Thermal power generating unit dynamic thermal buffer coating based on phase change material and preparation method of thermal power generating unit dynamic thermal buffer coating

Abstract

The invention belongs to the technical field of thermal power generating unit heating surface treatment, and provides a thermal power generating unit dynamic thermal buffer coating based on a phase-change material and a preparation method of the thermal power generating unit dynamic thermal buffer coating aiming at the technical problems that when a thermal barrier coating of a thermal power generating unit uses a single phase-change material, the thermal conductivity is low, the cycling stability is poor, and the binding force with a matrix is weak. Comprising a middle buffer layer and a surface functional layer which cover a thermal power generating unit metal matrix from inside to outside, the middle buffer layer comprises expanded graphite serving as a matrix, a porous structure located on the matrix and silicon carbide nanowires distributed in the matrix in a three-dimensional net shape, and pores of the porous structure are further filled with LiNO3-KNO3 eutectic salt and a nanometer reinforcing phase. A high-thermal-conductivity phase-change composite material is added in the middle buffer layer, yttrium oxide stabilized zirconium oxide is doped in the surface functional layer to be compounded with vanadium dioxide, vanadium dioxide phase change is used for adjusting radiation heat dissipation, a dual thermal buffer mechanism is formed with latent heat storage of the phase-change composite material, and cooperative regulation and control of the phase-change composite material and the thermal radiation material are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermal surface treatment of thermal power generating units, and particularly relates to a dynamic thermal buffer coating for thermal power generating units based on phase change materials and a preparation method thereof. BACKGROUND

[0002] During peak regulation operation, thermal power generating units frequently experience start-stop and load fluctuation, resulting in a temperature change rate of up to 200-400℃ / min, which causes metal components (such as turbine blades and boiler water walls) to bear severe thermal stress, greatly shortening the fatigue life of traditional nickel-based high-temperature alloys. In the prior art, yttria-stabilized zirconia (YSZ) thermal barrier coating is mainly used for the above-mentioned situation. However, the thermal conductivity of the traditional thermal barrier coating (YSZ) is fixed and cannot dynamically adjust the thermal conductivity according to the load change of the thermal power generating unit. When the local temperature gradient exceeds 300℃ / min under peak regulation conditions, it will accelerate the thermal fatigue failure of the substrate material and cause thermal stress fatigue cracks. Although phase change materials (such as eutectic salt and paraffin) can absorb heat through phase change latent heat, single phase change materials have low thermal conductivity (<0.5 W / m·K), poor cycle stability, and weak bonding force with the substrate. SUMMARY

[0003] The present application provides a dynamic thermal buffer coating for thermal power generating units based on phase change materials and a preparation method thereof, aiming at the technical problems of low thermal conductivity, poor cycle stability, and weak bonding force with the substrate when using single phase change materials for thermal barrier coating of thermal power generating units.

[0004] To achieve the above-mentioned purpose, the technical solutions adopted by the present application are as follows: In a first aspect, the present application provides a dynamic thermal buffer coating for thermal power generating units based on phase change materials, which comprises: an intermediate buffer layer and a surface functional layer covered on a metal substrate of a thermal power generating unit from inside to outside. The intermediate buffer layer comprises expanded graphite as a substrate, a porous structure on the substrate, and silicon carbide nanowires distributed in the substrate in a three-dimensional network; the pores of the porous structure are filled with LiNO3-KNO3 eutectic salt and a nano-enhanced phase; The surface functional layer comprises a gradient composite ceramic layer composed of yttria-stabilized zirconia and vanadium dioxide, and Al2O3 nanoparticles are added.

[0005] Further, in the intermediate buffer layer, the mass fraction of expanded graphite is 75-85wt%, the mass fraction of the nano-enhanced phase is 15-25wt%, and the porosity of the porous structure is 3-5%. The yttria-stabilized zirconia has a mass fraction of 70-85 wt%, the Al2O3 nanoparticles have a mass fraction of 0.5-1.2 wt%, and the vanadium dioxide has a mass fraction of 15-25 wt%.

