Cathode Plasma Electrolytic Deposition Research Articles

La2Zr2O7 TBCs toughened by Pt particles prepared by cathode plasma electrolytic deposition

La2Zr2O7 thermal barrier coatings (TBCs) with dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED) with ceramic balls added to the cathode region. Compared with the conventional CPED, when ceramic balls are used in the cathode region, the plasma discharge ignition current density decreases approximately 62-fold and the stable plasma discharges occur at the whole cathode surface. Such TBCs with a thickness of 100 μm exhibit a crack-free surface and are composed of pyrochlore-structured La2Zr2O7. Cyclic oxidation, scratching, and thermal insulation capability tests show that such TBCs not only exhibit high resistance to oxidation and spallation but also provide good thermal insulation. These beneficial effects are attributed to the excellent properties of TBCs, such as good thermal insulation because of low thermal conductivity, high-temperature oxidation resistance because of low-oxygen diffusion rate, and good mechanical properties because of the toughening effect of Pt particles.

Oxidation and hot corrosion behavior of Al2O3/YSZ coatings prepared by cathode plasma electrolytic deposition

Al2O3/YSZ double layer TBCs dispersed with Pt particles were prepared by cathode plasma electrolytic deposition (CPED) on the high temperature alloy (0.1%C, 12% Co, 6.5% Cr, 6.2% Al, 5% W, 1% Mo, 1.5% Hf, 6.5% Ta, 0.01% B, balance Ni, wt%). High temperature cyclic oxidation at 1100°C, hot corrosion at 900°C and thermal insulation tests at 1100°C were adopted to investigate the high temperature corrosion resistance of the coating. It is revealed that the mechanical property of composite coating is improved by the toughening effects of Pt particles. The Al2O3/YSZ double layer coatings dispersed with Pt possess well oxidation resistance and hot corrosion resistance, due to low oxygen diffusion rate and chemically inertness of the Al2O3 layer.

High temperature oxidation behavior of a novel Ni−Cr binary alloy coating prepared by cathode plasma electrolytic deposition

Abstract A Ni-20 wt.% Cr binary alloy coating was prepared by cathode plasma electrolytic deposition from nickel-trivalent chromium sulfate electrolyte directly. Microstructure and high temperature oxidation behavior of the coating were investigated by SEM, EDS, TEM, XRD and cyclic oxidation test. It is found that the deposited coating is well-alloyed, dense and uniform with a typically molten morphology, and possesses nanocrystalline structure with the grain size of 30–50 nm. This finer-grained structure contributes to the selective oxidation of chromium and the formation of a thin, compact and protective Cr 2 O 3 scale, which exhibits good properties of oxidation and spallation resistance.

Thermal barrier coatings with Al2O3–Pt composite bond-coat and La2Zr2O7–Pt top-coat prepared by cathode plasma electrolytic deposition

Abstract Thermal barrier coatings (TBCs) with Al2O3–Pt composite bond-coat and La2Zr2O7–Pt top-coat were prepared by cathode plasma electrolytic deposition (CPED). The Al2O3–Pt composite bond-coats about 6–8 μm thick have rough and porous surfaces, and show a good adhesion with the substrate. The La2Zr2O7–Pt top-coats with a thickness of 120 μm possess a crack-free surface and are composed of pyrochlore La2Zr2O7. Owing to the chemical interaction between the La2Zr2O7 and molten mixture of Na2SO4 + V2O5, such TBCs do not possess a good hot corrosion resistance. However, it is demonstrated, from the cyclic oxidation test, thermal insulation capability test and mechanical properties test, that such TBCs possess not only excellent resistance to oxidation and spallation, but also quite well thermal insulation. These beneficial effects can be attributed to that: such TBCs can prevent high-temperature oxidation owing to the low oxygen diffusion rate of Al2O3 and La2Zr2O7, provide well thermal insulation owing to the low thermal conductivity of La2Zr2O7–Pt top-coat, and possess good mechanical properties owing to the toughening effect of Pt particles.

