CN109680241B

CN109680241B - Preparation method of amorphous oxide ceramic composite coating integrating toughness, heat conduction and high-temperature microstructure stability

Info

Publication number: CN109680241B
Application number: CN201910143274.9A
Authority: CN
Inventors: 杨凯; 荣建; 庄寅; 倪金星; 盛靖; 邵芳; 赵华玉; 陶顺衍; 丁传贤
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2019-02-26
Filing date: 2019-02-26
Publication date: 2020-10-23
Anticipated expiration: 2039-02-26
Also published as: WO2020173151A1; CN109680241A

Abstract

The invention relates to a strong and tough, heat conduction and high-temperature microstructure stabilization integrationThe amorphous oxide ceramic composite coating is Al₂O₃-YAG amorphous ceramic coating, the preparation method comprising: (1) mixing Al₂O₃Powder and Y₂O₃Mixing the powders to obtain Al₂O₃/Y₂O₃Mixing the powder; (2) mixing the obtained Al₂O₃/Y₂O₃Carrying out heat treatment on the mixed powder at 1400-1600 ℃ to obtain Al₂O₃YAG composite powder; (3) al obtained by thermal spraying₂O₃Spraying the/YAG composite powder on the surface of the base material to obtain Al₂O₃-YAG amorphous ceramic coating.

Description

Preparation method of amorphous oxide ceramic composite coating integrating toughness, heat conduction and high-temperature microstructure stability

Technical Field

The invention relates to a preparation method of an amorphous oxide ceramic composite coating with toughness, heat conduction and high-temperature microstructure stability, belonging to the technical field of ceramic coatings.

Background

The material friction wear (often accompanied by high temperature, strong oxidation and large thermal shock) under the condition of high PV value (P is contact pressure and V is friction rate) is a key factor for determining the service reliability and service life of mechanical systems such as aerospace and aeroengines, space vehicles, high-end pump valves and the like. The harsh engineering application conditions require that the friction material should have high hardness, high toughness, high temperature resistance, oxidation resistance, wear resistance and good thermal shock resistance so as to ensure high reliability, long service life and the like. However, the existing single structural material cannot meet the requirements of the above special working conditions. The research shows that: the preparation of the ceramic coating on the surface of the high-strength heat-resistant metal is an important way for improving the performances of the substrate material such as wear resistance, high temperature resistance, thermal shock resistance, oxidation resistance and the like.

Under high PV wear conditions, the ceramic coating needs to withstand high pressures, high frictional rates and the resulting high frictional heat (maximum temperature of the frictional contact surface approaching or even exceeding 1000 ℃), severe thermal shock. In the face of the service working conditions, the traditional carbide and nitride ceramic materials are not suitable. The WC/Co coating shows excellent wear-resisting and corrosion-resisting properties, but the reliable service temperature is lower than 500 ℃; SiC and Si₃N₄Ceramics cannot be coated by a thermal spraying process; ZrC, B₄The thermal expansion coefficient of ceramics such as C, BN and the like is low, the matching property with a metal substrate is poor, and the coating is difficult to bear high and low temperature impact. Oxide ceramics (e.g. Al)₂O₃、Cr₂O₃、ZrO₂And TiO₂) The coating has the characteristics of wear resistance, high temperature resistance, oxidation resistance, higher thermal expansion coefficient and the like, and has better potential when being applied to harsh wear working conditions with high PV values as a thermal spraying coating. However, the low toughness and high crack sensitivity of oxide ceramics restrict the expansion application of the oxide ceramics. The abrasion under the condition of high PV value causes sudden increase of heat generated by friction, and the thermal stress between the coating and the metal substrate caused by the difference of thermal expansion coefficients is obviously increased, so that the coating is required to have good high-temperature microstructure stability and fracture toughness; the higher heat conductivity of the coating is beneficial to dissipating frictional heat, reducing thermal stress and improving the wear resistance of the coating, and the heat conductivity of the coating becomes an important factor influencing the wear resistance of the coating.

Among the common oxide wear-resistant ceramic materials, Al₂O₃(α-Al₂O₃Has a thermal conductivity of 36 W.m^-1·K^-1) The heat conductivity of the alloy is superior to that of Cr₂O₃、ZrO₂And TiO₂. Thermal spraying of oxide wear-resistant ceramic coatings with Al₂O₃And the research and application of the composite coating thereof are more. Representative improvement of Al₂O₃The coating method comprises the following steps: (1) the substrate deposition temperature is increased. Increasing the deposition temperature can improve Al₂O₃Bonding between the single-sheet layer (splat) and the substrate and single-sheet layer, thereby improving Al₂O₃Coating compactness, microhardness, toughness and thermal conductivity. However, gamma-Al in the coating₂O₃Phase (thermal conductivity 1.6 W.m)^-1·K^-1) Still in the main crystal phase, the deposition temperature is raised from 140 ℃ to 660 ℃, alpha-Al₂O₃The phase content is increased from 20 percent to 26 percent, the improvement effect of the coating on the toughness and the thermal conductivity is limited (alpha-Al)₂O₃Phase contrast of gamma-Al₂O₃The phase has better thermal stability, mechanical property and heat-conducting property); higher deposition temperatures are not suitable for preparing ceramic coatings on most metal substrate surfaces. (2) Dry ice assisted deposition. Plasma spraying Al by dry ice on-line spraying technology₂O₃The bonding strength of the coating is improved by 30 percent (the numerical value exceeds 60MPa), the porosity is reduced from 9.3 percent to 6.8 percent, and the residual compressive stress in the coating is improved by nearly one time, thereby being beneficial to inhibiting crack propagation and improving fracture toughness. However, the deposition temperature can be greatly reduced by the aid of dry ice deposition, the cooling rate is increased, effective interface bonding between single-chip layers is reduced, and introduction of an amorphous phase is increased, so that the high-temperature mechanical property of the coating is reduced. (3) And (5) laser remelting post-treatment. Plasma spraying of Al₂O₃The laser remelting on the surface of the coating can increase alpha-Al in the coating₂O₃The cladding layer with fine structure, low porosity and high hardness is obtained through the phase content, but the hardness of the cladding layer changes obviously along the thickness direction, the microstructure and the mechanical property are poor in consistency, the fracture toughness is reduced, the residual internal stress is large, and the cracking and the failure of the coating are easily caused in the severe abrasion process. (4) The coating microstructure is nanocrystallized. Nano-grade Al with fine crystal strengthening and toughening effects₂O₃The coating has higher hardness and toughness, better sliding resistance and erosion abrasion resistanceLoss of performance and alpha-Al in the coating₂O₃The phase content can reach more than 50 percent (pure alpha-Al with a nano structure can be prepared by utilizing a novel liquid-phase plasma spraying method₂O₃Phase coating). However, there are problems in that: under the high-friction heat service environment generated by the harsh abrasion working condition with a high PV value, the long-term stability of a nano coating microstructure is poor, and the toughness of the coating changes greatly under the conditions of high temperature and strong heat impact; secondly, the nano coating has more crystal boundaries, the phonon scattering is enhanced, and good heat-conducting property is difficult to obtain. (5) The metal phase is added to the coating. In Al₂O₃The addition of metal phase (such as Al) in the coating improves the toughness and thermal conductivity of the coating. In order to further improve the toughness and thermal conductivity of the coating to adapt to severe wear conditions with high PV values, the content of metallic Al needs to be increased continuously. However, the interface bonding performance of the excessive metal phase and the ceramic phase matrix is difficult to control, the number of interface defects is greatly increased, the hardness and strength of the coating are greatly reduced, and the coating is not favorable for being used under the harsh abrasion condition. (6) And compounding with other oxides. (ii) ZrO₂(or Y)₂O₃Partially stabilized ZrO₂(YSZ)) has low thermal conductivity and causes Al to be formed₂O₃–ZrO₂Or Al₂O₃The thermal conductivity of the YSZ composite coating is obviously reduced, a large amount of heat is accumulated under the condition of high PV value abrasion, stress is rapidly concentrated, microcrack of the coating is rapidly expanded, and the abrasion-resistant life of the coating is reduced. (II) TiO₂Good thermal conductivity, and Al₂O₃Can form vacancy solid solution and improve the bonding property, compactness and toughness of the coating phase interface. However, there is a problem that TiO₂The addition of (2) reduces the high-temperature creep resistance of the coating, and the high-temperature mechanical property of the coating is reduced, so that the wear resistance and the service life of the coating are reduced under the high-PV-value wear condition. Utilizing Cr₂O₃The heat conductivity of the alloy shows positive temperature coefficient characteristics, crystal structure and solid solution characteristics along with temperature rise, composite powder is prepared by a mechanical mixing method, and Al is prepared by plasma spraying₂O₃–Cr₂O₃And (4) composite coating. alpha-Al in coating by partial solid solution and heterogeneous nucleation₂O₃Increased phase content, composite coatingsHaving more than one Al₂O₃Or Cr₂O₃The coating has better obdurability, heat-conducting property and wear-resisting property. To further enhance the solid solution effect, more α -Al remains in the coating₂O₃Phase, nano-agglomerated powder is required. However, this would face the same problem: firstly, the grain boundary of the nano-structure coating is greatly increased, the phonon scattering is obviously enhanced, and the high thermal conductivity of the coating is difficult to ensure; secondly, the high PV value severe abrasion generates high friction heat to cause the growth of nano crystal grains in the coating, and the microstructure and the mechanical property of the coating are unstable. (7) Amorphous Al₂O₃And (3) base composite coating. With Al₂O₃YAG amorphous coating is taken as an example, and the amorphous composite ceramic coating is prepared by in-situ spraying by utilizing the characteristics of high enthalpy, steep temperature gradient and quick solidification of thermal spraying. The coating has compact structure, low porosity and good interlayer interface bonding, and the amorphous phase main body part contains more free volume and can effectively form a shear band during deformation so as to ensure that the shear band has high fracture toughness; the main body part of the amorphous structure can improve the corrosion resistance of the amorphous composite ceramic coating; meanwhile, a small amount of nano-crystalline grains dispersed in the coating can improve the mechanical property and the wear resistance of the coating. However, the amorphous ceramic coating is formed with nano Al₂O₃And Y₂O₃Powder is used as raw material, and spraying granulation is carried out to obtain sprayable Al₂O₃/Y₂O₃The composite powder and the amorphous coating prepared by in-situ spraying have the following two problems: firstly, Al is obtained in situ in the plasma spraying process₂O₃The proportion change range of an amorphous phase in the YAG amorphous coating is large, the component distribution is uneven, the content of dispersed crystal grains is high, and the microstructure stability and quality consistency are difficult to control; secondly, the glass transition temperature of the amorphous phase component is lower and close to 500 ℃, the coating is in service at high temperature, the microstructure stability is difficult to maintain, and the volume change accompanied in the crystallization process can induce the initiation and expansion of micro cracks of the coating, so that the service life of the coating is reduced. (8) Eutectic Al₂O₃And (3) base composite coating. Amorphous Al₂O₃After the base composite coating is subjected to heat treatment, eutectic ceramic coating can be obtainedLayer (e.g. Al)₂O₃-YAG、Al₂O₃-ZrO₂And the like), the eutectic phase forms a three-dimensional interpenetrating network self-locking structure, the phase size is difficult to grow up, and the high-temperature microstructure stability is good; meanwhile, the mechanical property and the heat conductivity of the eutectic composite ceramic coating are greatly improved, and the eutectic composite ceramic coating has a good application prospect under harsh working conditions such as high specific pressure, high temperature, oxygen enrichment, strong corrosion and the like. However, there are two major problems: obtaining eutectic Al₂O₃The heat treatment temperature of the base composite coating is over 1000 ℃, except for high-temperature alloy, most metal base materials can not meet the high heat treatment temperature, so the actual application range is greatly limited; secondly, in the process of obtaining the eutectic ceramic coating by the amorphous ceramic coating through heat treatment, along with the change of the volume, the high thermal stress exists between the amorphous ceramic coating and the high-temperature alloy base material with high thermal expansion coefficient, and the coating is easy to crack and peel.

