Microstructural characterization and corrosion resistance of Ni–Zn–P alloys electrolessly deposited from a sulphate bath

Electroless Ni–Zn–P alloy coatings were obtained on an iron substrate from a sulfate bath at various pH values. The effects of changes in bath pH on alloy composition, morphology, microstructure and corrosion resistance were studied. Scanning electron microscopy was performed to observe the morphological change of the deposits with bath pH. Coating crystallinity was investigated by grazing incidence asymmetric Bragg X-ray diffraction and transmission electron microscopy. A transition from an amorphous to polycrystalline structure was observed on increasing the bath alkalinity, and thus decreasing the phosphorus content of the alloys. A single crystalline phase corresponding to face-centred-cubic nickel was identified in the alloys obtained from a strong alkaline solution. An increase in zinc percentage up to 23% in the deposits does not change the f.c.c. nickel crystalline structure. Corrosion potential and polarization resistance measurements indicated that the corrosion resistance of electroless Ni–Zn–P alloys depends strongly on the microstructure and chemical composition. The deposits obtained at pH 9.0–9.5 and with 11.4–12.5% zinc and 11.8–11.2% phosphorous exhibited the best corrosion resistance.     

Electroless deposition of Ni–B, Co–B and Ni–Co–B alloys using dimethylamineborane as a reducing agent

Fundamental aspects of electroless Ni–B, Co–B and Ni–Co–B alloys have been systematically examined. The composition, crystal structure and deposition rate of the alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid), bath pH and Ni2+/Co2+ ratio. Changes in the deposition rate and metallurgical features of the alloys induced by the change in plating parameters are discussed, based on electrochemical polarization data and the formation enthalpy of the nickel and cobalt borides.     

Magnetothermal study of nanocrystalline particle formation in amorphous electroless Ni–P and Ni–Me–P alloys

The microstructure of amorphous Ni–P and Ni–Me–P materials and especially its change during the heat treatment is of great importance for their magnetic, mechanical and corrosion behavior. A new magnetic phase analysis method (magnetothermal) is presented that reveals the precipitation of nanoparticles with strong magnetic properties during phase transformation upon heat treatment. It is applied to electroless Ni–P, Ni–Cu–P and Ni–Sn–P amorphous alloys. The results acquired by this method are compared with data obtained by differential scanning calorimetry, as well as by microhardness measurements using identical heat treatment in all three cases. Due to the high sensitivity of the magnetothermal method a more detailed picture of the precipitation processes in Ni–P alloys is obtained and the new information is discussed. Magnetothermal measurements reveal several stages of precipitation of a phase with strong magnetic properties. This phase is Ni in the Ni–P alloy, and Ni(Me) solid solution in the Ni–Me–P alloys. Though Sn has a stronger effect on the Ni magnetization, Cu is more effective in preventing the appearance of high magnetization in a thermally treated Ni–Cu–P alloy. This is due to Cu incorporation in Ni particles in a quantity above four times larger than Sn.     

Ultrafine Ni–Co–W–B amorphous alloys and their activities in benzene hydrogenation to cyclohexane

Quaternary Ni–Co–W–B amorphous alloys were prepared by chemical reduction of the aqueous solution of nickel and cobalt salts and sodium tungstate with potassium borohydride. The catalytic activities of the as-prepared materials were measured through liquid phase hydrogenation of benzene under moderate pressure. In comparison with Ni–Co–B, the as-prepared Ni–Co–W–B amorphous alloys showed superior activity, attributable to the promoting effect of tungsten on the microstructure of the alloys as revealed by XPS, XRD and DSC measurements.     

Electrodeposition of Co–Ni alloys

Cobalt–nickel alloys were electrodeposited in an acid bath containing various ratios of metallic cations. The effect of the plating variables on the composition and morphology of the deposits obtained on vitreous carbon electrodes was investigated. Different proportions of the two metals can be obtained by using different deposition parameters, but at all Co(ii)/Ni(ii) ratios studied, preferential deposition of cobalt occurs and anomalous codeposition takes place. For a fixed solution composition, the nickel content in the deposit is enhanced by increasing the deposition potential. More homogeneous and fine-grained deposits can be obtained by increasing the cobalt(ii)/nickel(ii) ratio in solution and by ensuring that deposition takes place slowly. Deposits of constant composition throughout the depth of the deposit can be obtained only by stirring the solution during the deposition. In addition, the solution must be stirred in order to minimize the increase in local pH and to prevent hydroxide precipitation. An attempt was made to explain the anomalous codeposition. The results suggest the following sequence of events: first, nickel is deposited; then, cobalt(ii) adsorbs onto the freshly deposited nickel and begins to be deposited. The cobalt(ii) adsorption inhibits subsequent deposition of nickel, although it does not block it completely.     

