WO2020207155A1 - 抗熔融铝硅合金腐蚀复合涂层及其制备方法和应用 - Google Patents

抗熔融铝硅合金腐蚀复合涂层及其制备方法和应用 Download PDF

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WO2020207155A1
WO2020207155A1 PCT/CN2020/077573 CN2020077573W WO2020207155A1 WO 2020207155 A1 WO2020207155 A1 WO 2020207155A1 CN 2020077573 W CN2020077573 W CN 2020077573W WO 2020207155 A1 WO2020207155 A1 WO 2020207155A1
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layer
composite coating
silicon alloy
film layer
molten aluminum
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PCT/CN2020/077573
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English (en)
French (fr)
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李微
赵祎林
陈荐
任延杰
何建军
陈建林
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长沙理工大学
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Priority to US16/977,821 priority Critical patent/US11572627B2/en
Publication of WO2020207155A1 publication Critical patent/WO2020207155A1/zh

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    • C—CHEMISTRY; METALLURGY
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    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
    • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
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    • C23C10/36—Embedding in a powder mixture, i.e. pack cementation only one element being diffused
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
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    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
    • C23C16/45525—Atomic layer deposition [ALD]
    • C23C16/45527—Atomic layer deposition [ALD] characterized by the ALD cycle, e.g. different flows or temperatures during half-reactions, unusual pulsing sequence, use of precursor mixtures or auxiliary reactants or activations
    • C23C16/45529—Atomic layer deposition [ALD] characterized by the ALD cycle, e.g. different flows or temperatures during half-reactions, unusual pulsing sequence, use of precursor mixtures or auxiliary reactants or activations specially adapted for making a layer stack of alternating different compositions or gradient compositions
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    • C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
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    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
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Definitions

  • the invention relates to the technical field of corrosion coatings, in particular to a composite coating with excellent corrosion resistance to molten aluminum-silicon alloy, and a preparation method and application thereof.
  • solar thermal power generation has the advantages of heat storage, adjustable peak, and continuous power generation, and is developing towards the goal of high light-to-heat conversion efficiency, low cost and long life.
  • high-temperature heat storage materials are the core link to improve the operating efficiency of solar thermal power generation systems.
  • the heat storage media of commercial solar thermal power plants mainly use water vapor, molten salt and heat transfer oil.
  • Al-12Si alloy is the most ideal heat storage material due to its suitable phase transition temperature, excellent thermal conductivity and heat storage performance and abundant sources.
  • Si in the aluminum-silicon alloy will also react with Fe and Al to form brittle phases such as Fe3Si, Fe2Al7Si, which will further aggravate the dissolution of metal and non-metal elements in the heat exchange tube, and eventually cause corrosion damage. Therefore, improving the corrosion resistance of molten aluminum-silicon alloys of heat exchange tube materials is an urgent problem to be solved in the research and development of solar thermal power generation.
  • the heat insulation and corrosion resistance are usually achieved by coating high temperature protective coating on the surface of the heat exchange tube.
  • high temperature protective coating there are two types of resistance mechanisms for molten alloy corrosion resistance of high-temperature protective coatings on the surface of steel substrates, namely, reactive protection mechanisms and non-reactive protection mechanisms.
  • reaction protection aluminizing is a mature chemical heat treatment process. After aluminum enters the surface of the alloy, an intermetallic compound is formed, and a reaction diffusion zone is formed on the surface. During oxidation, Al 2 O 3 film will be formed on the surface of the aluminide , Thereby preventing the substrate from continuing to react with the environment.
  • the aluminized coating often has the problems that the infiltration layer is too thin, loose, not closely combined with the substrate, and easy to peel off. Moreover, the Si in the aluminum-silicon alloy easily penetrates the infiltrated layer and the substrate to form a brittle phase that is enriched between the infiltrated layer and the substrate, which makes the aluminized coating embrittle and degrades the high temperature corrosion resistance.
  • the patent application with application number 201010126855.0 uses a high-temperature coating method of surface coating mixed with ceramic powder (such as SiO2, TiB2) to prepare a molten aluminum-silicon alloy corrosion-resistant coating.
  • the coating prepared by this method has a large porosity
  • Al atoms easily pass through the pores in the coating and contact the stainless steel matrix, forming brittle (Fe, Cr, Ni) 2 Al 5 and (Fe, Cr, Ni) Al 3 phases and then fall off in the molten In the aluminum-silicon alloy, the new stainless steel matrix continues to react with the molten aluminum-silicon alloy, causing corrosion failure due to repeated cycles.
  • the operating temperature of the molten aluminum-silicon alloy during heat storage is around 620°C, and when TiB 2 is above 400°C It will react with the iron matrix to form a brittle layer (TiC+TiFe+Fe2B), resulting in a sharp drop in the mechanical properties of the material.
  • the use of a single coating for heat exchange tubes to protect against molten aluminum-silicon alloy corrosion still has obvious shortcomings. For example, the bonding force between the coating and the substrate is not high, it is prone to peeling, and it cannot completely isolate the contact between the substrate and the molten metal. The formation of brittle phases reduces structural stability and corrosion resistance at high temperatures.
  • the composite coating As a barrier between the substrate and the corrosive medium, the composite coating has excellent properties such as wear resistance, high temperature resistance, oxidation resistance, and corrosion resistance. It is widely used in aerospace, equipment remanufacturing, light industry, automobile industry and power generation industries. However, At present, composite coatings often have problems such as poor interlayer adhesion and easy shedding, defects in the coating structure, rough surface, easy generation of voids and micro-cracks, failures, mismatched thermal expansion coefficients and uneven internal stress distribution.
  • the document "High temperature oxidation resistance of ⁇ -TiAl alloy with pack aluminizing and electrodeposited SiO 2 composite coating” discloses a method for electroplating SiO 2 coating after aluminizing on ⁇ -TiAl alloy.
  • the composite coating can effectively improve the high-temperature oxidation resistance, but long cracks perpendicular to the surface appear on the infiltrated layer, and there are many micro-cracks on the surface of the electroplated SiO2 coating, which easily accelerates material failure in practical applications.
  • the patent application number 201010126852.7 discloses a solar thermal power generation anti-melting aluminum-silicon alloy corrosion gradient protective coating and its preparation method.
  • the MoB/CoCr gradient protective coating is prepared by low-pressure plasma spraying, which can improve the heat resistance of the coating Impact performance, but the interface with the matrix is not strong and easy to peel off.
  • the patent application number 201711388751.5 discloses a method for preparing an internally heated evaporative blue with a composite ceramic coating resistant to aluminum liquid corrosion.
  • the patent uses thermal spraying technology to spray a 0.8 ⁇ 1.5mm composite structure Al 2 O 3-8YSZ corrosion resistant layer.
  • the composite coating is non-wetting with molten metal liquid and has the advantage of heat corrosion, but the combination of the coating with the substrate and the particle layer is not enough, so that the coating has poor torsion resistance and shear resistance; and it is prepared by thermal spraying.
  • the coating is thicker, and the increasing internal stress of the coating is likely to cause problems such as cracking and falling off of the coating.
  • the technical problem to be solved by the present invention is to overcome the shortcomings of the prior art, and provide a uniform structure, low internal stress, tightly bonded composite coating, low coating porosity, capable of isolating the combination of molten metal and substrate, and being resistant to molten aluminum and silicon
  • the composite coating with excellent alloy corrosion performance also provides a simple process, uniform structure, low internal stress, strong bonding force between the infiltrated layer and the matrix, can isolate the combination of molten metal and the matrix, and has good spalling resistance.
  • the technical solution adopted by the present invention is:
  • An anti-corrosion composite coating of molten aluminum-silicon alloy the composite coating successively includes an aluminized layer and a TiO 2 film layer from the surface of the substrate.
  • the composite coating further includes an Al 2 O 3 thin film layer prepared by atomic layer vapor deposition, and the Al 2 O 3 thin film layer is located on the TiO 2 Between the thin film layer and the aluminized layer; the thickness of the Al 2 O 3 thin film layer is nanometers.
  • the aluminized layer includes an Fe(Al) phase diffusion layer, an Fe-Al compound layer, and an Al 2 O 3 layer in order from the substrate; the Fe(Al) The thickness of the phase diffusion layer, the Fe-Al compound layer, and the Al 2 O 3 layer are all micrometers.
  • the present invention also provides a method for preparing a molten aluminum-silicon alloy corrosion resistant composite coating, which includes the following steps:
  • a TiO2 thin film layer is deposited on the surface of the dried aluminized iron-based alloy by atomic layer vapor deposition.
  • the method for preparing the above-mentioned molten aluminum-silicon alloy corrosion-resistant composite coating preferably further includes depositing Al on the surface of the aluminized iron-based alloy obtained in step S3 by using an atomic layer vapor deposition method between step S3 and step S4. 2 O 3 Thin film layer.
  • the solid powder penetrating agent is a uniform mixture including the following components: aluminum powder with a particle size of 200 mesh, Al 2 O 3 A filler composed of Cr powder and its powdered NH 4 Cl permeation aid.
  • the aluminum powder accounts for 42 to 74%
  • the Al 2 O 3 powder accounts for 20-40%
  • the Cr powder accounts for 5-15%
  • the NH4Cl accounts for 1-3%
  • the conditions for the aluminizing are as follows: first heat preservation at 400-600°C for 20-40 minutes, then heat preservation at 900°C-1050°C for 10-15 hours, and then cool to room temperature along with the furnace.
  • the step of depositing a TiO2 thin film layer includes: using titanium isopropoxide as a precursor and a pressure of 0.1 to 0.3 torr Inflate for 0.1 ⁇ 0.5s, then pump for 30 ⁇ 50s, then fill with plasma water vapor for 0.01 ⁇ 0.03s, and finally pump for 30 ⁇ 50s, repeat the cycle of titanium isopropoxide charging-pumping-water vapor charging-pumping , Depositing a TiO 2 thin film layer; the number of cycles is 50 to 500 times.
  • the step of depositing an Al 2 O 3 thin film layer includes: using trimethyl aluminum as a precursor, a pressure of 0.05 to 0.2 torr, and an inflation of 0.01 to 0.03s, followed by pumping for 40-60s, and then filling with water vapor for 0.01-0.03s, and finally pumping for 20-60s, repeating the cycle of trimethylaluminum charging-pumping-water vapor charging-pumping to deposit Al 2 O 3 Film layer; the number of cycles is 50 to 500 times.
