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Article

Preparation and Characterization of Al2O3/h-BN Composite Coatings by Atmospheric Plasma Spraying (APS)

by
Yifeng Guo
1,†,
Lingxiao Lan
2,†,
Boying Qin
3,*,
Xinghua Liang
2,
Yujiang Wang
2,
Yu Wang
4 and
Zhikun Chen
4,*
1
School of Mechanical Engineering, Chengdu University, Chengdu 610106, China
2
Guangxi Key Laboratory of Automobile Components and Vehicle Technology, Guangxi University of Science and Technology, Liuzhou 545006, China
3
College of Science, Guangxi University of Science and Technology, Liuzhou 545006, China
4
Guangdong Provincial Key Laboratory of Modern Surface Engineering Technology, Institute of New Materials, Guangdong Academy of Sciences, Guangzhou 510651, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Crystals 2024, 14(12), 1035; https://doi.org/10.3390/cryst14121035
Submission received: 23 October 2024 / Revised: 25 November 2024 / Accepted: 25 November 2024 / Published: 28 November 2024
(This article belongs to the Section Inorganic Crystalline Materials)
Browse Figures
Versions Notes

Abstract

:
To improve the adhesion strength of polymer functional films, corona treatment is required. Corona rollers are key components for corona treatment, which are used in high-voltage electric fields for a long time. In this work, in order to improve electrical insulation, arc resistance, wear resistance, and chemical stability, a coating is usually sprayed on the surface of the corona roller. Al2O3/h-BN composite coatings are prepared on the surface substrate of a corona roller (20 steel) by atmospheric plasma spraying (APS) technology. Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) analysis showed that the Al2O3/h-BN composite coating had a layered structure and compactness. Two kinds of Al2O3/h-BN composite coatings are prepared under different APS process parameters; the porosities of A coating and B coating are 6.04% and 4.75%, the microhardnesses are 781 ± 0.5 Hv and 840.5 ± 0.5 Hv, and the adhesion strengths are 22.0 MPa and 22.3 MPa, respectively. The A and B volume resistivity of the coatings are 9.29 × 1010 Ω·cm and 3.55 × 1010 Ω·cm, respectively. The volume resistivity and porosity of the coatings are negatively correlated, and they decrease with the increase in spraying current. But for both coatings, volume resistivity is greater than 1 × 1010 Ω cm. These results indicate that the Al2O3/h-BN composite coatings, as a new type of electrode roller coating, satisfy the use requirement. Al2O3/h-BN composite coatings can become the potential for ceramic coatings that have good mechanics and insulation performance.

