An environmental barrier coating and a method of making the same

Abstract

The present application relates to an environmental barrier coating and a preparation method thereof, the coating comprises, from the substrate outward, a hafnium oxide modified silicon primer layer, which forms a high bonding strength with the substrate and improves the high-temperature oxidation and molten salt corrosion resistance by hafnium oxide modification; a lanthanum silicate transition layer, which realizes the gradient transition of the thermal expansion coefficient, relieves the thermal stress between the layers and optimizes the chemical compatibility of the primer layer and the surface layer; and a ytterbium silicate surface layer as the main thermal insulation layer, which is provided with a honeycomb-shaped pore microstructure on the surface and contains large pores with a pore size > 20 microns and micropores with a pore size < 5 microns. The structure promotes the rapid penetration and filling of the CMAS melt through the large pores to shorten the residence time and accelerate crystallization, and the micropores induce local supercooling through capillary action to form a dense barrier layer to block the penetration of the melt, and each layer is complementary in corrosion resistance, thermal shock resistance and CMAS protection, meeting the long-term stability requirements in extreme environments of 1200-1600 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature protective coating materials, in particular to an environmental barrier coating and a preparation method thereof. BACKGROUND

[0002] During service, the hot end components (such as turbine blades, combustion chambers, etc.) of high-temperature equipment such as aero-engines and gas turbines not only need to withstand extreme high temperatures of 1200-1600℃, but also need to face multiple harsh working condition challenges such as high-temperature gas scouring, molten salt deposition (such as CMAS: calcium magnesium aluminum silicate) corrosion and thermal stress cycle. As a key functional layer of the thermal protection system, the environmental barrier coating (EBC) is mainly used to isolate the high-temperature gas from direct contact with the base material. The core performance requirements include: forming a high bonding strength with the base material to ensure long-term service reliability, having excellent high-temperature oxidation and molten salt corrosion resistance to resist environmental erosion, reducing the base material temperature through the heat insulation function, and resisting performance degradation caused by gas scouring and CMAS melt penetration.

[0003] Traditional EBC systems mostly use single-layer or simple multi-layer structures, which can achieve heat insulation or basic corrosion protection to some extent, but have significant defects in extremely complex environments. On the one hand, the bonding strength between the base layer and the base material is insufficient or the thermal expansion mismatch of the transition layer easily causes coating peeling failure. On the other hand, the surface layer cannot simultaneously achieve heat insulation and thermal shock resistance, and has limited penetration resistance to CMAS melt. After the CMAS melt penetrates into the coating, it not only causes chemical reaction with the coating, leading to component degradation, but also causes micro-crack expansion due to solidification volume expansion, eventually causing the overall failure of the coating.

[0004] Therefore, developing an EBC coating system that takes into account corrosion resistance, gas thermal shock resistance and high-temperature stability has become a key technical direction to improve the reliability of the hot end components of high-temperature equipment. SUMMARY

[0005] In view of the problem of insufficient corrosion resistance, thermal shock resistance and CMAS protection performance of the existing environmental barrier coating in the extreme environment of 1200-1600℃, the present application provides a three-layer structure environmental barrier coating and a preparation method. The hafnium oxide modified silicon base layer realizes high bonding strength and high-temperature oxidation / molten salt corrosion resistance, the hafnium silicate transition layer gradient matches the thermal expansion coefficient to relieve interlayer stress, and the ytterbium silicate surface layer has a honeycomb-shaped pore microstructure to improve the thermal shock resistance and gas barrier performance. Through large pores to accelerate the filling and crystallization of CMAS melt, and micro-pores to induce dense barrier layer to block penetration, the synergistic effect of corrosion resistance, thermal shock resistance and CMAS protection is realized to meet the long-term high-temperature stable service requirement. The technical scheme provided by the present application is as follows:

[0006] In one aspect, the present application provides an environmental barrier coating, comprising from outside to inside of the substrate surface:

[0007] a hafnium oxide modified silicon primer layer with a thickness of 80-120 μm;

[0008] a hafnium silicate transition layer with a thickness of 50-80 μm;

[0009] a ytterbium silicate top layer with a thickness of 150-250 μm;

[0010] wherein the surface of the ytterbium silicate top layer is provided with a honeycomb pore microstructure, the depth of the honeycomb pore microstructure accounts for 45-55% of the total thickness of the hafnium oxide modified silicon primer layer and the hafnium silicate transition layer, the honeycomb pore microstructure comprises macropores with a pore size greater than 20 μm and micropores with a pore size less than 5 μm, and the volume ratio of the macropores to the micropores is 1:(3.2-5.0).

[0011] In another aspect, the present application also provides a preparation method of an environmental barrier coating, comprising the following steps:

[0012] (1) depositing a hafnium oxide modified silicon primer layer on the surface of the substrate by chemical vapor deposition process;

[0013] (2) preparing a hafnium silicate transition layer on the surface of the hafnium oxide modified silicon primer layer by atmospheric plasma spraying process, power 15-45 kW, argon 40-60 L / min, hydrogen 4-8 L / min, pressure 30-250 Pa, and using a diverging-converging nozzle;

[0014] (3) preparing a ytterbium silicate top layer on the surface of the hafnium silicate transition layer by low pressure plasma spraying process, power 20-43 kW, argon 40-65 L / min, hydrogen 4-9 L / min, helium 5-15%, pressure 50-150 Pa, and forming a honeycomb pore microstructure in the final stage.

[0015] In some specific embodiments, the deposition source selects hafnium tetrachloride (HfCl4) and silane (SiH4) as hafnium source and silicon source, wherein the molar ratio of silicon to hafnium is 3:1-5:1.

[0016] In the chemical vapor deposition process, the molar ratio of hafnium tetrachloride to oxygen is 1:10-1:20, and the molar ratio of silane to hydrogen is 1:5-1:10.

