Formation mechanism of electroless plating nickel-based composite coating on highly active rare earth magnesium alloys and its corrosion resistance and adhesion performance

The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on active anodic oxide film and the structure and properties of the composite coating were studied by several surface and electrochemical techniques.The results showed that Ag nanograins with an average size of 10 nm were embedded into the anodic oxide film with pores of 0.1−2μm.Ag nanoparticles provided a catalytic site for the deposition of Ni-B alloy,and the Ni crystal nucleus was first grown in horizontal mode and then in cylindrical mode.The corrosion potential of the composite coating increased by 1.37 V and the corrosion current reduced two orders of magnitude due to the subsequent deposition of Ni-P alloy.The high corrosion resistance was attributed to the misaligning of these micro defects in the three different layers and the amorphous structure of the Ni-P alloy in the outer layer.These findings provide a new idea for electroless nickel plating on anodic oxide film.

Effect of Rare Earth Element Cerium on Mechanical Properties and Morphology of TiN Coating Prepared by Arc Ion Plating

TiN coatings were deposited on polished substrates of W18Cr4V high speed steel by means of vacuum arc ion plating. The effect of cerium on adhesion between TiN coating and substrate was studied. The microstructures and composition of TiN coatings were also investigated by means of scanning electron microscope (SEM), Auger electron spectroscopy (AES), and X ray diffraction (XRD) technique. It was found that cerium is an effective modifying agent and the addition of suitable amount of cerium to TiN coatings can produce relatively excellent properties such as micro hardness, wear resistance, oxidation resistance and porosity. The experimental results show that the added cerium in TiN coatings makes a contribution to form the preferred direction along with a (111) or (222) close packed face, which may be one of the reasons that improves some properties mentioned above.

Effects of rare earth on microstructures and properties of Ni-W-P-CeO_2-SiO_2 nano-composite coatings

Ni-W-P-CeO2-SiO2 nano-composite coatings were prepared on common carbon steel surface by pulse electrodeposition of nickel, tungsten, phosphorus, rare earth （nano-CeO2） and silicon carbide （nano-SiO2） particles. The effects of nano-CeO2 concentrations in electrolyte on microstructures and properties of nano-composite coatings were studied. The samples were characterized with chemical compositions, elements distributions, microhardness and microstructures. The results indicated that when nano-CeO2 concentration was controlled at 10 g/L, the nano-composite coatings possessed higher microhardness and compact microstmctures with clear outline of spherical matrix metal crystallites, fine crystallite sizes and uniform distribution of elements W, P, Ce and Si within the Ni-W-P matrix metal. Increasing the nano-CeO2 particles concentrations from 4 to 10 g/L led to refinement in grain structure and improvement of microstructures, while when increased to 14 g/L, the crystallite sizes began to increase again and there were a lot of small boss with nodulation shape appearing on the nano-composite coatings surface.

Effect of Rare Earth Elements on Depositing Rate of Nickel Alloy Brush Plating Coatings

The effect of four kinds of rare earth elements on the depositing rate of Ni-based alloy brush plating coatings was investigated. The results indicate that all of the selected rare earth elements increase the depositing rate of Ni-based alloy coatings, and Sm increases the depositing rate most obviously. There is an optimum amount of rare earth addition in the plating solution. With the change of plating voltage to a certain extent, the results reveal no differences. The mechanism of the increase of the depositing rate was analyzed.

Improvement strategy on thermophysical properties of A_(2)B_(2)O_(7)-type rare earth zirconates for thermal barrier coatings applications:A review

The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments.This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines.Based on the first principles,molecular dynamics,and new data-driven calculation approaches,doping and high-entropy strategies have now been adopted in advanced TBC materials design.In this paper,the solid-state heat transfer mechanism of TBCs is explained from two aspects,including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature.This paper also provides new insights into design considerations of adaptive TBC materials,and the challenges and potential breakthroughs are further highlighted for extreme environmental applications.Strategies for improving thermophysical performance are proposed in two approaches:defect engineering and material compositing.

Improving Corrosion Resistance of C_f/Mg Composites using Rare Earth Conversion Coatings

The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.

