Ceramic Composite Coatings Research Articles

Microstructure and surface hardness of ceramic composite coated aluminium alloy

A ceramic composite coating of Cr2O3 + TiC was developed on the surface of Al-6061 alloy plates. The HVOF coating process depends on the parameters such as substrate temperature, powder gas carrier flow rate, pressure, feed rate, standoff distance, and angle between the torch and substrate. The evaluation of surface hardness and microstructure ceramic composite coatings are discussed in this paper. Surface hardness was tested using the Nano-Indentation Tester. The microstructural characterization was conducted using Scanning Electron Microscope (SEM). The hardness test was conducted with a maximum load of 60 mN. The results indicated a vast improvement in the surface hardness of both the coated specimens. The tests performed indicated that Cr2O3 + 10%TiC coatings had a higher average hardness and modulus of elasticity measured at 4.33 GPa, and 108 GPa respectively. Whereas TiC + 10%Cr2O3 indicated a lower hardness and modulus of elasticity measured at 1.62 GPa and 79 GPa respectively. Thus, the tests showed that the Cr2O3 + 10%TiC coatings were harder. The microstructural characterization was conducted using the SEM for both cross sectional view and top view. The microstructural images indicated that the TiC + 10%Cr2O3 coated samples had a better surface finish, as compared to the Cr2O3 + 10%TiC coated samples.

Creation of Bioactive Ceramic Composite Coatings on Zn–Mn–Mg Alloy via Micro-arc Oxidation and Hydrothermal Treatment for Orthopedic Implant Applications

Zinc alloys have emerged as promising biodegradable metals thanks to their critical physiological roles and encouraging degradation behavior. In this study, calcium phosphate (CaP) coatings were made on micro-arc oxidized Zn alloy using hydrothermal treatment (HT), which was motivated by the CaP-based minerals in natural bone tissue. The coating morphology was optimized by controlling the HT time, resulting in a homogeneous micro-CaP coating structure. The CaP coating significantly increased the cell viability and adhesion of MC3T3-E1 preosteoblasts and L-929 cells. Compared with the control group, the cell toxicity of the samples after MAO-HT was less, the number of cells was more, and the morphology was complete. Cell adhesion showed that the distribution of cells increased with the increase of HT time. In addition, the CaP coating significantly reduced the Zn ion release from the bulk material during the degradation process, resulting in a much lower Zn concentration and pH change in the surrounding environment. The micro-CaP coating structure and the regulated release of zinc ions are primarily responsible for the enhanced cytocompatibility and biomineralization of CaP-coated Zn biomaterials. In summary, the CaP coating on Zn-based biomaterial appears to be a viable approach to enhance its biocompatibility and to control its degradation rate. After that, the biocompatibility of the material can be improved by controlling the surface morphology of the material to adapt to the complex human environment.

High Temperature Oxidation and Oxyacetylene Ablation Properties of ZrB2-ZrC-SiC Ultra-High Temperature Composite Ceramic Coatings Deposited on C/C Composites by Laser Cladding

In order to improve the high temperature oxidation and ablation resistance of C/C composites, ZrB2-ZrC-SiC ultra-high temperature composite ceramic coatings were prepared on C/C composites by laser cladding using Zr, B4C, and Si as raw materials. The microstructure of the coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Air isothermal oxidation (1600 °C, 80 min) and oxyacetylene flame ablation (2400 kW/m2, 300 s) were used to evaluate the high-temperature oxidation and ablation properties of the coating, respectively. The results show that the microstructure of laser cladding coating is a totem of black and white. The white part is mainly the first solidified high melting point ZrB2 phase, and the black part is the latter solidified eutectic structure, which is mainly composed of ZrB2(ZrB12)-ZrC or ZrB2(ZrB12)-SiC two phases. After oxidation at 1600 °C and 80 min, the coating is mainly composed of ZrO2 and ZrSiO4 phases, and ZrSiO4 is basically distributed among ZrO2 particles. The high temperature oxidation and ablation properties of the coating are better than the C/C composite matrix, and the mass ablation rate of the coating is about 1/4 of the latter.

