Multilayer Alloy Coatings Research Articles

Development of Composition Modulated Multilayer (NiTi) Alloy Coatings for Improved Corrosion Protection of Mild Steel

Development of Composition Modulated Multilayer (NiTi) Alloy Coatings for Improved Corrosion Protection of Mild Steel

Compositionally modulated multilayer Cu-Zn alloy coatings fabricated using eco-friendly non-cyanide pulse electrochemical deposition

Pulse electrodeposition of Cu-Zn compositional modulated multilayer alloy (CMA) coatings was carried out onto AISI 304 stainless steel substrate using an environmentally friendly alkaline non-cyanide electrolytic bath. Cu-Zn alloy multilayer coating was co-electrodeposited using a trapezoidal pulse current. Multilayer coatings can have two different metals in layers or two-phase mixtures. Different sets of multilayers of 10, 20, 50, and 100 were done using a trapezoidal pulse current. In the trapezoidal pulse current module, during the higher current stage (0.1 A) Zn was deposited as compared to the lower current module (0.02 A) where Cu was deposited. Microstructural and structural analysis of the coatings confirmed nanocrystalline morphology with peaks corresponding to crystallographic planes of (002), (111), (020), and (022). Deposited coatings are hydrophilic in nature. The microhardness of the coatings is decreased with an increase in the number of layers deposited.

Microstructure evolution and defect characteristics of multilayer Fe-Cr alloy coatings fabricated by laser melting deposition

To clarify the microstructure evolution, defect characteristics and suppression methods for multilayer cladding by laser melting deposition (LMD), experimental research on multilayer LMD of Fe-Cr alloy with different laser energy densities was carried out. The phase composition and the evolution rules of the phase during the melting-solidification process were analyzed. The crystal growth trend, dendritic transition and dendrite spacing of multilayer Fe-Cr coatings were investigated. The formation mechanism of crack, porosity and surface spheroidization defects were revealed, the effects of laser energy densities on the defects were analyzed, and the defect suppression methods were proposed and verified. The results showed that the primary and secondary remelting zones of multilayer Fe-Cr coatings were fine equiaxed dendrites and irregular cellular structures, respectively. When the laser energy density increased from 22.74 J/mm2 to 55.70 J/mm2, the dendrite spacing increased gradually, and the porosity and spheroidization defects showed a trend of improvement and then deterioration. The cracks were considered cold cracks with transgranular characteristics. Meanwhile, when the residual stress exceeded the theoretical fracture strength of 1.6 GPa, the multilayer cladding experienced brittle fracture and formed cracks. Selecting an appropriate laser energy density and preheating treatment can effectively improve the forming quality and inhibit the formation of defects.

Improved lead-bismuth eutectic corrosion resistance and mechanical properties of reactive gas pulse sputtered AlCrFeMoTi/(AlCrFeMoTi)N composite multilayered high-entropy alloy coatings

The (HEA/HEAN)-n multilayer coatings consisting of alternating (AlCrFeMoTi)N (top) and AlCrFeMoTi layers were specially designed and successfully deposited on 12Cr2W2Mn F/M steel substrate by reactive magnetron sputtering technology. The dependence of microstructure, mechanical properties and lead-bismuth eutectic (LBE) corrosion resistance on interlayer interface density was systematically investigated. The multilayer structure design improved the mechanical properties and high-temperature structural stability of the multilayer coatings. Furthermore, after exposed to LBE at 650 °C for 1000 h, the (HEA/HEAN)-12 multilayer coatings with optimum interlayer interface density exhibited the most optimal LBE corrosion resistance. The oxidation corrosion mechanism of the (HEA/HEAN)-n multilayer coatings were also discussed intensively.

Tribocorrosion performance of 316L stainless steel enhanced by laser clad 2-layer coating using Fe-based amorphous powder

To improve the tribocorrosion performance of 316L stainless steel (SS), multi-layer (1, 2 and 3 layers) Fe-based alloy coatings were manufactured by laser cladding Fe-based amorphous powder on 316L SS, and the corrosive wear behavior was investigated against Alumina ball in Ringer's solution. With the increase of cladding layer number, the content of body-centered cubic (BCC) phase increases, and the hardness also improved. The volume loss rate of SS at 5 N load decreased over 3 times by the 2-layer coating. Under 10 or 20 N loads, the 2-layer coating still presents the best tribocorrosion performance with the lowest values of friction coefficient and volume loss rate. The multi-layer cladding caused surface chemical composition change leading to the decrease of Cr accompanied with the increase of Mo and Y, which is responsible for the increase of BCC content and hardness as well as the formation of lubricant Fe–Cr hydroxide film. The friction induced lubricating film may facilitate to design new metallic coatings for the low carbon steels applied in corrosive environment.