Electrochemical characterization of Ni–P and Ni–Co–P amorphous alloy deposits obtained by electrodeposition

Ni–P and Ni–Co–P amorphous alloy deposits were obtained by electrodeposition at 80 °C on carbon steel substrates. The influence of the electrolyte Co²⁺ concentration and of applied current density was investigated. The corrosion behaviour of amorphous and crystalline deposits was evaluated by polarization curves and electrochemical impedance spectroscopy in NaCl 0.1 M solution at room temperature. Impedances were measured for samples under total immersion (free potential against time) and for polarized samples in predefined regions of the polarization curves. It was found that the alloy deposit composition is highly affected by the composition of the electrolyte but displays no significant dependence on applied current density. The results showed that the presence of Co on Ni–P amorphous alloys improves the deposit performance in the studied corrosive medium. It was also verified that the amorphous structure provides higher corrosion resistance to both Ni–P and Ni–Co–P alloys.     

Ni—Fe—P,Ni—W—P合金与镀层性能

本文通过研究非晶态Ｎｉ－Ｐ合金电镀体系加入少量Ｆｅ、Ｗ等元素对镀层性能的影响,发现非晶态Ｎｉ－Ｐ合金镀层中引入少量Ｆｅ、Ｗ元素后既能保持镀层优良的耐蚀性又可大大提高镀层的硬度和耐磨性。     

Ni–Mo and Ni–W sulfide catalysts prepared by decomposition of binary thiometallates

Ni–Mo and Ni–W sulfide catalysts with atomic ratio R = 0.5 (Ni/(Ni + M), with M = Mo or W) prepared by decomposition of Ni-impregnated thiometallates were evaluated in the reaction of thiophene hydrodesulfurization. Catalysts derived from impregnated thiometallates (DTI samples) presented improved catalytic activity and higher synergistic effect than catalysts prepared by co-precipitation (HSP samples) despite the fact that co-precipitated catalysts showed larger surface area. Structure characterization by high-resolution electron microscopy (HREM) and X-ray diffraction (XRD) revealed different crystalline phases in DTI and HSP catalysts. A mixture of phases (MS₂, NiS_1.03 and MO₂) was observed in catalysts obtained by co-precipitation. Only the poorly crystalline MS₂ phase was observed in DTI catalysts suggesting that the Ni promoter is very well dispersed on the chalcogenide structure.     

Electroless deposition of ternary Ni–P alloy coatings containing tungsten or nano-scattered alumina composite on steel

The performance of ternary electroless deposited Ni–P–W and Ni–P–alumina composite coatings on low carbon steel substrates was studied. The effect of experimental parameters, such as temperature, pH, nickel sulfate concentration, sodium hypophosphite concentration, sodium citrate concentration, and deposition time on the deposition rate were investigated. The coating brightness, coherence, and uniform surface distribution were improved due to addition of W and alumina. The coating performance was evaluated based on the wear-resistance, micro-hardness, and corrosion resistance. The Ni–P–W ternary alloy coatings showed the highest micro hardness, wear-resistance, brightness, and corrosion resistance. The improvement in the performance of Ni–P–W coatings can be explained by the formation of a tungsten phosphide phase.     

Normal and anomalous codeposition of Zn–Ni alloys from chloride bath

The codeposition of Zn–Ni alloys from chloride bath has been studied by means of potentiostatic electrodeposition in the potential range –700 to –1100mV vs Ag/AgCl, where both normal and anomalous codeposition occurs. Deposition of alloys of different composition, morphology and structure, depending on the cathodic potential, was found. Analysis of the partial current densities showed that the production of nickel rich alloys in the potential range –700 to –900mV is due to the underpotential reduction of zinc, driven by nickel ion discharge. Morphological and microstructural analyses showed that these alloys have the face-centred-cubic structure of nickel ( phase) and that the addition of zinc in the nickel lattice causes internal stresses in the deposits, which are prevalently amorphous. At potentials more negative than –910mV, corresponding to the equilibrium potential of the zinc rich phase deposition, the rate of deposition of the phase decreases and the further increase in deposit zinc content leads to the formation of the phase, with a decrease in internal stress. In this range of potential, zinc and nickel reduction can occur separately, according to their respective exchange current densities.     