[0006] Further, the yttria-stabilized zirconia has a mass fraction of 93-95 wt% of ZrO2 and a mass fraction of 5-7 wt% of doped Y2O3.

[0007] Further, the expandable graphite has a carbon content of ≥99.5%.

[0008] Further, the LiNO3-KNO3 eutectic salt has a mass fraction of 82-88 wt% and a latent heat of phase transition of ≥180 J / g. The LiNO3-KNO3 eutectic salt has a component ratio of LiNO3 45-50 wt% and KNO3 50-55 wt%.

[0009] Further, the silicon carbide nanowires have a diameter of 50-80 nm, a length-diameter ratio of >100, and a volume fraction of 8-12%.

[0010] Further, the gradient composite ceramic layer is an alternating film formed by alternately depositing yttria-stabilized zirconia and vanadium dioxide, and the content of vanadium dioxide in the alternating film is gradient-distributed.

[0011] Further, the initial content of vanadium dioxide in the alternating film is 10 wt%, and the content of vanadium dioxide in the alternating film increases by 2 wt% per 10 layers.

[0012] In a second aspect, the present application provides a preparation method of the above-mentioned dynamic thermal buffer coating for thermal power generating units based on phase change materials, which comprises the following steps: Performing surface roughening treatment on a metal substrate of the thermal power generating unit; Melting and impregnating the eutectic salt LiNO3-KNO3 into the expandable graphite substrate, and then implanting the silicon carbide nanowires in a direction perpendicular to the expandable graphite substrate by plasma spraying to prepare an intermediate buffer layer; Preparation of a gradient composite ceramic layer composed of yttria-stabilized zirconia and vanadium dioxide by magnetron sputtering alternately depositing, and in the sputtering process, the protective gas is a mixed gas of Ar and H2, and Ar:H2=19:1.

[0013] Further, the target material for depositing the yttria-stabilized zirconia in the gradient composite ceramic layer is ZrO2-8 wt% Y2O3, the sputtering power is 200-250 W, and the substrate temperature is 400-450℃; the target material for depositing the vanadium dioxide in the gradient composite ceramic layer is VO2, the sputtering power is 150-180 W, and the oxygen partial pressure ratio is O2 / Ar=1:5.

[0014] Compared with the prior art, the present application has the following beneficial effects: The present application provides a thermal power unit dynamic thermal buffer coating based on phase change material, which comprises an intermediate buffer layer and a surface functional layer covered on a metal substrate of the thermal power unit from inside to outside, wherein the intermediate buffer layer comprises expanded graphite as a substrate, a porous structure on the substrate, and silicon carbide nanowires distributed in the substrate in a three-dimensional network, and the pores of the porous structure are filled with LiNO3-KNO3 eutectic salt and nano-enhanced phase, and high-thermal-conductivity phase change composite is added to the intermediate buffer layer, and yttria-stabilized zirconia and vanadium dioxide are compounded in the surface functional layer, the radiation heat dissipation is adjusted through the phase change of vanadium dioxide, and a double thermal buffer mechanism is formed by latent heat storage of the phase change composite and the phase change material, so that the phase change composite and the thermal radiation material are synergistically regulated and controlled, the surface temperature fluctuation is reduced, and the radiation cooling efficiency of the high-temperature section is improved. In addition, the nano-enhanced phase is added to the intermediate buffer layer, and the silicon carbide nanowires arranged in a direction improve the thermal conductivity and the mechanical strength at the same time, the bonding strength of the dynamic thermal buffer coating is improved, and the problems of low thermal conductivity and weak bonding force of the traditional phase change material are solved. Furthermore, the gradient composite ceramic layer in the surface functional layer has a gradient composite structure, so that the dynamic thermal buffer coating has adjustable thermal conductivity characteristics in the range of 200-800 DEG C, covering the main working temperature range of the thermal power unit, reducing the thermal stress damage of the thermal power unit during start and stop, and reducing the annual maintenance cost.