[0017] In some specific embodiments, in step (2), the atmospheric plasma spraying process comprises:

[0018] Preheating stage: power 20-25 kW, time 5-10 min, argon flow rate 40-60 L / min, hydrogen flow rate 5-8 L / min, pressure 80-140 Pa;

[0019] Main spraying stage: power 35-45 kW, time 12-18 min, argon flow rate 40-60 L / min, hydrogen flow rate 5-8 L / min, pressure 150-250 Pa;

[0020] Finishing stage: power 15-20 kW, time 2-5 min, argon flow rate 40-50 L / min, hydrogen flow rate 4-6 L / min, pressure 30-60 Pa.

[0021] In some specific embodiments, in step (2), the divergent-convergent nozzle structure comprises a divergent section and a convergent section, wherein:

[0022] Divergent section: diameter gradually expands from 7-9 mm at the inlet to 14-16 mm at the outlet, with a taper angle of 30-45°;

[0023] Convergent section: diameter suddenly shrinks from 14-16 mm at the inlet to 4-6 mm at the outlet, with a taper angle of 60-75°;

[0024] Total length of nozzle: 150-200 mm.

[0025] In some specific embodiments, in step (2), the volume flow rate ratio of argon to hydrogen is set to 8:1-10:1; the melting temperature of hafnium silicate particles is monitored in real time by an infrared thermal imager, and the coating porosity is detected online by a laser scanning confocal microscope, and the proportion of argon and hydrogen is dynamically adjusted according to real-time feedback data; wherein when the melting rate of hafnium silicate particles is monitored to be lower than the set threshold, the proportion of argon is increased; when the coating porosity is monitored to be higher than the set threshold, the proportion of hydrogen or helium is reduced.

[0026] In some specific embodiments, in step (2), a high-frequency pulse power supply is used, with a frequency of 10-50 kHz;

[0027] In step (3), a high-frequency pulse power supply is used, with a frequency of 20-60 kHz.

[0028] In some specific embodiments, in step (3), the low-pressure plasma spraying process comprises:

[0029] Preheating stage: power 35-40 kW, time 8-10 min, argon flow rate 50-55 L / min, hydrogen flow rate 6-7 L / min, helium proportion 12-15%, pressure 80-100 Pa;

[0030] Main spraying stage: power is 38-43 kW, time is 12-15 min, argon flow is 55-65 L / min, hydrogen flow is 7-9 L / min, helium proportion is 10-15%, and pressure is 120-150 Pa;

[0031] Honeycomb pore forming and finishing stage: power is 20-25 kW, time is 5-10 min, argon flow is 40-45 L / min, hydrogen flow is 4-5 L / min, helium proportion is 5-8%, and pressure is 50-80 Pa.

[0032] In some specific embodiments, in step (3), during the spraying process, the ultrasonic assisted powder feeding technology is used, the powder feeding rate is controlled to be 20-30 g / min, and the ultrasonic vibration frequency is 25-50 kHz.

[0033] In some specific embodiments, in step (3), during the spraying process, in the honeycomb pore forming and finishing stage, the intermittent spraying mode is used, and the interval time of each spraying is 30-60 s.

[0034] By adopting the technical scheme, the environmental barrier coating and the preparation method thereof provided by the application have the following beneficial effects:

[0035] 1. Through the three-layer structure design of the hafnium oxide modified silicon primer layer (high bonding strength interface and Hf element solid solution strengthening), the hafnium silicate transition layer (thermal expansion coefficient gradient transition) and the ytterbium silicate surface layer (main heat insulation layer structure integrity maintenance), the bonding performance of the coating and the substrate, the interlayer thermal stress regulation ability and the heat insulation function are synergistically improved, and long-time high-temperature stable service under 1200-1600 DEG C extreme environment is realized.

[0036] 2. The honeycomb pore microstructure (depth accounts for 45-55% of the total thickness of the primer layer and the transition layer) constructed on the surface of the ytterbium silicate surface layer accelerates the rapid penetration and filling of the CMAS melt through the large pores (>20 mu m) to shorten the residence time and promote early crystallization, and the micropores (<5 mu m) induce local supercooling of the melt through capillary action, and a dense barrier layer with a thickness of <5 mu m is quickly formed at the interface, which not only provides sufficient pore volume to accommodate the melt, but also retains the dense substrate to maintain the mechanical strength of the coating, and realizes the precise regulation and efficient barrier of the CMAS melt penetration path. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0038] Figure 1 A scanning electron microscope morphology diagram of a cross section of the environmental barrier coating provided by the embodiment of the present application is shown in Figure 1.

[0039] Figure 2 A schematic diagram of a flame thermal shock test process of the environmental barrier coating provided by the embodiment of the present application is shown in Figure 2. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0041] The environmental barrier coating provided by the embodiment of the present application comprises, from the surface of the substrate outward, in sequence:

[0042] The hafnium oxide modified silicon primer layer has a thickness of 80-120 μm, realizes high bonding strength with the substrate through high bonding interface and Hf element solid solution strengthening effect, and improves the high-temperature oxidation resistance and molten salt corrosion resistance of the coating at high temperature by using the chemical stability of hafnium oxide.

[0043] The hafnium silicate transition layer has a thickness of 50-80 μm, realizes smooth transition of the thermal expansion properties between the primer layer and the surface layer through the thermal expansion coefficient gradient design, effectively relieves the thermal stress concentration in the multilayer structure, optimizes the chemical compatibility between the primer layer and the surface layer, and improves the structural stability of the coating system.

[0044] The ytterbium silicate surface layer has a thickness of 150-250 μm, serves as the main thermal insulation layer, enhances the thermal stress buffering capacity of the coating to improve the thermal shock resistance by designing the surface honeycomb pore structure, and effectively inhibits the penetration of high-temperature combustion gas into the interior of the coating by using the low permeability of the porous structure.

[0045] The surface of the ytterbium silicate surface layer is provided with a honeycomb pore microstructure, the depth of the honeycomb pore microstructure accounts for 45-55% (specifically 45%, 50%, 52%, 55%) of the total thickness of the hafnium oxide modified silicon primer layer and the hafnium silicate transition layer, the honeycomb pore microstructure includes macropores with a pore size greater than 20 μm and micropores with a pore size less than 5 μm, and the volume ratio of the macropores to the micropores is 1:(3.2-5.0), preferably 1:4. The macropores mainly undertake the function of melt transport channels, and the micropores provide sufficient reaction / adsorption active sites. The pore size ratio of 1:(3.2-5.0) can not only realize accurate control of the pore size through particle size regulation, but also effectively avoid the risk of reduced pore connectivity or structural collapse. If the volume ratio of the macropores to the micropores is less than 1:3.2, the protection effect will be affected due to insufficient micropores, and if the volume ratio is higher than 1:5.0, the impact resistance of the material will be greatly weakened due to excessive micropore density, which cannot meet the actual engineering requirements.

