Corrosion behavior of electroless Ni–P/TiO2 nanocomposite coatings

Composite Ni–P/nano‐TiO₂ coatings were prepared by simultaneous electroless deposition of Ni–P and nano‐TiO₂ on a low carbon steel substrate. The deposition was carried out from stirred solutions containing suspended nano‐TiO₂ particles. The Ni–P and Ni–P/nano‐TiO₂ coatings before and after heat treatment were characterized by X‐ray diffraction, scanning electron microscopy and energy dispersive X‐ray spectroscopy. The micro‐structural morphologies of the coatings significantly varied with the nano‐TiO₂ content. The corrosion resistance of as‐plated and heat‐treated Ni–P and Ni–P/nano‐TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5% NaCl solution. Ni–P/nano‐TiO₂ coating exhibited superior corrosion resistance over Ni–P coating. Copyright © 2015 John Wiley & Sons, Ltd.     

Superlubricity behaviors of Si3N4/DLC Films under PAO oil with nano boron nitride additive lubrication

The tribological properties of Si₃N₄ ball sliding against diamond‐like carbon (DLC) films were investigated using a ball‐on‐disc tribometer under dry friction and oil lubrications, respectively. The influence of nano boron nitride particle as lubricant additive in poly‐α‐olefin (PAO) oil on the tribological properties of Si₃N₄/DLC films was evaluated. The microstructure of DLC films was measured by Raman spectroscopy and X‐ray photoelectron spectroscopy. The experimental results show coefficient of friction (COF) of Si₃N₄/DLC films was as low as 0.035 due to the formation of graphite‐like transfer films under dry friction condition. It also indicates that the tribological properties of Si₃N₄/DLC films were influenced significantly by the viscosity of oil and the content of nano boron nitride particle in PAO oil. COF increases with the viscosity of PAO oil increasing. Si₃N₄/DLC films exhibit the superlubricity behaviors (μ=0.001 and nonmeasurable wear) under PAO 6 oil with 1.0 wt% nano boron nitride particle lubrication, indicating that the improved boundary lubrication behaviors have indeed been responsible for the significantly reduced friction. Nano boron nitride additive is used as solid lubricant‐like nano scale ball bearing to the pointlike contact and a soft phase bond with the weak van der Waals interaction force on the contact surface to improve the lubrication behaviors of Si₃N₄/DLC films. The potential usefulness of nano boron nitride as lubricant additive in PAO oil for Si₃N₄/DLC films has been demonstrated under oil lubrication conditions. The present work will extend the wide application of nano particle additive and introduce a new approach to superlubricity under boundary lubrication in future technological areas. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Cu in electroless Ni–Cu–P coating on passivation process

Electroless Ni–P and Ni–Cu–P coatings were passivated by chromate conversion treatment respectively. The anticorrosive performances of passivated coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The passivated Ni–Cu–P coating exhibited a high corrosion resistance with the i_corr of 0.236 μA/cm,² while the value of passivated Ni–P coating was only 1.030 μA/cm,² indicating the passive film could improve the corrosion resistance of Ni–Cu–P coating to a significant extent. High‐resolution X‐ray photoelectron spectroscopy was used to determine the chemical states of elements detected in the passive film. Compared with passivated Ni–P coating, the passive film on Ni–Cu–P coating exhibited a higher ratio of Cr₂O₃ to Cr(OH)₃ with the value of 72:28, which was the main factor for passivated Ni–Cu–P coating showing excellent corrosion resistance. The effect of Cu in electroless Ni–Cu–P coating on passivation process was discussed by the contrast experiment. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of SiC/nano‐CeO2 on wear resistance and microstructures of Ti3Al/γ‐Ni matrix laser‐cladded composite coating on Ti–6Al–4V alloy