  • the sandblasting is performed under a high pressure nitrogen of 0.6-0.9MPa; the sandblasting time is 5-20min ;
  • the sandblasted abrasive is 300-500 mesh Al 2 O 3 particles; the sandblasting distance is 2-6cm;
  • the surface treatment includes first performing mechanical polishing treatment on the iron-based alloy, and then performing electrolytic polishing treatment;
  • the mechanical polishing treatment includes: polishing with 80-1200 mesh grit sandpaper until visible to the naked eye The scratches are then cleaned with acetone in ultrasonic for 5-20 minutes, and then washed with absolute ethanol for 5-20 minutes, and finally dried;
  • the electrolytic polishing treatment is to use iron-based alloy as anode and insoluble conductive material as cathode.
  • the iron base is subjected to electrolytic polishing treatment;
  • the electrolyte for the electrolytic polishing treatment includes concentrated sulfuric acid with a volume fraction of 60 to 80%, concentrated phosphoric acid with a volume fraction of 15 to 37% and distilled water with a volume fraction of 3 to 5%;
  • the DC voltage of electrolysis is 5-6V, the temperature of the electrolyte is 60-80°C, and the electrolytic polishing time is 2-5min.
  • the present invention also provides the application of the aforementioned molten aluminum-silicon alloy corrosion-resistant composite coating or the molten aluminum-silicon alloy corrosion-resistant composite coating prepared by the aforementioned method in solar thermal power generation heat exchange tubes.
  • the heat exchange tube for solar thermal power generation with aluminum-silicon alloy as the heat storage medium requires high resistance to corrosion of molten aluminum-silicon alloy and certain mechanical strength at high temperature (620°C) in the use environment of molten aluminum-silicon alloy.
  • the coating of the present invention includes an aluminized layer and a TiO 2 film layer in turn from the surface of the substrate.
  • the composite coating has a uniform structure, no cracks, and a gradient and smooth transition between the components of the infiltration layer and the infiltration layer. The interfacial stress and structural defects are small, the bonding force is strong, and the structure is stable. It effectively achieves the isolation of the contact between the substrate and the molten metal.
  • the resulting TiO 2 film layer has a uniform and dense surface, which can further effectively prevent the infiltration of molten metal, and the silicon in the aluminum-silicon alloy reacts with titanium dioxide to form a Ti-Si-O solid solution, which can effectively inhibit the movement of particles and increase the crystal phase
  • the variable barrier potential prevents the phase change of TiO2, ensures the stability of the TiO2 anatase structure, effectively prevents the diffusion of Al and Si elements, and ensures excellent corrosion resistance to molten aluminum-silicon alloys.
  • the composite coating of the present invention introduces the Al 2 O 3 film layer between the aluminized layer and the TiO 2 film layer by atomic layer vapor deposition.
  • the aluminum oxide film deposited by the atomic layer has strong step coverage and effectively fills Cracks and voids in the oxide film on the surface of the infiltration layer form a complete and dense aluminum oxide film, which more effectively prevents the diffusion of aluminum atoms; and at 620°C, the thermal expansion coefficient of Al 2 O 3 is between Fe-Al phase and TiO 2. It can effectively avoid thermal fatigue crack initiation or propagation caused by thermal expansion coefficient mismatch.
  • the aluminized layer is composed of Fe(Al) phase diffusion layer, Fe-Al compound layer (ie Fe-Al extrafiltration layer) and Al 2 O 3 layers from the inside to the outside of the substrate surface.
  • the composition between the infiltration layer and the infiltration layer presents a gradient and smooth transition, which significantly reduces the interface stress between the matrix and the infiltration layer, and effectively improves the binding force between the infiltration layers.
  • the present invention uses the process route of aluminizing-sandblasting-cleaning-atomic vapor layer deposition of TiO2 thin film layer to prepare the Fe(Al) phase diffusion layer, Fe-Al compound layer and Al2 from the substrate to the surface layer.
  • O The composite coating structure of the 3-layer aluminized layer and the TiO2 film layer.
  • the composite coating has a uniform structure, no cracks, and a gradient and smooth transition between the components of the infiltration layer and the infiltration layer. The interface stress and structural defects are small, the bonding force is strong, and the structure stability is good, which effectively realizes the contact between the insulating matrix and the molten metal.
  • the aluminum oxide film deposited by atomic layer has strong step coverage, which effectively fills the cracks and gaps in the oxide film on the surface of the infiltration layer to form a complete and dense aluminum oxide film, which more effectively prevents the diffusion of aluminum atoms and is for subsequent introduction
  • the TiO2 film layer provides good surface conditions.
  • the introduced TiO2 film layer does not have defects such as microcracks, has a dense surface and a uniform structure, which is beneficial to prevent the diffusion of Si elements and improve the structural stability and stability of the coating under high-temperature corrosion conditions. Corrosion resistance.
  • the method of the present invention can effectively improve the control precision of the structure by further controlling the composition of the permeating agent and the aluminizing conditions, that is, the Fe(Al) phase diffusion layer, the Fe-Al compound layer and the Al 2 O 3 layer in the aluminized structure
  • the thickness and microstructure are adjusted to obtain a more uniform aluminized coating with less internal stress and a tighter combination of composite coatings, which can effectively reduce the interface stress and organizational defects between the substrate and the infiltrated layer, and improve the relationship between the substrate and the infiltrated layer.
  • the bonding force between the layers inhibits the shedding of the infiltration layer, the initiation and propagation of cracks, and the dense and complete structure of the infiltration layer is obtained; by controlling the process parameters of the atomic layer vapor deposition Al2O3 film layer and TiO2 film layer , Can obtain dense and uniform Al 2 O 3 thin film layer and TiO 2 thin film layer without surface defects, which can effectively prevent the melt from entering the coating, effectively improve the barrier effect on the melt, and is tightly combined with the aluminized layer , Can effectively improve the stability of the composite coating; by performing mechanical polishing and electrolytic polishing on the aluminized layer, and by further controlling process parameters such as sandblasting time, sandblasting distance, mechanical polishing, electrolytic polishing, etc., the coating can be effectively reduced
  • the defects further improve the bonding strength between the substrate and the surface, the structural stability and density of the aluminized layer, and the bonding force between the aluminized layer and the atomic vapor deposition coating, and improve the peel
  • FIG. 1 is a cross-sectional morphology diagram of the aluminized steel after atomic layer vapor deposition and the comparison of the aluminized steel before atomic layer vapor deposition in Example 3 of the present invention and an EDS energy spectrum analysis diagram of corresponding points.
  • FIG. 2 is a comparison diagram of the corrosion rate of stainless steel with composite coating prepared in Examples 3 and 4 of the present invention, stainless steel without coating, and stainless steel with aluminized layer prepared in Comparative Example 1 after 72 hours of corrosion in molten aluminum silicon .
  • An anti-corrosion composite coating of molten aluminum-silicon alloy of the present invention includes an aluminized layer and a TiO 2 thin film layer in sequence from the surface of the substrate to the outside.
  • the matrix of the present invention is an iron-based material, preferably austenitic stainless steel.
  • the TiO2 thin film layer is preferably introduced by the atomic layer vapor deposition method.
  • the TiO2 thin film layer introduced by this method does not have defects such as microcracks, has a dense surface and a uniform structure.
  • the thickness of the TiO2 thin film layer can be controlled to a nanometer level to improve the performance of the composite coating, preferably 5-50nm.
  • the thickness of the TiO2 film is controlled to a small range, which can reduce the production cost of the composite coating.
  • the nano-thickness TiO2 film has a more regular anatase crystal structure, and the voids between the unit cells are basically negligible, which is very helpful to prevent the diffusion of Si elements.
  • the coating also includes an Al 2 O 3 thin film layer prepared by atomic layer vapor deposition, and the Al 2 O 3 thin film layer is located between the TiO 2 thin film layer and the aluminized layer; between the aluminized layer and the TiO A layer of Al 2 O 3 thin film layer prepared by atomic layer vapor deposition method is arranged between the 2 thin film layers, and this thin film layer is a continuous dense coating.
  • the thickness of the Al 2 O 3 thin film layer is on the order of nanometers; preferably, the thickness of the Al 2 O 3 thin film layer of the present invention is 5 to 50 nm.
  • the aluminized layer includes Fe(Al) phase diffusion layer, Fe-Al compound layer, and Al 2 O 3 layer in turn from the substrate; the Fe(Al) phase diffusion layer, Fe-Al compound layer and Al 2 O 3 layer
  • the thickness of the layers are all micrometers; among them, the Fe(Al) phase diffusion layer, which can also be called the Fe diffusion layer containing Al, is essentially the diffusion layer formed by the diffusion of Al to the substrate to replace part of the Fe atoms on the surface of the substrate, which is aluminum-poor Zone, the content of Al is low, and the atomic percentage of Al in the diffusion layer increases from 0at.% on the surface of the substrate to 8at.% on the outermost side of the Fe(Al) phase diffusion layer of the diffusion layer.
  • the Al 2 O 3 layer is a discontinuous coating with defects on the surface, and the Al 2 O 3 layer can play a role of anti-oxidation and isolation, but the oxidation corrosion grooves on the surface not only easily induce the initiation of thermal fatigue cracks, but also The corrosion resistance of Al liquid is reduced.
  • the thickness of the Fe-Al compound layer is 60-200 ⁇ m
  • the thickness of the Fe(Al) phase diffusion layer is 50-160 ⁇ m
  • the thickness of the Al 2 O 3 layer is 10-30 ⁇ m
  • the Fe-Al The compound layer includes FeAl, FeAl 2 and Fe 3 Al.
  • a method for preparing a molten aluminum-silicon alloy corrosion resistant coating of the present invention includes the following steps:
  • a TiO2 thin film layer is deposited on the surface of the dried aluminized iron-based alloy by atomic layer vapor deposition.
  • the iron-based alloy is an alloy plate, preferably an austenitic stainless steel alloy steel.