[0046] The embodiment of the present application also provides a preparation method of the environmental barrier coating, comprising the following steps:

[0047] (1) depositing a hafnium oxide modified silicon primer layer on the surface of the substrate by a chemical vapor deposition process;

[0048] (2) preparing a hafnium silicate transition layer on the surface of the hafnium oxide modified silicon primer layer by an atmospheric plasma spraying process, the power is 15-45 kW, the argon gas is 40-60 L / min, the hydrogen gas is 4-8 L / min, the pressure is 30-250 Pa, and a diverging converging nozzle is used;

[0049] (3) preparing a ytterbium silicate surface layer on the surface of the hafnium silicate transition layer by a low-pressure plasma spraying process, the power is 20-43 kW, the argon gas is 40-65 L / min, the hydrogen gas is 4-9 L / min, the helium gas accounts for 5-15%, the pressure is 50-150 Pa, and a honeycomb-shaped pore microstructure is formed in the tailing stage.

[0050] Specifically, first, a hafnium oxide modified silicon primer layer is prepared on the surface of the substrate by a chemical vapor deposition (CVD) process, taking hafnium tetrachloride (HfCl4) as a hafnium source and silane (SiH4) as a silicon source, and the molar ratio of HfCl4 to O2 is accurately controlled to be 1:10-1:20 to inhibit the chlorine ion (Cl -) residual, the molar ratio of SiH4 to H2 is controlled to be 1:5-1:10 to inhibit silicon particle agglomeration, form a layered structure that is well combined with the substrate, uniform in composition and dense in structure; then a hafnium silicate (HfSiO4) transition layer is prepared on the surface of the primer layer by atmospheric plasma spraying process, the process parameters are set as power 15-45 kW, argon 40-60 L / min, hydrogen 4-8 L / min, pressure 30-250 Pa and a diverging converging nozzle is configured, the flow ratio of primary gas (argon) to secondary gas (hydrogen) is precisely controlled to be 8:1-10:1 to realize multi-parameter collaborative gradient control, form a dense layer structure, and utilize the high melting point (>2000°C) and low thermal conductivity (<2 W / m·K) characteristics of hafnium silicate to maintain a stable monoclinic phase structure in a high temperature environment above 1400°C, effectively blocking the thermal shock of high temperature combustion gas on the substrate; finally, a ytterbium silicate (Yb2Si2O7) surface layer is prepared on the surface of the transition layer by low pressure plasma spraying process, the process parameters are set as power 20-43 kW, argon 40-65 L / min, hydrogen 4-9 L / min, helium ratio 5-15%, pressure 50-150 Pa, and the helium ratio is optimized to be 10-15% (when the helium ratio is >15%, the plasma energy is excessively dispersed, causing the jet temperature to drop to <2200°C and the melting rate to drop to <85%; when the helium ratio is <10%, the jet length is insufficient <300 mm, causing insufficient melting of particles (melting rate <90%), so the helium ratio of 10-15% can extend the jet to more than 350 mm by utilizing the high ionization energy characteristics of helium, and improve the melting uniformity of particles (melting rate >90%)), and form a honeycomb-like pore microstructure in the finishing stage, finally obtaining a multilayer structure environmental barrier coating system with excellent thermal shock resistance and CMAS protection capability. Among them, Figure 1 is a scanning electron microscope morphology diagram of the environmental barrier coating cross section; Figure 2 is a schematic diagram of the flame thermal shock test process of the environmental barrier coating.

[0051] In some specific embodiments, the deposition source selects hafnium chloride (HfCl4) and silane (SiH4) as hafnium source and silicon source, wherein the molar ratio of silicon to hafnium is 3:1-5:1, and can be 3:1, 4:1 or 5:1; when the Si:Hf molar ratio is greater than 3:1 (such as 4:1 or 5:1), a high silicon ratio can promote the densification of the silicon-based network skeleton, improving the bonding strength of the coating and the substrate; at the same time, an appropriate amount of hafnium element (i.e. the Hf content is controlled in the range of 1:3 to 1:5) generates dispersedly distributed hafnium oxide (HfO2) phase by oxidation, effectively inhibiting the initiation and propagation of coating cracks, and realizing the synergistic enhancement of mechanical properties.

[0052] In the chemical vapor deposition process, the molar ratio of hafnium tetrachloride to oxygen is 1:10-1:20, and the molar ratio of silane to hydrogen is 1:5-1:10, which can be 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10. By accurately adjusting the molar ratio of HfCl4 to O2, hafnium tetrachloride is oxidized to hafnium oxide (HfO2) and fused with silicon, effectively avoiding the residual of chloride ions (Cl - );At the same time, the ratio of SiH4 to H2 (1:5-1:10, such as 1:7) can inhibit the agglomeration of silicon particles and ensure the uniformity of the deposited layer composition; The process parameters cooperate with the hafnium silicate transition layer design to realize the gradient transition between the silicon substrate (thermal expansion coefficient CTE 4.5×10 -6 / ℃) and the upper layer of hafnium silicate (CTE 6.0×10 -6 / ℃), effectively relieving the thermal stress concentration between the layers, reducing the thermal stress by more than 60%, and improving the structural stability of the coating system.

[0053] In some specific embodiments, in step (2), the atmospheric plasma spraying process includes:

[0054] Preheating stage: power 20-25kW, time 5-10min, argon flow rate 40-60L / min, hydrogen flow rate 5-8L / min, pressure 80-140Pa;

[0055] Main spraying stage: power 35-45kW, time 12-18min, argon flow rate 40-60L / min, hydrogen flow rate 5-8L / min, pressure 150-250Pa;

[0056] Finishing stage: power 15-20kW, time 2-5min, argon flow rate 40-50L / min, hydrogen flow rate 4-6L / min, pressure 30-60Pa.