Application features of microarc oxidation technology

The technology of microarc oxidation of valve metals is one of the promising methods for engineering the working surface of friction units of modern technology. As a result of the versatility of the technology, it is possible to obtain composite ceramic coatings and materials of various types. Their properties are set by the electrical modes of material formation, the chemical composition of the electrolyte, and the possible further modification of the ceramic matrix with micro- and nanosized tribofillers. Based on the practical results of their research in the field of creating coatings of various types by microarc oxidation, an analysis is given of the main areas of application of microplasma electrolytic oxidation technology, their advantages over other methods of surface modification, structure and properties of the materials obtained. It is possible to distinguish the modification of the friction surface of a part by the method of microplasma electrolytic oxidation in order to increase its hardness and wear resistance. Good results were obtained in increasing the wear resistance of the hardened working surface of the spinning machine parts, the number of equipment repairs was reduced by more than 20 times. The use of microarc oxidation is promising for the preparation of composite coatings, which are a ceramic matrix in which solid lubricating dispersed particles are embedded. The technology of forming a matrix on aluminum, modified with dispersed magnetite, graphite and molybdenum disulfide, has been developed. According to the results of comparative tribotechnical tests, it was found that the intensity of linear wear of the material filled with MoS2 is 3 times, and Fe3O4 - 1.6 times lower than that of the coatings without filler. Based on the technology of microplasma electrolytic oxidation, an original technology has been developed for obtaining mineral-ceramic material, which is a matrix of aluminum oxide and dispersed diamond inclusions. Abrasive wheels made from this material have a consistently high volumetric cutting ability, 1.5-3.5 times higher than the traditional analogues and are characterized by high diamond retention. The possibilities of microplasma oxidation have not yet been fully explored, the most promising direction being the creation of nanostructured coatings for a specific technological task.

Plasma sprayed TiC–Ti5Si3–Ti3SiC2–SiC composite coatings using annealed Ti–SiC composite powders based on SiC content

The TiC–Ti5Si3–Ti3SiC2–SiC ceramic composite coatings were prepared with in-situ reaction by plasma spraying annealed Ti–SiC–C composite powders. The effect of SiC content in the annealed composite powders at 1200 °C on the microstructure and properties of the coatings was studied. With the increase of SiC content, the phases in the annealed Ti–SiC composite powders changed from Ti, SiC, TiC and Ti5Si3 to SiC, TiC, Ti5Si3 and Ti3SiC2. The phases of the sprayed coatings were mainly composed of TiC, Ti5Si3, Ti3SiC2 and a small amount of residual Si, and their content were closely related to SiC. The coating hardness first increased and then decreased, while their mass loss showed an opposite trend to that of hardness. The T1SCC (molar ratio of Ti-SiC-C is 3:1:1) coating had the highest hardness of HV 1509 and the lowest mass loss of 0.0019 g, whereas its fracture toughness was 3.51 MPa m−2.

Effects of air annealing treatments on the microstructure, components, and mechanical properties of magnetron sputtered Al2O3–Cr2O3–ZrO2 composite coatings

To investigate the effects of air annealing on the microstructure, components, and mechanical properties of ceramic composite coatings, Al2O3–Cr2O3–ZrO2 composite coatings were prepared on silicon substrate using radio frequency magnetron sputtering at room temperature, and then air-annealed in a temperature range of 450–850 °C for 30 min. The results indicated that the phase-structure and superficial characteristics, including morphology and surface roughness, were not visibly altered in the annealed coatings up to 600 °C; the elemental component distributions remained uniform. The improvement in the mechanical properties was attributed to the growth of oxide grains. There were no significant changes in the components of Al, Cr, Zr, and O in the annealed coatings. However, an increase in the Cr component and a decrease in the Zr component occurred on the coating surface; the overall structure of the composite coatings possessed a favorable heat resistance. Upon annealing at 750 °C, the thermally-driven formation of uniform and refined nanoparticles on the coating surface was responsible for the effective enhancement of the mechanical properties. Furthermore, annealing at 850 °C induced the enlargement of the precipitated Cr2O3 nanoparticles and the generation of micro-defects, resulting in a drastic morphological evolution, an evident increase in the surface roughness, and a significant decrease in the mechanical properties. This study provides new perspectives on designing novel thermal barrier coatings and understanding the role of high temperature air annealing on the microstructural transformation.