  • the method further includes depositing an Al 2 O 3 thin film layer on the surface of the aluminized iron-based alloy obtained in step S3 by using the atomic layer vapor deposition method, and the Al 2 O 3 thin film layer introduced by this method It is dense and uniform, and can strengthen the isolation effect on the substrate, and compensate for the defects such as oxidation corrosion grooves in the Al 2 O 3 layer on the surface of the aluminized coating obtained by the aluminizing method. Such defects are not only easy to induce thermal fatigue cracks. Initially, it also reduces the ability to resist Al liquid corrosion.
  • the present invention introduces the atomic deposition Al 2 O 3 thin film layer by atomic deposition, which supplements the discontinuous Al 2 O 3 thin film on the surface of the permeated layer, so that the sample surface is covered with a continuous and dense Al 2 O 3 thin film to block Al atoms.
  • the diffusion effect also provides a good surface environment for the subsequent deposition of TiO 2 films, preventing other interference elements from affecting the deposition effect, and at the same time, it is beneficial to reduce the interface stress and improve the bonding force and stability between the coatings.
  • the solid powder penetrating agent includes a homogeneous mixture of the following components: aluminum powder with a particle size of 200 mesh, filler composed of Al 2 O 3 and Cr powder, and powdered NH 4 Cl penetration aid,
  • the aluminum powder accounts for 42-74%
  • the Al 2 O 3 powder accounts for 20 to 40%
  • the Cr powder accounts for 5 to 15%
  • the NH 4 Cl accounts for 1 to 3%; by using the solid powder penetrating agent of this component, the control precision of the tissue can be effectively improved, thereby further improving the compactness and integrity of the tissue.
  • the aluminizing conditions are: drying at 150°C for 2 hours, first holding at 400-600°C for 20-40 minutes, heating at a rate of 10°C/min, then holding at 900°C to 1050°C for 10-15 hours, and then cooling to Room temperature.
  • the composite coating combines a tighter aluminized coating.
  • the step of depositing the TiO2 thin film layer includes heating the cavity to 300-450°C, using titanium isopropoxide (purity 99.99%) as a precursor, a pressure of 0.1-0.3 torr, and a gas filling of 0.1 ⁇ 0.5s, followed by pumping for 30-50s, and then filling with plasma water vapor for 0.01-0.03s, and finally pumping for 30-50s, depositing TiO2 film, repeating titanium isopropoxide inflation-pumping-water vapor charging-pumping Air circulation, deposition of TiO2 thin film layer; control the number of cycles is 50 to 500 times, can generate different thickness of TiO2 film.
  • the step of depositing the Al 2 O 3 thin film layer includes: using aluminized steel as a substrate, placing it in the equipment cavity, heating the cavity to 150-300°C, using trimethyl aluminum (TMA) (purity 99.99%) as Precursor, the pressure is 0.05 ⁇ 0.2torr, inflated for 0.01 ⁇ 0.03s, then pumped for 40 ⁇ 60s, then filled with water vapor for 0.01 ⁇ 0.03s, finally pumped for 20 ⁇ 60s, deposited Al 2 O 3 film, repeated Base aluminum inflation-pumping-water vapor inflation-pumping cycle to deposit Al 2 O 3 film.
  • the number of control cycles is 50 to 500, and Al 2 O 3 films of different thicknesses can be produced.
  • the sand blasting is performed under high pressure nitrogen of 0.6 to 0.9 MPa; the sand blasting time is 5 to 20 minutes; the abrasive of the sand blasting is 300 to 500 mesh Al 2 O 3 particles; The blasting distance is 2 ⁇ 6cm.
  • the surface treatment includes first performing mechanical polishing treatment on the iron-based alloy, and then performing electrolytic polishing treatment;
  • the mechanical polishing treatment includes: sanding with 80-1200 mesh grit sandpaper until no obvious scratches are visible to the naked eye, then washing with acetone in ultrasonic waves for 5-20 minutes to remove oil, and ultrasonic washing with absolute ethanol for 5-20 minutes to remove stains , The most drying; the electrolytic polishing treatment is to use the iron-based alloy as the anode, the insoluble conductive material as the cathode, the iron-based electrolytic polishing treatment, the electrolytic polishing treatment electrolyte includes a volume fraction of 60-80% Concentrated sulfuric acid, concentrated phosphoric acid with a volume fraction of 15 to 37% and distilled water with a volume fraction of 3 to 5%; the direct current voltage of the electrolysis is 5-6V, the temperature of the electrolyte is 60-80°C, and the electropolishing time is 2 ⁇ 5min.
  • the electrolytic polishing process specifically includes: connecting a 321 austenitic stainless steel plate to the anode, using insoluble conductive material (graphite plate) for the cathode, 50mm between the anode and the cathode, heating the electrolyte to 60-80°C (heating in a water bath), Input 5 ⁇ 6V DC voltage and polish for 2 ⁇ 5min in electrolysis, then take out the austenitic stainless steel plate, rinse and blow dry.
  • the composition of the electrolyte is as follows: Concentrated sulfuric acid with a volume fraction of 60 ⁇ 80% (purity 98 %), concentrated phosphoric acid with a volume fraction of 15 to 37% (purity of 85%) and distilled water with a volume fraction of 3 to 5%.
  • the step S3 is specifically: putting the sample in a beaker containing 3-8L of deionized water, heating and shaking for 2-7 minutes to remove the residual fines on the surface of the sample, and then placing the sample in a beaker containing 2-5L of acetone , Heating and shaking for 5-10min, take out the sample and place in a drying oven to dry for 10-30min.
  • the method for preparing a composite coating with excellent corrosion resistance to molten aluminum-silicon alloy of the present invention is to perform atomic layer vapor deposition on stainless steel after aluminizing, and the resulting coating has a multilayer structure with a thickness of 5nm-50nm from the outside to the inside.
  • the layers of the composite coating are tightly bonded, no cracks, clear and neat, and the thickness of the Al2O3/TiO2 film or TiO2 film deposited by atomic layer vapor deposition is controllable, and the growth is uniform, flat and has good step coverage. It is dense and has strong bonding force with the permeable layer structure, without changing the permeable layer structure.
  • the prepared stainless steel containing Al 2 O 3/TiO 2 thin film coating or TiO 2 thin film coating structure undergoes 72 hours of 620 °C molten aluminum-silicon alloy corrosion test, and the corrosion rate is 0.35 ⁇ 10-5g/mm 2 ⁇ h and 0.23 ⁇ 10-5g/mm 2 ⁇ h, compared with austenitic stainless steel (corrosion rate of 1.3 ⁇ 10-5g/mm 2 ⁇ h) decreased by 73.1% and 82.3%, respectively, showing excellent resistance to molten aluminum and silicon
  • the alloy performance meets the compatibility requirements of molten aluminum-silicon alloy as a heat storage medium and solar thermal power exchange tubes, and has extraordinary scientific research value and industrial application prospects.
  • An anti-corrosion composite coating of molten aluminum-silicon alloy of the present invention includes an aluminized layer, an Al 2 O 3 thin film layer and a TiO 2 thin film layer in order from the surface of the substrate outward.
  • the Al 2 O 3 thin film layer and the TiO 2 thin film layer are both introduced by atomic layer vapor deposition.
  • the thickness of the Al 2 O 3 thin film layer and the TiO 2 thin film layer are 5 nm and 20 nm in sequence; the aluminized layer includes Fe successively from the surface of the substrate.
  • (Al) phase diffusion layer, Fe-Al compound layer and Al 2 O 3 layer are the aluminized layer includes Fe successively from the surface of the substrate.
  • the Fe(Al) phase diffusion layer, the Fe-Al compound layer and the Al 2 O 3 layer all have micron-level thickness.
  • the hot-rolled austenitic stainless steel plate sample is polished with sandpaper of different grain sizes (80 mesh to 1200 mesh) until no obvious scratches are visible to the naked eye, and then cleaned with acetone in ultrasonic for 5 minutes to remove oil. Ultrasonic cleaning with absolute ethanol for 5 minutes, removing stains, and finally drying in a drying oven at 80°C for 20 minutes; 321 austenitic stainless steel is a rolled plate, and its chemical composition is C 0.04%, Si 0.38%, Mn 1.08%, Cr 17.02%, Ni 9.06%, N 0.05%, P 0.03%, Ti 0.22%, and the rest is Fe.
  • Electrolytic polishing connect the 321 austenitic stainless steel plate to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between anode and cathode, and heat the electrolyte to 60°C (heated by a water bath), and both poles enter the electrolyte at the same time
  • the electrolyzer apply 5V DC voltage, soak in the electrolysis for 2 minutes, take the sample out, rinse and blow dry; the electrolyte is composed of 60% concentrated sulfuric acid (purity 98%) and 37% concentrated sulfuric acid. Phosphoric acid (85% purity) and 3% volume fraction of distilled water.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al 2 O 3 and Cr powder are used as fillers.
  • the permeation aid composition of NH4Cl is fully mixed according to 5wt.%Cr, 64wt.%Al, 28wt.%Al2O3, 3wt.%NH4Cl.
  • Atomic layer vapor deposition Al 2 O 3/TiO 2 film Use aluminized steel as the substrate, put it in the equipment cavity, and heat the cavity at 150°C, using trimethyl aluminum (TMA) (purity 99.99%) as Precursor, the pressure is 0.05torr, the gas is charged for 0.03s, then the gas is pumped for 40s, then the water vapor is charged for 0.01s, and finally the gas is pumped for 30s, the Al 2 O 3 film is deposited, and the trimethyl aluminum gasification-pumping-water vapor charging is repeated -Pumping cycle, the number of cycles is 50 times to generate Al 2 O 3 film with a thickness of 5 nm; with aluminized steel/Al 2 O 3 film as the substrate, the cavity is heated to 300 °C, and titanium isopropoxide (purity 99.99 %) is the precursor, the pressure is 0.1torr, the gas is charged for 0.5s, then the gas is pumped for 30s, then the plasma water
  • An anti-corrosion composite coating of molten aluminum-silicon alloy of the present invention includes an aluminized layer, an Al 2 O 3 thin film layer and a TiO 2 thin film layer in order from the surface of the substrate outward.
  • the Al 2 O 3 thin film layer and the TiO 2 thin film layer are both introduced by atomic layer vapor deposition.
  • the thickness of the Al 2 O 3 thin film layer and the TiO 2 thin film layer are 30 nm and 50 nm in turn;
  • the aluminized layer includes Fe from the surface of the substrate.