Compositionally Modulated Multilayered Zn-Co Deposits for Better Corrosion Resistance

Zn-Co compositionally modulated multilayer alloy (CMMA) deposits have been developed onto mild steel using single bath technique. Multilayer alloy coatings have been galvanostatically produced using square current pulses. The switched cathode current density and number of layers have been designed for improved corrosion resistance. Experimental data revealed that multilayer coating with 120 layers at 10/30 mA/cm2 demonstrated ~ 125 times higher resistance to corrosion than monolayer alloy coating of the same thickness. The improved corrosion resistance of multilayer coatings is due to small changes in the wt.% cobalt, leading to change in the phase structure of deposit in alternate layers. The defects and failures occurring in a single layer in the deposition process are covered by the alternatively deposited coating layers. Therefore, the direction of the corrosive agent is extended or blocked. Further, the better corrosion resistances afforded by Zn-Co CMMA coatings were explained through changes in electronic properties at the interface, supported by Mott-Schottky’s plot. However, the decrease of corrosion resistance at a high degree of layering is attributed to the less relaxation time for redistribution of solutes in the diffusion layer, during plating. Potentiodynamic polarization and electrochemical impedance data showed its good protection ability. The enhanced corrosion resistance of multilayered deposits is due to small change in cobalt content, leading to alter the phase structure of the alternate-layers of the deposits. The structural morphology and the topographical structure of the coating were analyzed by scanning electron microscopy and atomic force microscopy. Evaluation of the chemical composition of the alloy coatings was carried out by x-ray photoelectron spectroscopy.

Zn–Ni compositionally modulated multilayered alloy coatings for improved corrosion resistance

ABSTRACT Zinc–Nickel monolayer (single layer) and compositionally modulated multilayer alloy coatings were developed on to mild steel from acidic sulphate bath; and their corrosion performance were studied using potentiodynamic polarization and electrochemical impedance spectroscopy methods. The coating layers were formed galvanostatically by single bath technique, using square current pulses and triangular current pulses. For the best efficiency of the deposits against corrosion, the switched cathode current density and the number of layers were optimized. Under optimized conditions, Zn–Ni multilayer alloy coatings were produced at the current density 3.0/5.0 A dm−2 having 300 layers were ∼65 (square) and ∼48 (triangular) times more corrosion resistant respectively than the single layer alloy coating of the same thickness. Scanning electron microscopy has been employed to investigate, the formation of multilayer alloy coatings as well as the morphology of the surface before and after corrosion studies.

Development of nanocrystalline multilayer Ni–Fe alloy coatings: characterization and its corrosion behaviour at elevated temperature

The present work deals with the galvanostatic fabrication of Ni–Fe nanostructured composition-modulated multilayer alloy (CMMA) coatings on steel panel from the newly optimized acid-sulphate bath solution. The recurring cathode current density combination (RCCC) and the number of layers have been optimized for enhanced performance of the coatings against corrosion. Corrosion behaviour of the nanostructured multilayered coatings was evaluated by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solution. Under optimal conditions, the CMMA coatings developed were more corrosion-resistant than the monolithic alloy coatings obtained from the same bath. Least corrosion rate (CR) was witnessed at 300 layers, above which saturation of corrosion resistance at a high temperature was found, which is attributed to a shorter relaxation time for redistribution of metal ions during multilayer deposition. Hardness and roughness of the coatings were evaluated using Vickers hardness test and atomic force microscope, respectively. Phase structure of the coatings was discussed using X-ray diffraction technique. The cross-sectional view of the coatings was characterized by scanning electron microscope. CR analysis and the surface morphology of the optimized coatings exposed to high temperature revealed the better performance of CMMA coatings at the elevated temperatures compared to the monolithic coatings.