[0015] The present application also provides a preparation method of the thermal power unit dynamic thermal buffer coating based on phase change material, which has all the advantages of the thermal power unit dynamic thermal buffer coating based on phase change material. DETAILED DESCRIPTION

[0016] In order to make those skilled in the art have a clearer understanding and knowledge of the present application, the present application is further described in detail below in combination with embodiments. It should be known that the specific embodiments described below are only used to explain the present application, facilitate understanding, and the technical solutions provided by the present application are not limited to the technical solutions provided by the embodiments, and the technical solutions provided by the embodiments should not limit the protection scope of the present application.

[0018] As the core component of the power system, thermal power units bear the important responsibility of ensuring stable power supply. With the increasing proportion of new energy generation (such as wind power and photovoltaic power), thermal power units need to frequently adjust their peak load to balance the power grid load. Peak load adjustment means that thermal power units need to frequently start, stop and rapidly change their load according to the demand of the power grid. This operation mode is widely used in power production and involves the operation and control of key equipment such as steam turbines and boilers. In the core components of thermal power units, such as turbine blades and boiler water walls, most of them are made of traditional nickel-based high-temperature alloy materials. These materials can maintain good performance under long-term high-temperature and high-pressure stable conditions, but they face severe challenges under the special conditions of peak load adjustment.

[0019] During the peak load adjustment of thermal power units, frequent start-stop and load fluctuation can cause the internal temperature of the unit to change rapidly, with a maximum rate of 200-400℃ / min. This rapid temperature change can cause the metal components such as turbine blades and boiler water walls to bear a large amount of thermal stress. Thermal stress refers to the internal stress of an object caused by temperature change. When the temperature changes rapidly, the thermal expansion and contraction of different parts of the metal component are different, causing mutual pulling or pressing stress. Under the action of such severe thermal stress for a long time, the fatigue life of traditional nickel-based high-temperature alloy will be greatly shortened. Fatigue life refers to the number of stress cycles a material can withstand before it fails. This not only increases the frequency and cost of equipment maintenance, but also may cause safety accidents due to component failure, seriously affecting the stability and safety of thermal power units, and further affecting the reliable power supply of the entire power grid.

[0020] In order to solve the problem of shortening of fatigue life of metal components caused by severe thermal stress in the peak regulation operation of thermal power generating units, the existing technology mainly uses thermal barrier coating technology to protect the metal components, among which the Yttria Stabilized Zirconia (YSZ) thermal barrier coating is widely used. The YSZ thermal barrier coating can effectively block the heat transfer to the metal substrate, reduce the temperature variation range of the metal component, and thus reduce the influence of thermal stress on the component. However, the traditional YSZ thermal barrier coating has a key defect, i.e. the fixed thermal conductivity, which cannot dynamically adjust the heat conduction performance according to the temperature variation caused by the load change of the thermal power generating unit. Under the peak regulation working condition of the thermal power generating unit, when the local temperature gradient exceeds 300℃ / min, the YSZ thermal barrier coating with fixed thermal conductivity cannot effectively cope with such severe temperature variation, cannot timely adjust the heat transfer efficiency, and thus further increases the temperature difference between the metal substrate and the coating and inside the coating, which in turn accelerates the thermal fatigue failure of the substrate material and causes the thermal stress fatigue cracks on the surface of the metal component. Meanwhile, although the phase change material can absorb a large amount of heat through the phase change process and utilize the phase change latent heat to relieve the temperature variation, the phase change latent heat refers to the heat absorbed or released by the material during the phase change, the single phase change material itself has obvious defects, i.e. the extremely low thermal conductivity, which cannot quickly realize the heat transfer and diffusion, and the poor cycle stability, i.e. the performance of the material is significantly reduced after multiple phase changes. In addition, the bonding force between the phase change material and the metal substrate is weak, which is easy to fall off during use and is difficult to play a long-term stable role, so these existing solutions cannot well meet the demand of the peak regulation operation of the thermal power generating unit for the protection of the components.

[0021] Based on the above, the present application proposes a dynamic thermal buffer coating for thermal power generating units based on phase change materials and a preparation method thereof, which will be described in detail below in combination with embodiments.

[0022] As a basic embodiment of the dynamic thermal buffer coating for thermal power generating units based on phase change materials of the present application, it can include an intermediate buffer layer and a surface functional layer covered on the metal substrate of the thermal power generating unit from inside to outside.