  • (Al) phase diffusion layer, Fe-Al compound layer and Al 2 O 3 layer are the Fe(Al) phase diffusion layer, the Fe-Al compound layer and the Al 2 O 3 layer all have micron-level thickness.
  • the hot-rolled austenitic stainless steel sample is polished with sandpaper of different grain sizes (80 mesh to 1200 mesh) until there are no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic for 10 minutes, degreasing, no Ultrasonic cleaning with water and ethanol for 10 minutes, removing stains, and finally drying in a drying oven at 80°C for 30 minutes; the 321 austenitic stainless steel is a rolled plate, and the mass fraction of its chemical composition is C 0.04%, Si 0.38%, Mn 1.08%, Cr 17.02%, Ni 9.06%, N 0.05%, P 0.03%, Ti 0.22%, the rest is Fe.
  • Electrolytic polishing connect 321 austenitic stainless steel to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between anode and cathode, and heat the electrolyte to 70°C (heated by a water bath), and both poles enter the electrolyte at the same time , Input 5V DC voltage, soak in the electrolysis for 5 minutes, take out the sample, rinse and blow dry, in which, the composition of the electrolyte is 70% concentrated sulfuric acid (purity 98%), and the volume fraction is 26% Concentrated phosphoric acid (85% purity) and 4% volume fraction of distilled water.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al 2 O 3 and Cr powder are used as fillers.
  • the permeation aid composition of NH4Cl is fully mixed according to 15wt.%Cr, 44wt.%Al, 40wt.%Al2O3, 1wt.%NH4Cl.
  • Sandblasting treatment Put the aluminized sample under 0.8MPa high pressure nitrogen for sandblasting, the abrasive is 400 mesh Al 2 O 3 particles, the sandblasting time is 10min, the sandblasting distance is 4cm, and the loose infiltration layer is removed. Impurities.
  • Atomic layer vapor deposition Al 2 O 3/TiO 2 film Use aluminized steel as the substrate, put it in the equipment cavity, and heat the cavity at 300°C, using trimethyl aluminum (TMA) (purity 99.99%) as Precursor, pressure 0.2torr, inflated for 0.01s, then pumped for 60s, then filled with water vapor for 0.03s, and finally pumped for 50s, deposited Al 2 O 3 film, repeated trimethyl aluminum inflation-pumping-water vapor inflation -Pumping cycle, the number of cycles is 300, to generate an Al 2 O 3 film with a thickness of 30 nm; with aluminized steel/Al 2 O 3 film as the substrate, the cavity is heated to 450 °C, and titanium isopropoxide (purity 99.99 %) is the precursor, the pressure is 0.3torr, the gas is charged for 0.5s, then the gas is pumped for 50s, then the plasma water vapor is charged for 0.03s, and the gas is pumped for
  • An anti-corrosion composite coating of molten aluminum-silicon alloy of the present invention includes an aluminized layer, an Al 2 O 3 thin film layer and a TiO 2 thin film layer in order from the surface of the substrate outward.
  • the Al 2 O 3 thin film layer and the TiO 2 thin film layer are both introduced by atomic layer vapor deposition.
  • the thickness of the Al 2 O 3 thin film layer and the TiO 2 thin film layer are 10 nm and 10 nm in sequence; the aluminized layer includes Fe successively from the surface of the substrate.
  • the (Al) phase diffusion layer, the Fe-Al compound layer and the Al 2 O 3 layer; among them, the Fe (Al) phase diffusion layer, the Fe-Al compound layer and the Al 2 O 3 layer all have micron-level thickness.
  • the hot-rolled austenitic stainless steel sample is polished with sandpaper of different sizes (80 mesh to 1200 mesh) until there is no obvious scratches visible to the naked eye, and then cleaned with acetone in ultrasonic for 20 minutes, degreasing, Ultrasonic cleaning with water and ethanol for 20 minutes, removing stains, and finally drying in a drying oven at 80°C for 40 minutes; among them, 321 austenitic stainless steel is a rolled plate, and the mass fraction of its chemical composition is C 0.04%, Si 0.38%, Mn 1.08%, Cr 17.02%, Ni 9.06%, N 0.05%, P 0.03%, Ti 0.22%, the rest is Fe.
  • Electrolytic polishing connect 321 austenitic stainless steel to the anode, use insoluble conductive material (graphite plate) for the cathode, 50mm between anode and cathode, and heat the electrolyte to 80°C (heated by a water bath), and both poles enter the electrolyte at the same time , Input 5V DC voltage, soak in the electrolysis for 3 minutes, take out the sample, rinse and blow dry; the composition of the electrolyte is 80% concentrated sulfuric acid (purity 98%), and 15% concentrated phosphoric acid ( The purity is 85%) and the volume fraction is 5% distilled water.
  • the solid powder infiltration agent is composed of aluminum source, filler, and permeation aid (activator).
  • the aluminum source uses aluminum powder with a particle size of 200 mesh, and Al 2 O 3 and Cr powder are used as fillers.
  • the permeation aid composition of NH4Cl is fully mixed according to 10wt.%Cr, 58wt.%Al, 30wt.%Al2O3, 2wt.%NH4Cl.
  • Organic solvent washing Put the sample in a beaker containing 5L of deionized water, heat and shake for 5 minutes to remove the residual fines on the surface of the sample, and then put the sample in a beaker containing 4L of acetone, heat and shake for 8 minutes, The sample was taken out and placed in a drying oven to dry for 20 minutes.
  • Atomic layer vapor deposition Al 2 O 3/TiO 2 thin film Use aluminized steel as the substrate, put it in the equipment cavity, and heat the cavity at 200°C, using trimethyl aluminum (TMA) (purity 99.99%) as Precursor, the pressure is 0.1torr, inflated for 0.02s, then pumped for 45s, then filled with water vapor for 0.015s, and finally pumped for 45s, deposited Al 2 O 3 film, repeated trimethyl aluminum inflation-pumping-water vapor inflation -Pumping cycle, 90 cycles, generating Al 2 O 3 film with a thickness of about 10nm; using aluminized steel/Al 2 O 3 film as the substrate, heating the cavity to 370°C, using titanium isopropoxide (purity 99.99 %) is the precursor, the pressure is 0.2torr, the gas is charged for 0.25s, then the gas is pumped for 40s, then the plasma water vapor is charged for 0.02s, and finally the gas is pumped for 40s
  • a composite coating for molten aluminum-silicon alloy corrosion resistance of the present invention The difference from the composite coating in Example 3 is that the composite coating in this embodiment does not contain Al 2 O 3 introduced by atomic layer vapor deposition. Film layer.
  • a method for preparing a molten aluminum-silicon alloy corrosion resistant composite coating of this embodiment is basically the same as the preparation method of the composite coating in Example 3. The difference is that the atomic layer deposition of Al is omitted in step (6). 2 O 3 thin film layer step, direct atomic layer deposition of TiO2 thin film layer on the surface of aluminized steel.
  • a composite coating that resists corrosion of molten aluminum-silicon alloy The difference from the composite coating in Example 3 is that the composite coating of this comparative example only contains an aluminized layer and does not contain Al2O deposited by atomic layer vapor deposition. 3 thin film and TiO 2 thin film layer.
  • a preparation method of the anti-melting aluminum-silicon alloy corrosion composite coating of this comparative example is different from the preparation method of the composite coating in Example 3 in that it does not contain step (6).
  • EDS penetrates into the matrix, in addition to the atoms in the coating, it is also observed in the matrix material Containing Cr and Fe atoms, the thickness of TiO 2 produced by atomic layer vapor deposition is in the nanometer level, so the Ti element is very small when observed in EDS.
  • Figure 2 shows the ALD Al 2 O 3/TiO 2 composite aluminized coating prepared in Example 3 and the ALDTiO2 composite aluminized coating 321 stainless steel prepared in Example 4 and the 321 containing aluminized layer prepared in Comparative Example 1 Corrosion rate histograms of stainless steel and uncoated 321 stainless steel after 72 hours of 620°C molten aluminum-silicon alloy corrosion.
  • the weight loss method is used to determine the corrosion degree of the samples.
  • the weight loss of the sample directly indicates the degree of corrosion of the material.
  • the evaluation of the corrosion of the metal sample is the corrosion rate V (g/mm 2 ⁇ h) of the sample, which is calculated by formula (1),
  • A is the surface area of the sample (mm 2); W 0 is the mass of the sample before corrosion (g); W is the mass of the sample after corrosion (g); t is the corrosion time (h).
  • the result is shown in Figure 2. It can be seen that compared with the corrosion rate of stainless steel against molten aluminum-silicon alloy, the corrosion rate of a single aluminized coating sample is reduced by 63.1%.
  • the ALD TiO 2 composite aluminized protective coating sample has The corrosion rate of molten aluminum and silicon was reduced by 73.1%, and the corrosion rate of molten aluminum and silicon of the ALD Al2O3/TiO2 composite aluminized protective coating sample was reduced by 82.3%.
  • the composite coating of the present invention exhibits excellent resistance to melting aluminum-silicon alloys, and the coating effect obtained by ALD Al 2 O 3/TiO 2 composite aluminizing is greatly improved compared with ALD TiO 2 composite aluminizing , which can well meet the compatibility requirements of molten aluminum-silicon alloy as a heat storage medium and solar thermal power generation heat exchange tubes.