1. Introduction

As a crucial basic component of modern tape casting equipment, the material and performance of corona rollers directly affect the effectiveness of corona treatment, as well as the reliability and service life of the corona rollers themselves. Because corona rollers are used in high-voltage electric fields for a long time, they are generally required to have good electrical insulation, arc resistance, corona resistance, and flame retardancy under normal working conditions. Because of the presence of high-frequency and high-voltage alternating current during the operation of a corona system, a large amount of ozone is generated during corona operation [1], which can easily lead to the breakdown of the thin film and affect the performance and lifespan of the corona equipment. It is indicated that the corona roller has good resistance to oxidation corrosion and wear resistance. The most common method to protect steel implements such as corona rollers from wear and prolong their service life is to prepare a protective coating on the surface of the steel [2]. The widespread application of APS coatings can improve the mechanical properties, corrosion resistance, wear resistance, insulation, and other aspects of steel [3].
Al2O3 coating has good insulation and thermal stability, and as a typical ceramic material, it has corrosion resistance and good wear resistance [4]. However, the brittleness of alumina coatings is relatively high, so it is prone to microcracks. In practical application scenarios, the performance of single-phase materials has its own defects. Therefore, the introduction of toughened phases and alumina to form composite materials has become a focus of application research. Hexagonal boron nitride (h-BN) is a white layered crystal with a structure similar to graphite, which has many excellent properties including thermal conductivity, insulation, corrosion resistance, and wear resistance. After adding h-BN, many composite materials can maintain their thermal stability and improve their mechanical properties. The effect of particle size on the wear resistance of h-BN is not significant, but rather sensitive to the amount added. Within a certain range, the friction coefficient of the composite material decreases with the increase in h-BN content, while the wear resistance increases with the increase in h-BN content.
The thermal spraying method is a process used to produce various types of coatings designed to improve the surface properties of materials. Atmospheric plasma spraying (APS) is a commonly used thermal spraying process [5,6,7]. The aluminum oxide (Al2O3) and magnesium spinel (MgAl2O4) coatings were prepared for insulation applications by APS technology [8]. The influence of coating microstructure, phase composition, and water vapor adsorption on the differences in electrical insulation performance of coating systems was studied. The ceramic coating was deposited on the substrate surface by jet spraying high-temperature plasma molten powder at high speed. I.N. Qureshi [9] et al. investigated the effect of thickness of the binder layer on the thermal corrosion resistance and found that the peeling resistance of thin binder-layer specimens was lower than that of thick binder-layer specimens, and the coatings with thick binder-layer coatings had better thermal corrosion resistance than those with normal binder-layer coatings. APS coatings can often be applied to large metal or ceramic parts, so TiO2 SiAlON ceramic coating was deposited on 316 stainless steel substrates using atmospheric plasma spraying, which exhibited excellent wear resistance [10]. In order to obtain a more compact and better performance coating, materials often added include TiO2 [11,12,13,14], Cr2O3 [15], and ZrO2 [16,17,18,19]. M. Vijay [12] et al. investigated the effect of parameters during plasma spraying of ceramic coatings on the deposition efficiency of alumina-13 wt % titanium dioxide composite coatings and found that the variation of the spraying parameters strongly affects the deposition efficiency, and that the microhardness, erosion, and sliding-wear properties of the coatings are affected by the spraying parameters. Leszek Latka [13] et al. investigated how the addition of titanium dioxide to alumina in agglomerated and sintered nanostructured powders improves the microstructural and functional properties of the layers and found that the addition of TiO2 to the powder provides a denser coating microstructure, improves inter-splash contact, prevents the coating from severe fragmentation and spalling during abrasion, and prolongs cavitation life. Pejman Zamani [15] et al. investigated the sliding-wear resistance of atmospheric plasma-sprayed AlO3, Cr2O3, and their composite coatings on tungsten carbide under mild conditions and found that alumina and alumina-rich coatings have higher wear resistance due to their denser microstructure, better toughness, and low coefficient of friction in the first stage of a sliding-wear test. H.Q. Li [18] investigated the tribological and corrosion resistance of three conformal ceramic coatings and found that the Al2O3-ZrO2 composite coating has better corrosion and wear resistance compared to ceramic coatings (Al2O3, ZrO2) and CoCrMo substrates.
The important process parameters in atmospheric plasma spraying (APS) technology include spraying currents, spraying distance, and spraying speed. S. T. Aruna and N. Balaji et al. [20] investigated the effects of different spraying currents (450 A, 550 A, and 625 A) on the morphology, microstructure, microhardness, surface roughness, and wear behavior of aluminum oxide coatings. The effect of the initial phase (α and γ-alumina) as a function of spraying currents on the preferential orientation of plasma-sprayed coatings were investigated, and the researchers found that spraying-current coatings prepared from γ-alumina as the starting material exhibited a synergistic combination of wear resistance, corrosion resistance, and thermal cycling resistance. Sahab [21] prepared Al2O3-TiO2 coatings using plasma-spraying technology for various application scenarios that require wear resistance, erosion, cracking, and peeling. The performance of coatings prepared based on three different process parameters (current, powder flow rate, and spray distance) was discussed. The results showed that increasing the current from 550 A to 650 A and the powder flow rate from 22.5 g/min to 26 g/min significantly improved the mechanical properties (adhesion strength and hardness) of the coating.
In this study, an Al2O3/h-BN composite coating was prepared on the surface of 20 steel substrates by atmospheric plasma-spraying method, and the microstructure, phase constitution, microhardness, adhesion strength, and insulation performance of the coatings were characterized systematically. The influence of different spraying currents on coating properties was explored. The potential of Al2O3/h-BN as coating material for electrode rollers was evaluated.