[0023] The intermediate buffer layer includes expanded graphite as a substrate, a porous structure on the substrate, and silicon carbide nanowires distributed in the substrate in a three-dimensional network.

[0024] The expanded graphite provides structural support and a basic heat conduction path, the porous structure provides storage space for the phase change material, the silicon carbide nanowires form a three-dimensional network heat conduction network to accelerate heat transfer, the LiNO3-KNO3 eutectic salt absorbs heat through the latent heat of phase change to buffer temperature change, and the nano-reinforced phase improves the overall structural strength. The intermediate buffer layer can quickly absorb and disperse heat, reducing the temperature fluctuation of the metal matrix, the three-dimensional network of silicon carbide nanowires solves the problem of low thermal conductivity of the phase change material, the nano-reinforced phase improves the mechanical properties of the coating and enhances the bonding force with the matrix.

[0025] The surface functional layer comprises a gradient composite ceramic layer composed of yttria-stabilized zirconia and vanadium dioxide, and Al2O3 nanoparticles are added. Among them, yttria-stabilized zirconia provides basic thermal insulation performance, vanadium dioxide dynamically adjusts the thermal conductivity of the coating when the temperature changes by using its phase change characteristics, the gradient structure reduces the thermal stress inside the coating, and Al2O3 nanoparticles enhance the density and oxidation resistance of the coating. It can dynamically adjust the thermal conductivity according to temperature changes, increase heat dissipation at high temperature, and enhance heat insulation at low temperature. In addition, the gradient structure of the gradient composite ceramic layer reduces the internal stress of the coating due to composition difference, and the Al2O3 nanoparticles improve the high-temperature oxidation resistance and structural stability of the coating.

[0026] The present application combines the intermediate buffer layer with the surface functional layer to construct a dynamic heat buffer coating suitable for thermal power units. The intermediate buffer layer uses expanded graphite as the matrix, enhances heat transfer efficiency by means of the three-dimensional heat conduction network of silicon carbide nanowires, absorbs heat by using the latent heat of phase change of LiNO3-KNO3 eutectic salt, and strengthens the structure through nano-reinforced phase. The surface functional layer adopts a gradient composite structure of yttria-stabilized zirconia and vanadium dioxide, combined with the strengthening effect of Al2O3 nanoparticles, to realize dynamic adjustment of thermal conductivity and improvement of coating stability. The two-layer structure forms a complete system from heat absorption, transmission to dynamic regulation, and solves the thermal stress problem in the peak regulation operation of thermal power units. The double-layer coating structure realizes all-round thermal protection of the metal parts of the thermal power unit. The intermediate buffer layer and the surface functional layer work together to quickly absorb a large amount of heat and buffer the rapid temperature change through the phase change material, and to optimize the heat transfer path according to different temperature conditions by means of the dynamically adjusted thermal conductivity, avoiding local overheating or excessive temperature difference. At the same time, the addition of three-dimensional network nanowires and nano-reinforced phase not only solves the problems of poor thermal conductivity and weak bonding force of traditional phase change materials, but also improves the mechanical properties and structural stability of the entire coating, effectively reduces the thermal stress of the metal matrix, significantly prolongs the fatigue life of the key parts of the thermal power unit under the peak regulation operating condition, and ensures the safe and stable operation of the unit. In addition, the design of the gradient composite structure reduces the stress concentration inside the coating, further improving the service life and reliability of the coating.

[0027] The application will be further described in detail below through some embodiments.

[0028] Embodiment 1 A dynamic thermal buffer coating based on phase change material for thermal power unit, comprising two layers of structures covered on a metal substrate, wherein the metal substrate is a nickel-based high-temperature alloy with a thickness of 5-20 mm, and in practical applications, the thickness of the metal substrate can be adjusted according to the type of the component. For example, the thickness of the thin-walled area of the turbine blade is 5-10 mm, and the thickness of the pressure-bearing part of the boiler pipe / header is 15-20 mm. As a preferred example, the composition and mass percentage of the nickel-based high-temperature alloy are as follows: Ni, 50-55wt%; Cr, 17-21wt%; Nb, 4.75-5.5wt%; Mo, 2.8-3.3wt%; Ti0, 65-1.15wt%; Al0, 2-0.8wt%; Co≤1.0wt%; C≤0.03wt%; and the balance is Fe.

