Corrosion Properties Of Coatings Research Articles

Effect of Ag content on the microstructure, tribological and corrosion properties of amorphous carbon coatings on 316L SS

The mechanical durability and stability of a-C:Ag nanocomposite coatings deposited on 316L stainless steel substrates were investigated with respect to Ag content. The coatings were prepared using graphite and Ag targets. The coatings were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). XPS and Raman spectroscopy confirmed the formation of sp2 clusters in the a-C coating with 4.46at.% Ag content. Surface roughness was found to be reduced by increasing the Ag content in a-C coatings as confirmed by AFM analysis. TEM analysis also showed the presence of nanostructured Ag in the a-C matrix. The tribological and corrosion properties of these coatings were also investigated. Hardness and Young's modulus were found to decrease with increase in Ag content. The experimental results revealed that the friction coefficient could be significantly reduced due to inclusion of Ag in the composite coating. In particular, the coating with an Ag content of 4.46at.% showed the best tribological behavior. Inclusion of Ag also improved the corrosion resistance of the composite coating. It was concluded that Ag content in a-C:Ag nanocomposite coating has a significant effect on the tribological and corrosion properties of the coating. Experimental results revealed that optimum Ag content (4.46at.%) in a-C:Ag nanocomposite coatings may be effectively utilized to protect 316L stainless steel substrates.

Influence of the Organic Additions on Structure, Corrosion Resistance and Tribological Properties of Ni/Al<sub>2</sub>O<sub>3 </sub>Composite Coatings

Composite Ni/Al2O3 coatings were electrochemically deposited from a Watts bath modified with the organic additions of dioctyl sulphosuccinate sodium salt C20H37NaO7S–(DSS) and 2,3-dihydroxy-1,2 benzisothiazol-3-one 1,1-dioxide C7H5NO3–(LSA). The effect of different amount (50 and 100 g/l) of Al2O3 powder and organic additions on microstructure, microhardness, corrosion resistance and tribological properties was investigated. The coatings were examined by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. The electrochemical behaviour of the coatings in corrosive solutions (1 M NaCl and 1 M Na2SO4) was investigated by potentiodynamic polarisation. The tribological properties were investigated by the Taber abrasive wear test, a standard test often applied in industrial practice. The results show that Al2O3 particles are uniformly distributed in the composite coatings compared with coatings without organic additions. The addition of organic compounds also reduced the size of the forming nickel crystallites and improved the tribological and corrosion properties of coatings containing the dispersed hard particles of Al2O3 added in an amount of 50 g/l and the addition of organic LSA and DSS compounds.

Effect of K2TiF6 and Na2B4O7 as electrolyte additives on pore morphology and corrosion properties of plasma electrolytic oxidation coatings on ZM21 magnesium alloy

Protection of magnesium alloys from faster degradation in physiological environment is of primary importance in order for them to be used as biodegradable implant materials. Present investigation reports the effect of sodium tetra borate (Na2B4O7·10H2O) and potassium titanium fluoride (K2TiF6) on corrosion behavior of oxide coatings developed on ZM21 magnesium alloy by plasma electrolytic oxidation (PEO) in Na2SiO3–KOH base electrolyte system. The effect of these additives on the microstructure and corrosion properties of coatings was investigated. The surface morphology and phase composition of these ceramic coatings were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Analysis of pores in the coating was done using a three-dimensional (3D) optical profilometer. The corrosion resistance was evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF) environment at a pH of 7.4. It was found that the use of additives significantly altered the pore morphology of the coating. Among the PEO treated samples, the coating formed in silicate based electrolyte system containing 2g/L of Na2B4O7·10H2O showed less porosity and improved corrosion resistance in SBF environment.