[0057] Specifically, the preheating stage sets the power to 20-25 kW (specifically, 20 kW, 22 kW, 24 kW or 25 kW), the time to 5-10 min (specifically, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min), the argon flow rate to 40-60 L / min (specifically, 40 L / min, 45 L / min, 50 L / min, 55 L / min or 60 L / min), the hydrogen flow rate to 5-8 L / min (specifically, 5 L / min, 6 L / min, 7 L / min or 8 L / min), and the pressure to 80-140 Pa (specifically, 80 Pa, 100 Pa, 120 Pa or 140 Pa); wherein the power is set to 20-25 kW to reduce the thermal stress of the substrate, the time is 5-10 min to achieve slow heating (ΔT < 200 ℃ / min) to avoid cracking of the coating and the substrate interface, the low hydrogen ratio of 40-60 L / min of argon and 5-8 L / min of hydrogen is used to reduce the plasma heat content, prevent the substrate from being over-oxidized, and the low pressure environment of 80-140 Pa slows down the particle impact speed to control the substrate surface roughness Ra < 3.2 μm; the main spraying stage is set to a power of 35-45 kW (specifically, 35 kW, 38 kW, 40 kW, 42 kW or 45 kW), a time of 12-18 min (specifically, 12 min, 14 min, 16 min or 18 min), an argon flow rate of 40-60 L / min (specifically, 40 L / min, 45 L / min, 50 L / min, 55 L / min or 60 L / min), a hydrogen flow rate of 5-8 L / min (specifically, 5 L / min, 6 L / min, 7 L / min or 8 L / min), and a pressure of 150-250 Pa (specifically, 150 Pa, 180 Pa, 200 Pa, 220 Pa or 250 Pa); wherein the power is set to 35-45 kW to enhance the hafnium silicate melting effect, the time is 12-18 min to ensure that the particles are fully melted (melting rate > 95%) and form a continuous and dense coating (porosity < 3%), the high argon-to-hydrogen ratio of 40-60 L / min of argon and 5-8 L / min of hydrogen is used to increase the plasma temperature (≥ 2500°C) and enhance the melting effect, and the high pressure of 150-250 Pa is used to accelerate the particle flight speed (≥ 400 m / s) and improve the coating bonding strength (> 50 MPa); the end stage is set to a power of 15-20 kW (specifically, 15 kW, 16 kW, 17 kW, 18 kW, 19 kW or 20 kW), a time of 2-5 min (specifically, 2 min, 3 min, 4 min or 5 min), an argon flow rate of 40-50 L / min (specifically, 40 L / min, 42 L / min, 45 L / min or 50 L / min), a hydrogen flow rate of 4-6 L / min (specifically, 4 L / min, 5 L / min, 6 L / min or 7 L / min), and a pressure of 30-60 Pa (specifically, 30 Pa, 40 Pa, 50 Pa or 60 Pa); wherein the power is set to 15-20 kW to inhibit interface oxidation, the time is 2-5 min to slow down oxidation (oxygen content < 0.5 wt.%) through short-time and low-power cooling, maintain the chemical stability of the coating, the argon flow rate of 40-50 L / min and the hydrogen flow rate of 4-6 L / min (hydrogen ratio < 10%) are used to inhibit the reaction between residual oxygen and hydrogen, avoid the formation of an oxidation layer at the interface (HfO2 layer thickness < 1 μm), and the low pressure of 30-60 Pa is used to reduce plasma turbulence and reduce the probability of unmelted particle deposition (< 2%), so as to realize uniform deposition and excellent bonding performance of the hafnium silicate transition layer through precise regulation of the above multi-stage parameters.

[0058] In some specific embodiments, in step (2), the divergent-convergent nozzle structure comprises a divergent section and a convergent section, wherein:

[0059] Divergent section: the diameter gradually expands from 7-9 mm at the inlet to 14-16 mm at the outlet, and the taper angle is 30-45°;

[0060] Converging section: diameter shrinks from 14-16 mm at the inlet to 4-6 mm at the outlet, with a taper angle of 60-75°;

[0061] Total length of the nozzle: 150-200 mm.

[0062] Specifically, the diverging-converging nozzle structure comprises a diverging section and a converging section, wherein the diverging section gradually expands from 7-9 mm (specifically 7 mm, 8 mm, or 9 mm) at the inlet to 14-16 mm (specifically 14 mm, 15 mm, or 16 mm) at the outlet (preferably 8 mm at the inlet to 15 mm at the outlet), with a taper angle of 30-45° (specifically 30°, 35°, 40°, or 45°), which adopts a gradual expansion design to reduce the jet turbulence intensity, prolong the residence time of the plasma high-temperature zone, and improve the melting uniformity of hafnium silicate particles; the converging section shrinks from 14-16 mm (specifically 14 mm, 15 mm, or 16 mm) at the inlet to 4-6 mm (specifically 4 mm, 5 mm, or 6 mm) at the outlet (preferably 15 mm at the inlet to 5 mm at the outlet), with a taper angle of 60-75° (specifically 60°, 65°, 70°, or 75°), which accelerates the jet velocity to supersonic speed (> 500 m / s) through the outlet shrinkage design, enhances the kinetic energy transmission, and prolongs the jet length to more than 400 mm; the total length of the nozzle is 150-200 mm (specifically 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, or 200 mm), which, in combination with the low-pressure plasma spraying (LPPS) process, effectively reduces the jet expansion energy loss, ensures that the melting rate of hafnium silicate particles is > 95%, and realizes the directional deposition of a hafnium silicate transition layer with high uniformity and high bonding strength through the precise geometric parameter design of the special-shaped nozzle.

[0063] In some specific embodiments, in step (2), the volume flow ratio of argon to hydrogen is set to 8:1-10:1; the melting temperature of the hafnium silicate particles is monitored in real time by an infrared thermal imager, and the coating porosity is detected online by a laser scanning confocal microscope, and the proportion of argon to hydrogen is dynamically adjusted according to the real-time feedback data; wherein when the melting rate of the hafnium silicate particles is monitored to be lower than the set threshold, the proportion of argon is increased; when the coating porosity is monitored to be higher than the set threshold, the proportion of hydrogen or helium is reduced.