[0029] The addition of Cr serves to improve the oxidation resistance and resist high-temperature corrosion on the flue gas side of the thermal power unit, and the addition of Nb+Mo serves to form Ni3Nb and carbide through composite strengthening, thereby enhancing the high-temperature creep strength. C is designed in a low content to inhibit the precipitation of grain boundary carbide and improve the thermal fatigue life.

[0030] Based on the above metal substrate, the coating comprises, from inside to outside, an intermediate buffer layer and a surface functional layer.

[0031] The intermediate buffer layer has a thickness of 30-50 μm, comprises an expandable graphite substrate with a mass fraction of 75-85wt%, a porous structure with a porosity of 3-5%, pores filled with LiNO3-KNO3 eutectic salt, and a nano-enhanced phase with a mass fraction of 15-25wt%, and silicon carbide nanowires are distributed in the expandable graphite substrate in a three-dimensional network. The expandable graphite substrate has a carbon content of ≥99.5% and is high-purity expandable graphite. The high-purity expandable graphite is subjected to high-temperature expansion treatment to form a porous structure with a porosity of 3-5%, and the porous structure is used to accommodate the eutectic salt while ensuring the connectivity of the heat conduction network.

[0032] The mass fraction of the LiNO3-KNO3 eutectic salt is 82-88%, and the latent heat of phase change is ≥180 J / g. The specific component ratio is: LiNO3 45-50wt%, KNO3 50-55wt%. The LiNO3-KNO3 eutectic salt is injected into the pores of the expandable graphite at 280°C through a vacuum impregnation process, and the impregnation efficiency is ≥95%. The shaped phase change material has no leakage risk and a cycle stability of >5000 times.

[0033] The silicon carbide nanowires have a diameter of 50-80 nm, an aspect ratio of >100, and a volume fraction of 8-12%. The silicon carbide nanowires are vertically implanted into the expanded graphite matrix by plasma spraying and are distributed in the expanded graphite matrix in a three-dimensional network.

[0034] In addition, the surface functional layer, with a thickness of 100-200 μm, is a gradient composite ceramic layer composed of yttrium-stabilized zirconium oxide (YSZ) and vanadium dioxide (VO2). The mass fraction of yttrium-stabilized zirconium oxide is 70-85 wt%, with 0.5-1.2 wt% Al2O3 nanoparticles added. The mass fraction of vanadium dioxide (VO2) is 15-25 wt% (based on the total mass of the surface functional layer). The phase transition characteristics of vanadium dioxide (VO2) are: a semiconductor-metal phase transition occurs at 68℃, and the infrared emissivity jumps from 0.3 (low temperature) to 0.8 (high temperature), dynamically adjusting the heat dissipation efficiency. The Al2O3 nanoparticles, with a particle size of 20-50 nm, fill the grain boundary pores of YSZ, reducing the coating porosity, improving the coating hardness and high-temperature oxidation resistance, and suppressing the high-temperature phase transition of YSZ, thus improving the coating stability.

[0035] Yttrium-stabilized zirconia (YSZ) comprises (based on the total mass of YSZ) 93-95 wt% ZrO2 and 5-7 wt% doped Y2O3. It forms a cubic phase structure, exhibits excellent high-temperature stability, provides basic thermal barrier performance and thermal shock resistance, and is well-matched with the intermediate buffer layer.

[0036] The gradient composite ceramic layer is formed by alternating deposition of YSZ and VO2, with a gradient distribution of VO2 content. The initial content is 10 wt% in this layer (near the middle buffer layer), and the content in the outermost layer is 30 wt%. The thickness of a single layer is 50 nm. For every 10 layers of YSZ / VO2 alternating film (50 nm per layer), the VO2 content increases by 2 wt%. The gradient distribution of VO2 content enables dynamic adjustment of emissivity over a wide temperature range (200-800℃), improving the radiative heat dissipation efficiency compared to traditional homogeneous coatings. At the same time, the gradient transition reduces the difference in thermal expansion coefficients and enhances the interfacial bonding strength.

