanolamine ETA, used as a pH modifier or chelating agent, can generate corrosive organic acids.

[0012] Coatings are widely used on turbine blades, vanes, and other components. There are several types of coatings, each addressing a specific problem: i) A heat-shielding coating applied to the hot zone blades to enable more efficient high-temperature operation of the turbine. ii) Abrasive coating applied to the blade end to cut the abrasive shroud to form an air / gas seal system, iii) Corrosion-resistant coating applied to prevent blade corrosion, and iv) Corrosion-resistant coating.

[0013] Coatings developed to address i) and ii) are often ineffective in addressing iii) and iv) because their properties differ.

[0014] This disclosure particularly concerns type iii) and iv) coatings designed to improve the resistance of turbine components to erosion (both droplet erosion and solid particle erosion) and also to corrosion.

[0015] US2012 / 0125980 (WO2011 / 009430) describes a method for coating turbine blades with Co-Cr alloy, where the hardfacing coating is manufactured separately and then bonded to the component surface in a high-temperature soldering process. Co-Cr alloys such as Stellite6 and Stellite21 in bulk material form exhibit excellent resistance to WDE. However, their use as protective hardfacings attached by soldering or brazing presents many difficulties. During turbine operation, soldered alloys can be corroded due to the possibility of bimetallic corrosion, or in some cases crevice corrosion. Residual stresses and other mechanical stresses in the brazed joint can further weaken the strength of the brazed joint during turbine operation. Depending on the turbine blade design, torsional deformation of the blade due to mechanical forces is permitted, which adds additional stress to the joint between the base steel and the Co-Cr hardfacing. Over time, these factors can cause the hardfacing layer to separate from the blade body. During turbine operation, blades often move at speeds close to, or sometimes exceeding, the speed of sound, and the shedding of hard, heavy, rigid sections can cause catastrophic damage to the turbine.

[0016] Laser cladding and thermal spraying are sometimes used to apply thinner layers of Co-Cr alloy. However, these methods can introduce tensile stress into the layer, which can lead to cracking over time. Surface cracks and microcracks can become stress concentration points, negatively impacting the fatigue characteristics of turbine blades, which are crucial for the durability of these high-speed, stress-sensitive components.

[0017] US2010 / 0266409 (WO2007 / 101465) discloses a thermal barrier coating for use on turbine blades. The hollow, internally cooled blades of a gas turbine are coated on the outside of the blade with an internal coating that includes an MCrAlY-based bonding layer, a zirconium oxide ceramic thermal barrier layer, and a Cr diffusion layer.

[0018] US2016 / 0312622 describes the fabrication of a two-layer coating having a bonding layer made of MCrAlX, where M is iron (Fe), cobalt (Co), or nickel (Ni), and X is the active element, which is at least one element selected from the group consisting of yttrium (Y) and / or silicon, scandium (Sc) and / or at least one rare earth element, or hafnium. The thickness of the bonding layer is 20 μm to 50 μm. The molten barrier coating is fabricated on the bonding layer by electron-photophysical vapor deposition (EB-PVD) and consists of, for example, ZrO2, Y2O3-ZrO2. In other words, materials destabilized, partially stabilized, or fully stabilized by yttrium oxide and / or calcium oxide and / or magnesium oxide may also be present on the MCrAlX. This two-layer coating can then be provided with connected cooling system flow ducts, for example, produced by selective laser melting.

[0019] RU2588973 discloses the production of a thermal barrier coating by plasma sputtering a yttrium-stabilized zirconium oxide coating onto a prepared surface of a component made from a nickel-based alloy. The coating may have a gradient transition layer provided by two magnetrons.

[0020] The above disclosure focuses on thermal insulation coatings. The heat insulation properties of the thermal insulation coating are determined by a ceramic layer with a low thermal conductivity, which represents an actual barrier to heat flow. The thermal insulation coating is used for turbine blades in the high-temperature part of a gas turbine. By using these coatings, the operating temperature of the turbine can be increased, and thus the efficiency is improved. The ceramic thermal insulation coating is an advanced material designed to have a specific combination of properties such as low thermal conductivity, high melting point, phase composition and chemical stability, a matched thermal expansion coefficient for all coating layers, high thermal fatigue and oxidation resistance. These materials are typically brittle and not mechanically strong, so they do not have erosion resistance. Furthermore, since the insulated blades typically operate in the high-temperature part of a gas turbine at 1000 °C to 1600 °C, there are no water droplets, so water droplet erosion is not a problem. Therefore, resistance to WDE is not required.

[0021] US2017 / 0009591 describes a compressor blade or vane made of a metal alloy having an aluminum diffusion zone with a thickness of 10 to 30 μm on the surface of a blade or vane substrate. The compressor blade or vane typically has a hard material coating including TiN, TiAlN, AlTiN, CrN as a single-layer or multi-layer ceramic produced by physical vapor deposition (PVD). The hard material coating provides erosion resistance, and the aluminum diffusion layer provides corrosion resistance. However, the hard PVD coating is typically only slightly thin, with a thickness of only 3 to 4 μm, and does not provide sufficient erosion protection.

[0022] US6800383 and US8043692 describe coatings developed as wear-resistant coatings for metal parts. The structure and mechanical properties of these coatings are not considered optimal for protecting turbine blades against WDE and combined erosion / corrosion attack. ]>

[0023] US6800383 describes coatings consisting mainly of single-phase tungsten carbides, mixtures thereof, and mixtures with carbon and metallic tungsten. For example: WC+WC, WC+WC, W2C, W2C+W2C, W2C+W3C, W2C+W 12 C, W2C+W3C+W 12 C, W3C+W 12 C, W3C+W 12 C, W 12 C, W 12 C, WC+W, WC+W, W2C+W, W 12 C+W, W3C+W, W3C+W. In all cases, US6800383 describes compositions having tungsten carbide as the main phase with tungsten being a mixed impurity, as proven by X-ray diffraction analysis. These tungsten carbide compositions have a high hardness up to 3500 kg / mm 2 2. The carbon content in these coating materials can be up to 15 wt% and the fluorine content can be up to 0.5 wt%. Similar to most other carbides, these materials are quite brittle and are subject to high mechanical stresses. Mixtures of different phases produced in this way tend to have very high residual stresses. The mechanically weak carbon and the brittle subcarbides W3C and W 12 C mixture can reduce the fracture toughness and impact resistance of the coating, and these properties are important for erosion resistance. These coatings can contain an excess amount of fluorine up to 0.5 wt%, which can be detrimental to the adhesion and protective properties of the coating, especially when the coated item is used in the presence of water or oxygen, as in the case of steam turbine and gas turbine blades.

[0024] US8043692 describes tungsten alloyed with 0.01 wt% carbon up to 0.97 wt% and 0.001 wt% fluorine up to 0.4 wt%. This material has a high hardness of up to 2000 Hv, and in some embodiments up to 2200 Hv, which is important for wear resistance, but surprisingly, this high hardness has been found to be detrimental to erosion resistance and especially WDE resistance. The process described in US8043692 does not control or prevent the presence of oxygen or water in the coating chamber, or oxygen adsorbed on the part being coated or present in the precursor gas. The fact that even trace amounts of oxygen and water in the CVD process chamber can affect the coating properties has only recently been discovered by the applicant. Industrial-grade hydrogen used as a reducing gas in known CVD processes contains water vapor, not trace amounts of oxygen. Industrial-grade hydrogen is usually produced by electrolysis, resulting in a considerable amount of water vapor and often trace amounts of oxygen. The applicant has placed 10m inside a vacuum chamber. 2Large CVD reactors, potentially having internal stainless steel surfaces of the above area, have been found to adsorb a significant amount of water vapor when the chamber is opened after CVD treatment. This is particularly relevant in water-cooled regions of the reactor chamber, such as the cooled vacuum seal region, where visible water condensation is a concern. Stainless steel surfaces are also known to adsorb oxygen. Surprisingly, the applicant has found that degassing the vacuum chamber before each CVD cycle and using higher-purity gases (particularly hydrogen reduction gases and alkane gases) results in a substantially oxygen-free coating with significantly improved mechanical properties. Surprisingly, even trace amounts of oxygen can form mechanically weak, non-volatile tungsten oxyfluoride inclusions, which can become stress concentration points and / or initiation points for subsurface microcrack initiation, and these have been found to be the main mechanisms of WDE. The material described in US8043692 may contain high amounts of carbon (up to 0.97 wt%), which can adversely affect fracture toughness and resistance to repeated impacts when exposed to solid particle or water droplet erosion. These materials may contain excess amounts of fluorine up to 0.4% by weight, which can adversely affect the adhesion and protective properties of the coating, particularly in the case of steam and gas turbine blades operating in the presence of water and oxygen over extended periods. The method described in US8043692 does not control residual stress and porosity in the resulting coating, which are important factors in the fatigue properties and resistance to erosion, especially to WDE, of the material.