2. Materials and Methods

The sprayed bond-coating material is Ni20Cr powder purchased on the market with a particle size of 40–90 μm, as shown in Figure 1 and it is composed of round particles with relatively smooth surface. Before spraying, the powder needed for the experiment was placed in the air-drying oven at a temperature of about 75 °C and baked for 8–12 h to remove the moisture adsorbed in the powder and enhance the fluidity of the powder in the powder feeding tube. The content of each element of 20 steel, Ni20Cr, Al2O3, and h-BN are shown in Table 1, Table 2, Table 3 and Table 4.
The specifications of the 20 steel substrates used in the experiment were φ25.4 mm × 6 mm. Before spraying, acetone and industrial alcohol were used to remove oil stains on the substrate surfaces, along with ultrasonic cleaning. After blowing them dry, the substrate surfaces were sandblasted to increase the roughness of the surfaces and increase the combination between the substrates and the coatings. The sandblasting material was 24# corundum sand, the air pressure was controlled at about 0.4 MPa, the sandblasting distance was controlled at about 120 mm, and the sandblasting angle was controlled at about 45°. After completion of the sandblasting, the residual gravel on the substrate surface was swept by the air-compressor nozzle. The sandblasted substrate should be sprayed as soon as possible to prevent oxidation.
MF-P-1000 atmospheric plasma-spraying equipment (Sulzer beauty surface technology Co., Ltd., Shanghai, China) was used to prepare the bonded coating and surface coating on the substrate surfaces. First of all, the powder was tested to calculate the amount of powder to ensure that the powder pipeline was unobstructed. Then, the height of the spray gun was adjusted to be consistent with the substrate and to make sure the angle was perpendicular to the substrate to be sprayed. After adjusting the spraying distance, the substrate surface was pre-sprayed without powder delivery, and the substrate surface was preheated. Finally, the process parameters were set for spraying. The spraying parameters of the Al2O3/h-BN coatings, sprayed at the plasma power of 550 A spraying current (A coating) and of 650 A spraying current (B coating), are shown in Table 5. Ar gas is a plasma-forming gas. H2 gas is a transport gas.
An X-ray diffractometer (XRD, DX-2700, Dandong, China, Cu-Kα, 40 kV × 30 mA) was used to analyze the phase structure of the coating, with a scanning range of 10–90° and a scanning speed of 0.02°/s. The phase structure and lattice parameter information were confirmed.
For microscopic observations and microhardness measurements, cross-sections of coated samples were cut using a cutting machine with a cutting speed of 0.02 mm/s, and metallographic samples were thermal inlaid prior to grinding and polishing.
A JEOLJSM-5910 Scanning Electron Microscope (SEM, JEOL Japan Electronics Co., Ltd., Tokyo, Japan) was used to observe the surface and cross-section morphology of the coatings. The element distributions in the cross-section of the coatings were characterized by Energy Dispersive X-ray Diffraction (EDX).
According to ASTM C633 standard [22], the bond strengths of coated samples were tested by a GDL-50KN universal electronic tensile testing machine (Shanghai Qingji Instrument & Meter Technology Co., Ltd., Shanghai, China). The microhardness values of the samples were tested by an MH-500D microhardness tester (Shanghai EVERONE Precision Instrument Co., Ltd., Shanghai, China) with loading load of 300 gf and loading time of 15 s. The average values of 10 points were taken.
The image analysis software Image J V1.8.0.112 (National Institutes of Health, Bethesda, MD, USA) was used to analyze the morphology of the cross-sectional coatings of different multiples, and the porosities were calculated. The volume resistivity ρv of coatings were measured according to GB/T 1410-2006 [23]“Methods of test for volume resistivity and surface resistivity of solid electrical insulating materials.”