Corrosive wear of multi-layer Fe-based coatings laser cladded from amorphous powders

Since amorphous alloys exhibit good wear and corrosion resistance, they are supposed to be applied as a candidate implant material. In this work, using laser cladding, Multi-layer Fe-based alloy coatings were fabricated from amorphous powders on 316L stainless steel (SS) substrate. When the number of cladding layers increases, the microstructure of the coating was mainly composed of γ-Fe firstly, then evolved to γ-Fe and α-Fe solid solutions, and then to a composite of amorphous and crystalline phases. The surface hardness of the coating was also enhanced consequently to over 1200 HV. During reciprocate sliding against an Alumina ball in a simulated body fluid (Ringer's solution), the volume loss and the coefficient of friction (COF) of the coatings generally decreased firstly and then increased with the number of cladding layers. During sliding at open circuit, the drop in open circuit potential (OCP) of all the Fe-based coatings, except for the 1-layer one, was not as significant as that of the 316 SS substrate. Moreover, when applying a cathodic potential during sliding, no obvious protective effect was obtained for the coatings, which indicates that the multi-layer Fe-based coatings possess a good corrosion-induced wear resistance in comparison to 316L SS. Because of the formation of an electric double layer, the fixed potential of 100 mVSCE or −600 mVSCE was beneficial to reduce the COF, especially for 316L SS. The tribocorrosion at OCP showed that the 2-layer coating possessed the best corrosive wear resistance, and its COF and volume loss were about 3 and 5.6 times lower than those of the substrate. The material loss in Ringer's solution at OCP is mainly controlled by the mechanical wear for the coatings and the synergism between corrosion and wear for the substrate. Furthermore, this work provides a way to optimize the tribology system by adjusting the number of cladding layers to reduce COF and wear in a simulated body fluid.

Zn–Fe multilayered alloy coatings produced by electrodeposition

Zn–Fe multilayered alloy coatings were deposited on mild steel substrates using the dual bath electrodeposition technique. The produced coatings consisted of alternate Zn–1 wt% Fe and Zn–10 wt% Fe alloy sub-layers. Their periodicity length (total thickness of two adjacent alternate sub-layers) ranged between 2 and 8 μm. The surface and the cross-sectional morphology of those coatings were studied with the aid of a metallurgical microscope and a scanning electron microscope. The crystal structure of the electrodeposited multilayered coatings was investigated using an X-ray diffractometer. The Zn–1 wt% Fe and Zn–10 wt% Fe alloy sub-layers consisted of two phases: the η-phase (Zn–Fe solid solution) and the δ1-phase (intermetallic FeZn7). A microhardness tester equipped with a Vickers intender was used to examine the microhardness of the produced coatings. It was found that the microhardness increased with the decrease of periodicity length, following a modified Hall–Petch relationship.

Solidification behavior and morphological evolution in laser surface forming of AlCoCrCuFeNi multi-layer high-entropy alloy coatings on AZ91D

The AlCoCrCuFeNi high-entropy alloy (HEA) coatings after one, two and three layers were laser cladded on the AZ91D substrate. Towards the coating interface, the substrate is composed of Mg dendrites and interdendritic Mg + Q eutectics. The formed coatings can be categorized into a low narrow composite region and a top thick dense HEA region. The dominated microstructures in the dense HEA region are columnar dendrites. Nevertheless, the average primary spacing of columnar dendrites became smaller when the coating grew thicker mainly due to the temperature gradient decreasing slowly. Moreover, the planar morphology at re-melted boundary of each clad layer is absence because of the local conditions being suitable for epitaxial growth. Additionally, it is found that the columnar to equiaxed transition (CET) had occurred in the top area of the three-layer HEA coating. This evolution of the microstructure can be explained by the CET theory combined with the sluggish diffusion kinetics and the abnormal variation of the thermal conductivity with the temperature of the AlCoCrCuFeNi HEA. Additionally, the problem associated with dilution by Mg can be completely suppressed by the HEA coating after three layers.