[0025] EP2256228 discloses a two-layer coating for protecting a surface from erosion by particles such as sand and dust, or from repeated high-speed fluid impacts such as rain or other fluids. The first layer is described as being in the form of a metal matrix with ceramic reinforcement having a hardness of 10–20 GPa and a thickness of 75–500 microns. The first layer can be applied by HVOF, cold spray, or other processes suitable for applying cermets, and the layer composition is selected from the following groups: WC / Co, WC / CoCr, chromium carbide-nickel chromium, diamond-nickel. The second layer is typically a ceramic with a hardness of 19–40 GPa or more and a thickness of 1–25 microns, coated by PVD or CVD, and made of materials selected from the following groups: TiN, diamond, diamond-like carbon, CrN, cubic boron nitride, boron carbide, TiC, or a combination thereof. The surfaces to be coated may be components of aircraft propulsion systems such as helicopter rotor blades, propeller blades, or fan blades, turbine blades, impellers, marine propellers, or large piping systems.

[0026] The coating layers described in EP2256228 are not considered optimal for providing WDE resistance in steam turbines. In particular, the hard ceramic second layer is brittle, and brittle materials are known to fracture rapidly under repeated WDE impacts, typically leading to catastrophic failure. HVOF and other thermal spray coating methods used to produce the first layer typically have tensile residual stress and are also brittle, making them unsuitable for providing effective WDE protection. HVOF and other spray coating methods produce coatings with uneven thickness and very rough surfaces, requiring post-coating grinding or polishing to achieve the desired surface finish on turbine blades. This post-coating grinding operation is relatively easy on parts with simple geometric shapes, such as cylindrical or flat parts. However, post-coating grinding of highly engineered turbine blades with complex 3D shapes would be extremely difficult. The application of a harder second layer by vacuum PVD or CVD coating methods imposes stringent requirements on the cleanliness of the substrate. This can be problematic because the first layer of porous HVOF coating after grinding will be contaminated with cutting-coolant and oil, making the application of the second hard layer extremely difficult.

[0027] US4741975 discloses a multilayer coating for gas turbine engine blades that improves resistance to erosion by sand and dust particles without exhibiting a sharp decrease in fatigue life. The coating has a first ductile layer containing palladium, platinum, or nickel, a second layer of substantially pure tungsten, and a third erosion-resistant layer of tungsten-carbon alloy or a tungsten metal matrix having a dispersed mixture of tungsten-carbon phases. The relatively hard outer coating has a hardness of 1600 DPH to 2400 DPH, preferably 1900 DPH to 2000 DPH. The film contains 93.88–97.8% tungsten and 2.12–6.12% carbon. The Diamond Pyramid Hardness (DPH) unit used herein is equivalent to the more widely used Vickers Pyramid Number (HV). This hard outer coating can be deposited by either CVD or sputtering. When sputtering is used, the layer composition range will include compounds from WC to W3C, and especially W2C. When CVD is used, refer to US4427445 described below.

[0028] US4427445 discloses a CVD process using WF6, hydrogen, dimethyl ether (CH3OCH3), and nitrogen. The material produced under the specific conditions of this patent is a two-phase mixture, one phase being 20–90 wt% pure tungsten and the other phase being an A15 structure, where the A15 structure is either tungsten carbide or a mixture of tungsten carbide and tungsten oxide. This is confirmed by X-ray diffraction analysis. The deposited material in US4427445 is extremely hard (equivalent to 1820–2500 VHN-HV), highly stressed, and may require additional heat treatment at 600–700°C. Such heat treatment is unacceptable for steel, as it may cause distortion and loss of certain desirable mechanical properties.

[0029] US4427445 recommends using oxygen-containing precursors such as methanol, ethanol, dimethyl ether, aldehydes, and ketones, and using a mixture of organic precursors to adjust the hardness of the resulting material.

[0030] US4741975 also states that the CVD gas mixture contains organic compounds containing carbon, oxygen, and hydrogen (column 6, lines 23-27). The use of oxygen-containing precursors results in substantial inclusions of tungsten oxides and oxyfluorides in the deposited material.

[0031] US4741975 discloses a coating for protecting gas turbine engines from erosion by sand and dust particles, and does not address issues related to steam turbine or water droplet erosion. Erosion by solid particles occurs through a different mechanism than that related to WDE, which is primarily micro-cutting, and therefore resistance to solid particle erosion requires high surface hardness. The hard coatings in US4741975 contain brittle tungsten carbide macrophases WC, W2C, and W3C, and do not contain unstable amounts of tungsten oxide or oxyfluorides. When exposed to WDE, hard coatings with these properties would undergo brittle fracture and fatigue microcracks and would not provide adequate protection.

[0032] WO2010 / 044936 discloses gas turbine blades (referring specifically to helicopter engines) and distinguishes leading-edge impact damage and airfoil erosion caused by luminous particle ejection due to solid particles entrained in the air intake of the engine. The turbine blades are coated with a multilayer PVD nitride ceramic coating of one of three compositions: TiAlN, CrN, or TiSiCN. This is said to be more corrosion-resistant than tungsten carbide coatings deposited by HVOF technology. It should also be noted that PVD coatings are susceptible to cracking and delamination when impacted by round particles. The specific problem of water droplet erosion is not considered. The coatings described in this patent are brittle ceramic materials under high residual stress and are prone to cracking and shattering when subjected to repeated impacts, making them unsuitable for providing protection against WDE.

[0033] WO2011 / 025596 is built upon WO2010 / 044936 to disclose a multilayer PVD nitride ceramic coating for protecting gas turbine blades. Only a portion of the blade airfoil is coated; for example, in some embodiments only the concave surface, and in others both the concave and convex surfaces are coated. The disclosure further contrasts the columnar microstructure of the PVD coating with the non-columnar "splat" nature of the thermal spray coating. It states that the columnar microstructure is particularly effective for PVD coatings of various nitrides, highlighting its advantages. Similar to WO2010 / 044936, the coating is not expected to provide sufficient protection against WDE due to its brittle nature and the high residual stress of the ceramic PVD coating. In addition, some PVD coatings have significant porosity, which can provide pathways for corrosive media to attack the underlying substrate.

[0034] US6447932 discloses a coating system for gas turbine components comprising a superalloy substrate having a nitrided region, an aluminum-rich coating, and optionally a thermally insulating ceramic layer. This patent focuses on the high-temperature regions of gas turbine engines, and the described coatings are developed to withstand high temperatures and high thermal cycling stresses. These coatings are not expected to protect blades from WDE, solid particle erosion, or corrosion.

[0035] EP1939318 relates to the carburizing of nickel substrates (e.g., superalloys) in particular in relation to components of the high-temperature section of a gas turbine, in order to suppress secondary reactions with subsequently applied aluminum-rich coatings. The carburizing surface treatments and coatings described in this patent do not protect blades from WDE, solid particle erosion, or water corrosion.

[0036] EP1634976 discloses a coating technique for use on high-temperature, high-pressure turbine components. A mixture of MCrAlY powder and abrasive powder may be applied by cold gas dynamic spraying and then heat-treated. This coating is described for protecting components in the high-temperature region of a gas turbine and is not considered adequate protection against WDE or water corrosion.

[0037] WO2014 / 143244 (US2014 / 0272166) discloses coatings to be applied to pre-selected outer surfaces of airfoil blades, such as the leading edge surface, concave surface, convex surface, or combination thereof. A very wide range of coatings and surface treatments applied by high-speed oxygen fuel spray, high-speed air fuel spray, solution plasma spray, cold spray, chemical vapor deposition, electro-spark deposition, plasma-accelerated chemical vapor deposition, or air-plasma spray are disclosed. The coatings can be formed from TiAIN, AITiN, TiAIN / TiN multilayer, TiAIN / Cr multilayer, tungsten-tungsten carbide, tungsten carbide cobalt, cobalt-chromium-tungsten carbide, chromium carbide-nickel, chromium carbide-nickel-chromium, or diamond-like carbon materials. Furthermore, nitriding and carburizing of the blade material and bonding are disclosed.

[0038] This paper focuses on the protection of gas turbine blades against solid particle erosion, particularly regarding coatings to provide enhanced high-angle three-dimensional particle erosion protection to the leading edge of compressor blades, and potentially to provide low-angle three-dimensional particle erosion protection to the concave 16 and convex 18 sides of the blades. This paper does not consider WDEs and does not mention steam turbine components.