Influence of polyethylene glycol on cathode plasma electrolytic depositing Al2O3 anti-oxidation coatings

Al2O3 anti-oxidation coatings were prepared by cathode plasma electrolytic deposition (CPED). The kinetics of CPED process was investigated by cathode current density–voltage curves on the samples with different surface placement directions. As polyethylene glycol (PEG) is added in solution, the spark ignition current density ic(spark ignition) is reduced significantly, and the influence of surface placement directions of cathode on CPED process becomes very weak. Consequently, plasma discharges ignite randomly at whole cathode surface, which would be favorable for the formation of uniform Al2O3 coatings on large-sized cathode with complex shapes. Owing to adding PEG in solution, the oxidation and spallation resistance of the coating are improved, and the critical load of coating is increased.

Porous α-Al2O3 thermal barrier coatings with dispersed Pt particles prepared by cathode plasma electrolytic deposition

Porous α-Al2O3 thermal barrier coatings (TBCs) containing dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED). The influence of the Pt particles on the microstructure of the coatings and the CPED process were studied. The prepared coatings were mainly composed of α-Al2O3. The average thickness of the coatings was approximately 100 μm. Such single-layer TBCs exhibited not only excellent high-temperature cyclic oxidation and spallation resistance, but also good thermal insulation properties. Porous α-Al2O3 TBCs inhibit further oxidation of alloy substrates because of their extremely low oxygen diffusion rate, provide good thermal insulation because of their porous structure, and exhibit excellent mechanical properties because of the toughening effect of the Pt particles and because of stress relaxation induced by deformation of the porous structure.

Structure and properties of Al2O3 coatings formed on NiTi alloy by cathodic plasma electrolytic deposition

Abstract Al 2 O 3 coatings were prepared on NiTi alloy by cathodic plasma electrolytic deposition (CPED) in an aluminum nitrate solution. Scanning electron microscopy (SEM) shows that the coating exhibits a typical porous surface, rough micro structure and excellent adhesive interface between the coating and the substrate. Energy dispersive X-ray spectrometer (EDS) shows that when the treatment time is 45 min, this ceramic coating is composed of Al, O, and C with the atomic concentration of 43.37%, 48.52% and 8.11%, respectively, and the concentration of Ni is lower than the minimum instrument detection standard. X-ray diffraction (XRD) indicates that the coating consists of α-Al 2 O 3 and γ-Al 2 O 3 crystal phase. Direct pull-off test shows that the coating on NiTi substrate has a mean coating-substrate bonding strength of 15 ± 2 MPa. Cross-sectional hardness measurement illustrates that the average microhardness of the coating is less than the values of this parameter for the substrate. The results of potentiodynamic polarization test indicate that the corrosion resistance of the coated sample is increased by 3 times compared with that of the uncoated sample on the basis of corrosion current density.

Al2O3–ZrO2–Pt composite coatings prepared by cathode plasma electrolytic deposition on the TiAl alloy

Abstract Al 2 O 3 –ZrO 2 –Pt composite coatings were prepared by cathode plasma electrolytic deposition (CPED) on the TiAl alloy. Such coatings can improve the cyclic oxidation resistance of the TiAl alloy effectively. The beneficial results can be attributed to the effects: such coatings can inhibit further oxidation of alloy substrate owing to its extremely low oxygen diffusion rate, possess excellent mechanical properties owing to the stress relaxation caused by the phase transformation of zirconia, and the toughening role of Pt particles. In addition, as polyethylene glycol (PEG) is added in solution during CPED process, the current density is reduced significantly, and CPED would be a promising technique to deposit the uniform coatings on large-sized samples.