[0037] Example 2 Based on Example 1, Example 2 is a further specific example.

[0038] A dynamic heat buffer coating for thermal power units based on phase change materials comprises a two-layer structure covering a metal substrate. The metal substrate is a nickel-based superalloy with a thickness of 5-20 mm. In practical applications, the thickness of the metal substrate can be adjusted according to the component type. For example: 5-10 mm for thin-walled areas of turbine blades; 15-20 mm for pressure-bearing parts of boiler pipes / headers. As a preferred example, the composition and mass percentage of the nickel-based superalloy are as follows: Ni, 52wt%; Cr, 19wt%; Nb, 5.3wt%; Mo, 3.2wt%; Ti, 1.0wt%; Al, 5wt%; Co, 0.8wt%; C, 0.02wt%, balance Fe.

[0039] Based on the aforementioned metal substrate, the coating consists of an intermediate buffer layer and a surface functional layer from the inside out.

[0040] The intermediate buffer layer is 40 μm thick and consists of an 80 wt% expanded graphite matrix with a porous structure of 3-5% porosity. The pores are filled with LiNO3-KNO3 eutectic salt, and the layer contains 20 wt% nano-reinforcing phase. Silicon carbide nanowires are distributed in a three-dimensional network within the expanded graphite matrix. The expanded graphite matrix is ​​made of high-purity expandable graphite with a carbon content ≥99.5%. This high-purity expandable graphite undergoes high-temperature expansion treatment to form a porous structure with a porosity of 4%. This porous structure accommodates the eutectic salt while ensuring the connectivity of the thermally conductive network.

[0041] The LiNO3-KNO3 eutectic salt has a mass fraction of 85% and a latent heat of phase change ≥180J / g. The specific composition ratio is: LiNO3 48wt%, KNO3 52wt%. The LiNO3-KNO3 eutectic salt is produced using a vacuum impregnation process, in which molten eutectic salt is injected into the pores of expanded graphite at 280℃. The impregnation efficiency is ≥95%, and the shaped phase change material has no leakage risk and a cycle stability of >5000 cycles.

[0042] The silicon carbide nanowires have a diameter of 65 nm, an aspect ratio of >100, and a volume fraction of 10%. The silicon carbide nanowires are vertically implanted into the expanded graphite matrix by plasma spraying and are distributed in the expanded graphite matrix in a three-dimensional network.

[0043] Furthermore, the surface functional layer, with a thickness of 200 μm, is a gradient composite ceramic layer composed of yttrium-stabilized zirconium oxide (YSZ) and vanadium dioxide (VO2). The mass fraction of yttrium-stabilized zirconium oxide is 80 wt%, with 1.0 wt% Al2O3 nanoparticles added. The mass fraction of vanadium dioxide (VO2) is 19 wt% (based on the total mass of the surface functional layer). The yttrium-stabilized zirconium oxide (YSZ) comprises (based on the total mass of YSZ) 94 wt% ZrO2 and 6 wt% doped Y2O3. This forms a cubic phase structure, exhibiting excellent high-temperature stability, providing fundamental thermal barrier performance and thermal shock resistance, and showing good compatibility with the intermediate buffer layer.

[0044] The gradient composite ceramic layer is formed by alternating deposition of YSZ and VO2, with a gradient distribution of VO2 content. The initial content is 10 wt% in this layer (near the middle buffer layer), and the content in the outermost layer is 30 wt%. The thickness of a single layer is 50 nm. For every 10 layers of YSZ / VO2 alternating film (50 nm per layer), the VO2 content increases by 2 wt%. The gradient distribution of VO2 content enables dynamic adjustment of emissivity over a wide temperature range (200-800℃), improving the radiative heat dissipation efficiency compared to traditional homogeneous coatings. At the same time, the gradient transition reduces the difference in thermal expansion coefficients and enhances the interfacial bonding strength.