[0039] To resist erosion by solid particles, the coatings described in WO2014 / 143244 (US2014 / 0272166) must have a high hardness of the coating layer between about 1,200 HV and about 2,000 HV, preferably between about 1,400 HV and about 1,600 HV. This high hardness of the coating increases the risk of fracture under impact. Furthermore, the porosity of the coating, which affects their resistance to WDE and their effectiveness as a corrosion barrier, and the issue of residual stress in the coating, which affects their resistance to the initiation and propagation of microcracks, are not considered. There is no detailed analysis of the coating composition. [Overview of the project]

[0040] This disclosure includes the following [1] through

[51] : [1] A corrosion-resistant material coated on a substrate, comprising, except for surface portions exposed to air or moisture, a substantially homogeneous nanostructure of carbon alloyed with metallic tungsten, wherein the material has a columnar crystalline microstructure. [2] A water droplet erosion resistant coating material coated on a substrate, wherein, apart from the surface portion exposed to air or moisture, the material contains metallic tungsten alloyed with carbon in a substantially uniform nanostructure that is substantially free of oxygen, and the material has a columnar crystalline microstructure. [3] The material according to [1] or [2] above, wherein the metallic tungsten is alloyed with 0.0001 to 0.37 wt% of carbon based on the total weight of the material, and optionally, with 0.0001 to 0.21 wt% of carbon based on the total weight of the material. [4] A material according to any one of the above [1] to [3], consisting essentially of metallic tungsten alloyed with carbon, and optionally further alloyed with fluorine. [5] The material according to any one of the above [1] to [4], wherein the metallic tungsten is further alloyed with fluorine. [6] The material according to [5] above, wherein the metallic tungsten is alloyed with fluorine in an amount of 0.0004 to 0.31 wt% based on the total weight of the material, and optionally, alloyed with fluorine in an amount of 0.0014 to 0.19 wt% based on the total weight of the material. [7] The material is the material according to [5] or [6] above, wherein the material is substantially free of oxyfluoride. [8] The material according to any one of the above [1] to [7], wherein the material does not show a peak characteristic of inclusions having an A15 crystal structure when subjected to X-ray diffraction analysis. [9] The material according to any one of the above [1] to [8], wherein the material does not exhibit peaks characteristic of tungsten carbide having an A15 crystal structure when subjected to X-ray diffraction analysis.

[10] The material is substantially non-porous, as described in any one of the above [1] to [9].

[11] The material according to any one of the above [1] to [9], wherein the material has a porosity of less than 0.5% by volume, optionally less than 0.3% by volume, optionally less than 0.2% by volume, and optionally less than 0.15% by volume.

[12] A material according to any one of the above [1] to

[11] , having a tungsten composition of 97.60 to 99.99 wt%.

[13] A material according to any one of the above [1] to

[12] , having a hardness of 4.4 GPa to 19 GPa, and optionally 8 GPa to 16 GPa.

[14] at least 9 MPa.m 1 / 2 A material according to any one of the above [1] to

[13] , having fracture toughness.

[15] The material according to any one of the above [1] to

[14] , wherein the material is substantially free of porosity, voids and / or inclusions that act as stress concentration areas.

[16] A chemical vapor deposition material coated on a substrate according to any one of the above items [1] to

[15] .

[17] A material coated on the substrate described in

[16] , wherein the material has a residual compressive stress of 520 MPa to 5.3 GPa, and optionally 810 MPa to 2.63 GPa.

[18] A material coated on the substrate described in

[16] or

[17] above, wherein the material has a thickness of at least 15 μm, and optionally at least 50 μm.

[19] The material is a material coated on any one of the substrates described in

[16] to

[18] above, having a thickness of 200 μm or less, and optionally 100 μm or less.

[20] A material coated on any one of the substrates described in

[16] to

[19] above, having a surface roughness of less than 1 μm Ra, and optionally less than 0.2 μm Ra.

[21] A material coated on any one of the substrates described in

[16] to

[20] above, wherein the material deposited by chemical vapor deposition has a surface roughness Ra of 1 μm or less than the surface roughness of the substrate without requiring polishing after deposition.

[22] A material coated on a substrate according to any one of

[16] to

[21] , comprising at least a softer layer of the coating, which is essentially a fluorine-alloyed metallic tungsten, and a harder layer of the coating, which comprises the material of any one of [1] to

[15] above.

[23] A material coated on the substrate described in

[22] above, wherein the metallic tungsten of the soft layer is alloyed with 0.0004 to 0.31 wt% of fluorine based on the total weight of the soft layer, and optionally, with 0.0014 to 0.19 wt% of fluorine based on the total weight of the soft layer.

[24] A material coated on a substrate according to

[22] or

[23] , further comprising a transition layer between the soft layer and the hard layer.

[25] A material coated on the substrate described in

[24] above, wherein the concentration of carbon in the transition layer increases in the direction from a softer layer to a harder layer.

[26] The transition layer is a material coated on the substrate described in

[24] or

[25] , having a thickness of at least 0.01 μm, and optionally at least 0.1 μm.

[27] A material coated on any one of the above

[22] to

[26] , wherein the ratio of the thickness between the soft layer and the hard layer is 1:10 to 10:1.

[28] A material coated on any one of the substrates described in

[22] to

[27] above, wherein the total thickness of the soft layer, the hard layer, and optionally the transition layer is 1 to 50 μm.

[29] A material coated on any one of the substrates described in

[16] to

[28] above, comprising multiple pairs of softer and harder layers so as to form a multilayer structure of alternating layers.

[30] A material coated on the substrate described in

[29] above, comprising 2 to 100 softer and harder layers.

[31] A turbine or compressor blade or vane at least partially coated with any of the materials described in any one of the above paragraphs [1] to

[15] .

[32] The blade or vane is a blade or vane of a steam turbine or steam compressor as described in

[31] above.

[33] Pump impellers, propellers, valves, or other components that undergo cavitation in a liquid and are at least partially coated with any of the materials described in [1] to

[15] above.

[34] A method for providing a turbine or compressor blade or vane resistant to water droplet erosion, comprising the step of at least partially coating the blade or vane with any one of the materials in [1] to

[30] above by chemical vapor deposition.

[35] The method according to

[34] , wherein the blade or vane is a blade or vane of a steam turbine or steam compressor.

[36] A method for providing a pump impeller, propeller, valve, or other component having resistance to cavitation, comprising coating the component at least partially with a material described in any one of the above [1] to

[30] by chemical vapor deposition.

[37] A method for producing the material according to any one of the above [1] to

[15] , comprising generating the gas phase having an oxygen content of 10 ppm or less and a water content of 3 ppm or less by chemical vapor deposition from a gas phase comprising a mixture of WF6, hydrogen and at least one hydrocarbon, and optionally an inert gas.

[38] The method according to

[37] above, wherein the gas phase is not ionized.

[39] The gas phase is chemically active during the deposition process, as described in

[37] or

[38] above.

[40] The method according to any one of the above

[37] to

[39] , wherein a gas-phase mixture of WF6, hydrogen and at least one hydrocarbon and optionally an inert gas is prepared at a pressure of 0.1 to 5 kPa for at least 10 minutes at a temperature of 320 to 580°C.

[41] The method according to any one of the above

[37] to

[40] , wherein at least one hydrocarbon comprises or consists of a gaseous alkane.

[42] The method according to any one of the above

[37] to

[41] , wherein the at least one hydrocarbon is thermally activated by heating to a temperature of 500 to 850°C before being mixed with WF6 and hydrogen.

[43] The method according to any one of the above

[37] to

[42] , wherein the chemical vapor deposition is carried out in a reaction chamber.

[44] The method according to

[43] , wherein the reaction chamber is degassed by heating in a vacuum before the introduction of the gas phase.

[45] The method according to

[43] or

[44] , wherein the reaction chamber is filled with an inert gas, heated, and then exhausted before the introduction of the gas phase.

[46] The method according to any one of the above

[43] to

[45] , wherein the reaction chamber is optionally vacuum-tested via a helium leak detector each time it is closed after it has been opened.

[47] The method according to any one of the above

[43] to

[46] , wherein the material is cooled to 200°C or below before the reaction chamber is opened.

[48] ​​The material is cooled after deposition at an average rate of 0.12°C to 1.9°C per minute, according to the method of any one of

[37] to

[47] above.

[49] The method according to any one of the above

[37] to

[48] , wherein the material is deposited at a speed of 3.5 to 82 μm per hour, and optionally 4 to 18 μm per hour.

[50] A method for resisting water droplet erosion of blades or vanes of a turbine or compressor, comprising coating the blades or vanes with the material described in any one of the above paragraphs [1] to

[15] .

[51] A method for resisting cavitation erosion of a pump impeller, propeller, valve or other component, comprising coating the component with the material described in any one of the above paragraphs [1] to

[15] . In a first aspect, a corrosion-resistant material coated on a substrate is provided, the material comprising metallic tungsten alloyed with carbon in a substantially homogeneous nanostructure that is substantially oxygen-free, except for surface portions exposed to air or moisture, and the material having a columnar crystalline microstructure.

[0041] In a second aspect, a water droplet erosion resistant material is provided coated on a substrate, the material comprising metallic tungsten alloyed with carbon in a substantially homogeneous nanostructure that is substantially oxygen-free, except for surface portions exposed to air or moisture, and the material having a columnar crystalline microstructure.

[0042] Metal alloying is a complex physicochemical phenomenon of significant practical interest. For example, alloying iron with varying amounts of carbon under different conditions can dramatically alter its mechanical and physical properties, transforming it from soft iron to low-carbon steel, high-carbon steel, and pig iron. The properties of steel, first and foremost its hardness and ductility, depend significantly on its carbon content and the form in which carbon exists within the steel (e.g., as free cementite Fe3C, or alternatively, as an interstitial solid solution of carbon in iron).

[0043] Alloying should be distinguished from simple mechanical mixing of inclusions or several materials. For example, free carbon inclusions in iron can negatively affect its mechanical properties, while alloying can improve them.

