Cathode Plasma Electrolytic Deposition Research Articles

Facile Synthesis of Metal/Carbide Hybrid toward Overall Water Splitting

The development of cost-effective and high-performance bifunctional catalysts for overall water splitting is crucial for achieving sustainable clean energy. In this study, a metal/carbide hybrid (NiFeMo/NiFeMoCx) was prepared through fast and facile cathodic plasma electrolytic deposition. Due to the synergistic effect between the metal and carbide, NiFeMo/NiFeMoCx exhibited high activity in both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), with overpotentials of 230 mV and 60 mV at 10 mA cm−2, respectively. In addition, robust stability was demonstrated during the overall water splitting (1.52 V at 10 mA cm−2, with little degradation after 18 h of catalysis). This work provides a useful strategy for designing advanced water splitting catalysts for real application.

Enhanced thermal performance of CeYSZ coating on Ni-based high temperature alloy with a unique Y-doped Al2O3 barrier layer via cathodic plasma electrolytic deposition

Cathodic plasma electrolytic deposition (CPED) has shown considerable potential in producing high-performance thermal barrier coatings (TBCs) for components operating in extreme thermal environments, such as gas turbines and aviation engines. However, the dendritic and porous structures greatly limited the use of CPED-coatings in some harsh environments. In this study, one Y-doped Al2O3 (Y/A) barrier layer was prefabricated before the deposition of CeO2 and Y2O3 stabilized ZrO2 (CeYSZ) thermal barrier coating using CPED. The results suggested that the prefabricated Y/A barrier layer can attenuate the plasma bombardment and promote the uniform discharge, resulting in the formation of a thinner gas film layer on the cathode surface, which significantly avoided the course dendritic defects and improved the density of the CeYSZ coating from 6.788 g/cm³ to 6.978 g/cm³. Consequently, the thermal insulation temperature of Y/A-CeYSZ coatings exceeded that of CeYSZ coatings by a factor of 1.3, and the thermal cycling performance at 1300 °C demonstrated a 52.5% improvement. This study provided a valuable method for the development of novel CPED TBCs.

Wear performance of MoS2 doped Al2O3 CPED coatings on TC6 titanium alloy

The innovative work presented in the paper focused on microstructures and wear performance of MoS2 doped Al2O3 coatings on TC6 alloy. Nano- and micron-sized MoS2 particles doped Al2O3 coatings (n and m-MoS2/Al2O3 coating) were fabricated on TC6 alloy via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and compositions of the coatings were characterized, the tribological behaviors were tested, and doping mechanism of MoS2 particles was discussed. The results showed that, doped coatings were composed of α-Al2O3, γ-Al2O3 and MoS2. The doping of MoS2 particles promoted the transformation from γ-Al2O3 to α-Al2O3 during CPED process, and increased the compactness and crystallinity of doped coatings. The friction coefficients of TC6 alloy, Al2O3 coating, n-MoS2/Al2O3 coating and m-MoS2/Al2O3 coating were about 0.7, 0.6, 0.55 and 0.45 in sequence, and the wear rates of n-MoS2/Al2O3 coating and m-MoS2/Al2O3 coating were about 75 % and 58 % of Al2O3 coating. MoS2 particles played the role of lubrication and contributed to improving wear performance of doped coatings, both friction coefficients and wear rates were declined, and micron-sized MoS2 particles presented better wear performance than nano-sized particles.

Low Current Density Cathode Plasma Electrolytic Deposition of Aluminum Alloy Based on a Bipolar Pulse Power Supply

The present paper reported a novel bipolar-pulse cathodic plasma electrolytic deposition (BP-CPED) technique with a low current density. This newly developed CPED technique can break down the barriers of the existing CPED technique with higher current density. In this report, ceramic coatings were successfully prepared on aluminum alloy via the BP-CPED technique in an aqueous carbamide-based electrolyte. Data recording results in the reacting process show that there is the current density of the cathode below 0.15 A/cm2 and that of the anode below 0.035 A/cm2, which approximately reaches the level of conventional MAO technique. Interestingly, the addition of PEG into the electrolyte can further reduce the current density and effectively improve the coating quality. The kinetic of the BP-CPED process was discussed based on the evolution of current density/voltage-time curves and spark discharge phenomena. SEM observations illustrate that BP-CPED coatings possess a typical porous-surface feature. XRD analysis indicates that the coating was mainly composed of Al2O3 and Al4C3. Al2O3/Al4C3/ZrO2 composite coatings fabricated after Zr-doping reflected the successful Zr-incorporation into the coating, which demonstrated that the BP-CPED technique can be used to design the coating composition by the doping modification. The direct pull-off and thermal shock tests confirmed that new BP-CPED coatings obtained under the cathodic plasma discharge have excellent bonding strength. It is possible that this novel BP-CPED technique can provide a promising choice in developing the large-area CPED surface treatment for the industrial application.