Al2O3-Modified Polymer-Derived Ceramic SiCN High-Temperature Anti-Oxidative Composite Coating Fabricated by Direct Writing.

A reliable protective layer is one of the main challenges in preventing oxidation of thin film sensors to achieve accurate, effective, and stable readings at high temperatures. In this work, an Al2O3-modified polymer-derived ceramic SiCN composite coating fabricated by a direct-writing technique is utilized as a protective layer for thin film sensors. The microstructure evolution of the Al2O3/SiCN films is examined herein. The protective layer exhibits excellent oxidation resistance and thermal stability at high temperatures up to 1000 °C, which contributes to improving the stability and lifetime of thin film sensors in extreme environments. The TiB2/SiCN thin film resistive grid with the Al2O3/SiCN composite film as a protective layer is fabricated and tested. The results indicate that the coating can protect the TiB2/SiCN thin film resistive grid at high temperatures up to 1000 °C, which is about 200 °C higher than that of the TiB2/SiCN thin film resistive grid without a protective layer. The resistance change rates of the TiB2/SiCN thin film resistive grid with a protective layer are 0.5%/h at 900 °C and 10.7%/h at 1000 °C.

ZrC, HfC, and ZrC/ZrxSiy coatings prepared via molten salt Solid–Liquid two-phase diffusion method and ablation properties

ZrC, HfC, and ZrC/ZrxSiy composite ceramic coatings were prepared on the surface of carbon-matrix composites via molten salt solid–liquid two-phase diffusion to improve the ablation resistance of the C/C composites. The preparation of the coating composition could be controlled by using different powders. The effects of temperature and holding time on the microstructures of ZrC coatings and their variation laws were studied. Results showed that the ZrC coating density increased with temperature and holding time. At a holding time of 16 h, the growth of the ZrC coating was slow. The volatilization of SiO2 caused loose ZrO2 to splash. Moreover, the Si content was found to affect the ablation performance of the ZrC/ZrxSiy composite ceramic coatings, and the ablation mechanism was studied. The ZrC, HfC, and ZrC/ZrxSiy composite ceramic coatings exhibited good ablation properties. The ablation rates of the ZrC and HfC coatings were 0.805 and 0.715 mg/s, respectively, after oxyacetylene flame ablation at 3000 °C for 60 s.

High‐Temperature‐Resistant, Mechanically Stable FeCrNiAl/Al2O3 Thermally Sprayed Thick Ceramic Coatings for Stealth Applications over X‐Band

To avoid radar detection during tactical operations, engine exhaust zones of aircrafts are difficult to treat with rubber/resin‐based stealth coatings, due to their thermal and mechanical instability at high temperature (>1000 °C). Further, monolithic fabrication of thick ceramic coatings without any crack/rupture and stability of functional fillers at such high temperatures is an additional challenge in the development. To overcome these difficulties, for the first time, FeCrNiAl/Al2O3 thick ceramic composite coatings are developed with excellent radar/microwave (MW) absorbing capability and good mechanical strength on the titanium alloy substrate using an in‐house developed gas flame‐spraying apparatus, without any cracks or deformations. The 50 wt% FeCrNiAl/Al2O3 ceramic coating is found to have excellent reflection loss (RL) >−20 dB (99% MW absorption) over X‐band (8.2–12.4 GHz) frequencies with capability of tuning the absorption frequency at different thicknesses, while maintaining the RL values. This coating has tensile strength of more than 23 MPa, which may be advantageous for prolonged use on aircraft surfaces.