[0044] In the context of this application, the term "carbon-alloyed tungsten" encompasses a matrix of metallic tungsten having interdispersed tungsten carbide nanoparticles. In other words, the material is primarily metallic tungsten. The tungsten carbide nanoparticles are small enough that they do not produce peaks characteristic of tungsten carbide under X-ray diffraction analysis.

[0045] Tungsten-carbon alloys are not the same as tungsten carbide compounds, nor are they simply mixtures of tungsten and carbon. Alloying should be distinguished from simple inclusions, etc. For example, free carbon inclusions in iron generally have a negative effect on its mechanical properties.

[0046] After extensive experimentation and analysis, the inventors of this application found that alloying tungsten with various predetermined amounts of carbon can significantly alter the properties of the material.

[0047] Too little carbon content has little to no effect on the physical properties of tungsten. On the other hand, too much carbon content can cause high stress and lead to cracking of the tungsten alloy layer. Under certain conditions, excess carbon can cause carbon or carbide precipitation at micrograin boundaries, negatively impacting both mechanical properties and corrosion resistance.

[0048] Furthermore, the substantially absence of oxygen or oxy compounds in the bulk material (neglecting any surface oxide layers resulting from exposure to air or moisture) helps improve the toughness of the material. In particular, inclusions of non-volatile and mechanically weak tungsten oxyfluoride compounds such as WOF4, WO2F2, WO2F4, and others can act as stress concentration points and initiation points for subsurface microcracks. Some tungsten oxyfluoride compounds react with oxygen and water, which can further affect the mechanical and corrosion-protective properties of the material. Surprisingly, substantially oxygen-free, alloyed tungsten has been found to enhance mechanical and fatigue properties and provide better protection against erosion, including WDE, and corrosion.

[0049] Embodiments of this disclosure have substantially uniform, microscale nanostructures, which help prevent the formation of stress concentration zones and thus reduce the risk of crack formation within the material or in coating layers made of the material. After extensive research and experimentation, these factors have been found to play a significant role in protecting turbine blades from WDE and against solid particle erosion and corrosion.

[0050] Through extensive experimental work by the applicant, it was determined that there are many factors to consider when attempting to protect turbine blades, vanes, and other parts from droplet erosion, solid particle erosion, and / or corrosion. An ideal coating for turbine blades, etc., should have one or more of the following properties and combinations of properties: i) Enhanced water droplet erosion resistance; ii) Enhanced resistance to solid particle erosion; iii) Corrosion protection properties and low porosity for insulating the substrate material from erosion by corrosive fluids; iv) Good uniformity of the deposited coating thickness so as to maintain the 3D shape of the airfoil blade without polishing after coating; v) Strong adhesive bonding of the coating to the metal blade; vi) Sufficient thickness, appropriate structure and mechanical properties to resist droplet erosion; vii) The coating should preferably be under compressive residual stress to prevent crack initiation and propagation and to enhance its fatigue resistance; viii) Avoid excessive compressive stress, as this can cause horizontal cracking and cohesive failure of the coating; ix) Hardness sufficient to resist mechanical wear, and enhanced toughness and ductility to prevent brittle fracture and microcracks in the coating under mechanical or thermal impact or multiple impact fatigue conditions; x) The coated surface in its "deposited" state should have low roughness and be suitable for polishing to the surface finish required for turbine blades, typically around 0.2 micron Ra (or less), if necessary (this is advantageous as the complex 3D airfoil shape of the turbine blade or vane complicates the post-coating finish).

[0051] The applicant has conducted extensive experiments to manufacture and analyze various coatings with different structural and mechanical properties, investigating the effects of these properties on the coatings' resistance to WDE, solid particle erosion, fatigue, and corrosion.

[0052] Through extensive experimentation, it was surprisingly discovered that optimal resistance to WDE could be achieved by using a coating of moderate hardness. This contradicts the generally accepted view that, for similar materials, erosion resistance is expected to be proportional to the square or 2.5th power of the Vickers hardness.

[0053] In regions where the tensile stress of a material exceeds the maximum tensile stress threshold, fracture may initiate and propagate. To address this problem, the applicant has developed a method for manufacturing coated materials under residual compressive stress. This can partially compensate for the propagating tensile stress waves caused by water droplet and solid particle collisions, and thus reduce the maximum tensile stress in the waves, which in turn can reduce the risk of fracture initiation and development. The applicant has further determined that very high residual compressive stress within the coating surface can be detrimental to WDE resistance because, due to the Poisson effect, it can generate tensile stress in a direction perpendicular to the surface. The Poisson effect is a phenomenon in which a material tends to expand in a direction perpendicular to the direction of compression. The tensile stress due to the Poisson effect can be added to stress waves in a metal generated by the collision of high-speed water droplets, and the expansion phase of the stress wave added to the Poisson effect tensile stress can exceed the yield strength or even the final strength of the coating material, resulting in deformation or fracture of the coating.

[0054] Through modeling and experimentation, the applicant determined that the optimal range of residual compressive stress within a coating used as protection against droplet erosion on turbine blades or vanes is between 520 MPa and 5.3 GPa, and optionally between 810 MPa and 2.63 GPa. Through extensive experimentation, the applicant found that one or more of the following process conditions can result in the optimal range of residual compressive stress: i) Maintain the coating process temperature within the range of 320°C to 580°C; ii) Maintain a coating adhesion rate in the range of 3.5 to 82 μm per hour, and optionally in the range of 4 to 18 μm per hour; iii) Maintain the average cooling rate after coating in the range of 0.12°C to 1.9°C per minute; iv) Polish the turbine components and optionally perform other finishing work after coating to achieve a surface roughness of 0.2 microns Ra or less.

[0055] The damaging effect of stress waves induced by WDE impact can be increased by the presence of porosity, structural defects, and mechanically weak inclusions in the coating, which can interact with the stress waves to become stress concentration points and sites for microcrack initiation. Analysis revealed that tungsten oxides and tungsten oxyfluorides, in particular, can form defects in the coating structure that can become mechanically weak inclusions and microcrack initiation sites. Furthermore, it was found that these undesirable inclusions are formed by the reaction of a precursor gas with trace amounts of oxygen and water, and that they are formed under certain temperature and pressure conditions that produce non-volatile, mechanically weak tungsten oxides and oxyfluorides when the process involves an oxygen-containing precursor gas such as methanol, ethanol, dimethyl ether, or other gases containing trace amounts of oxygen or water.

[0056] Metallic tungsten can be alloyed with carbon in amounts of 0.0001–0.37 wt% based on the total weight of the material; optionally, with carbon in amounts of 0.0001–0.21 wt% based on the total weight of the material. Extensive experiments have shown that alloying with carbon present at higher concentrations under certain conditions can lead to the precipitation of either tungsten carbide or free carbon at the grain boundaries. When present at sufficient density, such precipitates can reduce the fracture toughness of the material, as well as its ultimate strength, creep resistance, and other mechanical properties. Furthermore, it has been found that alloying carbon amounts exceeding the above limits lead to increased residual stress in the material, making it susceptible to cohesive fracture under WDE conditions.

[0057] The material essentially consists of metallic tungsten alloyed with carbon, and may optionally be further alloyed with fluorine. That is, the bulk material (excluding any surface oxide layers that may exist due to exposure to air and / or moisture) may contain components other than tungsten alloyed with carbon, except for trace amounts of impurities, and may optionally be alloyed with fluorine.

[0058] Metallic tungsten alloyed with carbon may be alloyed with fluorine in amounts of 0.0004–0.31 wt% based on the total weight of the material; optionally, with fluorine in amounts of 0.0014–0.19 wt% based on the total weight of the material. Extensive experiments have shown that alloying with higher concentrations of fluorine can negatively affect the adhesion and protective properties of the coating, particularly for steam and gas turbine blades operating in the presence of water and oxygen for extended periods.

[0059] The above materials may be substantially free of oxyfluorides.

[0060] The above material may have the characteristic of not showing peaks typical of inclusions with an A15 crystal structure, such as tungsten carbide, when subjected to X-ray diffraction analysis.

[0061] There are unique and unexpected technical advantages that can be obtained from a metallic tungsten matrix in which tungsten carbide nanoparticles, small enough to be invisible under X-ray diffraction analysis, are dispersed.

[0062] A unique aspect of nanotechnology is the significant increase in the surface area-to-volume ratio present in many nanoscale materials, opening up new possibilities in surface-based sciences such as catalysis. As the size of a system decreases, numerous physical phenomena become more pronounced. These include not only statistical mechanical effects but also quantum mechanical effects, such as the "quantum size effect," where a significant decrease in particle size alters the electronic properties of a solid. This effect is not observed from macroscopic to microscopic dimensions, but becomes dominant when reaching the nanometer scale. In addition, numerous physical properties change compared to macroscopic systems. One example is the increase in surface area relative to volume of a material.