Electrodeposition of high phosphorus Ni–P alloys in emulsified supercritical CO2 baths

The use of an emulsified supercritical CO₂ (sc-CO₂) bath for electrodeposition of Ni–P alloys was attempted. The material characteristics of the deposits with various P contents, formed by varying the electrolyte composition and deposition current density, were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) for surface morphology and chemical composition and crystal structure analyses. The experimental results showed that the presence of sc-CO₂ in the electrodeposition bath could substantially improve the microhardness and the corrosion performance of the as-deposited Ni–P coatings. The roles of phosphorus and carbon in modifying the material properties of the deposits are discussed in detail.     

Machine learning-assisted characterization of electroless deposited Ni–P particles on nano/micro SiC particles

In this experiment, Ni–P nanoparticles were deposited (ED) on SiC micro- and nanoparticles with different parameters. Our goal was to successfully prepare metal deposits and develop an effective method for comparing and evaluating the various procedures.During the experimental work, a three-step electroless Ni–P coating process was applied with different concentrations. The coated SiC particles were examined by scanning electron microscopy (SEM). The mass-specific surface area (SSA) of the coated SiC was measured by the Brunauer‒Emmett‒Teller (BET) method, while the volumetric-specific surface area (VSSA) was also calculated. The adhesion between the metal and the ceramic particle was analyzed by X-ray photoelectron spectroscopy (XPS).An image processing macroprogram was created (with a machine learning-based Trainable Weka Segmentation algorithm) to segment the SEM images of the ED metal particles to calculate the specific surface area (S_V).     

Thermal effects of a laser beam on the electrodeposition of Ni–P alloys

The paper deals with the effects of an incident laser beam on electrodeposition of Ni–P alloys from dilute acetate solutions. The kinetics of separate reductions of Ni2+ and H2PO?2 species were first investigated by linear sweep voltammetry, varying the hypophosphite concentration and the solution temperature: comparison of the kinetically limited current densities of the two reductions suggested that increasing temperature might reduce the significance of P codeposition. This tendency was confirmed by deposition runs carried out at controlled current. Deposition performance was discussed in terms of faradaic yield and deposit properties, namely P content together with the aspect and the structure of the alloys. Use of a continuous or pulsed laser beam was shown to reduce the P content in the deposit at high current densities; in some cases, amorphous structures were replaced by more crystalline forms with assistance of a laser beam.     

Synthesis,characterization, and infrared-emissivity study of Ni–P–CB nanocomposite coatings by electroless process

The Ni–P–CB (carbon black) nanocomposite coatings have been successfully deposited on an ABS plastic matrix via electroless plating process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectrometry techniques were employed to examine the surface morphology and structure of the as-plated coating. Energy dispersive spectroscopy (EDS) was adopted to obtain the component analysis of the Ni–P–CB composite coating, and the infrared emissivity of the coating was determined by the IRE-I Infrared Emissometer. SEM and XRD results indicated that the nanoparticles were dispersed homogeneously in the Ni–P coating; the result of EDS showed that the increased rate of CB content is in correspondence with its concentration. In the case that CB concentration is lower than 4 g/L, the increase rate is sharp, whereas when the concentration is higher than 4 g/L, the increase rate is reduced significantly. Furthermore, study of infrared emissivity shows that the nanocomposite coatings possessed low emissivity value. A comparison of the infrared emissivity dependence on surface resistivity obtained from the analysis of the experimental results and those calculated using the Hagen–Rubens relation indicates that the Hagen–Rubens relation is good for modeling the infrared emissivity of the Ni–P–CB nanocomposite coatings.     

Characterisation of electrodeposited nanocrystalline Ni–Mo alloys

Ni–Mo nanocrystalline layers were electrodeposited using direct current from citrate–ammonia solutions. The quartz crystal microbalance investigation confirms that the discharge process starts with hydrogen evolution before the onset of the alloy deposition. The grain size was estimated from X-ray line broadening. It decreases when the molybdenum content is increased. It is smaller for layers deposited at pH 9.5 than 8.5. The microhardness exhibits a maximum close to 800 Vickers for _Mo around 17 wt%. For higher _Mo a softening is observed showing a deviation from Hall-Petch behaviour due to small grain size. In deaerated hydrochloric solutions, the layers show a large passivation domain without any pitting. The corrosion currents as well as the passivation currents, higher than for the bulk Hastelloy B alloy, decrease when _Mo is increased.     