Enhanced mechanical properties and corrosion resistance of nickel and nickel-phosphorous coatings fabricated by electrodeposition embedding with TiB2 ceramic particles

Pure nickel (Ni), TiB2 reinforced nickel (Ni-TiB2), nickel-phosphorus (Ni-P), and TiB2 reinforced nickel-phosphorus (Ni-P-TiB2) composite coatings were deposited on AISI-1045 steel substrates from Watts bath and phosphorous-containing solution, respectively. The composition and microstructure of these coatings were analyzed by energy dispersive x-ray spectroscopy (EDS), scanning electron microscope (SEM) and x-ray diffraction (XRD) analysis. The properties of these coatings, including hardness, were assessed and compared. The electrochemical performance of these coatings was investigated in a 3.5 wt% sodium chloride solution using electrochemical spectroscopy (EIS) and the potentiodynamic polarization technique at room temperature. The effect of TiB2 on the microstructure, phase, and properties of the coatings was investigated. The results indicate that the incorporation of TiB2 particles in the nickel matrix greatly increased the hardness and anti-corrosion properties of the nickel coatings by refining of the microstructure and reducing the defects. The enhancement effect of TiB2 on Ni-P coating is not as significant as that of TiB2 on nickel coating. However, with the incorporation of TiB2 ceramic particles, the corrosion resistance and hardness of the Ni-P-TiB2 coating increased by about 50% and 10%, respectively, compared with the original Ni-P coating. The present study provides insight into the potential applications of novel TiB2 ceramic particle-reinforced nickel composite coatings in the areas of wear and corrosion resistance.

Structure and Properties of Ti-Si Composite Ceramic Coatings by Laser Cracking with SiO<sub>2</sub> Particles

Ti-Si composite ceramic coating containing SiO2 particles was prepared on 45 steel substrate by in-situ laser pyrolysis with laser power of 600W and laser wavelength of 980nm. The density and wear resistance of the composite ceramic coating were improved. By means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), reciprocating friction and wear tester, the element composition, existing forms, surface morphology and friction and wear properties of Ti-Si composite ceramic coatings with different mass fraction of SiO2 particles were analyzed. The results show that the addition of SiO2 particles can improve the surface density and inorganic degree of the composite ceramic coating. When the mass fraction of SiO2 is 1% and the load is 1N, the friction coefficient of the composite ceramic coating is 61% lower than that of 45 steel. When the mass fraction of SiO2 is 5% and the load is 3N, the friction coefficient of the composite ceramic coating is 51% lower than that of 45 steel. The composite ceramic coatings show good antifriction performance and wear resistance.

Microstructure and Mechanical Properties of TiC/TiB Composite Ceramic Coatings In-Situ Synthesized by Ultrasonic Vibration-Assisted Laser Cladding

Laser cladding coating has many advantages in surface modification, such as a small heat-affected zone, and good metallurgical bonding. However, some serious problems such as pores, and poor forming quality still exist in the coating. To suppress these problems, a novel process of ultrasonic vibration-assisted laser cladding process was adopted to in-situ synthesize TiC/TiB composite ceramic coating on the surface of titanium alloy. Results showed that the introduction of ultrasonic vibration effectively improved the surface topography of the coating, reduced the number of pores in the coating, refined the crystal grains of the coating, decreased the residual tensile stress in the coating, and increased the micro-hardness of the coating. The tribological properties of the coating were significantly improved by the ultrasonic vibration, the wear resistance of the coating fabricated with ultrasonic vibration at power of 400 W increased about 1.2 times compared with the coating fabricated without ultrasonic vibration, and the friction coefficient decreased by 50%.

Corrosion inhibition of Ti6Al4V alloy by a protective plasma electrolytic oxidation coating modified with boron carbide nanoparticles