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Abstract

一种抗熔融铝硅合金腐蚀复合涂层，由基体表面往外依次包括渗铝层和TiO2薄膜层。还公开了一种抗熔融铝硅合金腐蚀复合涂层的制备方法及应用。

Description

抗熔融铝硅合金腐蚀复合涂层及其制备方法和应用 技术领域
本发明涉及腐蚀涂层技术领域，尤其涉及一种抗熔融铝硅合金腐蚀性能优良的复合涂层及其制备方法和应用。
背景技术
传统化石能源已无法满足全球人口增长和工业化快速发展的需求，因此可再生能源的应用受到了各国政府的密切关注。与其他可再生能源发电技术相比，太阳能热发电具有可储热、可调峰、可连续发电的优点，并正朝着高光热转换效率、低成本及高寿命的目标发展。其中，高温储热材料是提高太阳能热发电系统运行效率的核心环节。目前商业化太阳能热发电发电站储热介质主要采用水蒸气、熔融盐以及导热油，由于水蒸气储热容量低，熔融盐导热系数低、高温易分解和固液分层，导热油高温(在400℃以上)易分解等特点，因此储热系统存在导热效率低、热稳定性差、过冷度大等缺陷，导致发电成本高，限制了太阳能热发电的发展。Al-12Si合金由于相变温度合适、导热储热性能优良且来源丰富，是最理想的储热材料。
但是在实际运用中，高温液态铝硅合金与铁基换热管接触时，与Fe反应生成(Fe，Cr，Ni)2 Al 5和(Fe，Cr，Ni)Al 3化合物，且Al的原子半径小，容易穿过(Fe，Cr，Ni)Al 3和(Fe，Cr，Ni)2 Al 5等化合物的孔洞，继续与Fe反应，持续生成(Fe，Cr，Ni)Al化合物，导致金属元素发生溶解。同时，铝硅合金中的Si也会与Fe、Al反应生成Fe 3 Si、Fe 2 Al 7 Si等脆性相，进一步加剧换热管件金属元素与非金属元素的溶解，最终发生腐蚀破坏。因此提高换热管材料的抗熔融铝硅合金腐蚀性能是太阳能热发电研发亟待解决的问题。
通常通过在换热管表面涂覆高温防护涂层来达到隔热、抗腐蚀的效果。一般而言，钢基体表面高温防护涂层的抗熔融合金腐蚀的机理有两种类型，即反应防护机理和非反应防护机理。对于反应防护，渗铝是一种成熟化学热处理工艺，铝进入合金表面后，形成一种金属间化合物，并在表面形成反应扩散区，氧化时，铝化物表面就会有Al 2 O 3薄膜形成，从而阻止基材与环境继续反应。但渗铝涂层往往会存在渗层过薄，疏松，与基体结合不紧密，容易剥落的问题。而且，铝硅合金中的Si容易穿过渗层与基体生成脆性相富集于渗层与基体间，使得渗铝涂层发生脆化，进而使得抗高温腐蚀能力退化。申请号为201010126855.0的专利申请采用表面涂敷掺和陶瓷粉末(如SiO 2、TiB 2)的高温涂料方法制备耐熔融铝硅合金腐蚀涂层，一方面，使用该方法制备的涂层孔隙率大，在熔融铝硅合金环境下Al原子易穿过涂层中的孔隙与不锈钢基体接触，生成脆性(Fe，Cr，Ni)2 Al 5和(Fe，Cr，Ni)Al 3相然后脱落于熔融铝硅合金中， 新的不锈钢基体继续与熔融铝硅合金反应，循环往复造成腐蚀失效，另一方面，熔融铝硅合金储热时的运行温度在620℃附近，而TiB 2在400℃以上时会与铁基体发生反应生成脆性层(TiC+TiFe+Fe 2 B)，致使材料力学性能急剧下降。总之，对换热管采用单一涂层进行耐熔融铝硅合金腐蚀的防护还存在明显不足，例如，涂层与基体结合力不高，容易发生剥落，无法完全隔绝基体与熔融金属的接触，容易生成脆性相降低结构稳定性和耐腐高温腐蚀性。
复合涂层作为基体与腐蚀介质的屏障，具有耐磨、耐高温、抗氧化、耐腐蚀等优良性能，被广泛应用于航空航天、装备再制造、轻工业、汽车工业和发电行业等领域，但是，目前复合涂层常出现层间粘合不紧易脱落、涂层结构存在缺陷、表面粗糙，容易生成空洞和微裂纹发生失效、热膨胀系数不匹配使内部应力分布不均等问题。例如，文献《Hightemperature oxidation resistance of γ-TiAl alloy with pack aluminizing andelectrodeposited SiO 2 composite coating》(Corrosion Science,2018.)公开了一种在γ-TiAl合金上渗铝后电镀SiO 2涂层的方法，该复合涂层能够有效提高抗高温氧化性能，但渗层上出现垂直于表面的长裂纹，电镀SiO 2涂层表面有许多微裂纹，在实际运用中易加速材料失效。专利申请号为201010126852.7的专利公开了一种太阳能热发电抗熔融铝硅合金腐蚀梯度保护涂层及其制备方法，采用低压等离子喷涂制备MoB/CoCr梯度保护涂层，该方法能够提高涂层抗热冲击性能，但与基体的界面结合力不强，容易剥落。专利申请号为201711388751.5公开了一种具有耐铝液腐蚀复合陶瓷涂层的内加热蒸发蓝制备方法，该专利采用热喷涂技术喷涂0.8～1.5mm复合结构Al 2 O 3-8YSZ耐侵蚀层，该复合涂层与熔融金属液体不润湿，具有耐热蚀的优点，但该涂层与基体以及粒子层间的结合不够，使涂层抗扭、抗剪切力差；且采用热喷涂法制备的涂层较厚，涂层内部应力的不断增大容易导致涂层开裂、脱落等问题。
发明内容
本发明要解决的技术问题是克服现有技术的不足，提供一种组织均匀、内应力小、复合涂层结合紧密、涂层孔隙率小、能够隔绝熔融金属与基体的结合且耐熔融铝硅合金腐蚀性能优良的复合涂层，还提供一种工艺简单、能制备出组织均匀、内应力小、渗层与基体结合力强、能够隔绝熔融金属与基体的结合、抗剥落性能好、在熔融铝硅合金的条件下抗腐蚀性能优良的复合涂层的方法。
为解决上述技术问题，本发明采用的技术方案是：
抗熔融铝硅合金腐蚀复合涂层，所述复合涂层由基体表面往外依次包括渗铝层和TiO 2薄膜层。
上述的抗熔融铝硅合金腐蚀复合涂层，优选地，所述复合涂层还包括由原子层气相沉积法 制备的Al 2 O 3薄膜层，且所述Al 2 O 3薄膜层位于所述TiO 2薄膜层和渗铝层之间；所述Al 2 O 3薄膜层的厚度为纳米级。
上述的抗熔融铝硅合金腐蚀复合涂层，优选地，所述渗铝层由基体往外依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层；所述Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层的厚度均为微米级。
作为一个总的发明构思，本发明还提供一种抗熔融铝硅合金腐蚀复合涂层的制备方法，包括如下步骤：
S1、对铁基合金进行表面处理，然后采用固体粉末渗剂进行渗铝；
S2、将渗铝后的铁基合金进行喷砂处理；
S3、将经喷砂处理的铁基合金进行洗涤、干燥；
S4、采用原子层气相沉积法在经干燥的渗铝的铁基合金表面沉积TiO 2薄膜层。
上述的抗熔融铝硅合金腐蚀复合涂层的制备方法，优选地，在所述步骤S3和步骤S4之间，还包括采用原子层气相沉积法在步骤S3所得的渗铝铁基合金表面沉积Al 2 O 3薄膜层。
上述的抗熔融铝硅合金腐蚀复合涂层的制备方法，优选地，所述步骤S1中，所述固体粉末渗剂为包括以下组分的均匀混合物：粒度为200目的铝粉，Al 2 O 3和Cr粉组成的填充剂及其粉末状NH 4 Cl的助渗剂，所述固体粉末渗剂中，按质量比计，所述铝粉占42～74％，所述Al 2 O 3粉占20～40％，所述Cr粉占5～15％，所述NH 4 Cl占1～3％；
所述渗铝的条件为：先于400～600℃保温20～40min，再于900℃～1050℃保温10～15h，然后随炉冷却至室温。
上述的抗熔融铝硅合金腐蚀复合涂层的制备方法，优选地，所述步骤S3中，所述沉积TiO 2薄膜层的步骤包括：以异丙醇钛为前驱体，压力为0.1～0.3torr，充气0.1～0.5s，随后抽气30～50s，再充入等离子水蒸汽0.01～0.03s，最后抽气30～50s，反复进行异丙醇钛充气-抽气-水蒸气充气-抽气循环，沉积TiO 2薄膜层；所述循环的次数为50～500次。
上述的抗熔融铝硅合金腐蚀复合涂层的制备方法，优选地，所述沉积Al 2 O 3薄膜层的步骤包括：以三甲基铝为前驱体，压力为0.05～0.2torr，充气0.01～0.03s，随后抽气40～60s，再充入水蒸汽0.01～0.03s，最后抽气20～60s，反复进行三甲基铝充气-抽气-水蒸气充气-抽气循环，沉积Al 2 O 3薄膜层；所述循环的次数为50～500次。
上述的抗熔融铝硅合金腐蚀复合涂层的制备方法，优选地，所述步骤S2中，所述喷砂处理于0.6～0.9MPa的高压氮气下进行；所述喷砂的时间为5～20min；所述喷砂的磨料为300～500目的Al 2 O 3颗粒；喷砂的距离2～6cm；
所述步骤S1中，所述表面处理包括先对铁基合金进行机械抛光处理，然后再进行电解抛光处理；所述机械抛光处理包括：采用80目～1200目粒度的砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min，再用无水乙醇超声波清洗5～20min，最后进行干燥；所述电解抛光处理为以铁基合金为阳极、以不溶性导电材料为阴极，对铁基进行电解抛光处理；所述电解抛光处理的电解液包括体积分数为60～80％的浓硫酸，体积分数为15～37％的浓磷酸和体积分数为3～5％的蒸馏水；所述电解的直流电压为5～6V，电解液的温度为60～80℃，电解抛光的时间为2～5min。
作为一个总的发明构思，本发明还提供一种前述的抗熔融铝硅合金腐蚀复合涂层或前述的方法制备的抗熔融铝硅合金腐蚀复合涂层在太阳能热发电换热管中的应用。
与现有技术相比，本发明的优点在于：
1、以铝硅合金作为储热介质的太阳能热发电换热管要求高温下(620℃)在熔融铝硅合金的使用环境下需要较高的抗熔融铝硅合金腐蚀性能和一定的机械强度。本发明的涂层由基体表面往外依次包括渗铝层和TiO 2薄膜层，该复合涂层组织均匀、无裂纹、渗层与渗层之间的组分呈梯度平滑过渡，基体与渗层之间的界面应力和组织缺陷小，结合力强，结构稳定性好，有效地实现了隔绝基体与熔融金属的接触，沉积于渗铝层表面的TiO 2薄膜层，尤其是采用原子层气相沉积法得到的TiO 2薄膜层，表面均匀致密，能进一步有效防止熔融金属的渗入，且铝硅合金中的硅和二氧化钛反应，形成Ti-Si-O固溶体，能够有效的抑制颗粒的移动，增加晶体相变的势垒电位，阻止TiO 2发生相变，保证TiO 2锐钛型结构稳定，有效阻止Al、Si元素的扩散，能保证耐熔融铝硅合金腐蚀性能优异。