3. Results and Discussion

Figure 2a and Figure 2b, respectively, show the SEM images of the surfaces of the Al2O3 coatings (A coating) sprayed at the plasma power of 550 A spraying current, and Figure 2c,d, respectively, show the SEM images of the surface of the Al2O3/h-BN coatings (B coating) sprayed at the plasma power of 650 A spraying current. The surface morphology of the prepared coating is typical of atmospheric plasma spraying [24,25]. The surfaces of the Al2O3/h-BN coatings prepared by two different spraying currents under atmospheric plasma spraying are relatively uniform and smooth, which is caused by the characteristics of thermal spraying. The powder can be fully melted at extremely high temperature, so the microstructure formed is of high density. Under a high-magnification field of view, we can observe the appearance of micropores and small cracks on the surface of both coatings. The presence of such intrasplat cracks is a typical result of residual stress relaxation in ceramic coatings [26]. The reason for the formation of micropores is that the gas carried by the molten powder in the spraying process is sprayed onto the substrate and then cooled and solidified and discharged. The formation of small cracks occurs when the molten powder impinges on the substrate surface and the sedimentary layer and the droplets spread around and quickly spread on the surface, resulting in temperature difference and solidification shrinkage, and ultimately resulting in microcracks.
Figure 3a and Figure 3b, respectively, show SEM images of the cross-sections of the A coating, and Figure 3d,e, respectively, show SEM images of the cross-sections of the B coating. It can be observed from the figure that the dark surface layer is Al2O3/h-BN, the thin and lighter color is a Ni20Cr layer, and the bottom layer is 20 steel substrate. The design of the middle sublayer of Ni20Cr is due to the fact that the coefficient of thermal expansion (CTE) of Al2O3 is 4.9 × 10−6 K−1 at high temperature, and the CTE of steel 20 is 10.07 × 10−6 K−1; these are quite different, and therefore huge internal stress will be generated after cooling, while the CTE of Ni20Cr is 8.1 × 10−6 K−1, which can relieve internal stress. Through observation, it can be found that the Al2O3/h-BN coating the steel 20 substrate, the Ni20Cr bonding layer, and the Al2O3/h-BN coating prepared by two different spraying currents under atmospheric plasma spraying are relatively clear, without cracks, and no obvious separation, and the bonding condition is good. It can be observed that the matrix and the bonding layer are well combined, and there are no holes, cracks, or other defects, which could be formed because the sandblasting treatment increases the bonding force [27]. Due to the large roughness of the bonding layer and the formation of the matrix between the coatings, it can also increase the bonding force between the bonding layer and the coating, improving the adhesion strength of the coating. As shown in Figure 3b,e, at high magnification, it can be found that the overall coating is relatively dense, but small cracks and holes can be observed in both coatings. As can be seen from Figure 3b,e, the cracks and holes of coating A are more numerous than those of coating B in Figure 3e, which is consistent with the test results of porosity in Image J software, indicating that increasing the spraying current can reduce the porosity of the coating. At the same time, in the cross-sections of both coatings, the small spot shown in Figure 3b,e is the unmelted Al2O3; the grayish-black lamelliform sediments are found distributed in the coating interior, which is the h-BN component added to the Al2O3/h-BN powder.
There are unmelted particles, micropores, and microcracks in the coating. The primary root cause is the temperature difference between the individual powder particles caused by the gradient. First of all, there is a difference in particle size between each powder particle and the angle of the powder going into the plasma jet, and once there, maybe changing to a melting or semi-melting state. Secondly, different molten powder particles fly at different speeds and hit the substrate to form a sedimentary layer with temperature differences. Thirdly, Al2O3 and h-BN are ceramic materials with low ductility, and the cooling/solidification takes place rapidly, usually within 3 microseconds. Some areas may have not been combined with the previous sedimentary layer but have been solidified, resulting in pores between the new sedimentary layer and the old sedimentary layer. Fourthly, the molten powder particles will produce splashing after hitting the old sedimentary layer, and the splashing edge area has low binding ability with the old sedimentary layer, which will also cause pores. Fifthly, as the main component, Al2O3 will change from the thermodynamically stable α-Al2O3 phase to the metastable γ-Al2O3 phase, which will also cause a volume change inside the coating [28]. The melting degree of powder particles depends on the low melting point and high thermal conductivity of the particles [29,30], and h-BN has excellent thermal conductivity and can melt into liquid solution with Al2O3.