Preparation and thermal cycling performance of Ce-doped YSZ thermal barrier coatings by a novel cathode plasma electrolytic deposition

The preparation and realization of highly reliable thermal barrier coatings (TBCs) on the internal surface of complex cavities is a bottleneck problem. Traditional coating methods are difficult to deposit and fulfil service requirements. In this study, a novel structure of YSZ and Ce-doped YSZ (CeYSZ) TBCs was prepared by a newly cathode plasma electrolytic deposition (CPED) technology. The results suggested that both the CPED-YSZ and CPED-CeYSZ coatings exhibited porous cross-linked dendritic structures. Because Ce doping significantly improved the phase stability of tetragonal structure and enhanced thermal insulation temperature during a burner-rig test at 1300 °C, resulting in a threefold increase in the thermal cycling life of the CPED-CeYSZ coating compared to the CPED-YSZ coating. This work provided a new strategy for tailoring multiple rare-earth principal components of high-performance TBCs and depositing them on the inner surface of complex cavities with high aspect ratios.

Characterization of Al2O3 coating of Nb fiber-reinforced TiAl composite

The Al2O3 coating was synthesized on surface of the Nb fiber via cathodic plasma electrolytic deposition (CPED) method. The microstructure and composition of the coating were elaborately analyzed. The results revealed that compact and uniform Al2O3 is fully contact with TiAl matrix and Nb fiber, which was composed of κ-Al2O3 and α-Al2O3 and successfully hold back the oxidation reactions at the juncture and refrain from formation of detrimental phases. Especially, three-dimensional characterization information can be obtained from two-dimensional converging beam electron diffraction (CBED) pattern, from which the crystal constants of Al2O3 can be obtained directly under only one applicable zone axis.

Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coating at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.

CATHODIC PLASMA ELECTROLYTIC DEPOSITION (CPED) TECHNIQUE FOR SURFACE STRENGTHENING OF TITANIUM AND TITANIUM ALLOYS: A MINI REVIEW

Due to the unique properties of titanium (Ti) and its alloys, it has a particularly wide range of applications in aerospace, automotive, medical and other fields. However, the problems of low surface hardness, high friction coefficient and low wear resistance of Ti alloys limit its development to a certain extent. The destruction of Ti and its alloys often occurs on the surface of materials such as wear damage, corrosion, and oxidation resistance. Therefore, the exploration and application of surface strengthening technology is particularly important. The cathodic plasma electrolytic deposition (CPED) technology, as a surface modification technology, can achieve better adhesion and facilitate the material to achieve better comprehensive performance. This paper briefly introduces the basic concepts, principles and development progress of CPED. Starting from the preparation of ceramic coatings, metal coatings, diamond-like carbon films and composite coatings, it summarizes the application of CPED in Ti and its alloys. Applications in alloys to improve thermal oxidation resistance, wear resistance, corrosion resistance, and film-based adhesion. At the end, its development in the new era environment is prospected.

Initial microstructure and composition evolution of Al2O3 coatings fabricated by cathode plasma electrolytic deposition under constant voltage

At present, the research on cathode plasma electrolytic deposition (CPED) mainly focuses on improving the coating properties, while the initial structure and formation mechanism of CPED coating are less studied. This work aims to study the initial deposition behavior of Al2O3 coating by CPED at different time scales systematically. The results show that the coating consists of lamellar Al(OH)3 in the pre-plasma discharge period. After reaching the breakdown potential, the preparation process of Al2O3 can be considered as a cyclic process: plasma discharge, injection of molten oxide, sintering and solidification, and stacking. Such an iterative process results in a gradual thickening of the coating. Later in the deposition process, the raised structure of the coating surface flaps off and coating thickness decreases. In addition, the high temperature during plasma discharge results in local melting of the substrate surface, which is co-deposited with Al2O3.