[0063] According to Scherrer's formula, the width of diffraction lines in an X-ray diffraction pattern increases with decreasing size of solid microcrystals. Typically, microcrystals smaller than about 10 nm in size dispersed in the matrix material do not produce clearly defined X-ray diffraction spectral lines. The fact that tungsten carbide particles forming the tungsten alloyed with the carbon material in embodiments of this disclosure are undetectable by X-ray diffraction as shown in Figure 1 (although in some cases they may be visible by high-resolution electron microscopy) confirms that the tungsten carbide particle precipitates actually have nanometer-scale sizes. The X-ray diffraction spectra of CVD partial tungsten carbide coatings in specific embodiments of this disclosure show all typical metallic tungsten lines, but various tungsten carbides WC, WC 1-x The lines characteristic of W2C and W3C are absent in the sample spectra. The resulting remarkable quantum mechanical effects include a combination of hardness, toughness, and impact resistance (low brittleness) of the material. While most hard materials are brittle, the materials of the embodiments of this disclosure combine both hardness and toughness in a remarkable and remarkably practically significant manner.

[0064] In some embodiments, the material is a single crystallographic phase of metallic tungsten having dispersed tungsten carbide nanoparticles, or comprises the same.

[0065] The tungsten carbide nanoparticles may have an average particle size of 100 nm or less; optionally 50 nm or less; or optionally 10 nm or less.

[0066] In contrast to the materials of US4427445 and US4741975, the materials of the embodiments of this disclosure are manufactured using different precursor gases, more specifically oxygen-free precursors, and have different compositions (significantly lower carbon content of 0.0001–0.37 wt% compared to 2.12–6.12% carbon in US4427445; substantially oxygen-free compared to containing A15 tungsten oxide and oxyfluoride), different tungsten carbide phases, different structures (nanostructures as opposed to micro / macrostructures), lower residual stress, and different mechanical properties (particularly hardness and toughness / brittleness).

[0067] The nanostructures of embodiments of this disclosure can be observed in their X-ray diffraction spectra, as shown in Figure 1, to contain only lines or peaks characteristic of tungsten. The nanostructured materials of this disclosure have improved toughness combined with better ductility, sufficient hardness, and significantly better resistance to both WDE and solid particle erosion. The material is alloyed with carbon to achieve enhanced hardness and does not require additional heat treatment. Inclusions of tungsten carbide in the form of micro or macroparticles containing carbides with an A15 structure are undesirable because these carbides are highly stressed and can act as initiation points for microcracks.

[0068] The material may be substantially non-porous. In some embodiments, the material has a porosity of less than 0.5% volume, optionally less than 0.3% volume, optionally less than 0.2% volume, and optionally less than 0.15% volume.

[0069] Pores in a coating can act as stress concentration points and initiation points for microcracks. High-speed droplet impact on the surface and near-surface porosity, through water pressure penetration and lateral water jets, can deform and expand voids, leading to metal tunnels and bulges. These processes are considered to contribute significantly to droplet erosion, and therefore, reducing or minimizing porosity is desirable.

[0070] The material composition can be 97.60–99.99 wt% tungsten.

[0071] The material can have a hardness of 4.4 GPa to 19 GPa, and optionally 8 GPa to 16 GPa. It is known that materials that are too hard may undergo brittle fracture mode or cracking when subjected to high-cycle, high-speed water droplet impact.

[0072] The material must have a minimum pressure of 9 MPa.m 1 / 2 It may possess fracture toughness. This helps provide better resistance to high-cycle, high-speed water droplet and solid particle impacts.

[0073] The material has a columnar or substantially columnar crystalline microstructure. This distinguishes it from materials formed by thermal spraying processes, which tend to have a laminar or "splat" microstructure.

[0074] The material is preferably substantially free of porosity, voids, and / or inclusions that act as stress concentration points.

[0075] In a third aspect, a chemical vapor deposition material coated on a substrate according to the first or second aspect is provided.

[0076] The coating material may have residual compressive stress on a substrate of 520 MPa to 5.3 GPa, and optionally 810 MPa to 2.63 GPa. Compressive residual stress can help improve fatigue resistance to high-cycle impacts of water droplets and prevent cracking of the coating. It should be noted that coatings applied by a thermal spraying process tend to have residual tensile stress rather than compressive stress.

[0077] The coating may have a thickness of at least 15 μm, and optionally at least 50 μm. The coating may have a thickness of 200 μm or less, and optionally 100 μm or less.

[0078] In the case of a coating on a substrate, stress waves arising from impacts on the coating surface will be reflected at least partially from the coating / substrate boundary. Care must be taken to ensure that constructive interference between direct and reflected stress waves does not exceed the strength limit of the coating, which can cause damage. Thicker coatings can dissipate stress waves better than thinner coatings. One factor is that the energy density of spherical stress waves decreases with the square of the distance, and therefore the energy density of stress waves reaching the coating / substrate boundary decreases with the square of the coating thickness. However, if the coating is too thick, it can distort the carefully engineered shape and profile of the turbine blade. It should also be remembered that adding a coating to a turbine blade increases its mass. It would be undesirable to apply a coating to a thickness that would mean the original blade design needs to be modified and retested.

[0079] The coating may have a surface roughness of less than 1 μm Ra. In some embodiments, a coating formed on a smooth substrate surface has a surface roughness of less than 1 μm Ra in its "as-deposited" state (without requiring subsequent polishing). However, it will be understood that a conformal coating formed on a substrate surface that already has some surface roughness will typically have surface roughness due to the surface roughness of the underlying surface. Therefore, in some embodiments, the coating is applied so that its surface roughness does not exceed 1 μm Ra compared to the surface roughness of the base substrate surface.

[0080] In some embodiments, when the coating is subjected to abrasion / sliding or rotational contact with a bearing or seal, the coating surface finish is polished and improved over time. This feature is often not present in many other coating materials, such as HVOF thermal spray coatings consisting of hard WC grains in a soft metal matrix of Co, CoCr, or Ni: the soft metal matrix is ​​selectively worn or corroded, leaving behind hard, sharp WC grains protruding from it, increasing its surface roughness and making the HVOF surface similar to sandpaper, which is highly abrasive for seals and other opposing materials.

[0081] The abrasiveness of the coatings of the embodiments of this disclosure can be explained by the homogeneous structure and mechanical properties of the coating, the absence of precipitates at grain boundaries, and the very small scale / fine size of the tungsten carbide nanoparticles that are generated as so-called coherent precipitates, typically having a crystal lattice of precipitates aligned with the matrix lattice. As a result, the coating wears uniformly without leaving harder "islands" or asperities protruding from the surface, which can cause undesirable wear on opposing surfaces and / or increase air resistance for moving turbine blades. Low roughness and the absence of asperities are also considered important factors in conferring resistance to WDE. This is because high-speed lateral water jets can be a prominent mechanism of WDE, and such jets can apply tearing action and high shear stress to asperities, resulting in material loss.

[0082] By providing a substantially uniform coating with a rough / smooth surface, the need for grinding, lapping, honing, polishing, and other finishing work after coating is reduced, and it becomes possible to coat parts with complex shapes that would be extremely difficult or impossible to polish if the coating were rough.

[0083] The ability of the specific coatings of this disclosure to maintain a good finish, or even become smoother and more polished during use, means that the coating remains non-abrasive to seals, bearings, and counter bodies with which it is in sliding or rotational contact. This can mean reduced seal wear and reduced leakage in hydraulic actuators, resulting in less maintenance required and a longer service life.

[0084] Therefore, in addition to the coated turbine blades or vanes of the present disclosure, the coatings of the present disclosure can be found useful as coatings on rotating and / or reciprocating shafts and plungers, such as hydraulic pistons and cylinders, gearbox shafts, pump shafts, and other components that move relative to seals or bearings and are applied to areas that come into contact with movable seals or bearings, where the coating is polished after application.

[0085] The mechanical processes involved in cavitation erosion are not different from those involved in droplet erosion, and it is generally known that materials that exhibit good resistance to WDE (water-drip erosion) can be expected to exhibit good resistance to cavitation. Therefore, in addition to coated turbine blades or vanes of the present disclosure, the coatings of the present disclosure can be found useful as coatings on components of pumps, valves, and other devices exposed to fluid cavitation, thereby extending their lifespan and improving their performance.

[0086] The coating may include at least a softer layer of the coating that is closer to a substrate consisting of metallic tungsten, which is essentially alloyed with fluorine and optionally alloyed with it, and a harder layer of the coating that includes the material of the first embodiment.

[0087] The metallic tungsten in the soft layer may be alloyed with fluorine in an amount of 0.0004 to 0.31 wt% based on the total weight of the soft layer; optionally, it may be alloyed with fluorine in an amount of 0.0014 to 0.19% based on the total weight of the soft layer.

[0088] The coating may further include a transition layer between the soft layer and the hard layer. The carbon concentration in the transition layer may increase from the softer layer to the harder layer. The transition layer may have a thickness of at least 0.01 μm, and optionally at least 0.1 μm. The thickness ratio between the soft layer and the hard layer may be 1:10 to 10:1. The total thickness of the softer layer, the harder layer, and optionally the transition layer may be 1 to 50 μm, optionally 1 to 100 μm, or optionally 1 to 200 μm.