[0064] Specifically, the volume flow rate ratio of argon to hydrogen is set to 8:1-10:1 (specifically, 8:1, 8.5:1, 9:1, 9.5:1, or 10:1), and the melting temperature (target value ≥ 2500°C) of hafnium silicate particles in the plasma flame flow is monitored in real time by an infrared thermal imager, while the coating porosity is detected online by a laser scanning confocal microscope (LSCM); based on the real-time feedback data, the argon-hydrogen ratio is dynamically adjusted, when the melting rate of hafnium silicate particles is detected to be lower than the set threshold (the proportion of unmelted particles > 5%), the argon ratio is increased to 10:1 to increase the plasma heat content and accelerate the complete melting of the particles; when the coating porosity is detected to be higher than the set threshold (> 3%), the hydrogen ratio (or the helium ratio) is reduced to adjust the argon-hydrogen ratio to 8:1, reduce the dilution effect of hydrogen on the plasma, enhance the particle kinetic energy, and promote densification, and finally control the coating porosity to be < 3%; through the linkage control of the argon-hydrogen ratio and the pressure gradient, the hafnium silicate particles are fully spread and fill the micropores when they impact the substrate, combined with the low-pressure plasma spraying (LPPS) technology (working pressure 50-200 Pa) and dynamic pressure adjustment, to ensure that the particles continuously absorb heat during flight, with a melting rate > 95%, realizing high densification deposition and excellent bonding performance of the hafnium silicate transition layer.

[0065] In some specific embodiments, in step (2), a high-frequency pulse power source with a frequency of 10-50 kHz is used to adjust the arc stability by high-frequency pulse modulation, reduce the local overheating effect of the substrate, and effectively reduce the thermal stress of the substrate.

[0066] In step (3), a high-frequency pulse power source with a frequency of 20-60 kHz is used to precisely control the dynamic characteristics of the arc by higher frequency pulse modulation, reduce the arc fluctuation, improve the uniformity of the ytterbium silicate surface layer deposition, and ensure that the coating thickness deviation is controlled within < ± 5 μm, thereby realizing stable preparation and performance consistency of the overall coating system.

[0067] In some specific embodiments, in step (3), the low-pressure plasma spraying process includes:

[0068] Preheating stage: power 35-40 kW, time 8-10 min, argon flow rate 50-55 L / min, hydrogen flow rate 6-7 L / min, helium proportion 12-15%, pressure 80-100 Pa;

[0069] Main spraying stage: power 38-43 kW, time 12-15 min, argon flow rate 55-65 L / min, hydrogen flow rate 7-9 L / min, helium proportion 10-15%, pressure 120-150 Pa;

[0070] The honeycomb pore forming finishing stage: the power is 20-25 kW, the time is 5-10 min, the argon flow rate is 40-45 L / min, the hydrogen flow rate is 4-5 L / min, the helium proportion is 5-8%, and the pressure is 50-80 Pa.

[0071] Specifically, the preheating stage adopts a power of 35-40 kW (specifically 35, 36, 37, 38, 39 or 40 kW), a time of 8-10 min (specifically 8, 9 or 10 min), an argon flow rate of 50-55 L / min (specifically 50, 52, 53 or 55 L / min), a hydrogen flow rate of 6-7 L / min (specifically 6, 6.5 or 7 L / min), a helium proportion of 12-15% (specifically 12, 13, 14 or 15%), and a pressure of 80-100 Pa (specifically 80, 85, 90, 95 or 100 Pa), the jet length is shortened by the low helium proportion (12-15%), the base body heat input (ΔT < 150℃ / min) is reduced, the hafnium silicate transition layer interface cracking is avoided, the high pressure (80-100 Pa) accelerates the particle impact on the base body, the transition layer surface is pre-compacted (Ra < 2 μm), and the interface thermal stress is effectively reduced; the main spraying stage adopts a power of 38-43 kW (specifically 38, 39, 40, 41, 42 or 43 kW), a time of 12-15 min (specifically 12, 13, 14 or 15 min), an argon flow rate of 55-65 L / min (specifically 55, 57, 59, 61, 63 or 65 L / min), a hydrogen flow rate of 7-9 L / min (specifically 7, 7.5, 8, 8.5 or 9 L / min), a helium proportion of 10-15% (specifically 10, 11, 12, 13, 14 or 15%), and a pressure of 120-150 Pa (specifically 120, 125, 130, 135, 140, 145 or 150 Pa), the ytterbium silicate melting effect is enhanced by the power of 38-43 kW, the jet length (300-350 mm) and the energy density are balanced by the helium proportion of 10-15%, the melting rate is ensured to be greater than 90%, and the particle flight speed (350-400 m / s) is maintained by the medium pressure (120-150 Pa), so as to promote the formation of the dense layer (porosity < 5%); the honeycomb pore forming tail end stage adopts a power of 20-25 kW (specifically 20, 21, 22, 23, 24 or 25 kW), a time of 5-10 min (specifically 5, 6, 7, 8, 9 or 10 min), an argon flow rate of 40-45 L / min (specifically 40, 41, 42, 43, 44 or 45 L / min), a hydrogen flow rate of 4-5 L / min (specifically 4, 4.2, 4.4, 4.6, 4.8 or 5 L / min), a helium proportion of 5-8% (specifically 5, 5.5, 6, 6.5, 7, 7.5 or 8%), and a pressure of 50-80 Pa (specifically 50, 55, 60, 65, 70, 75 or 80 Pa), and the honeycomb-like pore microstructure (the honeycomb layer accounts for 45-55% of the total thickness of the surface layer and the transition layer, contains large pores with a pore diameter greater than 20 μm and micropores with a pore diameter less than 5 μm, and the volume ratio of the large pores to the micropores is 1:(3.2-5.0), the volume ratio of macropores is 20%, and the volume ratio of micropores is 80%): the argon flow rate is reduced to 40-45 L / min, the hydrogen flow rate is controlled at 4-5 L / min, the argon-hydrogen ratio is adjusted to 8:1-10:1, the plasma energy density is reduced, the surface tension of the molten particles is increased, the pore skeleton is inhibited from being formed by excessive flow of the molten pool, the low hydrogen flow rate inhibits the high-temperature decomposition of ytterbia silicate (loss rate <2%); the helium ratio is suddenly reduced from 10-15% in the main spraying stage to 5-8%, the jet length is shortened to within 250 mm, the heat input of the molten pool is reduced, directional arrangement of the pores is induced to achieve a volume ratio of macropores to micropores of 1:(3.2-5.0); the pressure gradient adjustment reduces the environmental pressure to 50-80 Pa in an ultra-low pressure state, slows down the impact speed of the molten particles (<200 m / s), prolongs the solidification time (10-20 s), and promotes the natural formation of micropores by shrinkage between dendrites, and the macropores are dominated by bubble merging, so as to precisely control the uniformity of the pore distribution; the time and dynamic pause control strictly controls the continuous time to be 5-10 min, adopts an intermittent spraying mode (30-60 s / time) to reduce heat accumulation, prevents the pore connectivity from being too high (permeability <1×10. -14 m 2 ), and ensures that the deep honeycomb layer ratio is stably maintained at 45-55%. The above-mentioned parameters cooperatively form a process window of “low power (20-25 kW) + low helium (5-8%) + low pressure (50-80 Pa)”, directional regulation of the pore structure is achieved through balance of the molten pool dynamics and thermodynamics, and finally the honeycomb-like micro-nano structure can induce rapid crystallization of the CMAS melt to form a dense barrier layer (thickness <5 μm), reduce the infiltration depth to <30 μm, and at the same time, improve the thermal shock resistance of the coating (thermal cycle life >100 times), so as to meet the long-time stability requirements in an extreme environment of 1200-1600 °C.