Influence of LaCl3 addition on microstructure and properties of nickel-electroplating coating

The influence of rare earth chloride LaCl3·7H2O addition on the microstructural features, phase structure, corrosion resistance and microhardness of nickel-electroplating was investigated. The Watts-type with different additive amounts of LaCl3·7H2O (0–1.2 g/L) were used in the experiment. Surface morphologies of coatings were examined by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) was used to measure the coatings' grain size and the microstructure of coatings was detected by X-ray diffraction (XRD). Corrosive investigation was carried out in 3.5 wt.% NaCl solution. The microhardness values of the coatings with different amounts of LaCl3·7H2O were measured, and the mechanism of the variation in microhardness was studied. Results showed that the addition of rare earth lanthanum refined the grain size and improved the surface consistency of the coatings, meanwhile the microhardness and corrosion property of coatings were improved and achieved a maximum with arround 1.0 g/L LaCl3·7H2O addition in electrolyte. The preferred growth orientation of lanthanum doped coating was crystal face (200), meanwhile the La2Ni7 phase was detected in the nickel coating by XRD and this was due to the induced co-deposition of elements La and Ni. The reason maybe was that the special out-layer electronic structure of element La raised the polarization of Ni cathode deposition, accelerated the nucleation of Ni and reduced hydrogen evolution from cathode surface.

Preparation of ceramic coating on Ti substrate by plasma electrolytic oxidation in different electrolytes and evaluation of its corrosion resistance: Part II

The aim of this work is to discuss the growth characteristics and corrosion behavior of the prepared ceramic coatings on titanium by plasma electrolytic oxidation (PEO) technique in different electrolytes. PEO process was carried out on titanium under constant voltage regime using a pulse power supply. Three kinds of electrolytes, phosphate, silicate and borate based solutions, were used to evaluate the influence of electrolyte composition on the structure, surface morphology, phase composition and corrosion behavior of prepared ceramic oxide films (titania). The phase composition of the coatings was investigated by X-ray diffraction. Scanning electron microscopy was employed to evaluate the growth and surface morphology of coatings. Elements of coatings were investigated with energy dispersive spectrometer. Corrosion behavior of the coatings was also examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The spark voltage of oxide films had a significant effect on the surface morphology, size and homogeneity of micro-pores, thickness and corrosion properties of coatings.

Relation study of different properties for tertiary pulsed electrodeposited Ni-based nanocomposite with Al2O3/Y2O3/CNT nanopowders

Electrodeposition of tertiary alumina/yttria/carbon nanotube (Al 2 O 3 /Y 2 O 3 /CNT) nanocomposite by using pulsed current has been studied in this investigation. Coating process has been performed on nickel sulphate bath and nanostructure of obtained compound layer is examined with high precision figure analysis of SEM nanographs. The effects of process variables, i.e., Y 2 O 3 concentration, treatment time, frequency and duty cycle, have been experimentally studied. Statistical methods are used to achieve the minimum of corrosion rate and average size of nanoparticles. Finally the contribution percentage of different effective factors is revealed and confirmation run shows the validity of obtained results. Also it has been revealed that by changing the size of nanoparticles, corrosion properties of coatings will change significantly in the same trend. AFM and TEM analyses have confirmed smooth surface and average size of nanoparticles in the optimal coating.

Wear and corrosion properties of electroless nickel composite coatings with PTFE and/or MoS2 particles

This study focuses on the effect of co-deposition of PTFE and/or MoS2 particles on the morphology, wear, and corrosion properties of electroless nickel coating. The composite coating of EN–PTFE–MoS2 was heat treated at different temperatures for hardness investigations. The surface morphology of coatings was characterized by scanning electron microscopy. Pin-on-disk and potentiodynamic polarization tests were used to study the tribological and corrosion properties of the coatings, respectively. Results of hardness analysis revealed that the hardness of electroless nickel coatings was increased by the heat treatment, and its maximum was gained at 400°C. Wear investigations showed that simultaneous co-deposition of the PTFE and MoS2 particles into the nickel coating increased the wear resistance of the coating by about 30% and reduced the average value of friction coefficient to 0.25 from 0.65. Corrosion studies illustrated that simultaneous co-deposition of the PTFE and MoS2 particles led to reduction in corrosion resistance by 10 and 5 times that of EN coating in brine and acidic solution, respectively.