Figure 4 shows the XRD pattern of the coating. According to the intensity of the main diffraction peak, we can observe that the strongest peak corresponds to γ-Al2O3. The main crystal phase of the sprayed coating is mainly composed of γ-Al2O3 with a small part of α-Al2O3, and no other crystal phase of alumina is detected. Alumina has many crystal phases, and with the exception of α-Al2O3, the other crystal phases are in the metastable phase. Although the content is low, we found that the h-BN phase, as shown in the Figure below, improved the performance of the coating.
The Al2O3 in Al2O3/h-BN powder is mainly composed of α-Al2O3 phase, which is a stable phase. However, after the atmospheric plasma spraying, the inert gas ionizes into the ionizer under the action of arc, releasing a lot of heat, and changing the state of Al2O3 in this process. In the process of atmospheric plasma spraying, Al2O3/h-BN powder passes through the plasma jet outside the nozzle and is heated to a molten or semi-molten state. It impinges on the substrate constantly at a high speed, then jets to the substrate surface and rapidly accumulates, cools, and solidifies to form the coating. α-Al2O3 belongs to the tripartite crystal system; its structure is stable, and γ-Al2O3 is a face-centered cubic crystal system. Nucleation-free energy and cooling rate will affect the formation of crystal nuclei. According to the XRD pattern, in this process, alumina will transform from the thermodynamically stable α-Al2O3 phase to the metastable γ-Al2O3 state [31,32], which is due to the plasma-spraying conditions and the cooling process. Compared with the α-Al2O3 phase, the γ-Al2O3 phase has a lower specific surface energy [33]. When the temperature is lower than 1740 °C, the critical nucleation-free energy of the γ-Al2O3 phase is low, and it is easy to nucleate, but the nucleation ability of the α-Al2O3 phase is much weaker and is not easy to nucleate. Therefore, γ-Al2O3 is easier to nucleate from melt than α-Al2O3 [34]. The formation conditions of α-Al2O3 are relatively complex. After spraying, γ-Al2O3 is the main crystal-phase coating formed in the cooling process. Then in the cooling process, according to the different sizes, the cooling rates are different, different phases are formed. For larger size of alumina, cooling speed is slow, the local temperature is high enough, and part of the metastable γ-Al2O3 will gradually transform into steady α-Al2O3; however, the smaller size of alumina cools faster and forms metastable γ-Al2O3 until room temperature.
The residual α-Al2O3 phase in the coating is mainly the following two aspects. On the one hand, the temperature is very sensitive, and when the heat is not enough to quench quickly, the coating surface is still high in temperature, making a part of the formation of the γ-Al2O3 phase into the α-Al2O3 phase. On the other hand, because there are a small number of large-particle-size alumina particles in powder spraying, in the spraying process, it is not completely melted or even not in a half-molten state when directly sprayed on a substrate surface, forming a coating.
In order to further explore the composition of the prepared coating, the compositions of two kinds of coating samples were determined by EDX energy spectrometer under different spraying currents. The EDX spectrum is shown in Figure 5, and the data obtained are shown in Table 6. As shown in Figure 5a,b, the strong peaks are mainly derived from oxygen and aluminum, but nitrogen and boron can also be detected. In Figure 5a, the contents of O, Al, N, and B in A coating are 45.9 wt.%, 50.9 wt.%, 1.69 wt.%, and 1.51 wt.%. The content of B coating is similar to that of A coating (45.6 wt.%, 51.3 wt.%, 1.71 wt.%, and 1.39 wt.%, respectively).