[0072] In some specific embodiments, in step (3), in the spraying process, an ultrasonic assisted powder feeding technology is adopted, the powder feeding rate is controlled to be 20-30 g / min, and the ultrasonic vibration frequency is 25-50 kHz; specifically, in the spraying process, the ultrasonic assisted powder feeding technology is adopted, the powder feeding rate is accurately controlled to be 20-30 g / min, the ultrasonic vibration frequency is 25-50 kHz, the cavitation effect and mechanical disturbance effect of ultrasonic waves are utilized, the dispersion state in the powder conveying process is improved, the powder dispersion degree is >90%, the powder agglomeration phenomenon is effectively reduced, the uniform powder conveying and stable deposition in the spraying process are ensured, and the organization density and composition uniformity of the coating are improved.

[0073] In some specific embodiments, in step (3), during the honeycomb pore forming finishing stage, an intermittent spraying mode is adopted, and the interval time of each spraying is 30-60 s; specifically, during the honeycomb pore forming finishing stage, an intermittent spraying mode is adopted, and the interval time of each spraying is accurately controlled to be 30-60 s (i.e. 30-60 s / time), the heat accumulation of the substrate and the coating is effectively reduced by periodic dynamic stop, the cooling rate of the molten pool and the solidification process are accurately controlled, the excessive connection (permeability <1×10 -14 m 2 ) of the pores is prevented, the layer depth ratio of the honeycomb pore structure is stably maintained in the set range of 45%-55%, and the accurate control of the micro-nano structure morphology and distribution is realized.

[0074] The examples of the present application are described in detail below, which are exemplary and only used to explain the present application, and cannot be understood as a limitation of the present application.

[0075] Example 1

[0076] A preparation method of an environmental barrier coating: first, a hafnium oxide modified silicon primer layer is prepared on the surface of a substrate by a chemical vapor deposition process, using hafnium tetrachloride (HfCl4) as the hafnium source and silane (SiH4) as the silicon source, controlling the molar ratio of silicon to hafnium to be 4:1, the molar ratio of HfCl4 to O2 to be 1:15, and the molar ratio of SiH4 to H2 to be 1:8, to form a layer structure with uniform composition and dense structure; then a hafnium silicate transition layer is prepared on the surface of the primer layer by an atmospheric plasma spraying process, using a high-frequency pulse power supply with a frequency of 30 kHz, and the process is divided into three stages: a preheating stage (power 22 kW, time 7 min, argon 52 L / min, hydrogen 6 L / min, pressure 105 Pa), a main spraying stage (power 40 kW, time 15 min, argon 60 L / min, hydrogen 8 L / min, pressure 210 Pa, using a diverging-converging nozzle: the diverging section gradually expands from 8 mm to 15 mm, the taper angle is 40°, the converging section suddenly shrinks from 15 mm to 5 mm, the taper angle is 70°, the total length is 170 mm), by controlling the volume flow ratio of argon to hydrogen to be 7.5:1, combining real-time monitoring of the melting temperature of hafnium silicate particles by an infrared thermal imager and online detection of the porosity of the coating by a laser scanning confocal microscope, dynamically adjusting the gas ratio to ensure that the melting rate is >90% and the porosity is <5%; a finishing stage (power 17 kW, time 4 min, argon 45 L / min, hydrogen 5 L / min, pressure 50 Pa); finally, a ytterbium silicate top layer is prepared on the surface of the transition layer by a low-pressure plasma spraying process, using a high-frequency pulse power supply with a frequency of 40 kHz, and the process is divided into three stages: a preheating stage (power 36 kW, time 9 min, argon 52 L / min, hydrogen 6 L / min, helium proportion 13%, pressure 90 Pa), a main spraying stage (power 41 kW, time 13 min, argon 60 L / min, hydrogen 8 L / min, helium proportion 12%, pressure 130 Pa), and a honeycomb pore forming finishing stage (power 22 kW, time 8 min, argon 40 L / min, hydrogen 5 L / min, helium proportion 6%, pressure 60 Pa), wherein the finishing stage adopts an intermittent spraying mode (each spraying interval is 40 s), and an ultrasonic assisted powder feeding technology is introduced (powder feeding rate 25 g / min, ultrasonic vibration frequency 30 kHz).