[0089] In some embodiments, multiple pairs of softer and harder layers may be formed to create a multilayer structure of alternating layers. In some embodiments, there may be 2 to 100 pairs of softer and harder layers. In some embodiments, the multilayer structure may include softer layers, transition layers, harder layers, transition layers, softer layers, transition layers, harder layers, and so on. In each of the transition layers, the concentration of carbon, for example, in the form of tungsten carbide nanoparticles, may increase in the direction from softer layers to harder layers across the thickness of the transition layer. The formation of such transition layers can be facilitated by controlling the flow of precursor gas and pressure during the CVD process, which is beneficial in that it can reduce interlayer stress.

[0090] Introducing a transition layer with a carbon concentration gradient between a softer layer and a harder layer helps reduce residual stress, avoid abrupt thermal and mechanical mismatches at the layer boundary, and hinder crack propagation.

[0091] The substrate may be a blade or vane of a turbine or compressor. Embodiments of this disclosure are particularly suited to applications where the blade or vane is a blade or vane of a steam turbine or steam compressor, because these blades or vanes are subjected to high-cycle, high-speed droplet impact and must resist WDE during operation.

[0092] In a fourth aspect, a turbine or compressor blade or vane is provided which is at least partially coated with the material of the first or second aspect.

[0093] In a fifth aspect, a pump impeller, propeller, valve or other component that is subjected to cavitation in a liquid is provided, which is at least partially coated with the material of the first or second aspect.

[0094] In a sixth aspect, a method is provided for providing a turbine or compressor blade or vane resistant to water droplet erosion, the method comprising the step of at least partially coating the blade or vane with a material of the first, second, or third aspect by chemical vapor deposition.

[0095] In a seventh aspect, a method is provided for providing a pump impeller, propeller, valve, or other component having resistance to cavitation, the method comprising, at least in part, coating the component with a material of the first, second, or third aspect.

[0096] In an eighth aspect, a method is provided for producing a material of the first or second aspect by chemical vapor deposition from a gas phase containing WF6, hydrogen, and a mixture of at least one hydrocarbon, and optionally an inert gas, in a gas phase with an oxygen content of 10 ppm or less and a water content of 3 ppm or less. Advantageously, the surface of the portion coated with the material of the first aspect is treated or configured to be substantially free of oxygen and water vapor, as is the interior of any reaction chamber employed in the method.

[0097] The applicant determined that the presence of tungsten oxides and oxyfluorides could negatively affect the mechanical properties of materials and coatings produced by CVD in the CVD reactor chamber. Therefore, embodiments of the present disclosure use alkanes (e.g., methane, ethane, propane) as carbon-containing precursors—these do not contain oxygen. Steps to prevent or reduce the formation of tungsten oxides and oxyfluorides may also be taken. These steps may include one or more of the following: i) Vacuum-seal the CVD reaction chamber and its gas system to prevent air leakage into the chamber or gas system; this can be achieved by using vacuum-sealed system designs and components, and by testing the vacuum sealing of the chamber flanges and seals and other components with a helium leak detector after each reactor opening. The helium leak limit is, for example, 1 × 10⁻⁶ -9 The limit can be set to mbar.l / s. If this limit is exceeded, open the reactor, clean the flange and seals, close the reactor, and perform another helium leak test to confirm that the limit is met. ii) To remove adsorbed water and oxygen, the CVD reaction chamber and loaded components are purged and degassed by optionally performing a series of cycles in which the chamber is heated and, optionally, filled with an inert gas to a specified partial pressure before the chamber is evacuated to a specified vacuum pressure to remove any traces of adsorbed oxygen and / or water from the chamber surface and loaded components. The applicant has placed 10 m inside the vacuum chamber. 2We have found that large CVD reactors, which may have internal stainless steel surfaces of the above area, adsorb a considerable amount of water vapor when the chamber is opened and parts are loaded before CVD processing. Water-cooled areas of the reactor chamber, such as the cooled vacuum seal area, were found to be particularly exposed to such water condensation. It is also known that stainless steel surfaces can adsorb oxygen. Surprisingly, we have found that degassing the vacuum chamber before each CVD cycle and using higher purity gases (particularly hydrogen reduction gases and alkane gases) results in a substantially oxygen-free coating with significantly improved mechanical properties. iii) Using substantially oxygen-free and moisture-free precursor and process gases, a reactive mixed gas with an oxygen content of 10 ppm or less and a moisture content of 3 ppm or less is obtained. Since industrial-grade hydrogen is usually produced by electrolysis and as a result contains a considerable amount of water vapor and often trace amounts of oxygen, the purity of the precursor and process gases has been found to be particularly important when using hydrogen gas in coating processes. iv) Backfilling the CVD reaction chamber with a substantially oxygen-free and anhydrous inert gas after the completion of the coating process, while cooling the coated material. v) Cool the coated parts to a temperature of 200°C or lower before opening the reactor chamber to reduce subsurface oxidation of the deposited coating.

[0098] As a result, it is possible to avoid inclusions of tungsten oxide and oxyfluoride, and to deposit materials or coatings that are virtually oxygen-free within the bulk.

[0099] The gas phase does not have to be ionized. Alternatively, or in addition, the gas phase may be chemically active during the deposition process.

[0100] This method can be carried out using a gas-phase mixture of WF6, hydrogen, and at least one hydrocarbon and optionally an inert gas such as argon, at a pressure of 0.1 to 5 kPa for at least 10 minutes at a temperature of 320 to 580°C.

[0101] At least one hydrocarbon may contain, or may contain, a gaseous alkane.

[0102] At least one hydrocarbon may be thermally activated by heating to a temperature of 500–850°C before being mixed with WF6 and hydrogen.

[0103] In a ninth aspect, a method is provided for resisting water droplet erosion of a turbine or compressor blade or vane, which includes coating the blade or vane with the material of the first or second aspect.

[0104] In a tenth aspect, a method is provided for resisting cavitation erosion of a pump impeller, propeller, valve or other component, which includes coating the component with a material of the first or second aspect. Embodiments of the present invention will be further described below with reference to the attached drawings: [Brief explanation of the drawing]

[0105] [Figure 1] Figure 1 shows the X-ray diffraction spectrum of a material according to one embodiment of the disclosure. [Figure 2] Figure 2 is a plot of the number of droplet collisions against mass loss for various coated samples determined by the test apparatus. [Figure 3] Figure 3 is a plan view of an uncoated stainless steel sample after a water droplet erosion test involving approximately 10 million water droplet impacts. [Figure 4] Figure 4 is a perspective view of the sample shown in Figure 3. [Figure 5] Figure 5 is a plan view of the first sample coated according to this disclosure after a water droplet erosion test involving approximately 121 million water droplet impacts. [Figure 6] Figure 6 is a 3D scan of the first sample showing the surface height map of the first sample after the water droplet erosion test. [Figure 7]Figure 7 is a plot of height profiles taken across the test area of ​​the first sample after the water droplet erosion test. [Figure 8] Figure 8 is a plan view of a second sample coated according to this disclosure after a water droplet erosion test involving approximately 101 million water droplet impacts. [Figure 9] Figure 9 is a 3D scan of the second sample showing the surface height map of the second sample after the water droplet erosion test. [Figure 10] Figure 10 is a plot of height profiles taken across the test area of ​​the second sample after the water droplet erosion test. [Figure 11] Figure 11 is a plan view of the third sample coated according to this disclosure after a water droplet erosion test involving approximately 74 million water droplet impacts. [Figure 12] Figure 12 is a 3D scan of the third sample showing the surface height map of the third sample after the water droplet erosion test. [Figure 13] Figure 13 is a plot of height profiles taken across the test area of ​​the third sample after the water droplet erosion test. [Figure 14] Figure 14 is a plan view of a fourth sample coated according to this disclosure after a water droplet erosion test involving approximately 74 million water droplet impacts. [Figure 15] Figure 15 is a 3D scan of the fourth sample showing the surface height map of the fourth sample after the water droplet erosion test. [Figure 16] Figure 16 is a plot of height profiles taken across the test area of ​​the fourth sample after the water droplet erosion test. [Figure 17] Figure 17 shows a cross-section through a fifth sample coated according to this disclosure, with porosity analysis performed by a software package. [Figure 18] Figure 18 shows a cross-section through the fourth sample, demonstrating its resistance to the propagation of microcracks. [Figure 19] Figure 19 shows a cross-section of a CVD coating used to determine porosity according to ASTM E2109. [Figure 20]Figure 20 shows a test image according to the ASTM E2109-01 standard, demonstrating a minimum porosity level of 0.5%, which is used for visual determination of the area percentage porosity of the coating. [Figure 21] Figure 21 shows a cross-section of a CVD coating under a scanning electron microscope in shadow mode. [Figure 22] Figure 22 shows a cross-section of a CVD coating under electron backscatter diffraction (EBSD) analysis. [Modes for carrying out the invention]

[0106] To study the effects of water droplet erosion on turbine blades, a rig consisting of a high-speed rotor rotating at >5700 rpm was installed in a vacuum chamber. Sample material was fixed to one end of the rotor and subjected to water droplet impact through a nozzle of selected diameter and standoff distance. The tests were conducted at the National Physical Laboratory (NPL), the UK's national measurement laboratory. The NPL is a world-leading center for developing and applying the most accurate measurement standards, science, and technology available. [Table 1]

[0107] Various test samples were evaluated as follows: [Table 2]

[0108] Residual stress in the coating was measured using X-ray diffraction techniques: stress results in changes in interatomic distances within the crystal lattice of the coating material, which can be measured by the shift in characteristic X-ray diffraction lines. All measurements of various coating samples representing embodiments of this disclosure showed compressive residual stress. Measurements for CVD partial tungsten carbide coating type 1 with various thicknesses and other properties showed residual stress values ​​from 520 MPa to 1100 MPa, and after additional grinding and dressing operations, showed residual stress values ​​from 1094 MPa to 2552 MPa. Measurements for CVD partial tungsten carbide coating type 2 with various thicknesses and other parameters showed residual stress values ​​from 810 MPa to 2630 MPa, and after additional grinding and dressing operations, showed residual stress values ​​up to 5300 MPa.