The Ti–6Al–4V alloy is an important aviation material, but has a poor resistance to slide wear. Laser cladding of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ preplaced powders on the Ti–6Al–4V alloy can form the Ti₃Al/γ‐Ni matrix composite coating, which improves the wear resistance of the substrate. In this study, the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ laser‐cladded coating was researched by means of X‐ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The experimental results indicate that under the action of SiC/nano‐CeO₂, this composite coating exhibited a fine microstructure. Furthermore, the proper content of nano‐CeO₂ decreased the crack tendency. The results above indicated that, it is feasible to improve the tribological property of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ laser‐cladded coating by adding of SiC/nano‐CeO₂. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of P codeposition on the structure and microhardness of Co–W coatings electrodeposited from gluconate bath

Effects of addition of P to Co–W coatings from gluconate bath using direct current (DC) and pulse current (PC) methods have been investigated in this study. Co–W–P coatings with different P concentrations are prepared by varying hypophosphite concentration in the bath. Current efficiency of the Co–W–P electrodeposition is lower than that for Co–W coatings. Increase in NaH₂PO₂ concentration increases the cobalt content significantly and decreases the tungsten content drastically. Co–W–P coatings display ‘cauliflower‐like’ morphology and roughness of the coatings increases with increasing P content. As‐deposited Co–W–P deposits are amorphous while heat treatment at different temperatures has rendered them crystalline with the precipitation of stable species like, Co₃W, Co₂P, etc. Unlike Co–W coatings, Co–W–P shows two‐step crystallization in differential scanning calorimetry (DSC) and on heat treatment, which is similar to the behavior of Co–P electrodeposited from gluconate baths. Moreover, inclusion of phosphorous and heat treatment have led to significant increase in microhardness of the Co–W–P coatings. X‐ray photoelectron spectroscopy (XPS) studies provide a detailed insight into the nature of Co, W and P species in as‐deposited and sputtered coatings. Microhardness of the heat‐treated coatings is higher than the as‐deposited counterparts and is comparable with that of hard chromium. Copyright © 2016 John Wiley & Sons, Ltd.     

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV₁₀₀ at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV₁₀₀. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.     

Narrowly dispersed micrometer‐sized composite spheres based on diazonium–polystyrene

Diazonium group–substituted polystyrene (PS–N) micrometer‐sized spheres with narrow distribution were prepared from highly crosslinked polystyrene particles. Then a composite sphere was prepared with the micro‐PS–N sphere as core and submicrometer‐sized poly(styrene‐methyl methacrylate‐acrylic acid) [P(S‐MMA‐AA)] colloids or nanometer‐sized SiO₂ particles as shell via columbic interaction. The ionic linkages between the core and shell convert to covalent bonds in the thermal treatment process. As a result, the composite sphere becomes very stable toward polar solvents as well as toward ultrasonic treatment. A hollow SiO₂ micrometer‐sized sphere then was achieved by removing the core under sintering conditions (700 °C). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4284–4288, 2004     

Sol-enhanced triple-layered Ni–P–TiO2 composite coatings

A novel coating process, TiO₂ sol enhanced Ni–P electroless composite coatings on carbon steel, is presented in this paper. Transparent TiO₂ sol was added into the electroless plating Ni–P solution at a controlled rate, leading to in situ synthesis of a triple-layered Ni–P–TiO₂ composite coating, i.e. the inner, transition and outer layers. The inner layer has a thickness of ~3 μm, mainly composed of Ni and P elements. The transition layer of the coating has a relatively high content of TiO₂ with a thickness of ~500 nm and a columnar-structure. The thickness of the outer layer was ~7 μm, with almost evenly distributed Ni, P and TiO₂. The hardness and Young’s modulus of the composite coating were greatly improved to ~10 and ~200 GPa, respectively, compared to ~6 and ~110 GPa of the traditional Ni–P coating.     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

Sliding friction and wear behaviors of plasma sprayed aluminum–bronze coating in artificial seawater