Mixed rare earth metal conversion coatings on 2024 alloy and Al6061/SiC_p metal matrix composites

The processes of mixed rare earth metal (REM) conversion coatings on 2024 alloy and Al6061/SiC p metal matrix composites (MMC) were introduced. The coatings were examined to be honeycomb like feature by scanning electron microscope. X ray diffraction analysis revealed that the coatings are amorphous structure. The results of X ray photoelectron spectroscopy indicated that the mixed REM conversion coatings consist predominantly of Ce and O, the contents of other rare earth elements (such as La, Pr) are relatively low, the coatings are about 2～4 μm thickness with excellent adhesion and wearability. The results of mass loss test showed that the mixed REM conversion coatings produce corrosion resistant surface of 2024 alloy and Al6061/SiC p. [

Influence of rare earths addition on residual stress of Fe-based coating prepared by brush plating technology

The effect of rare earths（La, Ce and Pr） addition on residual stress in iron coatings prepared by brush plating was investigated. The results showed that the addition of rare earth transformed the residual stress in the coating from tensile to compressive. To relieve the residual stress, on the one hand, RE elements segregated at the grain boundaries which restricted the coalescence of the grains and provided more capability of grain deformation. On the other hand, RE elements could purify detrimental element and absorb hydrogen atoms in the coating. Among the three rare earths, elements lanthanum showed the most significant effect on surface morphology and residual stress.

Study on corrosion resistance of the BTESPT silane cooperating with rare earth cerium on the surface of aluminum-tube

Bis-3-(triethoxysilyl)propyltetrasulfide(BTESPT) silane-rare earth cerium composite coatings on aluminum-tube were prepared at 60 °C by immersion method.The performance of composite coatings to protect the aluminum-tube against corrosion was investigated with potentiodynamic polarization curves,electrochemical impedance spectroscopy(EIS),and salt spray test(SST).The results of potentiodynamic polarization curves and EIS indicated that the self-corrosion current decreased by two orders of magnitude and the i...

ELECTROLESS PLATING COMPOSITE COATINGS OF Ni-Ti-Re ON THE SURFACE OF DIAMOND

The coating of Ni W P was deposited as base layer, and then the composite coating of Ni Ti(particles) Re(rare earth) was deposited subsequently on the surface of diamond using electroless plating by adding 2～3 μm Ti particles and trace rare earth salt to bath solution. Ti particles deposited on the surface of diamond were found by SEM and formation of TiC was verified by X ray diffraction analysis after heat treatment of the coatings in vacuum at 900 ℃. The binding strength between the coated diamond and the metal matrix was improved effectively in the diamond composite based on metal cement.

Preparation and tribological performance of electrodeposited Ni-TiB_2-Dy_2O_3 composite coatings

TiB2 and Dy2O3 were used as codeposited particles in the preparation of Ni-TiB2-Dy2O3 composite coatings to improve its performance. Ni-TiB2-Dy2O3 composite coatings were prepared by electrodeposition method with a nickel cetyltrimethylammonium bromide and hexadecylpyridinium bromide solution containing TiB2 and Dy2O3 particles. The content of codeposited TiB2 and Dy2O3 in the composite coatings was controlled by adding TiB2 and Dy2O3 particles of different concentrations into the solution, respectively. The effects of TiB2 and Dy2O3 content on microhardness, wear mass loss and friction coefficients of composite coatings were investigated. The composite coatings were characterized by X-ray diffraction （XRD）, inductively coupled plasma-atomic emission spectrometer （ICP-AES） and scanning electron microscopy （SEM） techniques. Ni-TiBE-Dy2O3 composite coatings showed higher microhardness, lower wear mass loss and friction coefficient compared with those of the pure Ni coating and Ni-TiB2 composite coatings. The wear mass loss of Ni-TiB2-Dy2O3 composite coatings was 9 and 1.57 times lower than that of the pure Ni coating and Ni-TiB2 composite coatings, respectively. The friction coefficient of pure Ni coating, Ni-TiB2 and Ni-TiB2-Dy2O3 composite coatings were 0.723, 0.815 and 0.619, respectively. Ni-TiBE-Dy2O3 composite coatings displayed the least friction coefficient among the three coatings. Dy2O3 particles in composite coatings might serve as a solid lubricant between contact surfaces to decrease the friction coefficient and abate the wear of the composite coatings. The loading-bearing capacity and the wear-reducing effect of the Dy2O3 particles were closely related to the content of Dy2O3 particles in the composite coatings.