Plasma electrolytic oxidation (PEO) is a cost-effective and versatile technique to achieve protective oxide coatings in light metals. Composite coatings containing B 4 C nanoparticles were produced by the PEO technique on a Ti6Al4V alloy. The influence of nanoparticles on the microstructure and corrosion resistance of the prepared ceramic composite coatings, as well as its incorporation mechanism into the PEO layer, were investigated. B 4 C nanoparticles were added to aluminate-based electrolytes and a pulse power supply was used as a constant voltage regime to obtain PEO composite coatings. Improvement in corrosion protection was also assessed by electrochemical impedance spectroscopy (EIS) and polarization tests, illustrating that a reduction in the corrosion resistance ratio was 8 for the composite coating compared to 16 for the sample without nanoparticles, after three weeks of immersion. The effect of nanoparticles on the phase composition was examined by X-ray diffraction (XRD) tests. Moreover, scanning electron microscopy (SEM) images illustrated the capability of B 4 C nanoparticles in filling the inherent pores of PEO coatings. • Fabrication of plasma electrolytic oxidation coatings modified with B 4 C nanoparticles on Ti6Al4V alloy • The significant role of electrophoretic force and trapping in the melted oxide layer on particle absorption. • Sealing the inherent pores of the PEO coating by the B 4 C nanoparticles. • Employing the voltage of 400V protects the PEO composite coatings upon three weeks in 3.5% NaCl.

Study on the In-Situ Reinforced Phase Evolution and Wear Resistance of Nickel Based Ceramic Composite Coating by Nb Alloying in Wideband Laser Cladding

Study on the In-Situ Reinforced Phase Evolution and Wear Resistance of Nickel Based Ceramic Composite Coating by Nb Alloying in Wideband Laser Cladding

Laser damage resistance of plasma-sprayed alumina and honeycomb skeleton/alumina composite ceramic coatings

Al2O3 and honeycomb skeleton-Al2O3 composite coatings on Titanium alloy (Ti–6Al–4V) were prepared by atmospheric plasma spraying. A laser ablation experiment on as-sprayed coatings was performed. In this paper, the laser damage resistance, microstructure, phase composition of Al2O3 coatings were examined. 3D Dimensional Confocal Microscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Energy Dispersive Spectrometry (EDS) characterized the laser damage morphology, microstructure, phase composition, and element analysis, respectively. The influence of the honeycomb skeleton on the laser ablation damage on as-sprayed coatings was investigated by a comparative analysis of the laser damage morphology with different laser ablation times and gas flow. The results show that the honeycomb skeleton raises thermal conductivity and thermal diffusivity. Moreover, a “tower”-like dendrite was generated during the laser irradiation of the composite coating. The honeycomb skeleton refined the structure, suppressed crack propagation, and reduced the influence of gas flow on cracks. Under the same experimental laser ablation parameters, the laser damage area of the honeycomb skeleton-Al2O3 composite coating was smaller than that of the Al2O3 coating. It was demonstrated that the laser damage resistance of the honeycomb skeleton-Al2O3 composite coating was superior to that of the Al2O3 coating.

Technological aspects of the synthesis of ceramic coatings by the flow-through method of plasma electrolytic oxidation

A promising technology for using the traditional flowthrough plasma electrolytic oxidation scheme is presented on the example of restoring local surfaces of aluminum bushing parts. Ceramic composite coatings based on corundum were formed, which are characterized by a thickness of 70‒110 μm and a hardness of 9500‒10800 MPa.

The influence of material microstructural characteristics on the strength of porous or composite ceramic coatings

This paper is a follow-up study to our earlier research that identified several types of preferred stress concentration regions in a material with a porous coating and suggested certain microstructural factors to induce them (Zinoviev et al., 2020). This study takes a closer look at each of the factors indicated earlier, examining their effects on the deformation and fracture of a coating and a coated material as a whole. Porosity, including a pore distribution, size, number, and distance between them, elastic property difference in a composite coating, curvilinear coating-substrate interface, and thickness of the pore-free coating layer are among the causative factors analyzed in microstructure-based mechanical simulations. It is found that the pore distribution controls the crack-initiation strain and first crack location while having a low effect on the elastic modulus. A dimensionless parameter is proposed to characterize the effect of the pore size and minimum distance between them on the local stress–strain state of a coating. The research findings provide insights for the choice of filler materials to be induced in a polymer-derived ceramic coating, suggesting the material resulting in the highest strength properties of the coated material among the considered ones. Analysis of the non-porous layer effect suggests that cracks form either at the coating-substrate interface or pore surface, and defined the layer thickness when the location of crack initiation changes. The insights gained from this study may be of assistance for coating design and engineering.