The porosity, microhardness, adhesion strength, and insulation performance of the coatings depend on the atmospheric plasma-spraying process parameters [35]. From previous SEM topography, it can be observed that the densifications of the middle and lower parts of the coating are better than those of the middle and upper parts, because the molten powder particles constantly impact the old sediment layer, resulting in a “shot peening treatment.” In ceramic coatings, pores are composed of pores and cracks of various shapes, sizes, and orientations [36]. There are many methods to measure porosity, including the weighing method, image method, and so on. According to the SEM coating photos that were analyzed and processed, the porosity of the coatings were measured by an imaging method using Image J software [37]. As shown in Figure 6, the red area is the pore area. After calculation, the porosities of coatings A and B are 6.04% and 4.75%, respectively. The results show that the microstructure of the B coating is more compact than that of the A coating. Compared with pure alumina coating, a coating with fewer and smaller pores and better performance was prepared. Pore defects will affect the mechanical and adhesion strength of the material.
The calculated porosity volume fractions of coatings A and B obtained under different plasma-spraying currents are shown in Figure 7. Therefore, both the A and B coatings under this spray current are very dense, as observed in the SEM morphology. The porosity of the B coating is 1.29% lower than that of the A coating. The coating is formed by the accumulation of molten droplets. With the increase in plasma-spraying current, the spraying power, spraying speed, and deposition temperature also increase. These increases indicate that at higher plasma power, the complete melting of the particles and the higher velocity give the coating a smaller porosity and better interfacial bond strength.
The adhesion strength between substrate and coating is one of the basic properties of a coating and an important index to ensure its service effect. The plasma-spraying coating and the substrate are mainly bonded by mechanical occlusion. Adding a bonding layer can alleviate the residual stress caused by the difference of thermal expansion coefficient between the substrate and the ceramic coating and can also regulate the surface roughness of the bonding layer to improve the adhesion strength between the coating and the substrate. The fracture failure location was mostly located in the ceramic coating, and only a small amount of failure occurred at the interface between ceramic coating and bond coating. This shows that the adhesion strength between ceramic coating and bonding layer, and the bonding layer and substrate, is higher than that of the cohesive strength of ceramic coating.
In order to meet the insulation requirements of the coating, the coating must have appropriate mechanical and electrical properties. Table 3 compares the related properties of coatings A and B. The Vickers hardness values of A and B coatings were estimated to be 718.20 HV and 840.90 HV, respectively. The hardness of the Al2O3/h-BN coating obtained at 650 A spraying current is higher than that obtained at 550 A spraying current. Microstructure, residual stress, grain size, and crystalline phase structure significantly affect the hardness of oxide ceramics [38]. The higher microhardness of the B coating is probably due to the high spraying current, which makes the particles melt better and the coating denser, which corresponds to the smaller porosity of the coating that can be observed in Figure 7.
The adhesion strengths of coatings A and B are 22.0 MPa and 22.3 MPa, respectively. The calculated porosities of coatings A and B obtained under different plasma-spraying currents are shown in Figure 7. However, the volume resistivity decreases with increasing porosity.
In addition, the Al2O3/h-BN coating has excellent insulation performance, and the volume resistivity of the A coating and B coating are 9.29 × 1010 Ω·cm and 3.55 × 1010 Ω·cm, respectively, which means that the Al2O3/h-BN coating is an effective insulation material.
Table 7 shows the microhardness of Al2O3/h-BN coatings prepared on 20 steel substrate with different spraying parameters. The microhardness value increased with the increase in spraying current. In general, an increase in the spraying current results in a dense, nonporous coating because of the higher melting degree of the molten particles and the higher impact velocity. The comparative relationship between the volume resistivity of the A and B coatings is shown in Table 7. As shown in Figure 7, the coating with high current is denser than that with low current [39], and the volume resistivity of the B coating decreases with the increase in spraying current, which means that the Al2O3/h-BN coating will prevent electron conduction in the porous condition. However, the volume resistivity of both coatings is greater than 1 × 1010 Ω·cm. Therefore, these data indicate that both coatings prepared by us can meet the requirements of the corona roller surface-coating standard.