[0077] An environmental barrier coating prepared by the aforementioned preparation method, comprising from the substrate surface outwardly: a hafnium oxide modified silicon primer layer with a thickness of 110 μm, a hafnium silicate transition layer with a thickness of 53 μm, and a ytterbium silicate top layer with a thickness of 210 μm; wherein the ytterbium silicate top layer surface is provided with a honeycomb-shaped pore microstructure with a depth of 50% of the total thickness of the hafnium oxide modified silicon primer layer and the hafnium silicate transition layer (110 μm + 53 μm = 163 μm), i.e. about 81.5 μm, containing macropores with a pore size > 20 μm and micropores with a pore size < 5 μm, and the volume ratio of macropores to micropores is 1:4 (macropores account for 20% of the volume ratio, and micropores account for 80% of the volume ratio).

[0078] Example 2

[0079] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in step (1), the molar ratio of silicon to hafnium in the CVD source gas is 1:1.

[0080] Example 3

[0081] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in step (1), the molar ratio of silicon to hafnium in the CVD source gas is 1:5.

[0082] Example 4

[0083] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in the chemical vapor deposition process of step (1), the molar ratio of hafnium tetrachloride to oxygen is 1:5, and the molar ratio of silane to hydrogen is 1:5.

[0084] Example 5

[0085] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in step (2), a single constant power of 30 kW is used throughout the atmospheric plasma spraying process, and the "preheating-main spraying-tailing" three-stage program is not performed.

[0086] Example 6

[0087] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in step (2), the Ar:H2 volume flow ratio is fixed at 5:1, and the infrared / confocal online feedback system is turned off.

[0088] Example 7

[0089] Referring to the preparation method of the environmental barrier coating of Example 1, the difference is that in step (2), a continuous direct current power supply (0 kHz) is used, and the 10-50 kHz high frequency pulse is not enabled.

[0090] Example 8

[0091] Reference to the preparation method of environmental barrier coating of Example 1, except that step (3) low pressure plasma spraying constant power 30kW throughout the use of the "preheating-main spray-honeycomb end" three stages.

[0092] Example 9

[0093] Reference to the preparation method of environmental barrier coating of Example 1, except that step (3) honeycomb end stage He proportion remains 12% without step-down, still use the main spray level.

[0094] Example 10

[0095] Reference to the preparation method of environmental barrier coating of Example 1, except that step (3) low pressure plasma spraying constant pressure 110Pa throughout the use of the "preheating-main spray-honeycomb end" three stages.

[0096] Example 11

[0097] Reference to the preparation method of environmental barrier coating of Example 1, except that step (3) powder feeding mode is changed to ordinary carrier gas powder feeding, without applying 25-50kHz ultrasonic vibration, powder feeding rate fluctuation 15g / min.

[0098] Example 12

[0099] Reference to the preparation method of environmental barrier coating of Example 1, except that step (3) honeycomb end stage uses continuous spraying, without 30-60s intermittent stop.

[0100] Comparative Example 1

[0101] Reference to the environmental barrier coating of Example 1, except that the ytterbium silicate surface layer has no honeycomb-shaped pore microstructure.

[0102] Comparative Example 2

[0103] Reference to the environmental barrier coating of Example 1, except that the volume ratio of macropores to micropores is 1:1.

[0104] Comparative Example 3

[0105] Reference to the environmental barrier coating of Example 1, except that the depth of the honeycomb-shaped pore microstructure accounts for 20% of the total thickness of the hafnium oxide modified silicon primer layer and the lanthanum silicate transition layer.

[0106] Comparative Example 4

[0107] Reference to the environmental barrier coating of Example 1, except that the pore size of the honeycomb-shaped pore microstructure is uniform at 15μm.

[0108] Comparative Example 5

[0109] Reference is made to the preparation method of the environmental barrier coating of Example 1, except that in step (2), the nozzle structure is a straight pipe type nozzle.

[0110] Test Example

[0111] The environmental barrier coatings prepared in Examples 1-12 and Comparative Examples 1-5 were tested, and the test items included: high-temperature thermal stability: the coating was placed in a 1600℃ high-temperature environment for constant temperature keeping for 1000h, and the mass loss rate was tested to evaluate the structural stability and volatility resistance under long-term high temperature; high-temperature oxidation resistance: 100h oxidation experiment was carried out in a 1400℃ static air environment, and the coating weight gain after oxidation was determined to evaluate the oxidation protection performance of the coating in a high-temperature oxidation atmosphere; molten salt corrosion resistance: the coating sample was immersed in a 750℃ molten Na2SO4-K2SO4 mixed molten salt (mass ratio 1:1) for 50h, and the mass loss rate of the coating was tested to investigate its resistance to high-temperature molten salt corrosion; CMAS protection: the coating was exposed to a CMAS melt (composition: CaO-MgO-Al2O3-SiO2, mass ratio 25:10:15:50) at 1300℃ for 30min, and the penetration depth of the CMAS melt in the coating was determined to evaluate the protection effect of the coating on the typical calcium-magnesium-aluminum silicate melt (CMAS) of the aero-engine; thermal shock resistance: thermal cycle test was carried out at 1000℃ (1h holding)→room temperature (air cooling), and the maximum cycle number of the coating without peeling under the action of repeated thermal stress was counted to evaluate the thermal shock resistance and structural integrity of the coating; bonding strength: tested according to the national standard GB / T 8642 to determine the bonding strength between the coating and the substrate, reflecting the reliability of the coating interface bonding; stability of honeycomb pore structure: after 50 times of thermal cycle treatment at 1400℃, the pore size retention rate of the honeycomb pores was measured to evaluate the durability of the pore microstructure morphology and function during high-temperature cycle, and to ensure that the honeycomb structure can still effectively play a key role in promoting CMAS penetration and inducing dense barrier layer formation in long-term use. The characterization results are shown in Tables 1-3.