[0045] Example 3 This invention also provides a method for preparing a dynamic thermal buffer coating for thermal power units based on phase change materials, which may include: Step S1, metal substrate pretreatment.

[0046] Surface roughening treatment is performed on the nickel-based superalloy matrix. In practical applications, sandblasting can be used. For example, using Al2O3 abrasive with a particle size of 80-120 mesh can achieve a surface roughness Ra ≥ 2.5 μm. Then, ultrasonic cleaning is performed using a 1:1 volume ratio of acetone and ethanol to remove surface oil and oxide layers. Finally, solution treatment is carried out under argon protection to form Ni3Nb and carbides, enhancing high-temperature creep strength.

[0047] Step S2: Preparation of the intermediate buffer layer.

[0048] (1) The eutectic salt LiNO3-KNO3 is melt-impregnated into the expanded graphite matrix.

[0049] Expandable graphite can be expanded at 900℃ for 30 seconds to form a porous expanded graphite matrix with a porosity of 3-5%. Then, it can be further expanded at 280℃ for 10 seconds. -3 Under a vacuum of Pa, molten LiNO3-KNO3 is impregnated into the pores of an expanded graphite matrix.

[0050] (2) Silicon carbide nanowires were implanted into the expanded graphite matrix by plasma spraying in a direction perpendicular to the expanded graphite matrix.

[0051] The spraying power is set to 45-55kW, and the powder feeding rate is 8-12g / min. Atmospheric plasma spraying can be used, with SiC nanowires (50-80nm in diameter) vertically implanted into the expanded graphite matrix by rotating the substrate (20-30rpm). The process parameters are: power 45-55kW, powder feeding rate 8-12g / min, carrier gas (Ar) flow rate 40-50L / min, and silicon carbide nanowire implantation angle deviation ≤5°.

[0052] Step S3: Preparation of surface functional layer.

[0053] YSZ / VO2 multilayer films were deposited alternately by magnetron sputtering, with a single layer thickness of 50 nm and the VO2 content was distributed in a gradient from 10 wt% to 30 wt% from the inside to the outside.

[0054] During sputtering, a mixed gas of Ar:H2 = 19:1 can be introduced to suppress VO2 phase transition failure caused by high-temperature oxidation. The alternating deposition cycle of YSZ and VO2 is 20-40 times, with each cycle lasting 30-60 seconds. The sputtering chamber temperature is controlled at 400-600℃, and the water vapor partial pressure is 5 × 10⁻⁶. -3 -5×10 -2 Pa.

[0055] In YSZ layer deposition: the target material is ZrO2-8wt%Y2O3, the sputtering power is 200-250W, and the substrate temperature is 400-450℃. In VO2 layer deposition: the target material is VO2 (purity ≥99.9%), the sputtering power is 150-180W, and the oxygen partial pressure ratio is O2 / Ar=1:5.

[0056] After the surface functional layer is prepared, it can be laser remelted using an Nd:YAG laser with a power density of 10. 4 W / cm 2 The scanning speed is 5-10 mm / s, used to eliminate interlayer interface defects.

[0057] To verify the technical effects of the present invention, the following experimental examples were used: 1. Control group setup: Experimental group: The coating structure proposed in this invention sets an intermediate buffer layer and a surface functional layer on a metal substrate.

[0058] Control group 1: Traditional YSZ thermal barrier coating (plasma spraying of a single layer of YSZ, 200μm thick).

[0059] Control group 2: Single phase change material coating.

[0060] Control group 3: Metal substrate (without intermediate buffer layer or surface functional layer).