The friction and wear behaviors of plasma sprayed aluminum–bronze (CuAl) coating sliding against silicon nitride (Si₃N₄) in artificial seawater were investigated and compared with those in pure water and dry sliding. The morphologies of the worn surfaces were analyzed by three‐dimensional non‐contact surface mapping and scanning electron microscopy. Moreover, chemical states of the tribochemical products of CuAl/Si₃N₄ in seawater were characterized by X‐ray photoelectron spectroscopy. Results show that the plasma sprayed CuAl coating possessed a specific wear rate (in order of 10^?7 mm³/Nm) in seawater more than 600 times smaller than that in dry sliding due to the great alleviation in abrasion wear and splats delamination. Besides, the CuAl/Si₃N₄ had a friction coefficient of 0.06 in seawater, significantly lower and more stable than those in pure water and dry sliding. The tribochemical products of CuAl/Si₃N₄ in seawater, which were proved to be silica, alumina, and their hydrates, transformed into a loosened wear‐debris layer under the coagulation effect of the seawater and dominated the excellent lubrication state in artificial seawater. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanical and corrosion behavior of amorphous and crystalline electroless Ni–W–P coatings

Two types of electroless Ni–W–P coatings: nanocrystalline with low P and amorphous with higher P content are investigated. Scanning probe microscopy is applied to study their morphology. Textured nanocrystalline coatings consist of coarse pyramids built of nanometer thick lamellas. The surface morphology of amorphous coatings is much finer and uniform. Nanohardness of all coatings depends on W content. Microhardness is increasing during the heat treatment up to 350 °C due to nickel phosphide precipitation affected by tungsten also. The wear resistance of nanocrystalline Ni–W–P coatings is much higher than that of amorphous in spite of the similar tungsten content in both. Lower corrosion resistance of amorphous Ni–W–P coatings is found by weight loss method during long-term immersion in 5 % NaCl. Electrochemical tests by potentiodynamic polarization curves in two model corrosion media—solutions of 0.5 M H₂SO₄ and 5 % NaCl—are performed. The corrosion of bi-layered Ni–W–P/Ni–P and Ni–W–P/Ni–Cu–P deposits on mild steel is also investigated. The results prove that an electroless Ni–W–P coating on mild steel extremely improves its mechanical and corrosion behavior. It is demonstrated that in addition to deposit’s structure and composition, the distribution and chemical state of alloy ingredients are also responsible for its properties.     

Synthesis and performance of electroless Ni–P–TiCN composite coatings on Al substrate

Electroless Ni–P and Ni–P–TiCN composite coatings have been deposited successfully on Al substrates. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) techniques were applied to study the surface morphology and the chemical composition of the deposited films. Moreover, X‐ray diffraction (XRD) proved that Ni–P and Ni–P–TiCN deposits have amorphous structures. The properties of Ni–P–TiCN/Al composite films such as hardness, corrosion resistance and electrocatalytic activity were examined and compared with that of Ni–P/Al film. The results of hardness measurements reveal that the presence of TiCN particles with Ni–P matrix improves its hardness. Additionally, the performance against corrosion was examined using Tafel lines and electrochemical impedance spectroscopy techniques in both of 0.6 M NaCl and a mixture of 0.5 M H₂SO₄ with 2 ppm HF solutions. The results indicate that the incorporation of high dispersed TiCN particles into Ni–P matrix led to a positive shift of the corrosion potential and an increase in the corrosion resistance for all aluminum substrates after their coating with Ni–P–TiCN. In addition, Ni–P–TiCN/Al electrodes showed a higher electrochemical catalytic activity and stability toward methanol oxidation in 0.5 M NaOH solution compared with that of Ni–P/Al. Copyright © 2014 John Wiley & Sons, Ltd.     