Influence of a Zwitterionic Surfactant on the Surface Properties of Electroless Ni–P Coating on Mild Steel

3-(N,N-Dimethyl myristyl-ammonio) propane sulfonate zwitterionic surfactant (C14-SB) which possessed both positive and negative charges was evaluated in the electroless Ni–P coating process. It was observed that the deposition rate, morphology and microhardness of the deposits were enhanced by the addition of C14-SB surfactant. The excess attractive forces from the negative head of C14-SB were strong enough to draw metallic nickel particles towards the substrate. Ni particles attempting to deposit on the electrolyte container were eliminated by the repulsive force from the positive head of the surfactant monomers. Thus, the deposition rate of the coating process was improved. The surfactant at its critical micelle concentration (CMC) doubles the deposition rate when compared to the substrate without surfactant. In addition, the microhardness of the deposit at the surfactant CMC increased by 62 %. The corrosion rate of the substrate without surfactant was 7.15 mpy, while it was 3.97 mpy for the substrate deposited with C14-SB zwitterionic surfactant at the CMC.     

Dual-grained (Ti,W)C–Ni cermets by two-step carbonization: Hot isotropic press sintering of NiTiW alloys and colloidal graphite

Reactive sintering of crushed metals and carbon is advantageous for preparing toughened complete solid-solution cermets (CSCs). Here, dual-grained (Ti_0.6, W_0.4)C–18Ni cermets were prepared using a two-step carbonization method. High-energy milling of Ni–Ti–W–C (Ni(Ti_0.6, W_0.4)₄C) mixture afforded NiTiW solid solution, which was then transformed into Ni₆W₆C by heating at 1250°C. Twinned (Ti, W)C platelets were formed by the carbonization of Ni₂W₄C during liquid sintering. W atoms that accumulated in the (111) planes of TiC promoted the {111} twin formation, leading to sandwich-type (Ti, W)C platelets. Dense (Ti_0.6, W_0.4)C–18Ni cermets were obtained by hot isostatic press sintering in Ar with satisfactory Hv of 12.8 ± 0.2 GPa, high strength of 1960 ± 84 MPa and toughness of 15.80 ± 0.6 MPa·m^1/2. A higher sintering temperature or graphite content accelerated the carbonization, resulting in coarser platelets with decreased aspect ratio. This study provides a new approach to modify the microstructure of CSCs and a method for preparing dual-grained cermets.     

Electrodeposition of Ni–Co alloys from sulfamate baths

The paper describes the results of electrochemical investigations of Ni–Co deposition from a sulfamate bath in the presence of boric acid and two additives. The individual deposition of nickel was shown to be partly inhibited by the adsorption of sulfamate ions at low polarization; such inhibition was not observed for cobalt. The introduction of saccharin at 100 ppm, with a wetting agent seems to hinder sulfamate adsorption and Ni deposition departs at less cathodic potentials. The presence of cobalt has no effect on nickel deposition, whereas cobalt deposition is hindered by the presence of nickel in the bath. Galvanostatic deposition was carried out at the surface of a RDE and with a rotating cylinder Hull cell. At low current densities deposits with a Co content of approx. 40% were produced, but this content was shown to decrease with the applied current density. Examination of experimental data showed that cobalt deposition is diffusion-controlled and that Co content decreases with the applied current density relative to the limiting current density.     

Pulse current electrodeposition and corrosion properties of Ni–W alloy coatings

Ni–W alloy coatings were prepared on a mild steel substrate by means of pulse current (PC) and compared to the coatings electrodeposited by direct current (DC). In particular the study dealt with the influence of the frequency using pulse current on the surface morphology while maintaining a constant duty cycle. A constant charge for DC and PC electrodeposition of Ni–W alloy coatings was used. The morphology of the coatings was explored by scanning electron microscopy and the composition of the coatings was analysed by X-ray powder diffraction and energy dispersive X-ray analysis. Corrosion resistance of Ni–W alloy coatings was investigated by potentiodynamic polarization in a chloride medium. The corrosion products were analysed by Raman spectroscopy. It was found that the temperature of the electrolysis affects current efficiency of the DC and PC electrodeposition. The frequency of pulse electrodeposition alters the morphology of the Ni–W alloy coatings. There was evidence of the positive influence of increased tungstate concentration in the electrolyte on corrosion resistance of the Ni–W alloy coatings.