As described above, conventional Al₂O₃The main problems existing in the research of the composite coating are as follows: firstly, the traditional research aims at milder abrasion working conditions, is limited to the mechanical property of the coating, and neglects the special influences of a large amount of frictional heat accumulation, strong thermal impact stress and the like; secondly, the high-temperature mechanical property and the heat-conducting property of the coating are effectively improved and cannot be considered at the same time in a high-friction heat service environment generated by a high-PV-value harsh working condition; thirdly, under the severe service environment of high temperature and high stress for a long time, the stability of the microstructure of the coating is difficult to maintain due to factors such as grain boundary creep, desolvation effect, diffusible phase change and the like, and the heat conduction, mechanics and wear resistance of the coating are influenced; fourthly, the amorphous phase content of the amorphous ceramic coating has large variation range and low glass transition temperature, and the microstructure stability of the coating in service at high temperature is poor; fifthly, the eutectic ceramic coating needs high heat treatment temperature in the preparation process, and the coating is easy to crack and peel in the heat treatment process.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a preparation method of an amorphous oxide ceramic composite coating with toughness, heat conduction and stable integration of a high-temperature microstructure, so that the coating can obtain long service life and high reliability service under severe service environments such as high PV value, high temperature, strong oxidation, wide-temperature-range thermal shock, corrosion and the like, the high-temperature mechanical property and the heat conduction property of the coating are taken into consideration, and the amorphous phase content, the component distribution uniformity, the glass transition temperature, the high-temperature microstructure stability, the interlayer interface combination and the like of the coating are improved. The coating is obtained by in-situ spray deposition for the first time without subsequent heat treatment, so that the severe requirements of high-temperature heat treatment on the metal base material and the adverse effects of cracking or peeling failure of the coating easily caused by high thermal mismatch stress are avoided.

Therefore, the invention provides a preparation method of an amorphous oxide ceramic composite coating with toughness, heat conduction and stable and integrated high-temperature microstructure, wherein the amorphous oxide ceramic composite coating is Al₂O₃-YAG amorphous ceramic coating, the preparation method comprising:

(1) mixing Al₂O₃Powder and Y₂O₃Mixing the powders to obtain Al₂O₃/Y₂O₃Mixed powder of Al₂O₃/Y₂O₃Al in mixed powder₂O₃The mass fraction of the powder is 50-67 percent, and Y is₂O₃The mass fraction range of the powder is 33-50% (the sum of the mass fractions is 100%);

(2) mixing the obtained Al₂O₃/Y₂O₃Carrying out heat treatment on the mixed powder at 1400-1600 ℃ to obtain Al₂O₃YAG composite powder;

(3) al obtained by thermal spraying₂O₃Spraying the/YAG composite powder on the surface of the base material to obtain Al₂O₃-YAG amorphous ceramic coating.

In the present disclosure, Al is added₂O₃Powder (mass fraction range is 50% -67%) and Y₂O₃Mixing the powder (the mass fraction is 33-50%), and performing heat treatment (1400-1600 ℃) to enable Al to be formed₂O₃/Y₂O₃The composite powder undergoes solid phase reaction (chemical reaction is 5 Al)₂O₃+3Y₂O₃→2Y₃Al₅O₁₂(YAG)) to produce Al₂O₃a/YAG composite powder. In this case, the YAG phase is in Al₂O₃The YAG composite powder simultaneously forms a network structure (the solid phase reaction generates alpha-Al)₂O₃And YAG phase, which can be connected into a whole and is beneficial to Al₂O₃High-temperature microstructure stability of/YAG composite powder).

Preferably, in step (1), the Al is₂O₃The main crystal phase of the powder is alpha-Al₂O₃Said Y is₂O₃The main crystal phase of the powder is c-Y₂O₃. Wherein, alpha-Al₂O₃And c-Y₂O₃The phase forms of the alumina and the yttria with the most stable chemical property and better mechanical and heat-conducting properties are respectively adopted.

Preferably, in step (1), Al is added₂O₃And Y₂O₃Carrying out wet ball milling on the powder, mixing the powder uniformly, preparing suspension stable slurry, and carrying out spray granulation to obtain Al₂O₃/Y₂O₃And (3) composite powder. The invention adopts a spray granulation method to prepare Al₂O₃/Y₂O₃The method has the advantages of: the spray drying operation is continuous and controllable, is suitable for drying heat-sensitive and non-heat-sensitive materials, and is suitable for drying aqueous solution and organic solvent materials, the raw material liquid can be solution, slurry, emulsion, paste and the like, the flexibility is very high, the powder quality stability is good, the powder making efficiency is high, and the prepared powder has uniform components, good physical and chemical properties and good sphericity.

Preferably, in step (1), the Al is₂O₃The particle size of the powder is 2 nm-2 mu m, and the Y is₂O₃The particle size of the powder is 2 nm-2 mu m.

Preferably, the heat treatment time in the step (2) is 2 to 4 hours.

Preferably, the Al obtained is applied before thermal spraying₂O₃Plasma spheroidizing of/YAG composite powderAnd (6) processing. Preferably, the parameters of the plasma spheroidizing treatment comprise: argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the argon gas flow is 30-40 slpm, the hydrogen gas flow is 3-7 slpm, the current is 350-500A, the power is 20-35 kW, the powder conveying carrier gas argon gas flow is 3-4 slpm, the powder conveying speed is 5-15 g/min, and the spraying distance is 200-300 mm. More preferably, the plasma spheroidized Al₂O₃The particle size of the/YAG composite powder is 20-40 mu m. The purpose of plasma spheroidization is as follows: so that Al is present₂O₃The surface layer of the/YAG composite powder is fused and densified, the edge angle area on the surface of the powder is eliminated, better sphericity is obtained, the fluidity of the composite powder is promoted, and the phase composition of the composite powder is not changed. Spheroidizing the plasma treated Al₂O₃The YAG composite powder is filtered and dried, and then is screened to obtain the sprayable composite powder with certain particle size distribution, compact surface, good sphericity and good fluidity (preferably, the obtained composite powder has the particle size distribution range of 20-40 mu m and is suitable for subsequent thermal spraying).