2、本发明的复合涂层通过在渗铝层与TiO 2薄膜层间采用原子层气相沉积法引入Al 2 O 3薄膜层，原子层沉积的氧化铝薄膜，阶梯覆盖性强，有效的填补了渗层表面氧化膜存在的裂纹及空隙，形成完整致密的氧化铝膜，更有效的阻隔了铝原子的扩散；且在620℃下，Al 2 O 3的热膨胀系数介于Fe-Al相与TiO 2之间，可有效避免由热膨胀系数不匹配造成的热疲劳裂纹萌生或扩展行为。
3、本发明的复合涂层中，渗铝层由基体表面由内至外依次为Fe(Al)相扩散层、Fe-Al化合物层(即Fe-Al外渗层)和Al 2 O 3层，渗层与渗层之间的组分呈梯度平滑过渡，显著降低了基体与渗层之间的界面应力，有效提高了有效提高渗层之间的结合力。
4、本发明通过渗铝-喷砂-清洁-原子气相层沉积TiO 2薄膜层的工艺路线，制备出由基体往表层依次为包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层的渗铝层和TiO 2薄膜层的复合涂层结构，该复合涂层组织均匀、无裂纹、渗层与渗层之间的组分呈梯度平滑过渡，基 体与渗层之间的界面应力和组织缺陷小，结合力强，结构稳定性好，有效地实现了隔绝基体与熔融金属的接触。通过在经清洁后的渗铝层表面先采用原子层气相沉积法沉积Al 2 O 3薄膜层，后引入TiO 2薄膜层，能进一步提高复合涂层的化学惰性，阻隔Al、Si原子向基体扩散；原子层沉积的氧化铝薄膜，阶梯覆盖性强，有效的填补了渗层表面氧化膜存在的裂纹及空隙，形成完整致密的氧化铝膜，更有效的阻隔了铝原子的扩散且为后续引入TiO 2薄膜层提供了好的表面条件，引入的TiO 2薄膜层不存在微裂纹等缺陷、表面致密且组织均匀，有利于防止Si元素扩散，提高涂层在高温腐蚀条件下的结构稳定性和耐腐蚀性。
5、本发明的方法通过进一步控制渗剂组成、渗铝条件可以有效提高对组织的调控精度，即对渗铝组织中Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层厚度及微观结构的调控，获得组织更均匀、内应力小、复合涂层结合更紧密的渗铝涂层，能有效降低基体与渗层之间的界面应力和组织缺陷，提高基体与渗层之间的结合力，抑制渗层脱落、抑制裂纹萌生和扩展，获得组织的致密性和完整性良好的渗层结构；通过控制原子层气相沉积Al 2 O 3薄膜层和TiO 2薄膜层的工艺参数，可获得致密均匀、无表面缺陷的Al 2 O 3薄膜层和TiO 2薄膜层，能有效阻碍了熔体进入涂层内部，有效提高了对熔体的阻隔作用，且与渗铝层结合紧密，能有效提高复合涂层的稳定性；通过在渗铝层进行机械抛光和电解抛光处理，并通过进一步控制喷砂时间、喷砂距离、机械抛光、电解抛光等工艺参数，能有效降低涂层的缺陷，进一步提高基体与表面的结合强度、渗铝层的结构稳定性和致密度以及渗铝层与原子气相沉积的涂层之间的结合力，提高抗剥离性能、力学性能和耐熔体腐蚀性能。
附图说明
图1为本发明实施例3中经原子层气相沉积后的渗铝钢与原子层气相沉积前相比的渗铝钢的截面形貌图及对应点的EDS能谱分析图。
图2为本发明实施例3、4制备的含有复合涂层的不锈钢与不含涂层的不锈钢及对比例1制备的含有渗铝层的不锈钢在熔融铝硅中腐蚀72h后的腐蚀速率对比图。
具体实施方式
以下将结合说明书附图和具体实施例对本发明做进一步详细说明。
一种本发明的抗熔融铝硅合金腐蚀复合涂层，所述复合涂层由基体表面往外依次包括渗铝层和TiO 2薄膜层。具体地，本发明的基体为铁基材料，优选为奥氏体不锈钢。TiO 2薄膜层优选由原子层气相沉积法引入，采用该方法引入的TiO 2薄膜层不存在微裂纹等缺陷、表面致密且组织均匀。TiO 2薄膜层厚度可控制为纳米级，以提高复合涂层的性能，优选为5～50nm。一方面，由于原子层沉积法所使用前驱体生产成本较高，在保证涂层起到有效保护作用的同时， 将TiO 2薄膜厚度控制在较小的范围，可降低复合涂层的生产成本，另一方面，与较厚的TiO 2膜相比，纳米级厚度的TiO 2薄膜的锐钛型晶体结构更加规则，晶胞间的空隙基本可以忽略不计，这非常有利于防止Si元素扩散。
所述涂层还包括由原子层气相沉积法制备的Al 2 O 3薄膜层，且所述Al 2 O 3薄膜层位于所述TiO 2薄膜层和渗铝层之间；在渗铝层与TiO 2薄膜层之间设一层由原子层气相沉积法制备的Al 2 O 3薄膜层，该薄膜层为连续致密涂层。
所述Al 2 O 3薄膜层的厚度为纳米级；优选地，本发明的Al 2 O 3薄膜层的厚度为5～50nm。
所述渗铝层由基体往外依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层；所述Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层的厚度均为微米级；其中，Fe(Al)相扩散层，也可以称为含Al的Fe扩散层，本质上就是Al扩散至基体置换基体表面部分Fe原子形成的扩散层，为贫铝区，含Al较低，在该扩散层中的Al元素的原子百分比从基体表面的0at.％升高至扩散层Fe(Al)相扩散层最外侧的8at.％。其中Al 2 O 3层为表面具有缺陷的不连续涂层，Al 2 O 3层能够起到抗氧化隔绝的作用，但是表面存在的氧化腐蚀沟槽，不仅易诱发热疲劳裂纹起始，而且使抗Al液腐蚀的能力下降。
优选地，所述Fe-Al化合物层的厚度为60～200μm，所述Fe(Al)相扩散层的厚度为50～160μm，Al 2 O 3层的厚度为10～30μm；所述Fe-Al化合物层包括FeAl、FeAl 2和Fe 3 Al。
一种本发明的抗熔融铝硅合金腐蚀涂层的制备方法，包括如下步骤：
S1、对铁基合金进行表面处理，然后采用固体粉末渗剂进行渗铝；
S2、将渗铝后的铁基合金进行喷砂处理；
S3、将经喷砂处理的铁基合金进行洗涤、干燥；
S4、采用原子层气相沉积法在经干燥的渗铝的铁基合金表面沉积TiO 2薄膜层。
本方案中，铁基合金为合金板，优选为奥氏体不锈钢合金钢。
在所述步骤S3和步骤S4之间，还包括采用原子层气相沉积法在步骤S3所得的渗铝的铁基合金表面沉积Al 2 O 3薄膜层，采用该方法引入的Al 2 O 3薄膜层致密均匀、且能够加强对基体的隔离作用，弥补因采用渗铝法获得的渗铝涂层表面的Al 2 O 3层存在的氧化腐蚀沟槽等缺陷，这种缺陷不仅易诱发热疲劳裂纹起始，而且使抗Al液腐蚀的能力下降。本发明通过原子沉积引入原子沉积Al 2 O 3薄膜层，对渗层表面不连续Al 2 O 3薄膜进行了补充，使试样表面覆盖上连续且致密的Al 2 O 3薄膜，达到阻隔Al原子扩散的效果，且还为后续沉积TiO 2薄膜提供良好的表面环境，防止其他干扰元素影响沉积效果，同时，有利于降低界面应力，提高 涂层之间的结合力和稳定性。
所述步骤S1中，所述固体粉末渗剂包括以下组分的均匀混合物：粒度为200目的铝粉，Al 2 O 3和Cr粉组成的填充剂及其粉末状NH 4 Cl的助渗剂，所述固体粉末渗剂中，按质量比计，所述铝粉占42～74％，所述Al 2 O 3粉占20～40％，所述Cr粉占5～15％，所述NH 4 Cl占1～3％；通过采用该组分的固体粉末渗剂，可以有效提高对组织的调控精度，从而进一步提高组织的致密性和完整性。
所述渗铝的条件为：于150℃干燥2h，先于400～600℃保温20～40min，升温速率为10℃/min，再于900℃～1050℃保温10～15h，然后随炉冷却至室温。通过严格控制渗铝条件，能进一步提高对渗铝组织中Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层厚度及微观结构的调控，获得组织更均匀、内应力小、复合涂层结合更紧密的渗铝涂层。
所述步骤S4中，所述沉积TiO 2薄膜层的步骤包括：将腔体加热至300～450℃，以异丙醇钛(纯度99.99％)为前驱体，压力为0.1～0.3torr，充气0.1～0.5s，随后抽气30～50s，再充入等离子水蒸汽0.01～0.03s，最后抽气30～50s，沉积TiO 2薄膜，反复进行异丙醇钛充气-抽气-水蒸气充气-抽气循环，沉积TiO 2薄膜层；控制循环的次数为50～500次，可生成不同厚度的TiO 2薄膜。
所述沉积Al 2 O 3薄膜层的步骤包括：以渗铝钢为衬底，放入设备腔中，腔体加热至150～300℃，以三甲基铝(TMA)(纯度99.99％)为前驱体，压力为0.05～0.2torr，充气0.01～0.03s，随后抽气40～60s，再充入水蒸汽0.01～0.03s，最后抽气20～60s，沉积Al 2 O 3薄膜，反复进行三甲基铝充气-抽气-水蒸气充气-抽气循环，沉积Al 2 O 3薄膜。控制循环的次数为50～500次，可生成不同厚度的Al 2 O 3薄膜。
所述步骤S2中，所述喷砂处理于0.6～0.9MPa的高压氮气下进行；所述喷砂的时间为5～20min；所述喷砂的磨料为300～500目的Al 2 O 3颗粒；喷砂的距离2～6cm。通过控制喷砂处理的压力和时间，可有效去除渗铝层表面蓬松的表层和杂质，得到结合力强、均匀的渗铝组织，且为原子层沉积氧化铝薄膜提供了无外部元素掺杂的优良衬底，提高了反应前驱体与沉底结合的效率。
所述步骤S1中，所述表面处理包括先对铁基合金进行机械抛光处理，然后再进行电解抛光处理；
所述机械抛光处理包括：采用80目～1200目粒度的砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min以除油，无水乙醇超声波清洗5～20min以去渍，最进行干燥；所述电解抛光处理为以铁基合金为阳极、以不溶性导电材料为阴极，对铁基进行电解抛光 处理，所述电解抛光处理的电解液包括体积分数为60～80％的浓硫酸，体积分数为15～37％的浓磷酸和体积分数为3～5％的蒸馏水；所述电解的直流电压为5～6V，电解液的温度为60～80℃，电解抛光的时间为2～5min。