[0109] The chemical composition of each coating type was analyzed. Carbon content was analyzed using an Eltra® combustion analyzer: a self-supporting coated sample was placed in an induction furnace and burned in an oxygen atmosphere. During combustion, the carbon component of the sample was oxidized to carbon dioxide (CO2), which was selectively measured with an infrared detector. The readings were linearized, integrated, and divided by the sample weight as the weight percentage of total carbon before display. The following results were prepared for CVD partial tungsten carbide coated type 1 samples deposited in the same cycle as samples N3 and N7: [Table 3]

[0110] The following results were prepared for CVD partially tungsten carbide coated type 2 samples deposited using the same cycle as samples N26 and N29: [Table 4]

[0111] Other samples of CVD-coated partial tungsten carbide were prepared with carbon content ranging from 0.000927 wt% to 0.3697 wt%.

[0112] Fluorine content was analyzed using secondary ion mass spectrometry (SIMS). CVD partially tungsten carbide coated samples were prepared with fluorine content ranging from 0.0004 wt% to 0.3093 wt%.

[0113] After removing the outer oxide layer of the coating using ion beam etching, the oxygen content was analyzed using secondary ion mass spectrometry (SIMS). This analysis did not generate a measurable signal for oxygen from various coating samples representing embodiments of this disclosure.

[0114] Figure 1 shows the X-ray diffraction (XRD) spectra of the coating on sample N22, coated with samples N26 and N29. The spectra show all the characteristic peaks of metallic tungsten, but not a set of peaks characteristic of any of the tungsten carbides. This supports the view that the tungsten carbide particles forming the tungsten alloyed with the carbon material in the embodiments of this disclosure are indeed nanoparticles, and not macro or microparticles.

[0115] The fracture toughness of various coating samples representing embodiments of this disclosure was measured by preparing a series of diamond cube corner indentations and Vickers indentations, and by examining the indentations for cracks extending from the corners of the indentations. None of the samples showed cracks induced by these methods, which is at least 9 MPa.m 1 / 2 This demonstrated the lower limit of the coating fracture toughness.

[0116] Mass loss versus rotor arm / jet collision (interaction) versus time measurements were performed for the entire sample inventory. Samples N3 and N7 were coated with CVD partial tungsten carbide coating type 1, and N26 and N29 were coated with CVD partial tungsten carbide coating type 2. The substrate was 410 stainless steel. Several uncoated samples were used as controls to demonstrate rapid mass loss due to WDE.

[0117] The results were plotted as mass loss against time, as shown in Figure 2. The current test results are compared with previous results from previous studies on monolithic uncoated samples from martensitic 410 stainless steel and three different types of Stellite®. The 410 stainless steel material underwent five repeated tests, while the Stellite® 6 and Stellite® 21 materials each underwent two tests. Stellite® 6 is a cobalt-based alloy consisting of complex carbides in the alloy matrix. The nominal composition of the alloy is 27-32 wt% Cr, 4-6 wt% W, 0.9-1.4 wt% C, with the remainder being cobalt. Stellite® 21 (also known as Stellite® 8) is a cobalt-based alloy consisting of a CoCrMo alloy matrix with dispersed hard carbides. The nominal composition of the alloy is 26-29 wt% Cr, 4.5-6 wt% Mo, 0.2-0.35 wt% C, 2.0-3.0 wt% Ni, with the remainder being cobalt.

[0118] The good reproducibility of these tests is evident from the 410 SS results, which are very closely superimposed on each other. CVD partially tungsten carbide coated samples N3, N7, N26, and N29 all exhibit significantly lower mass loss than the 410 SS samples, although the amount of mass loss differs for each as the test duration increases. Sample N3 showed a very slow increase in mass loss. Stellite® 6 and Stellite® 21 samples showed 2 × 10⁻⁶ 8 Up to the first water droplet collision, there is almost no increase in mass loss. However, the other material, Stellite®, shows a 1 × 10⁻¹⁶ increase in mass loss. 8Significant mass loss was observed due to repeated water droplet impacts. CVD-coated partial tungsten carbide samples showed steps in the mass loss curve, suggesting significant material loss from the sample at these steps. It should be remembered that mass loss is a fairly coarse measure of water droplet erosion. For example, several samples (e.g., N26 and N29) were found to show some chipping in the outer edge regions of the main test area. This chipping is likely due to mechanical deformation of the sample when it is repeatedly removed for gravimetric measurements between each 2-hour test session and then refitted onto the test rig. The loss of coating material due to this chipping will be shown as significant mass loss on the plot in Figure 2, although the actual damage from water droplet erosion in the test area has been found to be negligible.

[0119] The surface of the sample was examined using an optical microscope. Figures 3 and 4 show a plan view and a perspective view, respectively, of the uncoated 410 SS sample after 107 water droplet impacts. Very clear abrasion marks, 8 mm in length, were observed across the entire width of the sample.

[0120] In the following tests, the surface of the abrasion-marked areas of the samples was examined using an Alicona® Infinitefocus microscope. This microscope provides high-quality images of the sample surface as well as 3D height information on the surface. The first figure in each set (Figures 6, 9, 12, and 15) shows a 3D projection of the surface showing the entire abrasion mark, while the second image (Figures 7, 10, 13, and 16) shows a plot of height profiles taken across the central region of each sample perpendicular to the direction of the water jet.

[0121] Figure 5 shows approximately 1.2 × 10 8 Figure 6 shows a plan view of sample N3 after a WDE test involving multiple water droplet impacts. The figure is approximately 1.0 × 10⁻⁶. 8A plan view of sample N7 after a WDE test with multiple water droplet impacts is shown. The WDE test was applied across the entire width of the sample, but unlike the control uncoated 410SS sample shown in Figure 4, both CVD partially carbonized tungsten-coated Type 1 samples showed only some localized damage near the sample corners, and no identifiable damage to the rest of the tested zone after exposure to WDE for more than 10 times longer. In both samples N3 and N7, there is discoloration of the sample on the sides in the areas where the water jet impacted the sample. This is thought to be due to oxidation of the sample surface due to the heating caused by the erosion process. The central zone of the abrasion marks on sample N3 in Figure 5 shows "blackening" which may indicate some damage. A clear notch is formed at one end of the sample where the water droplet impacted the sample.

[0122] Figure 6 shows the Alicona® scan of sample N3 after testing. The height map shows some damage near the edges of the sample in the tested area, but little to no damage in the center of the sample in the tested area (see Figure 7).

[0123] Sample N7, as shown in Figure 8, exhibits some damage at the edges of the wear marks, but very little damage across the sample. There may be some reduction in the visibility of scratches from the original sample preparation on the surface in the center of the wear marks.

[0124] Figure 9 shows the Alicona® scan of sample N7 after testing. The height map shows some damage near the edges of the sample in the tested area, but as shown in Figure 10, the sample has little to no damage in the center of the tested area.

[0125] In Figure 11, sample N29 shows chipping damage at one end of the sample outside the tested area. This damage may have been caused by deformation of the sample during repeated removal and re-mounting on the test rig for weight measurements between each two-hour test session. The central tested area of ​​the sample shows no visible damage due to WDE.

[0126] Figure 12 shows the Alicona® scan of sample N29 after testing. As shown in Figure 13, the height map does not show any detectable damage in the center of the tested area.

[0127] Sample N26, as shown in Figure 14, exhibits extensive chipping damage at the outer edge of the sample outside the test area, which is most likely due to stress or deformation during repeated removal and refitting of the sample to the test rig. The tested area showed some branching damage due to WDE extending approximately 2.7 mm across the sample.

[0128] Figure 15 shows an Alicona® scan of sample N26 after testing. The height map of this sample shows some damage to the edges of the sample surface, as well as several WDE damages on one side that appear branched, extending approximately 2.7 mm across the sample. This structure appears stepped and has a depth of 18 μm over most of the feature. The central portion of the tested area shows no measurable coating damage, as shown in Figure 16.

[0129] With the exception of sample N26, these scans show little discernible damage from droplet erosion in the central region of the abrasion marks visualized in both the 3D view and the sample profile. However, in sample N26, tree-like branching damage is observed over a significant portion of the sample's width.