Preferably, in the step (3), the thermal spraying is plasma spraying; the parameters of the plasma spraying include: plasma gas argon gas flow 45 ~ 55slpm, plasma gas hydrogen gas flow 7 ~ 10slpm, current 600 ~ 700A, power 45 ~ 50kW, powder feeding carrier gas argon gas flow 3 ~ 4slpm, powder feeding rate 30 ~ 40g/min, spraying distance 100 ~ 120 mm.

Preferably, the deposition temperature is maintained below Al during the thermal spraying process₂O₃-glass transition temperature of YAG system. Preferably, the deposition temperature is controlled to be lower than Al by adopting a cooling mode₂O₃-glass transition temperature of YAG system. More preferably, the cooling means comprises compressed air, recycled water or liquid nitrogen cooling.

Also, preferably, the deposition temperature is 100 to 250 ℃. In one scheme, the actual deposition temperature of spraying can be controlled to be 100-250 ℃ through the combined cooling of compressed air, circulating water or liquid nitrogen.

At the presence of Al₂O₃The YAG composite powder is thermally sprayedConstruction of Al by thermal spraying with greater supercooling₂O₃YAG deep eutectic system, the actual deposition temperature of the composite coating (the deposition temperature refers to the temperature of the liquid drop flying to the surface of the base material or the surface of the deposited coating after the powder is heated and accelerated by plasma flame flow, and then the liquid drop is impacted, spread, cooled and solidified, and the temperature of the front edge of the solid/liquid interface of the liquid drop in the solidification process after the base material is cooled by compressed air, circulating water or liquid nitrogen is defined as the actual deposition temperature) is lower than Al₂O₃The glass transition temperature of the YAG system (typically 500 ℃ C. and 900 ℃ C.), so that Al₂O₃Stopping growing of the/YAG eutectic phase and obtaining Al in situ₂O₃-YAG amorphous ceramic coating. And a larger supercooling degree is constructed in the thermal spraying process, so that the actual spraying deposition temperature is far lower than the glass transition temperature of the coating, and the amorphous ceramic coating is obtained in situ. And the level of the compressive stress in the coating is effectively controlled, the expansion of microcracks in the coating under the wide-temperature-range thermal shock condition of the high-PV-value abrasion working condition is retarded, and the long-term service reliability of the coating is improved. Furthermore, it is possible to avoid that too low deposition temperatures affect the interface bonding between the monolithic layer (splat) and the substrate and between the monolithic layers.

Preferably, the substrate is a metal substrate, a ceramic substrate, or a graphite substrate; preferably, the substrate is cleaned and grit blasted prior to spraying. Preferably, the thickness of the obtained amorphous oxide ceramic composite coating is 50-800 μm.

Has the advantages that:

the preparation method can be used for obtaining Al which is tough, heat-conducting and stable in high-temperature microstructure₂O₃-YAG amorphous ceramic composite coating. The amorphous phase content in the coating exceeds 90%, the components are uniformly distributed, and the coating has higher glass transition temperature, high-temperature microstructure stability, interlayer interface combination, density and the like, so that the coating can obtain long service life and high reliability service in severe service environments such as high PV value, high temperature, strong oxidation, wide-temperature-range thermal shock, corrosion and the like, and the high-temperature mechanical property and the heat-conducting property of the coating are taken into consideration. In addition, the amorphous ceramic coating with excellent high-temperature performance is obtained by in-situ spray deposition without the need ofSubsequent heat treatment is carried out, so that the severe requirements of high-temperature heat treatment on the metal base material and the adverse effects that the coating is easy to crack or peel and lose efficacy due to high thermal mismatch stress are avoided.

Drawings

FIG. 1 is a spray-granulated Al prepared in example 1₂O₃/Y₂O₃The morphology and element distribution diagram of the composite powder are as follows: (a) SEM photograph of the powder; (b) the morphology of a single powder particle; (c) - (f) EDS spectrum analysis of the individual powder particles;

FIG. 2 is Al after heat treatment at different heat treatment temperatures in example 1₂O₃YAG composite powder morphology (grey phase is alpha-Al)₂O₃White phase YAG): (a, b)1400 ℃; (c, d)1550 ℃;

FIG. 3 is spray-granulated Al prepared in example 1₂O₃/Y₂O₃XRD spectrum of the composite powder;

FIG. 4 shows Al obtained after heat treatment in example 1₂O₃XRD spectrum of/YAG composite powder;

FIG. 5 is a graph of Al build-up using plasma spray with greater undercooling₂O₃-YAG deep eutectic system, in situ obtaining Al₂O₃-a schematic view of the principle of YAG amorphous oxide ceramic coating;

FIG. 6 shows as-sprayed Al prepared in example 1₂O₃XRD pattern of YAG amorphous ceramic composite coating (amorphous phase content up to 90% or more);

FIG. 7 shows as-sprayed Al prepared in example 2₂O₃-TEM structural analysis of YAG amorphous ceramic composite coating;

FIG. 8 shows as-sprayed Al prepared in example 3₂O₃DSC curve of YAG amorphous ceramic composite coating (temperature rise rate 30K/min);

FIG. 9 shows as-sprayed Al prepared in example 2₂O₃-cross-sectional morphology and energy spectrum analysis of YAG amorphous ceramic composite coatings;

FIG. 10 is Al prepared in example 2₂O₃-element distribution diagram of YAG amorphous ceramic composite coatingThe element distribution in the amorphous matrix of the coating is uniform;

FIG. 11 shows as-sprayed Al obtained at different ramp rates in example 3₂O₃DSC curves (5K/min, 10K/min, 20K/min, 30K/min) of YAG amorphous ceramic composite coatings;

FIG. 12 is a graph of DSC curve sensitivity of characteristic temperature versus ramp rate, where the characteristic temperature versus ramp rate reflects the sensitivity of the characteristic temperature to ramp rate, which also reflects the thermal stability of the crystallization process for the characteristic temperature. It can be seen that the linear relationship between the characteristic temperatures T and ln (β) is consistent with the empirical formula of Losocka (i.e., T ═ A + Bln (β), where A and B are constants and T is the corresponding characteristic temperature (T)_g、T_c1、T_p1、T_c2、T_p2). A represents the characteristic temperature when the heating rate is 1K/min, B represents the sensitivity of the structural change of the material under different heating rates), the nucleation process of the YAG phase is sensitive to the heating rate, and the alpha-Al phase is sensitive to the heating rate₂O₃Is relatively sluggish (T)_cCorresponding to the nucleation process, T_pCorresponding to the growth process). In terms of sensitivity to heating rate, the nucleation process of YAG phase is more sensitive than the growth process, while alpha-Al₂O₃On the contrary, the crystal growth process is more sensitive than the nucleation process (T)_c1And T_p1Corresponding to YAG phase, T_c2And T_p2Corresponding to alpha-Al₂O₃Phase);

FIG. 13 is a graph showing the calculation of the activation energy at each stage for the characteristic temperature of the coating under non-isothermal conditions (Kissinger method, Augis-Bennett method and Ozawa method), from which it can be seen that: graphs of Kissinger, Augis-Bennett and Ozawa equations at different heating rates, in ln (T), respectively²The activation energies E (β) and n (β) are plotted on the Y-axis and 1000/T on the X-axis by linear fitting_g、E_c1、E_p1、E_c2、E_p2). The activation energies calculated by the three methods are similar, which indicates that the three methods are all suitable for analyzing the crystallization behavior of the amorphous coating. Furthermore, E_c2Well above E_c1Indicates alpha-Al₂O₃Is much more difficult to nucleate than the YAG phase. This is in combination with alpha-Al₂O₃The crystallization of (a) requires a higher temperature, i.e., a greater activation energy. At the same time, E_c2Greater than E_p2Indicates alpha-Al₂O₃Is more difficult than its grain growth process. In contrast, the nucleation of the YAG phase is easier than its growth process;

FIG. 14 shows alpha-Al during crystallization of an amorphous ceramic coating₂O₃And local activation energy E of YAG phase_c(x)；

FIG. 15 shows Al as sprayed under different ramp rates₂O₃The brittleness index F of YAG amorphous ceramic composite coatings (the invention uses non-isothermal DSC thermogram to test the brittleness index F of the coating (for amorphous materials, its kinetic properties, such as viscosity, etc., vary greatly during the glass transition; this temperature-dependent kinetic behavior is often called kinetic brittleness, which is considered to be related to many properties at the glass transition temperature, such as specific heat, elasticity, entropy of configuration, etc., when the kinetic behavior of the glass-forming liquid follows the temperature-dependent law of the Arrhenius equation over a wide temperature range, the glass-forming liquid is considered "strong", resembling the kinetic processes of chemical reaction rate and atomic diffusion in the crystal, when its kinetic behavior deviates greatly from the Arrhenius law, the glass-forming liquid is considered more brittle; the strong glass-forming liquid is more stable during the glass transition than brittle, and the change in configuration is less, such as specific heat. Therefore, the brittleness index is often used to evaluate the microstructural stability of amorphous materials during glass transition. The brittleness index F can be expressed as follows: f ═ E_g/RT_gln(β))；