Modification of corrosion and tribological properties of 316L stainless steel by cathodic plasma electrolytic deposition of zirconia

Purpose – This paper aims to study the deposition of ZrO2 on 316L stainless steel surface using cathodic plasma electrolytic deposition (CPED) technique in potassium hexafluorozirconate (K2ZrF6) electrolyte solution to promote its corrosion and tribological properties. Design/methodology/approach – Plasma electrolytic oxidizing (PEO) technique is commonly used to form zirconium dioxide (ZrO2) on various substrates. But, in this paper, cathodic type of this technique (CPED) was used. Findings – Composition of the surface layer was analyzed by X-ray diffraction (XRD) and the formation of ZrO2 on the substrate was confirmed. Scanning electron microscope (SEM) was used to observe the unique morphology of the surface layer. The corrosion resistance of the coated surface was investigated by electrochemical methods involving cyclic voltammetery in Ringer’s solution. The treated sample showed a better pitting resistance. Pin-on-disk wear tests revealed that the friction coefficient of the coated sample is lower than that of the substrate. Also, it was shown that hardness and roughness of the coated sample increased after plasma electrolytic treatment. Originality/value – This paper considers the CPED of ZrO2 coating on 316L stainless steel. Some recent research works with ZrO2 coating have been prepared by PEO. There is limited or no record on the study of ZrO2 coatings by CPED process. In this study, the effort has been made to prepare a zirconia (ZrO2) coating on the stainless steel substrate through cathodic plasma electrolytic process under 200 V. Due to the excellent wear resistance, ZrO2 may be used as a high resistant and protective coating on stainless steels, which are widely used in industries and biomedical applications.

Influence of adding glass beads in cathode region on the kinetics of cathode plasma electrolytic depositing ZrO2 coating

The ZrO2 coating was prepared by cathode plasma electrolytic deposition (CPED), the cathode current density–voltage curves were used to investigate the influence of adding glass beads in the cathode region on the kinetics of the CPED process. With adding glass beads in the cathode region, the cathode current density for plasma discharge ignition is reduced by 2 orders of magnitude, plasma discharges take place randomly on the whole cathode surface. Consequently, a uniform ZrO2 coating can be deposited on the cathode with a large area. These beneficial effects can be attributed to the fact that the transportation of gas bubbles in the solution near the cathode surface is inhibited and electric field distribution becomes more uniform in the presence of glass beads in the cathode region. Therefore, a thin and uniform bubble sheath is formed at a low cathode current density, and a high electric field strength is established to ionize this bubble sheath. This work is expected to promote the development of CPED technique towards deposition of various ceramic coatings on large samples.

Microstructure and characterization of a novel cobalt coating prepared by cathode plasma electrolytic deposition

A novel cobalt coating was prepared by cathode plasma electrolytic deposition (CPED). The kinetics of the electrode process in cathode plasma electrolytic deposition was studied. The composition and microstructure of the deposited coatings were investigated by SEM, EDS, XRD and TEM. The novel cobalt coatings were dense and uniform, showing a typically molten morphology, and were deposited with a rather fast rate. Different from the coatings prepared by conventional electrodeposition or chemical plating, pure cobalt coatings with face center cubic (fcc) structure were obtained by CPED. The deposited coatings were nanocrystalline structure with an average grain size of 40–50nm, exhibited high hardness, excellent adhesion with the stainless steels, and superior wear resistance. The properties of the novel cobalt coatings prepared by CPED have been improved significantly, as compared with that prepared by conventional methods. It reveals that cathode plasma electrolytic deposition is an effective way to prepare novel cobalt coatings with high quality.