Ultrasound induced multilayer Ni-Co alloy coatings for better corrosion protection

Ultrasound induced multilayer Ni-Co alloy coatings have been developed galvanostatically by periodic modulation of ultrasound effect, parallel to the process of conventional electroplating. Multilayer Ni-Co alloy having alternative layers of different composition were developed by turning the sonicator probe, ON and OFF periodically, while keeping the current density (c.d.) constant. The deposition conditions, in terms of pulsing power density (p.d.) and degree of layering have been optimized for the highest performance of coating against corrosion, evaluated by electrochemical testing methods. Corrosion data revealed that under optimal conditions, multilayer Ni-Co alloy coating having 150 layers, represented as (Ni-Co)2/2/150 is about 11 times more corrosion resistant than its homogeneous coating, represented as (Ni-Co)4.0Adm−2, deposited from the same bath for same duration of time. Improved corrosion resistance of multilayer Ni-Co alloy coatings was attributed to an increase in the number of interfaces, separating the layers of alloys of different composition, affected due to periodic pulsing of the sonicator. The dependence of corrosion behaviors at different combination of c.d. and p.d., on surface morphology, composition and phase structures were analyzed, using scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD) technique, respectively. Experimental results are compared, and discussed.

Galvanic Formation of Zn-Ni/Zn-Co Type Multilayer Alloy Coatings on Steel Substrate

Zn-Ni and Zn-Co monolayer and Zn-Ni/Zn-Co multilayer (from 2 to 128 layers) alloy coatings were formed on steel substrate by electrodeposition from acidic Zn-Ni bath and neutral Zn-Co bath. Samples were tested in salt chamber for corrosion resistance in neutral salt spray. Open circuit potential measurement and gravimetric study of corrosion were carried for samples immersed in the 5% NaCl solution.It was found that coatings of Zn-Ni surface layer occurred higher corrosion resistance then the coatings of Zn-Co surface layer. Sixteen-layer coating with Zn-Ni surface layer proved to be most effective in protecting the steel substrate. Zn-Ni monolayer showed the lowest corrosion potential, which affects the corrosion properties. Sample weight changes during exposure to a corrosive environment are related to digestion of the coating and the formation of corrosion products.

Nanofabricated multilayer coatings of Zn-Ni alloy for better corrosion protection

As an effort to increase the corrosion resistance of conventional monolayer Zn-Ni alloy coating, the multilayer Zn-Ni alloy coating have been done electrolytically on mild steel (MS), using gelatin and glycerol as additives. Multilayered, or more correctly composition modulated multilayer alloy (CMMA) coatings have been developed using square current pulse. Successive layers of alloys, in nanometric scale having alternately changing composition were fabricated by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings having different configuration, in terms of composition and thicknesses of individual layers were developed and their corrosion performances were evaluated by electrochemical methods. The corrosion rate (CR)’s were found to decrease drastically with progressive increase in number of layers (up to 300 layers), and then increased. The coating configurations have been optimized for best protection against corrosion. The CMMA Zn-Ni coating having 300 layers was found to be about 37 times more corrosion resistant than corresponding monolayer alloy, developed from same bath for same time. High protection efficacy of the coatings were attributed to alternate layers of alloys having different surface structure and composition, supported by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) study, respectively. Optimization procedure has been explained, and results are discussed.

Effect of heat treatment on structure and properties of multilayer Zn-Ni alloy coatings

Effect of heat treatment on structure and properties of multilayer Zn-Ni alloy coatings

Layered Coating of Zn–Co Alloys on Mild Steel using Triangular Current Pulses for Better Corrosion Protection

Cyclic multilayer alloy (CMA) coatings of Zn–Co were electrodeposited on to mild steel (MS) from acid sulphate bath having thiamine hydrochloride and citric acid as additives. Depositions were carried out galvanostatically from a single bath containing Zn+2 and Co+2 ions. The triangular current pulses cycling between two cathode current densities were used for gradual change in composition in each layer. CMA coatings were developed under different sets of cathode current densities and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy method, and results were compared with that of monolayer Zn–Co alloy coatings. At optimal configuration, CMA coating represented as (Zn–Co)3.0/5.0/300 was found to exhibit ~11 times better corrosion resistance compared to monolayer, (Zn–Co)4.0, deposited for same length of time from same bath. The formation of layered and corrosion mechanism was analyzed using Scanning Electron Microscopy. The corrosion protection of layered coatings of Zn–Co alloy was attributed to the different phase structure of the alloys in alternate layers, evidenced by XRD analysis.