FIG. 16 is Al prepared in example 4₂O₃-YAG amorphous ceramic composite coating, Al₂O₃-Cr₂O₃Coating layer, Al₂O₃The thermal diffusivity of the coating changes with temperature;

FIG. 17 is Al prepared in example 4₂O₃-YAG amorphous ceramic composite coating, Al₂O₃-Cr₂O₃Coating layer、Al₂O₃The fracture toughness of the coating is roughly evaluated by adopting an indentation method (the test load is 5kgf, the load retention time is 10s, and a simplified calculation formula of the fracture toughness is adopted, wherein K is_IC＝0.0752P(1/C)^3/2In which K is_ICFor coating fracture toughness, P is the indenter load and C is the 1/2 longitudinal crack length for the Vickers indentation. The fracture toughness of the coating is the average of 5 measurements);

FIG. 18 is Al prepared in example 5₂O₃-YAG amorphous ceramic composite coating, Al₂O₃-Cr₂O₃Coating layer, Al₂O₃Pictures of wear test and tribological properties of the coating: (a) - (b) pictures of abrasion tests of the coating; (c) the coefficient of friction of the coating; (d) the wear surface temperature of the coating;

FIG. 19 is a photograph of a coated wear ring after a wear test and an observation of the topography of the wear surface: (a) - (b) Al₂O₃Coating; (c) - (d) Al₂O₃-Cr₂O₃Coating; (e) - (f) Al prepared in example 5₂O₃-YAG amorphous ceramic composite coating;

FIG. 20 shows as-sprayed Al prepared in example 5₂O₃-plastic deformation strips and dimples of the YAG amorphous ceramic composite coating wear surface;

FIG. 21 is Al₂O₃Coating layer, Y₂O₃Coating layer, Al₂O₃-Cr₂O₃A picture of the coating after a 1000-hour salt spray corrosion test;

FIG. 22 shows Al₂O₃-YAG amorphous ceramic composite coating, Al₂O₃-Y₂O₃Coating layer, Al₂O₃Photograph of the coating after thermal shock test (first spalling): (a) al (Al)₂O₃；(b)Al₂O₃-Y₂O₃；(c)Al₂O₃-YAG；

FIG. 23 is Al₂O₃-YAG amorphous ceramic composite coating, Al₂O₃-Y₂O₃Coating layer, Al₂O₃Photos before and after abrasion test of coating abrasion ring(2000N and 500 rpm): (a) - (b) Al₂O₃；(c)-(d)Al₂O₃-Y₂O₃；(e)-(f)Al₂O₃-YAG；

FIG. 24 shows as-sprayed Al prepared in comparative example 2₂O₃-cross-sectional morphology observation of YAG amorphous ceramic composite coating after heat treatment at 1200 ℃ for different times: (a)24 h; (b)96 h; (c)240 h; (d)600 h; (e)800 h; (f)1000 h;

FIG. 25 shows as-sprayed Al prepared in comparative example 3₂O₃XRD pattern of-YAG amorphous ceramic composite coating (with Al)₂O₃/Y₂O₃Directly spraying and depositing the composite powder to obtain a coating layer);

FIG. 26 shows as-sprayed Al prepared in comparative example 3₂O₃DSC curve (with Al) of YAG amorphous ceramic composite coating₂O₃/Y₂O₃The composite powder is directly sprayed and deposited to obtain a coating).

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In the present disclosure, Al is caused to be present by heat treatment₂O₃/Y₂O₃The mixed powder is subjected to solid phase reaction to generate Al₂O₃a/YAG composite powder. In this case, the YAG phase is in Al₂O₃The YAG composite powder simultaneously forms a network structure (the solid phase reaction generates alpha-Al)₂O₃And YAG phase, which can be connected into a whole and is beneficial to Al₂O₃High-temperature microstructure stability of/YAG composite powder). In addition, the Al is constructed by utilizing the larger super-cooling degree of the thermal spraying for the first time₂O₃A YAG deep eutectic system, the actual deposition temperature is lower than the glass transition temperature, so that Al with toughness, heat conduction and stable and integrated high-temperature microstructure is obtained in situ₂O₃-YAG amorphous ceramic coating. The preparation method of the invention also considers the high-temperature mechanical property, the heat conduction property and the corrosion resistance of the coating, and realizes the integration of the obdurability, the heat conduction and the high-temperature microstructure stability of the coatingThe coating can obtain long service life and high reliability service under severe service environments such as high PV value, high temperature, strong oxidation, wide temperature range thermal shock, corrosion and the like. The following exemplarily illustrates a method for preparing an amorphous oxide ceramic composite coating provided by the present invention.

Al₂O₃/Y₂O₃Composite powder (Al)₂O₃/Y₂O₃Mixed powder) is prepared. The adopted raw material is Al₂O₃And Y₂O₃And (3) powder. Wherein the two powders have particle sizes of nanometer or submicron, and the powder components are respectively alpha-Al₂O₃And c-Y₂O₃. This Al₂O₃Powder and Y₂O₃The mass percentages of the powder are respectively 50-67% and 33-50%. The main reasons for adopting the two raw material powders in percentage by mass are as follows: firstly, refer to Al₂O₃-Y₂O₃Determining the component distribution ratio corresponding to the eutectic point by using a balance phase diagram of the system; secondly, the phenomenon of pseudo-eutectic crystal can be generated when plasma spraying is carried out at a larger supercooling degree, namely the component range of the eutectic crystal area is enlarged; the variation of the plasma spraying process parameters causes the change of enthalpy and temperature gradient, and the composite powder can be subjected to different thermal histories and has certain influence on the formation of an amorphous phase; and fourthly, spraying a large supercooling degree by using the plasma to construct a deep eutectic phenomenon, greatly reducing the actual deposition temperature, leading to a solute trapping (trapping) phenomenon when the actual deposition temperature is lower than the glass transition temperature, and stopping the growth of the eutectic phase so as to form an amorphous phase.

In an alternative embodiment, Al is added₂O₃And Y₂O₃Ball milling the powder with wet method, mixing, and carrying out Al₂O₃/Y₂O₃Composite powder (Al)₂O₃/Y₂O₃Mixed powder) is prepared. In one example, in wet ball milling, the two powders are placed in a ball milling tank, and alumina or zirconia grinding balls are used for mixing raw materials, wherein the preferred ball-to-material ratio is 2: 1-4: 1. In addition, a dispersant, a binder, and the like may be added. The addition amount of the dispersant can be powder mass0.2-1.0% of the total weight of the powder, and the addition amount of the binder can be 0.5-2.0% of the weight of the powder. In addition, the addition amount of the solvent can be 50-150% of the mass of the powder. The dispersant includes, but is not limited to, one or a combination of sodium silicate, sodium metasilicate, sodium citrate, sodium humate, polyacrylamide, hydroxymethyl cellulose and hydroxymethyl cellulose sodium. The binder includes, but is not limited to, one or a combination of polyvinyl alcohol, paraffin, glycerol and sodium lignosulfonate. As the solvent, one or a combination of two of water (preferably deionized water) and ethanol is included, but not limited thereto. Then ball milling and mixing evenly to prepare suspension stable slurry, and sieving to remove grinding balls. Then mechanically stirring at the rotating speed of 40-100 rpm, and carrying out spray granulation to obtain Al₂O₃/Y₂O₃And (3) composite powder. Preferably, centrifugal spray granulation is used. Centrifugal spray granulation can select the atomizer rotational speed to be 10000 ~ 15000rpm, and the charge pump rotational speed is 15 ~ 40rpm, and the temperature of air inlet is 200 ~ 300 ℃, and the air-out temperature is 90 ~ 120 ℃.

Al is obtained by heat treatment in-situ solid-phase reaction₂O₃a/YAG composite powder. For Al₂O₃YAG composite powder (preferably Al obtained by spray granulation)₂O₃/Y₂O₃Composite powder) and the necessary heat treatment is required. Mixing Al₂O₃/Y₂O₃The composite powder is put into a corundum crucible and then is put into a muffle furnace for heat treatment. The furnace is in an atmosphere environment. Heating from room temperature at a heating rate of 5 ℃/min to 1400-1600 ℃, preserving heat for 2-4 hours, and then cooling along with the furnace. In-situ high-temperature stepwise solid-phase reaction: al (Al)₂O₃+2Y₂O₃→Y₄Al₂O₉(YAM)、Al₂O₃+Y₄Al₂O₉→4YAlO₃(YAP)、Al₂O₃+3YAlO₃→Y₃Al₅O₁₂(YAG) to obtain Al₂O₃a/YAG composite powder. And regulating the growth form of the YAG phase by controlling the heat treatment temperature and the heat preservation time to form a network structure in the composite powder. Network nodeThe structure has the advantages that: phi alpha-Al for single powder particle₂O₃The YAG phase is uniformly distributed, so that deep eutectic can be effectively realized in the spraying process, and an amorphous phase is formed in situ to the maximum extent, so that the content of the amorphous phase is effectively improved; secondly, the strength, the density and the stability of the composite powder are improved; and thirdly, the uniformity of the components in the spray-deposited composite coating is promoted.

Thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating. Al prepared by thermal spraying₂O₃Depositing the/YAG composite powder on the surface of the base material to prepare Al₂O₃-YAG amorphous ceramic coating. The substrate is not particularly limited, and includes, but is not limited to, metal, ceramic, or graphite. Before deposition, the substrate may be cleaned and grit blasted to remove grease and adsorbates and increase the roughness of the substrate surface to improve the interfacial bonding between the coating and the substrate for deposition.

Preferably, the thermal spraying is plasma spraying (the melting point of the ceramic powder is higher to ensure that the ceramic powder can be effectively melted in the spraying process, so that the better spreading and deposition characteristics of powder molten drops on the surface of the base material are obtained, and gaps and cracks between solidified sheet layers are reduced). It should be understood that other thermal spray methods such as supersonic flame spraying, detonation spraying, etc. may be used. Argon and hydrogen can be used as working gas for plasma spraying. In one example, the plasma spray parameters are: plasma gas argon gas flow 45 ~ 55slpm, plasma gas hydrogen gas flow 7 ~ 10slpm, current 600 ~ 700A, power 45 ~ 50kW, powder feeding carrier gas argon gas flow 3 ~ 4slpm, powder feeding rate 30 ~ 40g/min, spraying distance 100 ~ 120 mm. The thickness of the coating of the amorphous ceramic in a spraying state is 50-800 mu m.

In the spraying and depositing process, the front surfaces of the base material and the coating are cooled by compressed air, the cooling air comprises cooling air and Venturi cooling air carried by the side surface of a spray gun, the back surface of the base material is cooled by circulating water or liquid nitrogen, and the actual spraying and depositing temperature is controlled to be 100-250 ℃. In order to increase Al in a sprayed state₂O₃The content of amorphous phase in YAG coating needs to be effective to construct a 'deep eutectic' system, so that the actual spraying deposition temperature is far lower than that of glassAt the glass transition temperature, the eutectic phase stops growing and an amorphous phase is formed in situ. The thermal spraying has the characteristics of high enthalpy, steep temperature gradient and rapid cooling and solidification. For Al₂O₃-YAG eutectic system, alpha-Al₂O₃And YAG, so that the equilibrium partition coefficient k is low, which means that the solid-liquid interface front has a large supercooling degree. The use of compressed air, circulating water or liquid nitrogen during the spraying process will further increase the degree of supercooling during the deposition process. Further, alpha-Al₂O₃Formation of the/YAG eutectic phase requires alpha-Al₂O₃The phase and YAG alternate nucleation and growth, consuming more time than single phase crystallization. Under the condition of the deep supercooling degree, the eutectic phase is more difficult to nucleate and grow, so that the amorphous phase is effectively formed, and the deposition of the amorphous ceramic coating is promoted. By implementing active and passive cooling in the spraying and depositing process, the pressure stress level in the coating is controlled, the expansion of microcracks in the coating under the wide-temperature-range thermal shock condition under the high-PV-value abrasion working condition is effectively retarded, and the long-term service reliability of the coating is improved. Furthermore, the actual deposition temperature must not be too low, in order to avoid that too low deposition temperatures affect the interface bonding between the monolithic layer (splat) and the substrate and between the monolithic layers. Herein, Al after solid-phase reaction is treated with heat₂O₃the/YAG composite powder is sprayed and deposited without directly adopting Al₂O₃/Y₂O₃The composite powder is sprayed, and the main reasons are as follows: firstly, Al in the thermal spraying process₂O₃/Y₂O₃The composite powder particles will experience different thermal histories and alpha-Al cannot be guaranteed₂O₃And c-Y₂O₃Can fully react in a short time to generate enough YAG phase; if a YAG phase is formed in situ in the spraying process, the forms and the contents of the YAG phase are different in different powder particle molten drops, so that the uniformity of components in the final deposited coating cannot be ensured; ③ if spraying Al directly₂O₃/Y₂O₃Composite powder of alpha-Al₂O₃And c-Y₂O₃More heat energy is consumed in the process of generating YAG through reaction, so that the practical deposition supercooling degree is reduced, and the amorphous coating is formedThe phase content is reduced, the change range is large, and the glass transition temperature is reduced. In view of this, Al is selected₂O₃The coating obtained by spraying and depositing the/YAG composite powder has the amorphous phase content of over 90 percent, uniform component distribution, higher glass transition temperature and high-temperature microstructure stability.

Al may be applied prior to thermal spraying₂O₃Plasma spheroidizing of the/YAG composite powder. The parameters include: argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the argon gas flow is 30-40 slpm, the hydrogen gas flow is 3-7 slpm, the current is 350-500A, the power is 20-35 kW, the powder conveying carrier gas argon gas flow is 3-4 slpm, the powder conveying speed is 5-15 g/min, and the spraying distance is 200-300 mm. Al (Al)₂O₃the/YAG composite powder is sent to the center of plasma flame flow and sprayed into room temperature deionized water. And then filtering, drying and sieving the composite powder in the deionized water to obtain the composite powder with the particle size distribution range of 20-40 mu m, which is suitable for thermal spraying.

The plasma spheroidizing treatment has the advantages that: (ii) Al obtained by Heat treatment alone₂O₃Melting the surface or the sub-surface of the/YAG composite powder, eliminating the corner area on the surface of the powder, obtaining better sphericity, and not changing the strength and phase composition of the whole powder particles; the density of the surface layer of the powder particles is improved, and the fluidity of the composite powder is promoted; and the compactness of the deposited coating and the interface combination between single-layer layers (splats) are improved.

In a detailed example of a method of preparing an amorphous oxide ceramic composite coating, the method may include the steps of: (1) preparation of Al₂O₃/Y₂O₃Composite powder (preferably spray granulation method), wherein Al₂O₃The mass fraction of the powder is 50-67 percent, and Y is₂O₃The mass fraction of the powder is 33-50%, and Al₂O₃Powder and Y₂O₃The powder particle size is nano-scale or submicron scale. (2) Al is obtained by heat treatment in-situ solid phase reaction₂O₃a/YAG composite powder, and the YAG phase forms network in the composite powderAnd (5) structure. (3) Plasma spheroidizing of the composite powder to obtain the sprayable composite powder with certain particle size distribution, compact surface, good sphericity and good fluidity. (4) Thermal spraying in-situ Al₂O₃YAG amorphous ceramic coating, amorphous phase content in the coating exceeds 90%, the composition is distributed evenly, and the coating has higher glass transition temperature and high temperature microstructure stability.

The invention has the advantages and beneficial effects that:

(1) the invention designs and prepares Al₂O₃YAG composite powder, and Al is constructed by utilizing large supercooling degree of plasma spraying₂O₃YAG deep eutectic system, the actual deposition temperature is far lower than the glass transition temperature, so that Al is obtained in situ₂O₃-YAG amorphous ceramic coating. The amorphous ceramic coating has the advantages of high amorphous phase content, uniform component distribution, glass transition temperature, good high-temperature microstructure stability, interlayer interface combination, compactness and the like. The preparation method of the invention also considers the high-temperature mechanical property, the heat-conducting property and the corrosion resistance of the coating, realizes the stable integration of the toughness, the heat-conducting property and the high-temperature microstructure of the coating, and ensures that the coating can obtain long service life and high reliable service under severe service environments such as high PV value, high temperature, strong oxidation, wide-temperature-range thermal shock, corrosion and the like;

(2) the high-performance amorphous ceramic coating is obtained by utilizing in-situ spray deposition, and the high-temperature performance and the microstructure stability can be realized without carrying out subsequent heat treatment, so that the harsh requirement of the high-temperature heat treatment on a metal base material and the adverse effect that the coating is easy to crack or peel off and lose efficacy due to higher thermal mismatch stress are avoided.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1

A preparation method of an amorphous oxide ceramic composite coating with toughness, heat conduction and stable integration of a high-temperature microstructure comprises the following steps:

(1)Al₂O₃/Y₂O₃preparation of composite powder

Weighing Al₂O₃And Y₂O₃Powder (main crystal phase is alpha-Al respectively)₂O₃And c-Y₂O₃) The two kinds of powder have particle size distribution ranges of 30-150 nm and 50-200 nm, respectively, and Al₂O₃The mass fraction of the powder is 67%, Y₂O₃The mass fraction of the powder was 33%. Mixing Al₂O₃And Y₂O₃The powder is placed in a ball milling tank, an alumina grinding ball (the diameter is 3mm) is adopted, the ball material ratio is 4:1, the adding amount of the hydroxymethyl cellulose dispersing agent is 0.8 percent of the mass of the powder, the adding amount of the polyvinyl alcohol binding agent is 1.5 percent of the mass of the powder, and the adding amount of the deionized water is 120 percent of the mass of the powder. The raw materials are ball-milled and mixed for 48 hours to prepare suspension stable slurry, the suspension stable slurry is sieved to remove grinding balls, and then the suspension stable slurry is mechanically stirred at the rotating speed of 60rpm to carry out centrifugal spray granulation. The parameters of spray granulation are as follows: the rotation speed of the atomizer is 12000rpm, the rotation speed of the feed pump is 25rpm, the air inlet temperature is 230 ℃, the air outlet temperature is 120 ℃, and the original spray granulation composite powder (shown in figure 1) is obtained, elements are uniformly distributed, the particle size is 10-60 mu m, and the granulation powder is prepared from alpha-Al₂O₃And c-Y₂O₃Composition (see fig. 3).