To improve corrosion resistance and hemocompatibility of magnesium alloy via cathodic plasma electrolytic deposition combined with surface thiol-ene photopolymerization

To improve corrosion resistance and hemocompatibility of magnesium alloy (Mg alloy), a polymerized 2-methacryloyloxyethyl phosphorycholine (PMPC) coating was fabricated via surface thiol-ene photopolymerization onto Mg alloy treated by cathodic plasma electrolytic deposition (CPED). Surface morphology, chemical composition and phase composition of CPED layer and CPED/PMPC composite coating were investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) illustrated that the corrosion resistane of Mg alloy in simulated body fluid (SBF) was significantly enhanced after the formation of CPED/PMPC composite coating. Platelets adhesion measurement indicated that CPED/PMPC treated Mg alloy possesses promising hemocompatibility. The approach presented here affords an effective alternative for surface modification of Mg alloy to meet the requirements of vascular scaffold materials.

The morphology change of Co coatings prepared by cathode plasma electrolytic deposition

Co coatings were prepared by conventional electrode position and cathode plasma electrolytic deposition respectively in the electrolyte with different CoSO4 and H2SO4 concentration. The morphologies of coatings were investigated by optical microscope and scanning electron microscope. It is found that the morphology change of Co coatings prepared by cathode plasma electrolytic deposition is quite different from that of conventional electrodeposition. To obtain uniform and dense Co coatings by cathode plasma electrolytic deposition, lower CoSO4 concentration and higher H2SO4 concentration are required in the electrolyte, compared with that of conventional electrodeposition. Otherwise, the deposited Co coatings will be rough or dendritical in the electrolyte with higher CoSO4 concentration and lower H2SO4 concentration.

Properties of nanocrystalline Cr coatings prepared by cathode plasma electrolytic deposition from trivalent chromium electrolyte

Pure Cr coatings were prepared directly from trivalent chromium sulfate electrolyte by cathode plasma electrolytic deposition (CPED). Composition and microstructure of the coatings were investigated by EDS, XRD, SEM and TEM. The deposited Cr coatings are crack-free with the thickness up to approximately 30μm, and exhibit nanocrystalline structure, high hardness, excellent adhesion and corrosion resistance with the stainless steels. The quality of Cr coatings prepared by CPED is improved significantly compared with that prepared by traditional chromium electroplating. It indicates that cathode plasma electrolytic deposition is an effective way to prepare high quality Cr coatings.

Carboxymethyl chitosan functionalization of CPED-treated magnesium alloy via polydopamine as intermediate layer

To improve the corrosion resistance and cytocompatibility of magnesium alloy (Mg alloy), an anticorrosive and bioactive composite coating was triumphantly prepared on Mg alloy surface. First, Mg alloy substrates were treated by cathodic plasma electrolytic deposition (CPED). Then, bioactive carboxymethyl chitosan (CMCS) was covalently immobilized on CPED-treated Mg alloy via polydopamine as intermediate layer. X-ray photoelectron spectroscopy and scanning electronic microscopy were employed to detect the change of chemical composition and surface morphology of Mg alloy substrate at various stages of surface modification. Results of water contact angle measurement showed that the hydrophilicity of the surface has improved significantly after surface modification. Potentiodynamic polarization data and hydrogen evolution test demonstrated that corrosion resistance of modified Mg alloy significantly increased compared with that of pristine sample. Cytotoxicity test and cell morphology analysis confirmed that adhesion and proliferation of osteoblasts on CMCS-modified Mg alloy surface were improved remarkably. The approach presented here would be attractive for surface modification of biomaterials.

Surface Modification of NiTi Alloy via Cathodic Plasma Electrolytic Deposition and its Effect on Ni Ion Release and Osteoblast Behaviors