所述电解抛光处理具体为：将321奥氏体不锈钢板接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至60～80℃(可通过水浴加热)，通入5～6V直流电压，在电解中抛光2～5min后，将奥氏体不锈钢板取出冲水清洗吹干，其中电解液的成分如下：体积分数为60～80％的浓硫酸(纯度为98％)、体积分数为15～37％的浓磷酸(纯度为85％)和体积分数为3～5％的蒸馏水。
所述步骤S3具体为：将样品放入盛装3～8L去离子水的烧杯中，加热震荡2～7min，去除样品表面残留的细屑，再将样品放入盛放2～5L丙酮的烧杯中，加热震荡5～10min，将样品取出，放置干燥箱干燥10～30min。
本发明的抗熔融铝硅合金腐蚀性能优良的复合涂层的制备方法，对不锈钢渗铝后进行原子层气相沉积，得到的涂层为多层结构，从外往里依次分别是5nm～50nm厚的TiO 2薄膜、5nm～50nm厚的Al 2 O 3薄膜、不连续10～30μm的Al 2 O 3层、60～200μm厚的Fe-Al外渗层(FeAl、FeAl 2和Fe 3 Al等)、50～160μm厚的含Fe(Al)相扩散层以及基体。复合涂层各层之间结合紧密、无裂缝、界限明显且整齐，原子层气相沉积的Al 2 O 3/TiO 2薄膜或TiO 2薄膜厚度可控，生长均匀、平整且阶梯覆盖性好，表面致密且与渗层结构结合力强，不改变渗层结构。制得的含有Al 2 O 3/TiO 2薄膜涂层或TiO 2薄膜涂层结构的不锈钢经过72小时620℃熔融铝硅合金腐蚀试验，腐蚀速率分别为0.35×10-5g/mm 2·h和0.23×10-5g/mm 2·h，与奥氏体不锈钢相比(腐蚀速率为1.3×10-5g/mm 2·h)分别降低了73.1％和82.3％，表现出优异的抗熔融铝硅合金性能，满足了熔融铝硅合金作为储热介质与太阳能热发电换热管的相容性要求，具有非凡的科研价值和工业应用前景。
实施例1：
一种本发明抗熔融铝硅合金腐蚀复合涂层，所述复合涂层由基体表面往外依次包括渗铝层、Al 2 O 3薄膜层和TiO 2薄膜层。其中Al 2 O 3薄膜层和TiO 2薄膜层均由原子层气相沉积法引入，Al 2 O 3薄膜层和TiO 2薄膜层的厚度依次为5nm和20nm；渗铝层由基体表面往外依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层。其中，Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层均为微米级厚度。
一种本实施例的抗熔融铝硅合金腐蚀复合涂层的制备方法，包括如下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢板试样经不同粒度(80目～1200目)砂纸 打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5min，除油，无水乙醇超声波清洗5min，去渍，最后放入干燥箱80℃干燥20min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％，Ti 0.22％，其余为Fe。
(2)电解抛光：将321奥氏体不锈钢板接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至60℃(可通过水浴加热)，两极同时进入电解液中，通入5V直流电压，在电解中浸泡2min，试样取出冲水清洗吹干；电解液的成分由体积分数为60％的浓硫酸(纯度为98％)，体积分数为37％的浓磷酸(纯度为85％)和体积分数为3％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al 2 O 3和Cr粉作填充剂为和粉末状NH 4 Cl的助渗剂组成，按照5wt.％Cr，64wt.％Al，28wt.％Al 2 O 3，3wt.％NH 4 Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，400℃保温20min，升温速率为10℃/min，在900℃保温15h后随炉冷却至室温；
(4)喷砂处理：将渗铝后试样放在0.6MPa高压氮气下进行喷砂，磨料为300目的Al 2O3颗粒，喷砂时间5min，喷砂距离6cm，去除疏松的渗层以及杂质；
(5)有机溶剂洗涤和干燥：将样品放入盛装3L去离子水的烧杯中，加热震荡7min，去除样品表面残留的细屑，再将样品放入盛放5L丙酮的烧杯中，加热震荡10min，将样品取出，放置干燥箱干燥30min。
(6)原子层气相沉积Al 2 O 3/TiO 2薄膜：以渗铝钢为衬底，放入设备腔中，腔体加热150℃，以三甲基铝(TMA)(纯度99.99％)为前驱体，压力为0.05torr，充气0.03s，随后抽气40s，再充入水蒸汽0.01s，最后抽气30s，沉积Al 2 O 3薄膜，反复进行三甲基铝充气-抽气-水蒸汽充气-抽气循环，循环次数50次，生成厚度为5nm的Al 2 O 3薄膜；以渗铝钢/Al 2 O 3薄膜为衬底，将腔体加热300℃，以异丙醇钛(纯度99.99％)为前驱体，压力为0.1torr，充气0.5s，随后抽气30s，再充入等离子水蒸汽0.01s，最后抽气30s，沉积TiO 2薄膜，反复进行异丙醇钛充气-抽气-水蒸汽充气-抽气循环，循环次数200次，生成厚度为20nm的TiO 2薄膜。
实施例2：
一种本发明抗熔融铝硅合金腐蚀复合涂层，所述复合涂层由基体表面往外依次包括渗铝层、Al 2 O 3薄膜层和TiO 2薄膜层。其中Al 2 O 3薄膜层和TiO 2薄膜层均由原子层气相沉积法引入，Al 2 O 3薄膜层和TiO 2薄膜层的厚度依次为30nm和50nm；渗铝层由基体表面往外 依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层。其中，Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层均为微米级厚度。
一种本实施例的抗熔融铝硅合金腐蚀复合涂层的制备方法，包括如下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢试样经不同粒度(80目～1200目)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗10min，除油，无水乙醇超声波清洗10min，去渍，最后放入干燥箱80℃干燥30min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％，Ti 0.22％，其余为Fe。
(2)电解抛光：将321奥氏体不锈钢接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至70℃(可通过水浴加热)，两极同时进入电解液中，通入5V直流电压，在电解中浸泡5min，试样取出冲水清洗吹干，其中，电解液的成分由体积分数为70％的浓硫酸(纯度为98％)，体积分数为26％的浓磷酸(纯度为85％)和体积分数为4％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al 2 O 3和Cr粉作填充剂为和粉末状NH 4 Cl的助渗剂组成，按照15wt.％Cr，44wt.％Al，40wt.％Al 2 O 3，1wt.％NH 4 Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，600℃保温40min，升温速率为10℃/min，在1050℃保温10h后随炉冷却至室温。
(4)喷砂处理：将渗铝后试样放在0.8MPa高压氮气下进行喷砂，磨料为400目的Al 2 O 3颗粒，喷砂时间10min，喷砂距离4cm，去除疏松的渗层以及杂质。
(5)有机溶剂洗涤和干燥：将样品放入盛装8L去离子水的烧杯中，加热震荡7min，去除样品表面残留的细屑，再将样品放入盛放5L丙酮的烧杯中，加热震荡10min，将样品取出，放置干燥箱干燥30min。
(6)原子层气相沉积Al 2 O 3/TiO 2薄膜：以渗铝钢为衬底，放入设备腔中，腔体加热300℃，以三甲基铝(TMA)(纯度99.99％)为前驱体，压力为0.2torr，充气0.01s，随后抽气60s，再充入水蒸汽0.03s，最后抽气50s，沉积Al 2 O 3薄膜，反复进行三甲基铝充气-抽气-水蒸汽充气-抽气循环，循环次数300次，生成厚度为30nm的Al 2 O 3薄膜；以渗铝钢/Al 2 O 3薄膜为衬底，将腔体加热450℃，以异丙醇钛(纯度99.99％)为前驱体，压力为0.3torr，充气0.5s，随后抽气50s，再充入等离子水蒸汽0.03s，最后抽气50s，沉积TiO 2薄膜，反复进行异丙醇钛充气-抽气-水蒸汽充气-抽气循环，循环次数500次，生成同厚度为50nm的TiO 2薄膜。
实施例3：
一种本发明抗熔融铝硅合金腐蚀复合涂层，所述复合涂层由基体表面往外依次包括渗铝层、Al 2 O 3薄膜层和TiO 2薄膜层。其中Al 2 O 3薄膜层和TiO 2薄膜层均由原子层气相沉积法引入，Al 2 O 3薄膜层和TiO 2薄膜层的厚度依次为10nm和10nm；渗铝层由基体表面往外依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层；其中，Fe(Al)相扩散层、Fe-Al化合物层和Al 2 O 3层均为微米级厚度。
一种本实施例的抗熔融铝硅合金腐蚀复合涂层的制备方法，包括如下步骤：