(2) Al is obtained by heat treatment in-situ solid-phase reaction₂O₃YAG composite powder

Al obtained by spray granulation₂O₃/Y₂O₃And carrying out heat treatment on the composite powder to promote the in-situ solid-phase reaction. And putting the granulated powder into a corundum crucible, wherein the powder accounts for 1/2-2/3 of the total volume of the crucible, and then putting the corundum crucible into a muffle furnace for heating. The furnace is in an atmosphere environment. Starting from room temperatureHeating at a heating rate of 5 ℃/min to 1500 ℃, keeping the temperature for 3 hours, then closing a heating power supply, and cooling to room temperature along with the furnace. After the heat treatment, Al is obtained₂O₃The shape of the/YAG composite powder is shown in figure 2. The YAG phase (white) forms a network structure in the composite powder. The composite powder obtained by the heat treatment solid phase reaction is made of alpha-Al₂O₃And Y₃Al₅O₁₂(YAG) composition (see fig. 4);

(3) plasma spheroidizing treatment of composite powder

To Al obtained by heat treatment₂O₃Carrying out plasma spheroidization on the/YAG composite powder. Argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow rate of argon gas is 35slpm, the flow rate of hydrogen is 5slpm, the current is 450A, the power is 30kW, the flow rate of powder feeding carrier gas argon gas is 4slpm, the powder feeding speed is 10g/min, and the spraying distance is 270 mm. Al (Al)₂O₃the/YAG composite powder is sent to the center of plasma flame flow and sprayed into room temperature deionized water. Filtering out the composite powder in the deionized water by using a filter screen, and then putting the powder into an oven for drying treatment at the temperature of 120 ℃. And sieving the dried composite powder through 400-mesh and 700-mesh screens respectively to obtain the composite powder with the particle size distribution range of 20-40 mu m, which is suitable for thermal spraying.

(4) Thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the cleaned and sand-blasted high-strength graphite base material, and the spraying process parameters are as follows: the plasma gas argon flow rate is 49slpm, the plasma gas hydrogen flow rate is 9slpm, the current is 660A, the power is 48kW, the powder feeding carrier gas argon flow rate is 4slpm, the powder feeding speed is 35g/min, and the spraying distance is 110 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.2MPa) and Venturi cooling air (0.4MPa), the back surface of the base material is cooled by circulating water, the flow rate is 0.1L/s, and the actual deposition temperature of spraying is controlled to be 200 +/-20 ℃. The thickness of the amorphous ceramic coating in the spraying state is 760 μm. Construction of Al by using plasma spraying with large supercooling degree₂O₃YAG deep eutectic system, making actual deposition temperature lower than glass transition temperature, stopping eutectic phase growth, and obtaining Al in situ₂O₃YAG amorphous oxide ceramic coating, the schematic diagram is shown in figure 5. XRD analysis showed (see fig. 6): practically obtained as-sprayed Al₂O₃The YAG composite ceramic coating mainly consists of an amorphous phase, wherein the content of the amorphous phase is 94 percent, and a very small amount of alpha-Al is contained₂O₃And YAG grains.

Example 2

(1)Al₂O₃/Y₂O₃preparation of composite powder

Spray granulation of Al₂O₃/Y₂O₃The preparation method of the composite powder is the same as that of the embodiment 1, wherein the difference is that: al (Al)₂O₃Powder mass fraction of 50%, Y₂O₃The mass fraction of the powder is 50 percent;

For the granulated Al prepared in the step (1)₂O₃/Y₂O₃The composite powder was heat-treated in the same manner as in example 1, except that: the heat treatment temperature is 1600 ℃, and the temperature is kept for 2 hours;

(3) plasma spheroidizing treatment of composite powder

For Al obtained in the step (2)₂O₃Carrying out plasma spheroidization on the/YAG composite powder. Argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow rate of argon is 37slpm, the flow rate of hydrogen is 7slpm, the current is 500A, the power is 35kW, the flow rate of the powder feeding carrier gas argon is 4slpm, the powder feeding speed is 10g/min, and the spraying distance is 230 mm. Al (Al)₂O₃the/YAG composite powder is sent to the center of plasma flame flow and sprayed into room temperature deionized water. Filtering, drying and sieving the composite powder in the deionized water, and the method is similar to the embodiment 1The same, the obtained particle size distribution range is 20-40 mu m, and the method is suitable for thermal spraying.

(4) Thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the cleaned and sand-blasted high-strength graphite base material, and the spraying process parameters are as follows: the plasma gas argon flow rate is 49slpm, the plasma gas hydrogen flow rate is 10slpm, the current is 640A, the power is 47kW, the powder feeding carrier gas argon flow rate is 4slpm, the powder feeding speed is 35g/min, and the spraying distance is 110 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.3MPa) and Venturi cooling air (0.35MPa), the back surface of the base material is cooled by circulating water, the flow rate is 0.2L/s, and the actual deposition temperature of spraying is controlled to be 180 +/-20 ℃. The thickness of the amorphous ceramic coating in the sprayed state is 420 μm. TEM analysis shows that: selected areas of the as-sprayed coating showed significant amorphous halo features by electron diffraction over a significant portion of the area (see fig. 7). Thus, as-sprayed Al₂O₃The YAG coating consists mainly of an amorphous phase. And (3) displaying the cross section morphology of the coating: high compactness, low porosity and good interface bonding (see figure 9). The Al, Y and O elements in the amorphous matrix of the coating are uniformly distributed (see figure 10).

Example 3

(1)Al₂O₃/Y₂O₃preparation of composite powder

Spray granulation of Al₂O₃/Y₂O₃The preparation method of the composite powder is the same as that of the embodiment 1, wherein the difference is that: al (Al)₂O₃Powder mass fraction of 60%, Y₂O₃The mass fraction of the powder is 40 percent;

For the granulated Al prepared in the step (1)₂O₃/Y₂O₃The composite powder was heat-treated in the same manner as in example 1, except that: the heat treatment temperature is 1400 ℃, and the heat preservation is carried out for 4 hours;

(3) plasma spheroidizing treatment of composite powder

For Al obtained in the step (2)₂O₃Carrying out plasma spheroidization on the/YAG composite powder. Argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow rate of argon gas is 40slpm, the flow rate of hydrogen is 6slpm, the current is 400A, the power is 28kW, the flow rate of powder feeding carrier gas argon gas is 4slpm, the powder feeding speed is 15g/min, and the spraying distance is 300 mm. Al (Al)₂O₃the/YAG composite powder is sent to the center of plasma flame flow and sprayed into room temperature deionized water. The composite powder in the deionized water is filtered, dried and sieved, the method is the same as that of the embodiment 1, the obtained particle size distribution range is 20-40 mu m, and the composite powder is suitable for thermal spraying.

(4) Thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the cleaned and sand-blasted high-strength graphite base material, and the spraying process parameters are as follows: the plasma gas argon flow rate is 49slpm, the plasma gas hydrogen flow rate is 8slpm, the current is 680A, the power is 49kW, the powder feeding carrier gas argon flow rate is 4slpm, the powder feeding speed is 32g/min, and the spraying distance is 120 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.2MPa) and Venturi cooling air (0.4MPa), the back surface of the base material is cooled by circulating water, the flow rate is 0.15L/s, and the actual deposition temperature of spraying is controlled to be 220 +/-20 ℃. Obtained as-sprayed Al₂O₃The YAG coating consists essentially of an amorphous phase and has a thickness of 510 μm.

For the prepared spraying state Al₂O₃DSC differential thermal analysis of the YAG coating (see FIG. 8) with two distinct exothermic peaks (T)_p1And T_p2) Corresponding to YAG and alpha-Al, respectively₂O₃Phase crystallization process. Under different heating rates (5K/min, 10K/min, 20K/min and 30K/min), the characteristic temperature (T) is researched by adopting non-isothermal crystallization kinetics_g: the glass transition temperature of the amorphous coating; t is_c1: the crystallization initial temperature of the YAG phase; t is_p1: YAG phase crystallization peak-to-peak temperature; t is_c2：α-Al₂O₃The crystallization initiation temperature of the phase; t is_p2：α-Al₂O₃Phase crystallization peak-to-peak temperature) and the temperature increase rate β (see fig. 11 to fig. 13), YAG and α -Al were obtained₂O₃A plot of crystallization activation energy of phase E (x) as a function of crystallization volume fraction x. The functional relationship of E (x) -x indicates (see FIG. 14): difficult growth of YAG phase, alpha-Al₂O₃The most difficult phase nucleation process, which is favorable for promoting Al₂O₃High temperature microstructural stability of the YAG amorphous coating. Compared with the crystallization kinetic data of 30 amorphous materials (ceramics, alloys, polymers and the like) which are published and reported in the prior literature, the Al prepared by the method disclosed by the invention₂O₃YAG amorphous coating with higher glass transition temperature (T)_g) Crystallization initiation temperature (T)_c) Peak temperature (T)_p) And crystallization activation energy (E)_c) And resistance to nucleation (E)_c/RT_g) See in particular the following table (using the Kissinger method):

. In summary, the comparison of the crystallization kinetics data shows that: al prepared by the invention₂O₃The YAG amorphous ceramic coating has excellent high-temperature microstructure stability and has good application potential under the working conditions of high temperature and high PV value abrasion.