4. Conclusions

In order to improve the arc resistance, wear resistance, and chemical stability of the corona roller, an Al2O3/h-BN composite coating was prepared on the surface of steel 20 by atmospheric plasma-spraying technology. The porosity, microhardness, adhesion, and volume resistivity of the coating prepared by 550 A and 650 A spraying currents were compared, and the following conclusions were obtained:
  • The porosity of B coating (650 A) is lower than that of A coating (550 A), and the microhardness is better than that of A coating;
  • Both coatings are well bonded to the substrate. The adhesions of the coatings prepared by the two spraying currents are not much different, but both are greater than 20 MPa, and the coating prepared by the high spraying current (650 A) is relatively large;
  • The volume resistivity of the two coatings is greater than 1 × 1010 Ω·cm, which meets the application requirements of the corona rollers;
  • The Al2O3/h-BN composite coating prepared by high spraying current (650 A) has better performance than that prepared by low spraying current (550 A).

Author Contributions

Conceptualization, Y.G.; methodology, Y.G.; software, X.L.; validation, X.L.; formal analysis, Y.G.; investigation, Y.W. (Yujiang Wang) and Y.W. (Yu Wang); resources, Y.W. (Yu Wang); data curation, Y.G.; writing—original draft preparation, Y.G.; writing—review and editing, B.Q. and L.L.; visualization, Z.C.; supervision, B.Q.; project administration, L.L.; funding acquisition, Y.W. (Yu Wang). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Guangxi Science and Technology Major Project (No. AA22068101), National Natural Science Foundation of China (No. 52161033 and No. 22262005), Project of Foshan Taoyuan Institute of Advanced Manufacturing (No. TYKF202203001), Project of the Key Lab of Guangdong for Modern Surface Engineering Technology (No. 2020B1212060049), and Guangxi Innovation Driven Development Project (No. AA18242036-2).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Crystals 14 01035 g001
Figure 1. Spray powder morphology of Ni20Cr.
Figure 1. Spray powder morphology of Ni20Cr.
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Figure 2. Surface morphology of Al2O3/h-BN coatings with different multiples. (a) A coating 200×; (b) A coating 2500×; (c) B coating 200×; (d) B coating 2500×.
Figure 2. Surface morphology of Al2O3/h-BN coatings with different multiples. (a) A coating 200×; (b) A coating 2500×; (c) B coating 200×; (d) B coating 2500×.
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Figure 3. Cross-section of Al2O3/h-BN coatings with different multiples. (a) A coating 200X; (b) A coating 2500×; (c) EDS; (d) B coating 200×; (e) B coating 2500×; (f) EDS.
Figure 3. Cross-section of Al2O3/h-BN coatings with different multiples. (a) A coating 200X; (b) A coating 2500×; (c) EDS; (d) B coating 200×; (e) B coating 2500×; (f) EDS.
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Figure 4. XRD of (a) A coating and B coating under different operating currents. (b) Al2O3-sprayed powder material.
Figure 4. XRD of (a) A coating and B coating under different operating currents. (b) Al2O3-sprayed powder material.
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Figure 5. Energy dispersive X-ray diffraction (EDX) results of (a) A coating and (b) B coating under different spraying currents.
Figure 5. Energy dispersive X-ray diffraction (EDX) results of (a) A coating and (b) B coating under different spraying currents.
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Figure 6. Using Image J software to process SEM section pore images of (a) A and (b) B coatings.
Figure 6. Using Image J software to process SEM section pore images of (a) A and (b) B coatings.
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Figure 7. Porosity of A and B coatings obtained under different plasma-spraying currents.
Figure 7. Porosity of A and B coatings obtained under different plasma-spraying currents.
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Table 1. The 20 steel substrate material compositions.
Table 1. The 20 steel substrate material compositions.
CSiMnPSNiCrCu
0.17~0.23%0.17~0.37%0.35~0.65%≤0.035%≤0.035%≤0.30%≤0.25%≤0.25%
Table 2. Ni20Cr material composition.
Table 2. Ni20Cr material composition.
FeCrCuNiAlTiCMnSi
1.50%22.00%0.20%73.63%0.15%0.35%0.12%0.70%0.80%
Table 3. Al2O3 material composition.
Table 3. Al2O3 material composition.
AlO
52.68%47.32%
Table 4. h-BN material composition.
Table 4. h-BN material composition.
NB
56.4%43.6%
Table 5. Plasma-spraying parameters.
Table 5. Plasma-spraying parameters.
Spraying ParametersCoatingCurrent/AInput Power/kWAr/L min−1H2/L min−1Powder Feed Rate/(g min−1)Spraying Distance/mm
BondNi20Cr6004545930110
coating
AAl2O3/h-BN55041401045100
BAl2O3/h-BN65050401045100
Table 6. Composition of A and B obtained by energy dispersive X-ray diffraction (EDX).
Table 6. Composition of A and B obtained by energy dispersive X-ray diffraction (EDX).
ElementsA Coating (wt.%)B Coating (wt.%)
Oxygen element45.945.6
Aluminum element50.951.3
Nitrogen element1.691.71
Boron element1.511.39
Table 7. Mechanical and electrical properties of A and B.
Table 7. Mechanical and electrical properties of A and B.
Mechanical PerformanceAB
Vickers hardness (HV)781 ± 0.5840.5 ± 0.5
Adhesion strength (MPa)22.022.3
Volume resistivity (Ω cm)9.2 × 10103.55 × 1010
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Guo, Y.; Lan, L.; Qin, B.; Liang, X.; Wang, Y.; Wang, Y.; Chen, Z. Preparation and Characterization of Al2O3/h-BN Composite Coatings by Atmospheric Plasma Spraying (APS). Crystals 2024, 14, 1035. https://doi.org/10.3390/cryst14121035

AMA Style

Guo Y, Lan L, Qin B, Liang X, Wang Y, Wang Y, Chen Z. Preparation and Characterization of Al2O3/h-BN Composite Coatings by Atmospheric Plasma Spraying (APS). Crystals. 2024; 14(12):1035. https://doi.org/10.3390/cryst14121035

Chicago/Turabian Style

Guo, Yifeng, Lingxiao Lan, Boying Qin, Xinghua Liang, Yujiang Wang, Yu Wang, and Zhikun Chen. 2024. "Preparation and Characterization of Al2O3/h-BN Composite Coatings by Atmospheric Plasma Spraying (APS)" Crystals 14, no. 12: 1035. https://doi.org/10.3390/cryst14121035

APA Style

Guo, Y., Lan, L., Qin, B., Liang, X., Wang, Y., Wang, Y., & Chen, Z. (2024). Preparation and Characterization of Al2O3/h-BN Composite Coatings by Atmospheric Plasma Spraying (APS). Crystals, 14(12), 1035. https://doi.org/10.3390/cryst14121035

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