Interfacial optimization by CPED coating for improving mechanical properties of Nbf/TiAl composite

Continuous Nb fiber-reinforced TiAl-matrix (Nbf/TiAl) composites with low density and excellent high temperature performance has been considered as a potential structural material to satisfy the service requirements in space industry. However, premature cracking failure caused by serious interfacial reaction (forming brittle phases and micro-crack) in the interface accelerates the failure of the composite. Depositing the inert coating on the Nb fiber surface could reduce and even prevent the interfacial reaction, improving the interfacial structure between Nb fiber and TiAl matrix. In this work, an efficient coating technology, cathodic plasma electrolytic deposition (CPED), was utilized to deposit Al2O3 coating on the Nb fiber surface, which successfully prevented the brittle phases formation at the interface between Nb fibers and TiAl matrix. The reliable and simple interface composed of Nb/Al2O3/TiAl was prepared through the careful adjustment of CPED parameters. The high-strength interface ameliorated the stress distribution, especially increasing the stress borne of Nb fibers by 40 % during the loading process. As a result, the optimized interface avoided premature cracking in interfacial region at initial loading stage and promoted the crack deflection and bifurcation at the overall deformation. Finally, the fracture toughness of the composite after interfacial optimization is increased by 30 % than that of without coating and 70 % than that of TiAl matrix. The above findings validate the feasibility of CPED technology in regulating the interface structure of composite materials, and provide a new method for interface structure design.

Effect of voltage and duty cycle on microstructure and corrosion resistance of ZrO2 coating by cathode plasma electrolytic deposition

Power parameters are of importance to determine the microstructure and property of coatings deposited by cathode plasma electrolytic deposition (CPED). In the present study, the effect of power parameters including voltage and duty cycle on the microstructure and anti-corrosion property of zirconia (ZrO2) CPED-coatings was investigated. The results suggested that the as-deposited coatings consisted of t-ZrO2 and m-ZrO2, while the content of t-ZrO2 exceeded 50 %. The content of t-ZrO2 increased with the increase of voltage and decreased with the increase of duty cycle, reaching a maximum of 89.9 %. In addition, as the voltage and duty cycle increased, the porosity of the coating increased from 3.7 % to 15.5 %. Due to the high t-ZrO2 content, high thickness and relatively dense structure, the coatings deposited at 250 V had a superior corrosion resistance in 3.5 wt% NaCl solution. This work will provide a guideline for tailoring high performance ZrO2 CPED-coatings.

Preparation, microstructure and corrosion resistance of Al2O3 coatings by cathodic plasma electrolytic deposition on sintered NdFeB permanent magnet

The Al2O3 ceramic coatings were prepared on the sintered NdFeB magnets by cathodic plasma electrolytic deposition (CPED) method in aluminum nitrate alcohol solution. The surface and cross-sectional morphologies, element and phase composition, corrosion resistance and magnetic properties of the coatings were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermal shock, hydrothermal weight loss, electrochemical corrosion and physical property measurement system (PPMS), respectively. The results show that the coatings mainly consist of γ-Al2O3 and α-Al2O3 phases, and the volume of α-Al2O3 increases with increasing the voltages. The surface of the coatings shows a typical coral reef structure, and the thickness of the coatings increases from 29 µm to 53 µm with increasing the voltages. The Al2O3 coatings have excellent thermal shock resistance as well as the excellent corrosion resistance in hydrothermal conditions. The corrosion resistance of the coatings enhances with increasing the voltages, reaching the strongest at 470 V, and then decreases. This study provides a new method for forming ceramic coatings on the surface of sintered NdFeB magnets to improve its corrosion resistance.

Improving the performance of titanium bipolar plate in proton exchange membrane water electrolysis environment by nitrogen-chromium composite cathode plasma electrolytic deposition

In the proton exchange membrane water electrolysis (PEMWE), the titanium bipolar plate coated with noble metals is usually used, which puts forward higher requirements for costs. This study investigates the cathode plasma electrolytic deposition (CPED) for the titanium and obtains TiN and TiN/CrN coatings. The TiN coating exhibits the diffusion resistance in the anode PEMWE environment, resulting in an increase in the interfacial contact resistance (ICR). The denser TiN/CrN coating eliminates the diffusion resistance and increases the polarization resistance (Rp) value from 3873 Ω cm2 of TiN coating to 12,320 Ω cm2 of TiN/CrN. After long-term potentiostatic polarization, the ICR of TiN/CrN coating is 8.5 mΩ cm2, which is 3.5 times lower than that of TiN coating. Therefore, the low-cost TiN/CrN coating obtained by CPED has brought a good application prospect for bipolar plates in PEMWE.