Effect of hybrid aluminum dihydrogen phosphate on the corrosion resistance of PTFE composite ceramic coatings

AbstractIn this study, the polytetrafluoroethylene (PTFE) composite ceramic coatings with hybrid aluminum dihydrogen phosphate (AP) are prepared on AISI 304L stainless steel by spraying and heat curing to improve the corrosion resistance of the coatings. AP is hybridized with methyltriethoxysilane (MTES), and the structure of the hybrid AP is characterized by Fourier‐transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Contact angle tests, scratch tests, and electrochemical experiments are used to investigate the corrosion behavior of composite ceramic coatings. In addition, scanning electron microscopy is used to examine the microscopic morphology of the coatings after corrosion to investigate the mechanism of the hybrid AP on the corrosion resistance of the composite ceramic coatings. The findings reveal that MTES successfully hybridizes with AP and implants the –CH3 hydrophobic group in AP, which improves the hydrophobicity of composite coatings. The corrosion potential of hybrid AP coatings all move in a positive direction, and the corrosion current density is lower than that of unhybridized AP coatings. The corrosion current density of the coating is about 2.931e−008 A/cm2 when the MTES content is 5 wt%, which is 20% less than that of the unhybridized AP coating. Results indicate hybrid AP can significantly improve the corrosion resistance of PTFE composite ceramic coatings with the best corrosion resistance occurring when the content of MTES is 5 wt%.

Tribological Behavior of Al2O3-MoO2-SiO2 Composite Ceramic Coating on Al-Zn-Mg-Cu Alloy

In order to enhance wear properties of Al-Zn-Mg-Cu alloy parts, Al2O3-MoO2-SiO2 composite ceramic coatings are formed on Al-Zn-Mg-Cu alloy by the DC micro-arc oxidation (MAO) method in the silicate electrolyte with sodium molybdate. Effects of sodium molybdate concentration on the structure characteristics and wear resistance of the composite ceramic coatings are analyzed by scanning electron microscopy, X-ray diffraction and the wear test, respectively. Analyses indicate that the composite coating consists of different states of Al2O3, MoO2 and mullite phase. With the addition of molybdate in the electrolyte, the morphology and structure are changed. The tribological behavior is greatly affected by the surface characteristics and hardness of the coatings. The composite coatings formed by adding 3 g/L of sodium molybdate electrolyte have the best wear resistance.

Role of KOH and NaNO2 on the structural and corrosion properties of anodic spark electrolysis coatings produced on aluminium

Doping light elements into ceramic coatings on different metal substrates by anodic-spark electrolysis (ASE) to improve their properties, such as wear and corrosion resistance, has recently attracted a lot of attention. In this study, nitrogen-doped Al2O3 composite ceramic coatings had been fabricated in eco-friendly KOH–NaNO2 electrolytes using the anodic-spark electrolysis (ASE) method after 9 min at a fixed applied ASE voltage (75 V higher than the breakdown voltages). To deposit a nitrogen-doped coating with high amounts of oxynitride phases possible, we thoroughly studied the ASE coatings deposited in different total variable salts concentrations (KOH+NaNO2) and NaNO2/KOH ratios of ASE electrolytes. The coating properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), and the electrochemical impedance spectroscopy (EIS) tests. The results indicated that the coating produced in the KOH–NaNO2 electrolyte with a low total variable salts concentration (2 gr.L−1) and a high NaNO2/KOH ratio value (3) is optimum in the investigated conditions. It has the highest percentage of nitrogen-doped phases, such as N-doped γ-Al2O3 and γ-AlON (γ-Al2.78O3.65N0.35), and a homogeneous morphology of surface with the smallest average size of pores (<14 μm2). This coating showed the significantly higher corrosion resistance with a 4.101104 × 106 Ω cm2 value compared to the uncoated aluminium substrate with a corrosion resistance value of 0.094195 × 106 Ω cm2 after 48 h of immersion in the 3.5 wt% NaCl solution. The approach presented herein provides an attractive way to modify the surface of aluminium alloys to improve corrosion behaviour.