[0112] Table 1: High-temperature thermal stability, high-temperature oxidation resistance, and molten salt corrosion resistance

[0113]

[0114] Table 2: CMAS protection and thermal shock resistance

[0115]

[0116] Table 3: Bonding strength and stability of honeycomb pore structure

[0117]

[0118] According to the test data of examples 1-12 and comparative examples 1-5, example 1 exhibits the optimal comprehensive performance: 1600℃ thermal stability weight loss of only 0.4%, CMAS penetration depth of 25μm, no spalling after 120 thermal shocks, bonding strength of 55MPa, and honeycomb pore structure aperture retention rate of up to 95% after 1400℃ thermal cycle; examples 2-12 have performance oriented degradation (bonding strength of 38-48MPa, CMAS penetration of 30-40μm, and thermal shock of 70-95 times) due to single parameter deviation (such as Si:Hf ratio, spraying process, etc.), but still significantly better than comparative examples 1-5; comparative examples 1-5 have serious failure of protective performance (CMAS penetration >75μm, thermal shock <40 times, molten salt corrosion >2.0%, bonding strength 35-52MPa, and pore structure almost invalid) due to missing honeycomb structure or using conventional process (such as straight pipe nozzle), and cannot meet the long-term service requirement in extreme environment. The above results fully verify the scientificity and necessity of the system design scheme of "three-layer gradient structure + precise honeycomb pore + strict process parameter" of the present application, and only when each structure layer and process parameter is fully compliant, the coating can realize multiple protection of high temperature oxidation resistance, CMAS resistance, molten salt resistance, thermal shock resistance, high bonding, and structure stability, etc., and meet the long-term reliable service requirement in 1200-1600℃ extreme environment.

Claims

1. An environmental barrier coating, characterized in that, From the substrate surface outwards, the following are included sequentially: Hafnium oxide-modified silicon is used as the base layer, with a thickness of 80-120 μm; The hafnium silicate transition layer has a thickness of 50-80 μm; Ytterbium silicate surface layer, with a thickness of 150-250 μm; The surface of the ytterbium silicate layer is provided with a honeycomb-shaped porous microstructure. The depth of the honeycomb-shaped porous microstructure accounts for 45-55% of the total thickness of the hafnium oxide modified silicon underlayer and the hafnium silicate transition layer. The honeycomb-shaped porous microstructure includes macropores with a pore size greater than 20 μm and micropores with a pore size less than 5 μm, and the volume ratio of the macropores to the micropores is 1:(3.2-5.0).

2. A method for preparing an environmental barrier coating based on claim 1, characterized in that, The preparation method includes the following steps: (1) A hafnium oxide modified silicon underlayer was deposited on the substrate surface using a chemical vapor deposition process; (2) An atmospheric plasma spraying process was used to prepare a hafnium silicate transition layer on the surface of the hafnium oxide modified silicon substrate. The power was 15-45kW, the argon gas was 40-60L / min, the hydrogen gas was 4-8L / min, the pressure was 30-250Pa, and a divergent-convergent nozzle was used. (3) A ytterbium silicate surface layer is prepared on the surface of the hafnium silicate transition layer using a low-pressure plasma spraying process with a power of 20-43kW, argon gas of 40-65L / min, hydrogen gas of 4-9L / min, helium gas of 5-15%, and pressure of 50-150Pa. A honeycomb-like porous microstructure is formed in the final stage.

3. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (1), hafnium tetrachloride (HfCl4) and silane (SiH4) are selected as the deposition source and silicon source, respectively, wherein the molar ratio of silicon to hafnium is 3:1-5:1; In the chemical vapor deposition process, the molar ratio of hafnium tetrachloride to oxygen is 1:10-1:20, and the molar ratio of silane to hydrogen is 1:5-1:

10.

4. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (2), the atmospheric plasma spraying process includes: Preheating stage: power 20-25kW, time 5-10min, argon flow rate 40-60L / min, hydrogen flow rate 5-8L / min, pressure 80-140Pa; Main spraying stage: power 35-45kW, time 12-18min, argon flow rate 40-60L / min, hydrogen flow rate 5-8L / min, pressure 150-250Pa; Final stage: power 15-20kW, time 2-5min, argon flow rate 40-50L / min, hydrogen flow rate 4-6L / min, pressure 30-60Pa.

5. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (2), the divergent-convergent nozzle structure includes a divergent section and a convergent section, wherein: Diverging section: The diameter gradually expands from 7-9mm at the inlet to 14-16mm at the outlet, with a cone angle of 30-45°; Converging section: The diameter abruptly narrows from 14-16 mm at the inlet to 4-6 mm at the outlet, with a cone angle of 60-75°; Total nozzle length: 150-200mm.

6. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (2), the volume flow ratio of argon to hydrogen is set to 8:1-10:1; the melting temperature of hafnium silicate particles is monitored in real time by an infrared thermal imager, and the porosity of the coating is detected online by a laser scanning confocal microscope. The ratio of argon to hydrogen is dynamically adjusted based on the real-time feedback data. When the melting rate of hafnium silicate particles is detected to be lower than the set threshold, the argon ratio is increased; when the porosity of the coating is detected to be higher than the set threshold, the hydrogen ratio or helium ratio is decreased.

7. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (2), a high-frequency pulse power supply with a frequency of 10-50kHz is used; In step (3), a high-frequency pulse power supply with a frequency of 20-60kHz is used.

8. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (3), the low-pressure plasma spraying process includes: Preheating stage: power 35-40kW, time 8-10min, argon flow rate 50-55L / min, hydrogen flow rate 6-7L / min, helium content 12-15%, pressure 80-100Pa; Main spraying stage: power is 38-43kW, time is 12-15min, argon flow rate is 55-65L / min, hydrogen flow rate is 7-9L / min, helium content is 10-15%, pressure is 120-150Pa; The final stage of honeycomb pore formation: power is 20-25kW, time is 5-10min, argon flow rate is 40-45L / min, hydrogen flow rate is 4-5L / min, helium content is 5-8%, and pressure is 50-80Pa.

9. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (3), during the spraying process, ultrasonic-assisted powder feeding technology is used, with the powder feeding rate controlled at 20-30 g / min and the ultrasonic vibration frequency at 25-50 kHz.

10. The method for preparing the environmental barrier coating according to claim 2, characterized in that, In step (3), during the final stage of forming the honeycomb pore microstructure, an intermittent spraying mode is adopted, with an interval of 30-60 seconds between each spraying.

Images