To reduce Ni ion release and improve biocompatibility of NiTi alloy, the cathodic plasma electrolytic deposition (CPED) technique was used to fabricate ceramic coating onto a NiTi alloy surface. The formation of a coating with a rough and micro-textured surface was confirmed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. An inductively coupled plasma mass spectrometry test showed that the formed coating significantly reduced the release of Ni ions from the NiTi alloy in simulated body fluid. The influence of CPED treated NiTi substrates on the biological behaviors of osteoblasts, including cell adhesion, cell viability, and osteogenic differentiation function (alkaline phosphatase), was investigated in vitro. Immunofluorescence staining of nuclei revealed that the CPED treated NiTi alloy was favorable for cell growth. Osteoblasts on CPED modified NiTi alloy showed greater cell viability than those for the native NiTi substrate after 4 and 7 days cultures. More importantly, osteoblasts cultured onto a modified NiTi sample displayed significantly higher differentiation levels of alkaline phosphatase. The results suggested that surface functionalization of NiTi alloy with ceramic coating via the CPED technique was beneficial for cell proliferation and differentiation. The approach presented here is useful for NiTi implants to enhance bone osseointegration and reduce Ni ion release in vitro.

Preparation and properties of ceramic Al2O3 coating as TBCs on MCrAly layer applied on Inconel alloy by cathodic plasma electrolytic deposition

Inconel alloys (IN738) have found a wide range of applications in industries such as high-temperature resistance materials. Furthermore, different surface treatments and coatings have been developed for improving the properties of Inconel alloys. In this study, Al2O3 as a ceramic coating was deposited on the surface of the MCrAly as a ground coat layer on Ni-based super alloy, by cathodic plasma electrolytic deposition (CPED). The CPED process was carried out in Ethanol solution of Al (NO3)3.9H2O (18g/l). Several samples were obtained in different deposition conditions and analyzed using XRD, SEM and EDS. The XRD analysis shows the presence of Al2O3 and Ni3Al phases. Based on thermal expansion, this is in agreement with the composition of the MCrAlY used as bond coat. SEM micrograph showed changes in microstructure of specimen by varying the pH of the solution in different PH of solutions.

Al2O3–ZrO2 ceramic coatings fabricated on WE43 magnesium alloy by cathodic plasma electrolytic deposition

Al2O3–ZrO2 ceramic coatings were successfully prepared on WE43 magnesium alloy by cathodic plasma electrolytic deposition (CPED) technique. Surface morphology, elemental and phase composition of the coatings were investigated by scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). Furthermore, the electrochemical corrosion behavior of the coated magnesium alloy in simulated body fluids was evaluated. The results showed that the ceramic coatings were composed of t-ZrO2, α-Al2O3 and γ-Al2O3 phases with rough and coarse surfaces. The potentiodynamic polarization test indicated that corrosion resistance of WE43 magnesium alloy was significantly improved by CPED treatment. The approach presented here should be an attractive way for surface modification of Mg and its alloys.

Influence of treating frequency on microstructure and properties of Al 2O 3 coating on 304 stainless steel by cathodic plasma electrolytic deposition

Alumina ceramic coatings were fabricated on 304 stainless steel by cathodic plasma electrolytic deposition (CPED). Influence of treating frequency of the power supply on the microstructure and properties of the coatings were studied. The results indicated that coatings obtained at various frequencies on 304 stainless steels were all composed of α-Al 2O 3 and γ-Al 2O 3, and α-Al 2O 3 was the dominant phase. The contents of α-Al 2O 3 decreased gradually in a very small rate with increasing the frequency and γ-Al 2O 3 gradually increased. The surface of alumina ceramic coating was porous. With increasing the frequency, the coating surface gradually became less rough and more compact, resulting in low surface roughness. The bonding strength of Al 2O 3 coating was higher than 22 MPa and was not strongly affected by treating frequency. With increasing the frequency, the alumina coated steels showed better and gradually increasing corrosion resistance than the uncoated one in 3.5% NaCl solution. The coating steel with desirable corrosion resistance was obtained at 800 Hz whose corrosion current potential and corrosion density were −0.237 V and 7.367 × 10 −8 A/cm 2, respectively.

ΖrO2-Υ2Ο3 Ceramic Coatings Prepared by Cathodic Plasma Electrolytic Deposition

ΖrO2-Υ2Ο3 Ceramic Coatings Prepared by Cathodic Plasma Electrolytic Deposition