Study of corrosion resistance and nanostructure for tertiary Al2O3/Y2O3/CNT pulsed electrodeposited Ni based nanocomposite

Electrodeposition of nickel based tertiary Al2O3/Y2O3/CNT nanocomposites by using pulsed current has been studied in this investigation. The coating process has been performed in a nickel sulphate bath and the nanostructure of the obtained compound layer was examined with high precision figure analysis of SEM nanographs. The effects of process variables, i.e. Y2O3 concentration, treatment time, current density and temperature of electrolyte have been experimentally studied. Statistical methods were used to achieve the minimum corrosion rate and average size of nanoparticles. Finally the contribution percentage of different effective factors was revealed and a confirmation experiment has shown the validity of the obtained results. In addition, it has been revealed that by changing the size of nanoparticles, the corrosion properties of coatings will change significantly with this trend. Atomic force microscopy and transmission electron microscopy analyses have confirmed the smooth surface and average size of nanoparticles in the optimal coating.

Characteristics of plasma electrolytic oxide coatings on Mg-Al-Zn alloy prepared by powder metallurgy

Mg-6 wt.%Al-1 wt.%Zn alloy powders were produced by gas atomization, and subsequently compacted and sintered under various conditions of temperature, time, and pressure. The bulk Mg-6 wt.%Al-1 wt.%Zn alloy was coated by the plasma electrolytic oxidation (PEO) method. The optimum condition of compaction and sintering for PEO coatings was established based on the investigation of microstructure, microhardness, and corrosion properties of coatings which were compared to those of cast Mg-6 wt.%Al alloy. The coatings on Mg-6 wt.%Al and Mg-6 wt.%Al-1 wt.%Zn alloys consisted of MgO, MgAl2O4, and Mg2SiO4. The Mg-6 wt.%Al-1 wt.%Zn alloy compacted at room temperature for 10 min and sintered at 893 K for 3 h showed the most porous and nonuniform coating layer because the coatings had grown through grain boundaries that resulted from poor bonding between powder particles in the substrate. However, the coated Mg-6 wt.%Al-1 wt.%Zn alloy hot-compacted at 593 K for 10 min had the thickest coating layer and the highest microhardness. In addition, it demonstrated the best corrosion resistance as verified by polarization curves in 3.5% NaCl solution.

Corrosion Properties of Cold-Sprayed Tantalum Coatings

Cold spraying enables the production of pure and dense metallic coatings. Denseness (impermeability) plays an important role in the corrosion resistance of coatings, and good corrosion resistance is based on the formation of a protective oxide layer in case of passivating metals and metal alloys. The aim of this study was to investigate the microstructural details, denseness, and corrosion resistance of two cold-sprayed tantalum coatings with a scanning electron microscope and corrosion tests. Polarization measurements were taken to gain information on the corrosion properties of the coatings in 3.5 wt.% NaCl and 40 wt.% H2SO4 solutions at room temperature and temperature of 80 °C. Standard and improved tantalum powders were tested with different spraying conditions. The cold-sprayed tantalum coating prepared from improved tantalum powder with advanced cold spray system showed excellent corrosion resistance: in microstructural analysis, it showed a uniformly dense microstructure, and, in addition, performed well in all corrosion tests.

Effect of SPS on Surface Characteristics of Gas-Atomized Mg-6wt%Al-1wt%Zn Alloy by Non-Hazardous PEO Treatment

The Mg-6wt%Al-1wt%Zn alloy powders mixture produced by gas atomization were spark plasma sintered (SPSed). The SPSed sample was coated by plasma electrolytic oxidation (PEO) method, and the microstructure, mechanical and corrosion properties were investigated and compared to the normally sintered sample. The SPSed sample exhibited a microstructure of well-bonded grains with approximately 48 ,m in grain size, which was bigger than that of the normally sintered sample. The coatings on the SPSed sample were characterized by dense and porous layers, while, in the case of the normally sintered sample, the coatings had grown through the grain boundary of substrate with increasing the coating time. The surface roughness, thickness and micro-hardness of coatings on the SPSed sample increased gradually with increasing the coating time. The corrosion property of coatings on the SPSed sample had a tendency to improve with increasing the coating time in 3.5%NaCl solution. However, it was worse than that of coatings on the normally sintered sample.