Zn–HA–TiO2 nanocomposite coatings electrodeposited on a NiTi shape memory alloy

In this work, zinc–hydroxyapatite (Zn–HA) and zinc–hydroxyapatite–titania (Zn–HA–TiO₂) nanocomposite coatings were electrodeposited onto a NiTi shape memory alloy, using a chloride zinc plating bath. The structure of the composite coatings was characterized by X‐ray diffraction, scanning electron microscopy and high‐resolution transmission electron microscopy. According to the results, the Zn–HA–TiO₂ coating exhibited a plate‐like surface morphology, where the addition of the nanoparticles caused to an increase in roughness. It was also found that due to applying a proper stirring procedure during co‐deposition, a homogenous dispersion of the nanoparticles in the coatings was achieved. Also, the addition of the TiO₂ nanoparticles to the Zn–HA–TiO₂ coating enhanced the microhardness and wear resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Magnetic Properties of Ni‐Co‐B Coated Carbon Nanofibers

Continuous and uniform Ni‐Co‐B coatings were successfully deposited onto carbon nanofibers via electroless plating. SEM images of the prepared Ni‐Co‐B coated carbon nanofibers were presented. The magnetic properties of the coated carbon nanofibers were investigated. The CoSO₄/(CoSO₄+NiSO₄) ratio in the electroless bath has obvious influence on the coercivity and residual magnetic flux density of the Ni‐Co‐B coated carbon nanofibers.     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Structure–tribological property relationship of nanoparticles and short carbon fibers reinforced PEEK hybrid composites

In a previous work, the roles of low‐loading, that is, 1 vol %, nano‐SiO₂ particles on the tribological behavior of short carbon fibers (SCFs)/polytetrafluoroethylene (PTFE)/graphite filled polyetheretherketone (PEEK) were studied. In the present work, the effects of nanoparticle content, varying from 1 to 4 vol %, on the structure and the tribological performance of the composite was investigated. The polished cross sections of the composites were inspected using a scanning electron microscope (SEM). The incorporated nanoparticles significantly reduce the friction coefficients of the composite. With low pressure‐sliding velocity (pv) factors, nanoparticle agglomerates seem to exert an abrasive effect on SCF, and thereby lead to high wear rates. Under such conditions, an increase in nanoparticle content decreases the wear resistance. With high pv factors, the nanoparticles remarkably improve the wear resistance of the composite and the nanoparticle contents do not play an important role on the wear resistance. The worn surfaces, transfer films and wear debris of the composites were analyzed. The tribological mechanisms were discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 801–811, 2010     

The evolution of growth morphology and corrosion behavior of electrodeposited Ni–P coatings on alumina borate whisker‐reinforced pure aluminum composite

The Ni–P alloy coatings were obtained on alumina borate whisker‐reinforced pure aluminum composite by electro‐deposition. The initial electro‐deposition behavior of the Ni–P alloys on the composite and pure aluminum was studied, respectively. It was found that the composition and the morphology of materials had a distinct effect on the initial electro‐deposition behavior of the Ni–P alloys. The Ni–P alloy coatings preferred to nucleate at the composite as compared with the pure aluminum. Moreover, the Ni–P particles were prone to deposit at the whisker/Al interface in the composite. The Ni–P coatings were barely depositing upon the surface of whisker during the plating process. As the deposition time increased, the Ni–P particles that were deposited on the surface of the composite grew gradually. These Ni–P particles linked to each other and eventually covered the whisker surface. Moreover, it can be found that the surfaces of the composite were gradually covered by Ni–P coatings and the anticorrosion performance of the coated composite increased remarkably with the increase in the deposition time. When the deposition time is 60 min, only the Ni–P diffraction peak could be detected. In this case, the coated composite had significantly better corrosion resistant, which is attributed to the surface of composite was perfectly covered by the Ni–P coatings. Copyright © 2012 John Wiley & Sons, Ltd.     