Effect of heat treatment on structure and properties of multilayer Zn-Ni alloy coatings

Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni were electrodeposited galvanostatically on mild steel (MS) for enhanced corrosion protection using single bath technique. Successive layers of Zn-Ni alloys, having alternately different composition were obtained in nanometer scale by making the cathode current to cycle between two values, called cyclic cathode current densities (CCCD’s). The coatings configuration, in terms of compositions and thicknesses were optimized, and their corrosion performances were evaluated in 5 % NaCl by electrochemical methods. The corrosion rates (CR)’s of multilayer alloy coatings were found to decrease drastically (35 times) with increase in number of layers (only up to 300 layers), compared to monolayer alloy deposited from the same bath. Surface study was carried with SEM, while XRD was used to determine metal lattice parameters, texture and phase composition of the coatings. The effect of heat treatment on surface morphology, thickness, hardness and corrosion behaviour of multilayer Zn-Ni alloy coatings were studied. The significant structural modification due to heat treatment is not accompanied by any decrease in corrosion rate. This effect is related to the formation of a less disordered lattice for multilayer Zn-Ni alloy coatings.

Surface modification by multilayered Zn–Co alloy coatings

Nanostructured multilayer alloy or composition modulated multilayer alloy coatings of Zn–Co have been developed, and their corrosion behaviours were studied by potentiodynamic polarisation and electrochemical impedance spectroscopy methods. The coatings were developed galvanostatically using square, triangular and sawtooth current pulses through single bath technique. The cyclic cathode current density and the numbers of layers have been optimised for peak performance of the coatings against corrosion. Under optimal conditions, the coatings developed using square, triangular and sawtooth current pulses were found to be respectively ∼100, 80 and 90 times more corrosion resistant than monolithic alloy of same thickness. The better corrosion resistances of the composition modulated multilayer alloy coatings were attributed to the dielectric barrier at the interface, as evidenced by dielectric spectroscopy. Surface morphology, multilayer formation and surface after corrosion tests were examined by scanning electron microscopy.

Electrodeposition of Cyclic Multilayer Zn-Co Films Using Square Current Pulses and Investigaions on Their Corrosion Behaviors

The cyclic multilayer alloy (CMA) coatings of Zn-Co have been developed galvanostatically on mild steel (MS), using single bath technique. Depositions were carried out using square current pulses. Corrosion behaviors of the coatings were evaluated by potentiodynamic polarization and electrochemical impedance method, supported by dielectric spectroscopy. The cyclic cathode current densities (CCCD’s) and number of layers were optimized for highest corrosion stability of the coatings. The CMA coating developed at 3.0/5.0 A/dm2, having 300 layers, represented as (Zn-Co) 3.0/5.0/300 was found to exhibit ~ 40 times better corrosion resistance compared to monolayer coating, developed from same bath for same time. Substantial improvement in the corrosion resistance of CMA coatings is attributed to layered coating, having alternatively different phase structures, evidenced by XRD study. The formation of multilayer and corrosion mechanism was analyzed using Scanning Electron Microscopy.

Corrosion resistant Zn-Co alloy coatings deposited using saw-tooth current pulse

Micro/nanostructured multilayer coatings of Zn-Co alloy were developed periodically on mild steel from acid chloride bath. Composition modulated multilayer alloy (CMMA) coatings, having gradual change in composition (in each layer) were developed galvanostatically using saw-tooth pulses through single bath technique (SBT). CMMA coatings were developed under different conditions of cyclic cathode current densities (CCCDs) and number of layers, and their corrosion resistances were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) method. Optimal configuration, represented as (Zn-Co)2·0/4.0/300 was found to exhibit ∼ 89 times better corrosion resistance compared to monolithic (Zn-Co)3·0 alloy deposited for same time, from same bath. The better corrosion resistance of CMMA coatings was attributed to changed interfacial dielectric properties, evidenced by dielectric spectroscopy. Improved corrosion resistance was attributed to formation of n-type semiconductor film at the interface, supported by the Mott-Schottky plot. Further, the formation of multilayer and corrosion mechanism was analysed using scanning electron microscopy (SEM).