Mechanical and Electrochemical Properties of Plasma Electrolytic Oxide Coatings on Aged Mg-Al alloy

Plasma electrolytic oxidation (PEO) treatment was performed on cast Mg-6 wt%Al alloy solution-treated at 693K for 16h and aged at 498K. The surface roughness, thickness, micro-hardness, wear and corrosion properties of coatings on solution-treated and aged Mg-6 wt%Al alloy were investigated. The coatings on aged Mg-6 wt%Al alloy had thinner layer and lower micro-hardness and wear resistance than the solution-treated Mg-6 wt%Al alloy. As the aging time increased, the thickness of coatings decreased while the surface roughness was almost no changed. In addition, the micro-hardness and wear property of coatings decreased with increasing the aging time unlike the uncoated Mg-6 wt%Al alloy showing the peak micro-hardness and the best wear property after aging for 16 h. However, the coatings on Mg-6 wt%Al alloy peak-aged for 16h revealed the best corrosion resistance in 3.5% NaCl solution, which was explained based on the microstructural characteristics.

Corrosion properties of plasma-sprayed Al2O3-TiO2 coatings on Ti metal

Three different oxides of CrO2-TiO2, Al2O3 and Al2O3-TiO2 were plasma-sprayed on Ti substrate to evaluate the crystal structure and the corrosion properties of the coatings. No phase change of the coatings after corrosion test in 0.5 M H2SO4 solution at 25°C was found regardless of the presence of the NiCoCrAlY bond layer. Electrochemical measurements and SEM results revealed that the single coatings without the bond layer were always effective against corrosion resistance due to lower current density within the passive region. Pitting corrosion of the surface was observed for the Al2O3 coating. It can be concluded that the Al2O3-TiO2 coating without the bond layer may be the best oxide among the oxides investigated due to low porosity (5.4%), smooth surface roughness (4.5 μm), low current density (6.3 × 10‒8 A/cm2) in the passive region, low corrosion potential (Ecorr, ‒0.55 V) and no pitting corrosion.

Tribological Properties of Finely-Dispersed Coatings with Electric-Spark Alloying of Materials of the System Ti ― Al ― N

Mass transfer, composition, structure, and also the tribological and corrosion properties of coatings prepared with electric-spark alloying (ESA) of titanium alloy VT6 and steels 45 and 40Kh with electrode materials of the systems Ti ― Al and TiN ― AlN with different component ratios are studied. In both cases a finely-dispersed island structure forms with high wear and corrosion resistance. The best results are obtained for ESA with intermetallics. The main phase of ESA-coatings prepared with intermetallics is Al2O3, and from the nitrides it is TiN. It is suggested that the difference in tribological behavior of “intermetallic” and “nitride” coatings is due to the difference in their roughness and phase composition.

Surface structure and corrosion properties of binary Ti-C and Mo-C coatings co-deposited by filtered vacuum arc plasma deposition system

Thin (Ti,C) and (Mo,C) binary coatings were respectively formed on the surface of H13 steel by Ti ++C + and Mo ++C + dual beams deposition using filtered vacuum arc plasma deposition (FVAPD) system with three MEVVA sources. Using the three-electrode potential-kinetic polarization technique, the corrosion properties of these coatings in acetic acid and sodium acetate solutions or sodium chloride solutions were measured. The results indicate that the binary coatings fabricated by this technique have good compactness and corrosion resistance. A comparison between (Ti,C), (Mo,C) coatings and H13 steel with pure Ti coating in terms of the corrosion resistance was given. Electron diffraction and XRD results show that the structure of the binary coatings presents a mixed polycrystalline and amorphous state.

Microstructure and properties of laser treated arc sprayed and plasma sprayed coatings

The effect of laser melting on the microstructure, porosity, chemical homogeneity of nickel based alloy plasma sprayed and (Fe–Cr–B)+Al based electric arc sprayed coatings has been investigated. Laser melting markedly improves coating microstructure and density, and much better chemical homogeneity is obtained. Laser treatment of coatings was carried out with the help of a CW CO2 laser (λ=10.6μm) using the graphite based antireflection coating. The results demonstrate an improvement of mechanical and corrosion properties of coatings.

Corrosion properties of titanium based hard coatings on steel

AbstractTitanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA‐CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA‐CVD process parameters.The incorporation of chlorine in the coating can be varied by the process parameters with TiCl4 or completely avoided using metallo‐organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel.A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN‐coated substrates of complex geometry. The PA‐CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low‐alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.