On the tribological behavior of cobalt-based nanocomposite coatings containing ZnO@Graphene oxide core-shell nanoparticles

A hybrid nanocrystalline cobalt-based coating was prepared by cathode plasma electrolytic deposition (CPED). Zinc oxide and graphene oxide (GO) nanoparticles were mixed to form a core-shell structure through electrostatic self-assembly by using (3-aminopropyl)triethoxysilane (APTES) modifier. ZnO@GO nanoparticles were used as additives to improve wear and friction properties of deposited coatings. The concentration effect of core-shell ZnO@GO addition (0.1, 0.2 and 0.3 %wt) on the friction, wear, coating thickness and mechanical properties was investigated. The composition and microstructure of deposited coatings were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and energy dispersive spectroscopy (EDS). Reciprocating sliding wear tests using a ball-on-plate configuration were carried out on a PLINT TE67 tribometer. AISI 52100 steel was used as ball and the coating deposited onto a AISI 304 stainless steel substrate was used as plate. Coatings were dense, nanocrystalline and uniform with a FCC metastable cobalt structure. Core-shell concentration above to 0.2 %wt resulted in a decrease of grain size and an increase of hardness and wear resistances. Nanoparticles act as nucleation sites for grain formation, decreasing grain sizes. Samples using 0.3% ZnO@GO displayed the lowest wear and friction coefficients. ZnO@GO nanoparticles enables the formation of a protective layer consisting of oxide and exfoliated GO on the top of worn surfaces.

Tribological Behavior of Cathode Plasma Electrolytic Deposited Al2Y4O9 Coating on Aluminum Alloy

Ceramic coatings are widely used as protective barriers on the surfaces of various metals and alloys. Herein, a novel surface ceramic treatment, i.e., cathode plasma electrolytic deposition (CPED), is proposed for the surface of an Aluminum (Al) alloy. The coating, prepared in an Y(NO3)3 aqueous solution on the surface of the Al alloy, consists of Al2Y4O9 as the major phase component, Y2O3 as a minor phase component, and amorphous Al2O3 in the grain boundaries. As the applied voltage and deposition time increased, the crystallization of the coatings was enhanced. When deposited at 130 V for 10 min, the contact angle of the ceramic coating reached 141.0° ± 2.6°, indicating an enhanced self-cleaning effect. The ceramic coating also exhibited excellent self-lubricating and anti-wear effects. The friction coefficient of the CPED-treated sample vs. ZrO2 ball or bearing steel ball decreased from 0.55–0.65 to 0.26–0.31 when the load was 3 N and the reciprocating velocity was 10 mm/s. Correspondingly, the wear rate of the CPED-treated sample vs. the ZrO2 ball or bearing steel ball was significantly reduced. Results indicated that CPED is effective for the formation of self-cleaning and anti-wear ceramic coatings on Al alloys.

Solid-phase microextraction coatings based on anodic and cathodic plasma electrolytic deposition on titanium wire for determination of nerolidol in aqueous samples

Solid-phase microextraction coatings based on anodic and cathodic plasma electrolytic deposition on titanium wire for determination of nerolidol in aqueous samples

Investigation of interfacial thermal stabilities of Nbf/TiAl composites with and without Al2O3 coating in interface

Continuous Nb fiber-reinforced TiAl-matrix composites have tremendous potential for replacing brittle TiAl alloy. However, at elevated temperature, interfacial reaction between fiber and matrix is aggravated, causing instability of the interfacial microstructure and mechanical property of Nbf/TiAl composite. Fortunately, the problem could be solved by introducing fiber coating. Consequently, in this study, Al2O3 coating was prepared on Nb fiber by cathodic plasma electrolytic deposition (CPED) technique. Concurrently, interfacial microstructure changes of the composites were explored during thermal treatment at 1100 and 1200 °C. The results show that, during heat treatment at 1100 °C for up to 100 h, for the composite without Al2O3 coating, the interfacial microstructure changes are as follows: Nb/σ/α2/TiAl→Nb/σ/B2/α2/TiAl→Nb/σ/TiAl, which leads to serious thermal residual stress and cracks in interface. Inversely, the introduction of Al2O3 coating can prevent the formation of brittle σ phase during preparation and the 1100 °C heat treatment. However, under 1200 °C heat treatment, the Al2O3 coating gradually fads away and be replaced by α2-Ti3Al phase. Finally, the interfacial phases including σ and α2 are formed. The existence of the Al2O3 coating can delay the formations of the brittle phases and avoid cracks for a long time, which greatly improves interfacial thermal stability of the Nbf/TiAl composite.