[0130] Figure 17 shows a cross-section of the CVD partial tungsten carbide coating layer of sample N34, and porosity analysis was performed using Gwyddion image analysis software. The porosity was determined to be 0.00%.

[0131] Figure 18 shows a cross-section through a WDE-tested coating sample N26 on a steel substrate according to one embodiment of the present disclosure, the coating comprising a softer, metallic tungsten layer on the substrate and a harder, tungsten layer alloyed with a carbon layer applied above the softer layer. Here, we show a region of damage branched from the WDE on the coating surface. It can be seen that microcracks initiated in the upper, harder layer by the WDE tend to halt at the boundary between the upper, harder layer and the lower, softer layer. When this sample cross-section was examined by SEM, surprisingly, in the branched damage region, the thickness of the remaining region was measured at many points around the thickness of the softer metallic tungsten layer, which is 10–12 μm. This demonstrates that in the branched damage region, the top coating layer made of the harder tungsten alloyed with carbon was significantly damaged or lost, while the softer, more ductile metallic tungsten layer closest to the substrate remained largely undamaged. Therefore, the applicant has surprisingly demonstrated that a layered coating structure comprising alternating layers of ductile tungsten and harder carbon alloy tungsten can provide effective protection against WDE.

[0132] Figure 19 shows a cross-section of a CVD coating used to determine porosity, according to ASTM E2109-01, "Standard test method for determining area percentage porosity of thermal spray coatings." The coating is substantially free of porosity and inclusions.

[0133] Figure 20 is a test image according to the ASTM E2109-01 standard, showing a minimum porosity level of 0.5%, which is used for visual determination of the area percentage porosity of the coating.

[0134] Figure 21 shows a cross-section of a CVD coating under a shadow-mode scanning electron microscope. The columnar crystalline microstructure of the film is clearly visible.

[0135] Figure 22 shows a cross-section of the CVD coating obtained by electron backscatter diffraction (EBSD) analysis, in both false-color and mono-color. Here again, this clearly reveals the columnar crystalline microstructure of the coating. EBSD analysis is an effective method for the microstructure-crystallographic characterization of materials.

[0136] Throughout this description and claims, the terms “including” and “inclusion” and their variations mean “including but not limited to” and are not intended (and do not exclude) other parts, additives, ingredients, integers or steps.

[0137] Features, entities, properties, compounds, chemical parts, or chemical groups described in conjunction with specific aspects, embodiments, or examples of the present invention should be understood to be applicable to any other aspects, embodiments, or examples described herein, insofar as they do not contradict each other. All features disclosed herein (including the appended claims, abstract, and drawings) and / or all steps of any method or process disclosed herein may be combined in any combination, except for any combination in which at least a portion of such features and / or steps are mutually exclusive. The present invention is not limited to the details of the embodiments described above.

[0138] The reader's attention is directed to all papers and documents filed concurrently with or prior to this specification and published and examined together with this specification in connection with this application, the contents of which are incorporated herein by reference.

Claims

1. A corrosion-resistant chemical vapor deposition material coated on a substrate, comprising a softer coating layer closer to the substrate, which is essentially made of metallic tungsten, which may be alloyed with fluorine; and a harder coating layer on the softer coating layer, which comprises metallic tungsten alloyed with carbon in the form of a matrix of metallic tungsten having interdispersed tungsten carbide nanoparticles in a substantially uniform nanostructure that is oxygen-free except in the surface portion exposed to air or moisture; further comprising a transition layer between the softer coating layer and the harder coating layer, wherein the harder coating layer has a columnar crystalline microstructure.

2. A water droplet erosion resistant chemical vapor deposition coating material coated on a substrate, comprising a softer coating layer closer to the substrate, which is essentially made of metallic tungsten, which may be alloyed with fluorine; and a harder coating layer on the softer coating layer, which comprises metallic tungsten alloyed with carbon in the form of a matrix of metallic tungsten having interdispersed tungsten carbide nanoparticles in a substantially uniform nanostructure that is oxygen-free except in the surface portion exposed to air or moisture; further comprising a transition layer between the softer coating layer and the harder coating layer, wherein the harder coating layer has a columnar crystalline microstructure.

3. The material according to claim 1 or 2, wherein the metallic tungsten in the harder coating layer is alloyed with 0.0001 to 0.37 wt% of carbon based on the total weight of the harder coating layer, and optionally, is alloyed with 0.0001 to 0.21 wt% of carbon based on the total weight of the harder coating layer.

4. The material according to any one of claims 1 to 3, wherein the metallic tungsten in the harder coating layer is further alloyed with fluorine, optionally, the metallic tungsten is alloyed with fluorine in an amount of 0.0004 to 0.31 wt% based on the total weight of the harder coating layer, and optionally, the metallic tungsten is alloyed with fluorine in an amount of 0.0014 to 0.19 wt% based on the total weight of the harder coating layer.

5. The material according to claim 4, wherein the material does not contain an oxyfluoride.

6. The material according to any one of claims 1 to 5, wherein the material does not show a peak characteristic of inclusions having an A15 crystal structure when subjected to X-ray diffraction analysis, and optionally does not show a peak characteristic of tungsten carbide having an A15 crystal structure when subjected to X-ray diffraction analysis.

7. The material according to any one of claims 1 to 6, wherein the material is substantially non-porous.

8. The material according to any one of claims 1 to 6, wherein the material has a porosity of less than 0.5% by volume, optionally less than 0.3% by volume, optionally less than 0.2% by volume, and optionally less than 0.15% by volume.

9. The material according to any one of claims 1 to 8, wherein the harder coating layer has a tungsten composition of 97.60 to 99.99 wt%.

10. 4. A material according to any one of claims 1 to 9, having a hardness of 4.4 GPa to 19 GPa, optionally 8 GPa to 16 GPa.

11. At least 9 MPa·m １／２ A material according to any one of claims 1 to 10, having fracture toughness.

12. The material according to any one of claims 1 to 11, wherein the material substantially does not contain voids and / or inclusions that act as stress concentration areas.

13. The material according to any one of claims 1 to 12, wherein the material has a residual compressive stress of 520 MPa to 5.3 GPa, and optionally 810 MPa to 2.63 GPa.

14. The material according to any one of claims 1 to 13, wherein the material has a thickness of at least 15 μm, optionally at least 50 μm, or the material has a thickness of 200 μm or less, optionally 100 μm or less.

15. The material according to any one of claims 1 to 14, wherein the metallic tungsten in the softer coating layer is alloyed with 0.0004 to 0.31 wt% of fluorine based on the total weight of the softer coating layer, and optionally, alloyed with 0.0014 to 0.19 wt% of fluorine based on the total weight of the softer coating layer.

16. The material according to any one of claims 1 to 15, wherein the concentration of carbon in the transition layer increases in the direction from a softer coating layer to a harder coating layer.

17. The transition layer has a thickness of at least 0.01 μm, and optionally at least 0.1 μm, according to any one of claims 1 to 16.

18. The material according to any one of claims 1 to 17, comprising a plurality of pairs of softer coating layers and harder coating layers so as to form a multilayer structure of alternating layers, wherein the multilayer structure optionally includes 2 to 100 pairs of softer coating layers and harder coating layers.

19. A component at least partially coated with a material according to any one of claims 1 to 12, wherein the component is selected from one or more of the group consisting of turbine blades, compressor blades, turbine vanes, compressor vanes, steam turbine blades, steam compressor blades, steam turbine vanes, steam compressor vanes, gas turbine blades, gas turbine vanes, pump impellers, propellers, valves, and components that undergo cavitation in a liquid.

20. A method for providing a component resistant to at least one of water droplet erosion and cavitation, comprising the step of coating the component at least partially by chemical vapor deposition with the material according to claim 1 or 2, wherein the material has a columnar crystalline microstructure, and the component is selected from one or more of the group consisting of turbine blades, compressor blades, turbine vanes, compressor vanes, steam turbine blades, steam compressor blades, steam turbine vanes, steam compressor vanes, gas turbine blades, gas turbine vanes, pump impellers, propellers, valves, and components that undergo cavitation in a liquid.

21. A method for producing a material containing metallic tungsten, alloyed with carbon in the form of a metallic tungsten matrix having mutually dispersed tungsten carbide nanoparticles in a substantially uniform nanostructure that is oxygen-free except for surface portions exposed to air or moisture, wherein the material has a columnar crystalline microstructure and WF ６ A method for generating a gas phase having an oxygen content of 10 ppm or less and a water content of 3 ppm or less by chemical vapor deposition from an unionized gas phase comprising a mixture of hydrogen and at least one hydrocarbon, and optionally an inert gas, wherein the at least one hydrocarbon optionally includes or consists of a gaseous alkane.

22. The at least one hydrocarbon is WF ６ The method according to claim 21, wherein the material is thermally activated by heating to a temperature of 500 to 850°C before being mixed with hydrogen.

23. The material is cooled at an average rate of 0.12°C to 1.9°C per minute after deposition, according to the method of claim 21 or 22.

24. The method according to any one of claims 21 to 23, wherein the material is deposited at a speed of 3.5 to 82 μm per hour, and optionally 4 to 18 μm per hour.

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