Example 4

(1)Al₂O₃/Y₂O₃preparation of composite powder

Spray granulation of Al₂O₃/Y₂O₃The preparation method of the composite powder is the same as that of the embodiment 1, wherein the difference is that: al (Al)₂O₃Powder mass fraction of 55%, Y₂O₃The mass fraction of the powder is 45 percent;

For the granulated Al prepared in the step (1)₂O₃/Y₂O₃The composite powder was heat-treated in the same manner as in example 1, except that: the heat treatment temperature is 1550 ℃, and the heat preservation time is 2 hours;

(3) plasma spheroidizing treatment of composite powder

For Al obtained in the step (2)₂O₃Carrying out plasma spheroidization on the/YAG composite powder. Argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow rate of argon gas is 32slpm, the flow rate of hydrogen is 4slpm, the current is 380A, the power is 23kW, the flow rate of the powder feeding carrier gas argon gas is 3.5slpm, the powder feeding speed is 8g/min, and the spraying distance is 250 mm. Al (Al)₂O₃the/YAG composite powder is sent to the center of plasma flame flow and sprayed into room temperature deionized water. Filtering, drying and sieving the composite powder in the deionized water by the same method as the embodiment 1 to obtain the composite powder with the particle size distribution range of 20-40 mu m, which is suitable for thermal spraying;

(4) thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the cleaned and sand-blasted high-strength graphite base material, and the spraying process parameters are as follows: the plasma gas argon flow rate is 46slpm, the plasma gas hydrogen flow rate is 7slpm, the current is 670A, the power is 46kW, the powder feeding carrier gas argon flow rate is 3.5slpm, the powder feeding speed is 37g/min, and the spraying distance is 110 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.3MPa) and Venturi cooling air (0.4MPa), the back surface of the base material is cooled by circulating water, the flow rate is 0.2L/s, and the actual deposition temperature of spraying is controlled to be 160 +/-20 ℃ is used. Obtained as-sprayed Al₂O₃The YAG coating consists essentially of an amorphous phase and has a thickness of 350 μm.

Non-isothermal crystallization kinetics study was performed on the coating prepared above, YAG and alpha-Al₂O₃Activation energy of crystallization of crystalline phase (E)_c) 820.7kJ/mol and 1849.5kJ/mol respectively, which are far larger than the crystallization activation energy values of other amorphous materials which have been published and reported at present. The brittleness index F calculation results show (see fig. 15): prepared Al₂O₃YAG amorphous ceramic coating, the average value of brittleness index F is 41, which shows that the amorphous ceramic coating has small configuration change around the glass transition temperature, thus having good high-temperature microstructure stability and obdurability (F)>100, a brittle material; 30<F<100, a material with better obdurability; 16<F<30, material with excellent toughness).

Al prepared in inventive example 4₂O₃-YAG amorphous ceramic coating with Al₂O₃Coating and Al₂O₃-Cr₂O₃The coatings were compared and the thermal diffusivity of each coating was measured as a function of temperature. The results show that: spray-coated Al₂O₃The higher thermal diffusivity of the YAG amorphous ceramic coating (see fig. 16) means that it has better thermal conductivity.

Al₂O₃-YAG amorphous ceramic coating, Al₂O₃-Cr₂O₃Coating and Al₂O₃The fracture toughness of the coating is respectively 4.3 +/-0.5 MPa.m^1/2、2.7±0.4MPa·m^1/2And 1.6. + -. 0.2 MPa. m^1/2(see FIG. 17). Thus, it can be seen that Al is produced₂O₃The YAG amorphous ceramic coating has high fracture toughness.

Example 5

(1)Al₂O₃/Y₂O₃preparation of composite powder

Spray granulation of Al₂O₃/Y₂O₃The preparation method of the composite powder is the same as that of the embodiment 1, wherein the difference is that: polyacrylamide is used as a dispersing agent;

For the granulated Al prepared in the step (1)₂O₃/Y₂O₃The composite powder was heat-treated in the same manner as in example 1 to obtain a composite powder composed of α -Al₂O₃YAG phase forms a network structure in the composite powder;

(3) plasma spheroidizing treatment of composite powder

For Al obtained in the step (2)₂O₃Carrying out plasma spheroidization on the/YAG composite powder, wherein the plasma spheroidization method is the same as that in the embodiment 1, and then filtering, drying and sieving are carried out, the method is the same as that in the embodiment 1, the obtained particle size distribution range is 20-40 mu m, and the method is suitable for thermal spraying;

(4) thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the stainless steel base material which is cleaned and subjected to sand blasting treatment, and the spraying process parameters are as follows: the plasma gas argon flow is 53slpm, the plasma gas hydrogen flow is 7slpm, the current is 610A, the power is 46kW, the powder feeding carrier gas argon flow is 4slpm, the powder feeding speed is 36g/min, and the spraying distance is 120 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.1MPa) and Venturi cooling air (0.3MPa), the back surface of the base material is cooled by liquid nitrogen, and the actual deposition temperature of spraying is controlled to be 120 +/-20 ℃. Obtained as-sprayed Al₂O₃The YAG coating consists essentially of an amorphous phase and has a thickness of 300. mu.m.

Non-isothermal crystallization kinetics study was performed on the coating prepared above, YAG and alpha-Al₂O₃Activation energy of crystallization of crystalline phase (E)_c) 830.6kJ/mol and 1860.3kJ/mol respectively, which are far larger than the crystallization activation energy values of other amorphous materials which have been published and reported at present.This means that Al₂O₃The YAG amorphous ceramic coating has excellent high-temperature microstructure stability.

Al prepared by the invention₂O₃-YAG amorphous ceramic coating with Al₂O₃Coating and Al₂O₃-Cr₂O₃Coatings were compared and the tribological wear performance of the coatings at high PV values was measured. Under the conditions of 2000N load and 500rpm rotating speed, Al₂O₃YAG amorphous ceramic coatings show a more stable coefficient of friction and lower wear surface temperatures (see fig. 18). Al alone after abrasion₂O₃The surface of the YAG amorphous ceramic coating is perfect and smooth, and has no peeling, cracking and bubbling. However, Al₂O₃Coating and Al₂O₃-Cr₂O₃The surface of the coating cracked and all showed significant grid-like cracks, indicating that the coating had failed (see fig. 19). Further analysis showed that Al₂O₃Some plastically deformed strips or dimples appear on the wear surface of YAG amorphous ceramic coatings (see fig. 20). This indicates that Al is present₂O₃The YAG amorphous ceramic coating has higher toughness, can relieve stress concentration in a wear process through certain surface plastic deformation, and releases a part of stress, thereby ensuring the surface integrity, the wear service reliability and the service life.

Example 6

(1)Al₂O₃/Y₂O₃preparation of composite powder

Spray granulation of Al₂O₃/Y₂O₃The preparation method of the composite powder was the same as that of example 1, and the obtained granulated powder was composed of α -Al₂O₃And c-Y₂O₃Composition is carried out;

(3) plasma spheroidizing treatment of composite powder

(4) thermal spraying in-situ Al₂O₃-YAG amorphous ceramic coating

Spraying the Al prepared in the step (3) by adopting plasma₂O₃The YAG composite powder is deposited on the surface of the stainless steel base material which is cleaned and subjected to sand blasting treatment, and the spraying process parameters are as follows: the plasma gas argon flow is 48slpm, the plasma gas hydrogen flow is 10slpm, the current is 700A, the power is 50kW, the powder feeding carrier gas argon flow is 4slpm, the powder feeding speed is 35g/min, and the spraying distance is 110 mm. The front surfaces of the base material and the coating are cooled by compressed air, the compressed air comprises spray gun cooling air (0.1MPa) and Venturi cooling air (0.2MPa), the back surface of the base material is cooled by liquid nitrogen, and the actual deposition temperature of spraying is controlled to be 140 +/-20 ℃. Obtained as-sprayed Al₂O₃The YAG coating consists essentially of an amorphous phase and has a thickness of 270 μm.

Non-isothermal crystallization kinetics study was performed on the coating prepared above, YAG and alpha-Al₂O₃Activation energy of crystallization of crystalline phase (E)_c) 807.6kJ/mol and 1836.0kJ/mol respectively, which are far larger than the crystallization activation energy values of other amorphous materials which have been published and reported at present. This means that Al₂O₃The YAG amorphous ceramic coating has excellent high-temperature microstructure stability.