Preparation of Al2O3 coating on Nb fiber and the effect on interfacial microstructure of Nbf/TiAl composite

Continuous Nb fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. However, the premature cracking failure is resulted from the brittle reaction products formed at the interface between Nb fiber and TiAl matrix, which accelerates the structural failure of Nb f /TiAl composite. Fortunately, Al 2 O 3 coating could be introduced on the surface of Nb fiber to tackle the problem. In this study, Al 2 O 3 coating was prepared on the surface of Nb fiber by the cathodic plasma electrolytic deposition (CPED) technology, and then the Al 2 O 3 -coated Nb fibers were used to reinforce TiAl alloy by using vacuum hot-pressing sintering. Furthermore, the influence of the Al 2 O 3 coating on the interfacial microstructure of Nb f /TiAl composite after hot-pressing sintering and thermal exposure was studied. The results show that deposition voltage plays a key role in the microstructure of Al 2 O 3 coating on the Nb fiber. As the voltage increases from 200 V to 400 V, the thickness, density and Al 2 O 3 content of the coating increase. Meanwhile, the bonding between Nb fiber and Al 2 O 3 coating is better when the deposition voltage exceeds 350 V, and the components of Al 2 O 3 -coated Nb fibers prepared from fiber to coating are as follows: Nb/Nb 2 O 5 /Nb 2 O 5 + Al 2 O 3 /Al 2 O 3 . The Al 2 O 3 coating can restrain the formation of the interfacial brittle phases including σ-Nb 2 Al and α 2 -Ti 3 Al during hot-pressing sintering process of Nb f /TiAl composite. In addition, the introduction of Al 2 O 3 coating can reduce the defects in interface, as well as avoid the formation of the crisscrossed and deleterious oxides, which improves interfacial oxidation resistance of the Nb f /TiAl composite. • A uniform and dense Al 2 O 3 coating with a thickness of 4–6 μm can be obtained on Nb fiber surface by CPED technology. • Al 2 O 3 coating can prevent the formation of interfacial brittle phases during the preparation of Nb f /TiAl composite. • Al 2 O 3 coating with excellent thermal stability can avoid the formation of crisscross harmful oxides.

Electrochemical and biological properties of mono- and bilayer nitride coatings deposited on Ti–6%Al–4%V alloy

Mono- and bilayer coatings were deposited by plasma nitriding process, cathodic plasma electrolytic deposition, and cathodic arc evaporation methods to improve the corrosion resistance and biological properties of the Ti–6Al–4V substrate. Coatings characterizations include phase analysis, surface morphology, and film microstructure observations were done using X-ray diffraction (XRD) analysis, atomic force microscope, and field emission scanning electron microscopy (FESEM), respectively. The results confirmed the formation of titanium nitride phases (TiN and Ti2N) in plasma nitriding and cathodic arc evaporation processes and deposition of oxy-nitride phases (TiNxOy) in plasma electrolytic nitriding process. The electrochemical study of coated and uncoated samples in a simulated body fluid (SBF) solution revealed the lower corrosion current density for bilayer nitride coating in comparison to the monolayer coating and substrate. Lower penetration of solution and more stable phases such as TiO2 improved the corrosion resistance of bilayer coatings. Hemocompatibility and MTT assay were performed on the coated and uncoated sample to determine the blood compatibility and cell viability. The statistical results showed better cell growth on the bilayer nitride coatings after three days.

Improvement of Structures and Properties of Al2O3 Coating Prepared by Cathode Plasma Electrolytic Deposition by Incorporating SiC Nanoparticles

A serious issue in the preparation of Al2O3 coatings by cathode plasma electrolytic deposition (CPED) is that the coatings have a porous structure, which is detrimental to their protective performance. Therefore, to address this problem, SiC nanoparticles are incorporated into the Al2O3 coating in this study. A series of Al2O3–SiC composite coatings are efficaciously prepared on the surface of 316L stainless steel by CPED. The microstructures, compositions and phase components of the composite coatings are characterized; the electrochemical corrosion resistance and tribological behavior are evaluated; and the mechanism of SiC nanoparticles in the coating formation process is discussed in detail. The results indicate that the Al2O3 coating prepared by CPED consists of α-Al2O3 and γ-Al2O3, and the former is the main crystalline phase. With the incorporation of SiC nanoparticles in the coating, the content of α-Al2O3 gradually decreases, almost disappearing, accompanied by an increase in γ-Al2O3 as the main crystalline phase. The incorporation of SiC nanoparticles significantly reduces the surface irregularity and roughness of Al2O3 coatings and remarkably improves the corrosion resistance and wear resistance of the Al2O3 coatings. The improvement in corrosion resistance and anti-wear properties can be explained by the fact that the SiC nanoparticles effectively weaken electrical breakdown and increase the compactness of the coatings.