[0061] 2. Test methods and conditions: Thermal buffering performance: 600℃ thermal shock test (temperature difference ΔT=400℃ / min, 2000 cycles); Thermal conductivity: Laser flash method (ASTM E1461); Mechanical properties: bond strength (ASTM C633), nano-indentation hardness; Environmental adaptability: Corrosion rate test in high-alkali coal combustion environment; 3. Experimental equipment: Thermal shock testing machine (THERMOTRON SM-3.5); Thermal conductivity analyzer (NETZSCH LFA 467); Universal testing machine (INSTRON 5985); 4. The experimental results are compared as shown in Table 1 below: Table 1

[0062] Based on the above experiments, it can be seen that the experimental group achieved dynamic adjustment of thermal conductivity from 0.8 to 18 W / m·K through the gradient structure, which reduced temperature fluctuation compared with the traditional coating (control group 1); the experimental group used VO2 phase change layer to reduce the corrosion rate of high-alkali coal environment to 0.08 mm / year, which is better than all control groups.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A dynamic thermal buffer coating for thermal power units based on phase change materials, characterized in that, include: An intermediate buffer layer and a surface functional layer cover the metal substrate of the thermal power unit from the inside out; The intermediate buffer layer includes expanded graphite as a matrix and a porous structure located on the matrix, as well as silicon carbide nanowires distributed in a three-dimensional network in the matrix; the pores of the porous structure are filled with LiNO3-KNO3 eutectic salt and nano-reinforcing phase; The surface functional layer comprises a gradient composite ceramic layer composed of yttrium oxide-stabilized zirconium oxide and vanadium dioxide, and contains Al2O3 nanoparticles.

2. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 1, characterized in that: In the intermediate buffer layer, the mass fraction of expanded graphite is 75-85 wt%, and the mass fraction of the nano-reinforcing phase is 15-25 wt%; the porosity of the porous structure is 3-5%. In the surface functional layer, the mass fraction of yttrium oxide-stabilized zirconium oxide is 70-85 wt%, the mass fraction of Al2O3 nanoparticles is 0.5-1.2 wt%, and the mass fraction of vanadium dioxide is 15-25 wt%.

3. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 2, characterized in that: In the yttrium-stabilized zirconium oxide, the mass fraction of ZrO2 is 93-95 wt%, and the mass fraction of doped Y2O3 is 5-7 wt%.

4. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 1, characterized in that: The expanded graphite used is expandable graphite with a carbon content of ≥99.5%.

5. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 1, characterized in that, The mass fraction of the LiNO3-KNO3 eutectic salt is 82-88 wt%, and the latent heat of phase change is ≥180 J / g; The composition ratio of the LiNO3-KNO3 eutectic salt is: LiNO3 45-50 wt%, KNO3 50-55 wt%.

6. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 1, characterized in that, The silicon carbide nanowires have a diameter of 50-80 nm, an aspect ratio of >100, and a volume fraction of 8-12%.

7. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 1, characterized in that, The gradient composite ceramic layer is an alternating film formed by the alternating deposition of yttrium-stabilized zirconium oxide and vanadium dioxide, and the content of vanadium dioxide in the alternating film is distributed in a gradient.

8. The dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 7, characterized in that, The initial content of vanadium dioxide in the alternating film is 10 wt%, and the content of vanadium dioxide in the alternating film increases by 2 wt% for every 10 layers.

9. A method for preparing a dynamic thermal buffer coating for thermal power units based on phase change materials as described in any one of claims 1 to 8, characterized in that, include: Surface roughening treatment is performed on the metal substrate of the thermal power unit; The eutectic salt LiNO3-KNO3 was melt-impregnated into the expanded graphite matrix, and then silicon carbide nanowires were implanted in a direction perpendicular to the expanded graphite matrix by plasma spraying to prepare an intermediate buffer layer. A gradient composite ceramic layer composed of yttrium-stabilized zirconium oxide and vanadium dioxide was prepared by alternating deposition of magnetron sputtering. During the sputtering process, a mixture of Ar and H2 was introduced as the protective gas, with Ar:H2 = 19:

1.

10. The method for preparing a dynamic thermal buffer coating for thermal power units based on phase change materials according to claim 9, characterized in that, The target material for yttrium oxide-stabilized zirconium oxide deposition in the gradient composite ceramic layer is ZrO2-8wt%Y2O3, the sputtering power is 200-250W, and the substrate temperature is 400-450℃; the target material for vanadium dioxide deposition in the gradient composite ceramic layer is VO2, the sputtering power is 150-180W, and the oxygen partial pressure ratio is O2 / Ar=1:5.

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