Al prepared by the invention₂O₃YAG amorphous ceramic coatings have excellent salt spray corrosion resistance, which benefits from the amorphous phase matrix, high density and strong interface bonding of the coating. Subjected to 1000h neutral salt spray corrosion testAfter inspection, Al₂O₃The YAG amorphous ceramic coating surface was almost intact, while Al₂O₃Coating layer, Y₂O₃Coating layer, Al₂O₃-Cr₂O₃A large area of rust was present on the surface of the coating (see fig. 21).

Comparative example 1

In order to fully illustrate the superiority of the preparation method of the amorphous oxide ceramic composite coating with the integrated toughness, heat conduction and high-temperature microstructure stability, Al is also prepared₂O₃-Y₂O₃The coating was used as a comparative example. Using micron-sized Al₂O₃Powder (15-45 μm) and Y₂O₃Taking powder (15-45 mu m) as a raw material, and directly and mechanically mixing to prepare composite powder, wherein Al₂O₃The mass fraction of the powder is 67 percent, Y₂O₃The powder mass fraction was 33%, and the component ratio was the same as in example 1. Preparation of Al by plasma spraying₂O₃-Y₂O₃The composite coating is prepared by the same process parameters as the example 1. The phase composition of the sprayed coating is as follows: alpha-Al₂O₃、γ-Al₂O₃、c-Y₂O₃、m-Y₂O₃And small amounts of YAM, YAP, YAG. Furthermore, the coating is not an amorphous coating but a crystalline coating, and the composition distribution is not uniform.

Mixing Al₂O₃Coating layer, Al₂O₃-Y₂O₃Coating and Al prepared by the invention₂O₃YAG amorphous ceramic coating (examples 1 and 6) for comparison of properties: firstly, after 1000 hours of salt spray corrosion test, Al₂O₃-Y₂O₃The surface of the coating shows a large area of rust, while Al₂O₃The YAG amorphous ceramic coating surface is almost intact (see fig. 21); ② carrying out repeated thermal shock examination from room temperature cold water to 500 ℃, and Al₂O₃Coating layer, Al₂O₃-Y₂O₃Coating layer, Al₂O₃The thermal shock times of the first stripping of the YAG amorphous ceramic coating are respectively as follows: 29 times (twice)41 times, 67 times (see FIG. 22), and thus, Al₂O₃-Y₂O₃The thermal shock resistance of the coating is inferior to that of Al₂O₃-YAG amorphous ceramic coating; ③ Al under the conditions of load of 2000N and rotating speed of 500rpm₂O₃The YAG amorphous ceramic coating has perfect surface, no peeling, no cracking and no bubbling. However, Al₂O₃Coating and Al₂O₃-Y₂O₃The surface of the coating cracked and all showed significant grid-like cracks, indicating that the coating had failed (see fig. 23).

Comparative example 2

Al was obtained according to the preparation method of example 1₂O₃-YAG amorphous ceramic coating, except that the substrate is a high temperature alloy (GH 3128). Heat treatment at 1200 c for various times in order to crystallize the coating throughout and thus obtain a eutectic coating. However, the large thermal stress between the high-temperature alloy substrate with the high coefficient of thermal expansion along with the change of the volume causes the coating to crack and peel (see fig. 24), and the subsequent wear service under severe working conditions cannot be carried out.

Comparative example 3

First, granulated Al was obtained in accordance with the step (1) in example 1₂O₃/Y₂O₃The difference of the composite powder is that Al is obtained without the heat treatment in situ solid phase reaction of the step (2)₂O₃Plasma spheroidizing of/YAG composite powder and step (3) composite powder, while spray-coated Al was obtained directly according to step (4) in example 1₂O₃-YAG amorphous ceramic coating.

To the above-mentioned spray-coated Al₂O₃XRD and DSC analysis of the YAG amorphous ceramic coating shows that: the amorphous phase content of the coating is 54 percent (see figure 25), which is obviously lower than that of the coating prepared in the example 1; ② the glass transition temperature of the coating is 508 ℃ (see fig. 26), and is also significantly lower (T) than the glass transition temperature of the coating prepared in example 3_g＝893℃)。

Comparative example 4

Al₂O₃Preparing a coating: directly adopts micron-sized meltingMelting and crushing Al₂O₃Plasma spraying of the powder, Al₂O₃Median particle diameter D of the powder₅₀Plasma spray parameters 17.5 μm Al prepared as in example 4₂O₃The YAG amorphous ceramic coating process parameters are the same.

Comparative example 5

Y₂O₃Preparing a coating: y directly adopting micron-sized agglomeration granulation₂O₃Powder material is plasma sprayed, Y₂O₃Median particle diameter D of the powder₅₀Plasma spray parameters 28 μm Al prepared as in example 4₂O₃The YAG amorphous ceramic coating process parameters are the same.

Comparative example 6

Al₂O₃-Cr₂O₃Preparing a coating: al crushed by micron-sized melting₂O₃And Cr₂O₃The powder is directly and mechanically mixed, wherein the Cr is₂O₃Is 70 wt.%, Al₂O₃Is 30 wt.%. Al (Al)₂O₃And Cr₂O₃The median particle diameter of the powder is D₅₀17.5 μm and D₅₀Plasma spray parameters 16.7 μm Al prepared as in example 4₂O₃The YAG amorphous ceramic coating process parameters are the same.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto, and those skilled in the art can make modifications and variations to the invention without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are within the protection scope of the technical solution of the present invention, unless the content of the technical solution of the present invention is departed from.

Claims

1. A preparation method of an amorphous oxide ceramic composite coating with integrated toughness, heat conduction and high-temperature microstructure stability is characterized in thatCharacterized in that the amorphous oxide ceramic composite coating is Al₂O₃-YAG amorphous ceramic coating, and Al₂O₃-the content of amorphous phase in the YAG amorphous ceramic coating exceeds 90%, the preparation method comprising:

(1) mixing Al₂O₃And Y₂O₃Carrying out wet ball milling on the powder, mixing the powder uniformly, preparing suspension stable slurry, and carrying out spray granulation to obtain Al₂O₃/Y₂O₃Mixed powder of Al₂O₃/Y₂O₃Al in mixed powder₂O₃The mass fraction of the powder is 50-67 percent, and Y is₂O₃The mass fraction range of the powder is 33-50%, and the Al is₂O₃The main crystal phase of the powder is alpha-Al₂O₃Said Y is₂O₃The main crystal phase of the powder is c-Y₂O₃；

(2) Mixing the obtained Al₂O₃/Y₂O₃Carrying out heat treatment on the mixed powder at 1400-1600 ℃ for 2-4 hours to obtain Al₂O₃YAG composite powder;

(3) mixing the obtained Al₂O₃Carrying out plasma spheroidization on the/YAG composite powder, then adopting thermal spraying to spray on the surface of the base material, and keeping the deposition temperature lower than Al in the thermal spraying process₂O₃Glass transition temperature of YAG system to obtain Al₂O₃-YAG amorphous ceramic coating;

the parameters of the plasma spheroidizing treatment comprise: argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow of argon is 30-40 slpm, the flow of hydrogen is 3-7 slpm, the current is 350-500A, the power is 20-35 kW, the flow of powder conveying carrier gas argon is 3-4 slpm, the powder conveying speed is 5-15 g/min, and the spraying distance is 200-300 mm;

the thermal spraying is plasma spraying; the parameters of the plasma spraying include: plasma gas argon gas flow 45 ~ 55slpm, plasma gas hydrogen gas flow 7 ~ 10slpm, current 600 ~ 700A, power 45 ~ 50kW, powder feeding carrier gas argon gas flow 3 ~ 4slpm, powder feeding rate 30 ~ 40g/min, spraying distance 100 ~ 120 mm.

2. The method according to claim 1, wherein in the step (1), the Al is₂O₃The particle size of the powder is 2 nm-2 mu m, and the Y is₂O₃The particle size of the powder is 2 nm-2 mu m.

3. The method according to claim 1, wherein the parameters of the plasma spheroidization process include: argon and hydrogen are used as plasma gases, and the specific process parameters are as follows: the flow of argon is 30-40 slpm, the flow of hydrogen is 3-7 slpm, the current is 350-500A, the power is 20-35 kW, the flow of powder conveying carrier gas argon is 3-4 slpm, the powder conveying speed is 5-15 g/min, and the spraying distance is 200-300 mm; plasma spheroidized Al₂O₃The particle size of the/YAG composite powder is 20-40 mu m.

4. The method of claim 1, wherein the deposition temperature of the composite coating is controlled to be lower than Al by cooling₂O₃-glass transition temperature of YAG system.

5. The method of claim 4, wherein the cooling comprises compressed air, circulating water, or liquid nitrogen cooling.

6. The method according to claim 4, wherein the deposition temperature is 100 to 250 ℃.

7. The production method according to any one of claims 1 to 6, wherein the substrate is a metal substrate, a ceramic substrate, or a graphite substrate.

8. The method of claim 7, wherein the substrate is cleaned and grit blasted prior to spraying.