(1)表面机械抛光：将热轧板材奥氏体不锈钢试样经不同粒度(80目～1200目)砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗20min，除油，无水乙醇超声波清洗20min，去渍，最后放入干燥箱80℃干燥40min；其中321奥氏体不锈钢是轧制板材，其化学成分的质量分数为C 0.04％，Si 0.38％，Mn 1.08％，Cr 17.02％，Ni 9.06％，N 0.05％，P 0.03％，Ti 0.22％，其余为Fe。
(2)电解抛光：将321奥氏体不锈钢接在阳极，阴极用不溶性导电材料(石墨板)，阴阳极间距50mm，电解液加热至80℃(可通过水浴加热)，两极同时进入电解液中，通入5V直流电压，在电解中浸泡3min，试样取出冲水清洗吹干；电解液的成分由体积分数80％的浓硫酸(纯度为98％)，体积分数为15％的浓磷酸(纯度为85％)和体积分数5％的蒸馏水组成。
(3)渗铝：固体粉末渗剂由铝源、填充剂、助渗剂(活化剂)组成，其中铝源采用粒度为200目的铝粉，Al 2 O 3和Cr粉作填充剂为和粉末状NH 4 Cl的助渗剂组成，按照10wt.％Cr，58wt.％Al，30wt.％Al 2 O 3，2wt.％NH 4 Cl充分混合。将渗剂与试样装入耐热不锈钢料罐中，压紧，耐火泥密封，进行渗铝：随炉升温，150℃干燥2h，500℃保温30min，升温速率为10℃/min，在950℃保温12h后随炉冷却至室温。
(4)喷砂处理：将渗铝后试样放在0.9MPa高压氮气下进行喷砂，磨料为500目的Al 2 O 3颗粒，喷砂时间为5min，喷砂距离为2cm，去除疏松的渗层以及杂质。
(5)有机溶剂洗涤：将样品放入盛装5L去离子水的烧杯中，加热震荡5min，去除样品表面残留的细屑，再将样品放入盛放4L丙酮的烧杯中，加热震荡8min，将样品取出，放置干燥箱干燥20min。
(6)原子层气相沉积Al 2 O 3/TiO 2薄膜：以渗铝钢为衬底，放入设备腔中，腔体加热200℃，以三甲基铝(TMA)(纯度99.99％)为前驱体，压力为0.1torr，充气0.02s，随后抽气45s，再充入水蒸汽0.015s，最后抽气45s，沉积Al 2 O 3薄膜，反复进行三甲基铝充气-抽气-水蒸汽充气-抽气循环，循环次数90次，生成约10nm厚度的Al 2 O 3薄膜；以渗铝钢/Al 2 O  3薄膜为衬底，将腔体加热370℃，以异丙醇钛(纯度99.99％)为前驱体，压力为0.2torr，充气0.25s，随后抽气40s，再充入等离子水蒸汽0.02s，最后抽气40s，沉积TiO 2薄膜，反复进行异丙醇钛充气-抽气-水蒸汽充气-抽气循环，循环次数90次，生成约10nm厚度的TiO 2薄膜。
实施例4：
一种本发明抗熔融铝硅合金腐蚀复合涂层，与实施例3中的复合涂层的不同点在于，本实施例的复合涂层中不含采用原子层气相沉积法引入的Al 2 O 3薄膜层。
一种本实施例的抗熔融铝硅合金腐蚀复合涂层的制备方法，与实施例3中的复合涂层的制备方法基本相同，其不同点在于，步骤(6)中省略了原子层沉积Al 2 O 3薄膜层的步骤，直接在渗铝钢表面原子层沉积TiO 2薄膜层。
对比例1：
一种抗熔融铝硅合金腐蚀复合涂层，与实施例3中的复合涂层的不同点在于，本对比例的复合涂层中仅含有渗铝层，不含原子层气相沉积的Al 2 O 3薄膜和TiO 2薄膜层。
一种本对比例的抗熔融铝硅合金腐蚀复合涂层的制备方法，与实施例3中的复合涂层的制备方法的不同点在于，不含步骤(6)。
对实施例3所得复合涂层表面进行SEM分析，其结果如图1(b)所示，与原子层气相沉积前相比的渗铝钢表面形貌(图1(a))相比，未发现明显差异，说明该工艺不改变渗层表面的结构。对图1(b)中A点进行能谱分析，能检测到Fe、Cr、Al、Ti、O原子，由于EDS透入了基体，因此除了涂层内的原子外，还观察到了基体材料中含有的Cr和Fe原子，因原子层气相沉积产生的TiO 2厚度尺寸为纳米级别，因此在EDS中观察Ti元素非常微量。
图2为实施例三制备的含ALD Al 2 O 3/TiO 2复合渗铝涂层和实施例四制备的含ALDTiO2复合渗铝涂层的321不锈钢与对比例1制备的含渗铝层的321不锈钢及不含涂层的321不锈钢经过72小时620℃熔融铝硅合金腐蚀得到的腐蚀速率柱状图。
对不同腐蚀时间的金属试样，采用失重法测定试样的腐蚀程度。试样的失重直接表征材料的腐蚀程度，金属试样腐蚀性的评定即试样的腐蚀速率V(g/mm 2·h)，由式(1)计算，
Figure PCTCN2020077573-appb-000001
其中，A为样品表面积(mm 2)；W 0为试样侵蚀前质量(g)；W为试样侵蚀后质量(g)；t为腐蚀时间(h)。结果如图2所示，可以看出与不锈钢抗熔融铝硅合金的腐蚀速率相比，单一的渗铝涂层试样抗腐蚀速率降低63.1％，ALD TiO 2复合渗铝保护涂层试样的熔融铝硅腐蚀速率 降低了73.1％，ALD Al 2 O 3/TiO 2复合渗铝保护涂层试样的熔融铝硅腐蚀速率降低了82.3％。可见，本发明的复合涂层表现出优异的抗熔融铝硅合金性能，且采用ALD Al 2 O 3/TiO 2复合渗铝相比于ALD TiO 2复合渗铝所得的涂层效果得到很大改善，能很好地满足熔融铝硅合金作为储热介质与太阳能热发电换热管的相容性要求。
虽然本发明已以较佳实施例揭示如上，然而并非用以限定本发明。任何熟悉本领域的技术人员，在不脱离本发明技术方案范围的情况下，都可利用上述揭示的技术内容对本发明技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本发明技术方案的内容，依据本发明技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均应落在本发明技术方案保护的范围内。

Claims (10)

  1. 抗熔融铝硅合金腐蚀复合涂层，其特征在于，所述复合涂层由基体表面往外依次包括渗铝层和TiO2薄膜层。
  2. 如权利要求1所述的抗熔融铝硅合金腐蚀复合涂层，其特征在于，所述复合涂层还包括由原子层气相沉积法制备的Al2O3薄膜层，且所述Al2O3薄膜层位于所述TiO2薄膜层和渗铝层之间；所述Al2O3薄膜层的厚度为纳米级。
  3. 如权利要求1或2所述的抗熔融铝硅合金腐蚀复合涂层，其特征在于，所述渗铝层由基体往外依次包括Fe(Al)相扩散层、Fe-Al化合物层和Al2O3层；Fe(Al)相扩散层、Fe-Al化合物层和Al2O3层的厚度均为微米级。
  4. 如权利要求1～3任一项所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，包括如下步骤：S1、对铁基合金进行表面处理，然后采用固体粉末渗剂进行渗铝；S2、将渗铝后的铁基合金进行喷砂处理；S3、将经喷砂处理的铁基合金进行洗涤、干燥；S4、采用原子层气相沉积法在经干燥的渗铝的铁基合金表面沉积TiO2薄膜层。
  5. 如权利要求4所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，在所述步骤S3和步骤S4之间，还包括采用原子层气相沉积法在步骤S3所得的渗铝铁基合金表面沉积Al2O3薄膜层。
  6. 如权利要求4所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，所述步骤S1中，所述固体粉末渗剂为包括以下组分的均匀混合物：粒度为200目的铝粉，Al2O3和Cr粉组成的填充剂及其粉末状NH4Cl的助渗剂，所述固体粉末渗剂中，按质量比计，所述铝粉占42～74％，所述Al2O3粉占20～40％，所述Cr粉占5～15％，所述NH4Cl占1～3％；所述渗铝的条件为：先于400～600℃保温20～40min，再于900℃～1050℃保温10～15h，然后随炉冷却至室温。
  7. 如权利要求4所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，所述步骤S3中，所述沉积TiO2薄膜层的步骤包括：以异丙醇钛为前驱体，压力为0.1～0.3torr，充气0.1～0.5s，随后抽气30～50s，再充入等离子水蒸汽0.01～0.03s，最后抽气30～50s，反复进行异丙醇钛充气-抽气-水蒸气充气-抽气循环，沉积TiO2薄膜层；所述循环的次数为50～500次。
  8. 如权利要求5所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，所述沉积Al2O3薄膜层的步骤包括：以三甲基铝为前驱体，压力为0.05～0.2torr，充气0.01～0.03s，随后抽气40～60s，再充入水蒸汽0.01～0.03s，最后抽气20～60s，反复进行三甲基铝充气-抽气-水蒸气充气-抽气循环，沉积Al2O3薄膜层；所述循环的次数为50～500次。
  9. 如权利要求4～8任一项所述的抗熔融铝硅合金腐蚀复合涂层的制备方法，其特征在于，所述步骤S2中，所述喷砂处理于0.6～0.9MPa的高压氮气下进行；所述喷砂的时间为5～20min； 所述喷砂的磨料为300～500目的Al2O3颗粒；喷砂的距离2～6cm；所述步骤S1中，所述表面处理包括先对铁基合金进行机械抛光处理，然后再进行电解抛光处理；所述机械抛光处理包括：采用80目～1200目粒度的砂纸打磨至肉眼可见无明显划痕，然后在超声波中采用丙酮清洗5～20min，再用无水乙醇超声波清洗5～20min，最后进行干燥；所述电解抛光处理为以铁基合金为阳极、以不溶性导电材料为阴极，对铁基进行电解抛光处理；所述电解抛光处理的电解液包括体积分数为60～80％的浓硫酸，体积分数为15～37％的浓磷酸和体积分数为3～5％的蒸馏水；所述电解的直流电压为5～6V，电解液的温度为60～80℃，电解抛光的时间为2～5min。
  10. 如权利要求1～3任一项所述的抗熔融铝硅合金腐蚀复合涂层或如权利要求4～9任一项所述的方法制备的抗熔融铝硅合金腐蚀复合涂层在太阳能热发电换热管中的应用。
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