Study on the Structures and Properties of Ni-W-B-CeO_2 Composite Coatings Prepared by Pulse Electrodeposition

The aim of this research is to pulse co-deposit nano-CeO2 particles into Ni-W-B alloy coatings in order to improve the surface properties. The influence of pulse frequency and duty circle on deposition rate, microhardness and microstructures, and the influence of heat treatment temperature on phase structures, microhardness and abrasivity of Ni-W-B-CeO2 composite coatings were investigated. The results indicated that the pulse co-deposition of nickel, tungsten, boron and nano-CeO2 particle from the bath which nano-CeO2 particle was suspended by high speed mechanical stirring led to the Ni-W-B-CeO2 composite coatings, possessing better microhardness and abrasion resistance when heat-treated at 400 ℃ for 1 h. The microhardness as-deposited with 636 Hz and the deposition rate with 0.0281 mm·h-1 was the highest at pulse frequency with 1000 Hz and pulse duty circle with 10%. Microstructures analysis displays that decreasing pulse duty cycle leads to refinement in grain structures and the improvement of microstructures. X-ray diffraction shows that the composite coating as-deposited was mainly in the amorphous state and partially crystallized, but when heat treated at 400 ℃, the crystallization trend was strengthened further.

Al_2O_3-Y_2O_3 Nano- and Micro-Composite Coatings on Fe-9Cr-Mo Alloy

Al2O3-Y2O3 nano- and micro-composite coatings were deposited on Fe-9Cr-Mo substrates by using sol-gel composite coating technology. The processing includes dipping samples in a sol-gel solution dispersed with fine ceramic powders, which are prepared by high-energy ball milling. High-resolution microscopy （FE-SEM） analyses show that the coating is composed of composite particle clusters with an average diameter of 1μm, and the coating is relatively dense without cracking during drying and sintering stages. XRD analyses show that the oxide coating is mainly composed of α-Al2O3 and γ-Al2O3. The oxidation tests performed at 600℃ in air show that the coatings are provided with much improved resistance against high temperature oxidation and scale spallation. It is indicated that nano-structured composite particles and reactive elements are integrated into the coatings, which plays an important role in preventing agglomeration of nano-particles and initiation of cracks.

Corrosion Behavior of Electrodepositing Ni/Al_2O_3 Composite Coatings under the Presence of NaCl Deposit

The morphology and corrosion behavior of Ni/Al2O3 composite coatings prepared using double-pulsed electrodepositing technique after oxidized under 800 ℃ NaCl deposit in air environment were analyzed by scanning electrical microscope (SEM), X-ray diffraction(XRD) and energy dispersive spectrum(EDS). The results showed that the corrosion of all composite coatings was accelerated under NaCl deposits, and the corrosion products were rather porous with poor adherence to the matrix. Al2O3 particles in the coatings can refine the grain size and improve the high temperature corrosion resistance of the coatings. Within the test scope, the more Al2O3 particles in the coatings, the lower corrosion rates could be obtained, and the corrosion mechanism was also discussed.

Influence of SiO_2 Particles on Microstructures and Properties of Ni-W-P-CeO_2-SiO_2 Nano-Composite Coatings

Ni-W-P-CeO2-SiO2 nano-composite coatings were prepared on the carbon steel surface by pulse co-deposition of nickel, tungsten, phosphorus, nano-CeO2 and nano-SiO2 particles. The influence of nano-SiO2 particles concentrations in electrolyte on microstructures and properties of the nano-composite coatings were researched, and the characteristics were assessed by chemical compositions, element distribution, deposition rate, microhardness and microstructures. The results indicate that when nano-SiO2 particles concentrations in electrolyte are controlled at 20 g·L-1, the deposition rate with 27.07 μm·h-1 and the microhardness with 666 Hv of the nano-composite coatings are highest, element line scanning and area scanning analyses show that the average contents of elements W, P, Si and Ce in the nano-composite coatings are close, displaying that the distribution of every element within the nano-composite coatings is even. An increase in nano-SiO2 particles concentrations in electrolyte (when lower than 20 g·L-1) leads to refinement in grain structure of nano-composite coatings, but when it improved to 30 g·L-1, the crystallite sizes increase again and in the meantime there are a lot of small boss with nodulation shape appearing on the surface of nano-composite coatings.