Optimization of electroless Ni?P coatings based on multiple roughness characteristics

This paper presents an experimental study of roughness characteristics of electroless Ni? P coatings. Optimization of coating process parameters is done with multiple surface roughness characteristics based on Taguchi method coupled with grey relational analysis. Experiments are carried out by utilizing the combination of process parameters based on L₂₇ Taguchi orthogonal design with three process parameters, viz. bath temperature, concentration of nickel source solution and concentration of reducing agent. Results show that concentration of the reducing agent and its interaction with concentration of the nickel source solution have significant influence in controlling the roughness characteristics of electroless Ni? P coating. Grey‐based Taguchi method is found to optimize the coating parameters fairly well. The surface morphology and composition of coatings are also studied with the help of scanning electron microscopy, energy dispersed X‐ray analysis and X‐ray diffraction analysis. No significant change in nickel and phosphorous content of coatings occurs with annealing. The Ni? P deposit is nanocrystalline in the as‐plated condition, and upon heat treatment at 400 °C it produces Ni₅P₂, Ni₂P, and NiP₂ as major compound constituents. Copyright © 2008 John Wiley & Sons, Ltd.     

Neue Vertreter des Er6[Si11N20]O‐Strukturtyps Hochtemperatur‐Synthesen und Kristallstrukturen von Ln(6+x/3)[Si(11–y)AlyN(20+x–y)]O(1–x+y) mit Ln = Nd,Er, Yb,Dy und 0 ≤ x ≤ 3, 0 ≤ y ≤ 3

New Representatives of the Er₆[Si₁₁N₂₀]O Structure Type. High‐Temperature Synthesis and Single‐Crystal Structure Refinement of Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) with Ln = Nd, Er, Yb, Dy and 0 ≤ x ≤ 3, 0 ≤ y ≤ 3 According to the general formula Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) (0 ≤ x ≤ 3, 0 ≤ y ≤ 3) four nitridosilicates, namely Er₆[Si₁₁N₂₀]O, Yb_6.081[Si₁₁N_20.234]O_0.757, Dy_0.33Sm₆[Si₁₁N₂₀]N, and Nd₇[Si₈Al₃N₂₀]O were synthesized in a radiofrequency furnace at temperatures between 1300 and 1650 °C. The homeotypic crystal structures of all four compounds were determined by single‐crystal X‐ray diffraction. The nitridosilicates are trigonal with the following lattice constants: Er₆[Si₁₁N₂₀]O: a = 978.8(4) pm, c = 1058.8(3) pm; Yb_6.081[Si₁₁N_20.243]O_0.757: a = 974.9(1) pm, c = 1055.7(2) pm; Dy_0.33Sm₆[Si₁₁N₂₀]N: a = 989.8(1) pm, c = 1078.7(1) pm; Nd₇[Si₈Al₃N₂₀]O: a = 1004.25(9) pm, c = 1095.03(12) pm. The crystal structures were solved and refined in the space group P31c with Z = 2. The compounds contain three‐dimensional networks built up by corner sharing SiN₄ and AlN₄ tetrahedra, respectively. The Ln³⁺ and the “isolated” O^2– ions are situated in the voids of the structures. According to Ln_(6+x/3)[Si_(11–y)Al_yN_(20+x–y)]O_(1–x+y) an extension of the Er₆[Si₁₁N₂₀]O structure type has been found.     

Li4Ca3Si2N6 and Li4Sr3Si2N6 – Quaternary Lithium Nitridosilicates with Isolated [Si2N6]10– Ions

The isotypic nitridosilicates Li₄Ca₃Si₂N₆ and Li₄Sr₃Si₂N₆ were synthesized by reaction of strontium or calcium with Si(NH)₂ and additional excess of Li₃N in weld shut tantalum ampoules. The crystal structure, which has been solved by single‐crystal X‐ray diffraction (Li₄Sr₃Si₂N₆: C2/m, Z = 2, a = 6.1268(12), b = 9.6866(19), c = 6.2200(12) Å, β = 90.24(3)°, wR₂ = 0.0903) is made up from isolated [Si₂N₆]^10– ions and is isotypic to Li₄Sr₃Ge₂N₆. The bonding angels and distances within the edge‐sharing [Si₂N₆]^10– double‐tetrahedra are strongly dependent on the lewis acidity of the counterions. This finding is discussed in relation to the compounds Ca₅Si₂N₆ and Ba₅Si₂N₆, which also exhibit isolated [Si₂N₆]^10– ions.