Effect of rare earth addition on structure and properties of Ni-P coating on SiCp/Al composites

The aim of this work was to improve the properties of Ni-P coating on SiCp/Al composites. The effect of rare earths addition on Ni-P coating structure was investigated by means of scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and electrochemistry methods. The results showed that as Y or La concentration was 0.15 g/L in plating solution, the highest value of deposition rate of Ni-P coating was found. And the structure of the obtained coating was modified...

Effects of Binary Mixture of Yb_2O_3-La_2O_3 on Pd/Ag Co-Deposition by Electroless Plating

The binary mixture of Yb2O3-La2O3 was used as an additive to improve the traditional electroless plating for Pd-Ag co-deposition on the inside surface of a porous ceramic tube. The main attention were paid to investigating the effects of Yb2O3-La2O3 on Pd-Ag co-deposition rate, plating temperature, Ag content in film and Pd/Ag reduction potentials. The experimental results show that the co-deposition rate is increased by 63 % , the plating temperature is decreased by 10 ~ 20℃for obtaining the same co-deposition rate and the Ag content in film basically remains unchangeable when Yb2O3-La2O3 is added into the traditional electroless plating solution. The experiment also shows that Pd/Ag reduction potentials basically remain unchangeable with the binary rare earths based on the electrochemical mathematical models An inorganic composite membrane with alloy film of 76.8(mol)% Pd-23.2(mol) % Ag and the thickness of 7.7μm on the porous ceramic tube was prepared and the permeation fluxes of hydrogen and nitrogen through the membrane are 8.65×10-3 and 1.92×10-6m3·m-2·s-1 at 350℃and 0.3 MPa respectively.

Effect of Rare Earths on the Quality of Brush-plated Coating

The effect of rare earth(RE) additives on the quality of brush plated coating was studied by adding RE into brush plating solution. The results show that RE make the surface smooth and shiny, reduce residual stress within the coating and reinforced bond, and increase the wearability and corrosion resistance.

Probe into deposition mechanism of double pulse electrodepositing Ni-W-P matrix composite coatings containing CeO_2 and SiO_2 nano-particles

Ni-W-P matrix composite coatings reinforced by CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by double pulse electrodeposition and the deposition mechanism was discussed.The results showed that the composite coatings with amorphous structure were obtained as-deposited.The initial growth behavior had alternatives and the nucleation was inhomogeneous because of obvious composition fluctuation.With the pulse deposition time increasing,some pearlite microstructures of the substrate were covered by some deposits and the composition fluctuation disappeared.Forward pulse currents promoted to form a great number of atomic beams composed of Ni,W and P atoms or CeO2 and SiO2 nano-particles as the core,which inhabited the growth of atomic beams.Reverse pulse currents eliminated concentration polarization and dissolved some surface boss of atomic beams.The solution of W and P atoms within Ni grains and embedding of CeO2 and SiO2 nano-particles within Ni-W-P matrix metal made atomic arrangement disordered.Finally,the atomic beams grew to amorphous small particles.

Effect of gadolinium doping on phase transformation and microstructure of Gd_2O_3-Y_2O_3-ZrO_2 composite coatings prepared by electrophoretic deposition

4 mol.% Y203 stabilized ZrO2 （YSZ） doped with various quantifies of Gd203 （G-YSZ） ceramic comings were synthesized by electrophoretic deposition method, and followed by vacuum sintering and isothermally annealing at 1000 ℃ for different durations. X-ray diffraction （XRD） was used to investigate their phase composition. Scanning electron microscopy （SEM） was employed to examine their microstructure, while energy dispersive X-ray spectrometer （EDS） was used to assess composition of the composite coatings. The results indicated that YSZ coating was composed of tetragonal and monoclinic phase after vacuum sintefing at 1000 ~C for 2 h under vacuum （〈103 Pa）. G-YSZ composite coatings were composed of tetmgonal, monoclinic phase and a small amount of Gd2Zr207 phase after vacuum sintering at 1000 ℃ for 2 h, whereas the content ofmonoclinic phase in G-YSZ composite coatings in- creased with increasing Gd203 concentration. It was found that G-YSZ composite coatings were composed of tetragonal ZrO2 phase, monoclinic ZrO2 phase and cubic phase, whereas Gd2Zr207 phase disappeared, after G-YSZ composite coatings were isothermally annealed at 1000 ℃ in air for 100 h. A detailed description of the results and their discussion was presented in the paper.