Wear-resistant Ti–Al–Ni–C–N coatings produced by magnetron sputtering of SHS-targets in the DC and HIPIMS modes

The hard wear-resistant nanocomposite Ti–Al–Ni–C–N coatings were deposited by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) in the Ar, Ar+15%N_2, and Ar+25%N₂ atmospheres. The structure of coatings was analyzed using the X-ray diffraction analysis, glow discharge optical emission spectroscopy, and scanning electron microscopy. Mechanical and tribological properties were measured using the nanoindentation and scratch testing as well as by tribological testing using the “pin-on-disc” scheme. Electrochemical corrosion resistance and oxidation resistance of coatings were investigated. The results suggest that the coatings are based on the FCC phases TiCN and Ni₃Al with crystallites size ~3 and ~15 nm, correspondingly. DCMS coatings with optimal composition were characterized by hardness 34 GPa, stable friction coefficient <0.26 and wear rate <5 × 10^-6 mm³N^-1m^-1. Application of HIPIMS mode allowed the increase of adhesion strength, tribological properties and corrosion resistance of coatings.     

Zn–Ni/nano-TiO2 composite electrodeposits: surface modifications and protective properties

Zn–Ni composite coatings were obtained by electrochemical co-deposition of TiO₂ nano-particles (mean diameter 21 nm). Zn–Ni alloy coating was also produced under the same experimental conditions for comparison. The surface morphology, crystallographic structure, and the grain size of the deposits were investigated, along with the percentage of the embedded nano-particles in Zn–Ni matrix, as a function of concentration of TiO₂ nano-particles in the bath. As the titania incorporation percentage is increased, a grain refinement in the nanometer region was revealed followed enhanced microhardness values and an improvement of the content of the nickel in the alloy. Annealing of all coatings at 200 °C revealed the crystallization of the matrix accompanied by a decrease of microhardness followed by stability for 24 h. The corrosion behavior of Zn–Ni/nano-TiO₂ composite coatings with various amount of particle content was mainly studied by electrochemical impedance spectroscopy in 3 % NaCl. It was seen that Zn–Ni/nano-TiO₂ composite coatings exhibited higher corrosion resistances comparing to Zn–Ni alloy coating and corrosion protection improved with increasing nano-TiO₂ in coatings.     

Effects of duty cycle and pulse frequency on microstructures and properties of electrodeposited Ni–Co–SiC nanocoatings

In this study, Ni–Co–SiC nanocoatings were fabricated using pulse current electrodeposition (PCE) method. Effects of duty cycle and pulse frequency on surface appearance, microstructure, phase structure, wear behavior, and corrosion resistance of as-deposited Ni–Co–SiC nanocoatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, nanoindentation, and both wear and corrosion tests. Results indicate that numerous small-sized grains formed on Ni–Co–SiC nanocoatings at 20% duty cycle to provide smooth, uniform, and fine microstructures. The content of SiC nanoparticles in Ni–Co–SiC nanocoatings decreased from 11.2 wt% to 7.4 wt% as duty cycle increased from 20% to 60%. However, the content of SiC nanoparticles in Ni–Co–SiC nanocoatings increased from 6.3 wt% to 9.7 wt% as pulse frequency increased from 100 Hz to 300 Hz. Ni–Co–SiC nanocoatings prepared at pulse frequency of 300 Hz and duty cycle of 20% exhibited average microhardness of 934.4 Hv and average thickness of 43.2 μm. Weight loss of Ni–Co–SiC nanocoatings at 300 Hz was only 17.2 mg, indicating significant wear resistance. In addition, Ni–Co–SiC nanocoatings produced at duty cycle of 20% and pulse frequency of 300 Hz exhibited the maximum impedance, indicating optimal corrosion resistance.     

Effect of current density and deposition time on microstructure and corrosion resistance of Ni-W/TiN nanocomposite coating

Ni-W/TiN nanocomposite coatings were successfully prepared via pulse electroplating from an electrolyte containing suspended TiN nanoparticles. The effects of applied current density and deposition time on microstructure, morphology, composition, hardness and electrochemical behaviors of the obtained coatings were investigated. Results showed that the current density and deposition time affect remarkably the electrochemical co-deposition process and then the structure and characteristics of the composites. It illustrated that the nanocomposites are uniform, compact and crack-free. The nanocomposites prepared at I_a =?3?A?dm^?2 and t?=?20?min had the finest structure, showing a fine and smooth surface. EDS mapping and XPS spectra illustrated that the TiN nanoparticles had been homogeneously dispersed throughout the coating. 2.34?wt% TiN nanoparticles were embedded in Ni–W (68.56?wt% Ni and 29.1?wt%?W) alloy matrix at I_a=?3.0?A?dm^?2. The inclusion of TiN nanoparticles in Ni–W could promote the nucleation and cause a distinct microstructural change. The crystallite size was in the range of 11–15?nm. The average roughness value (R_a) is 65.7?nm and 73.8?nm for coating formed at 20?min and 40?min, respectively. The electrochemical measurements illustrated that I_a =?3–5?A?dm^?2 and t?=?40–60?min was the optimal operating parameters for the excellent anti-corrosion properties of Ni–W/TiN nanocomposites. The embedded TiN in Ni–W matrix could fill defects then improve its corrosion resistance. This electrodeposited Ni–W/TiN nanocomposites possess excellent hardness and superior corrosion resistance, and is expected to be applied in aggressive environment as a protective 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.     

Wet abrasive wear behavior of WC-based cermet coatings prepared by HVOF spraying

In this study, three kinds of WC-based cermet coatings including WC–CoCr coating, WC–Ni coating and WC–Cr₃C₂–Ni coating were prepared by the high-velocity oxygen-fuel (HVOF) spraying process. Scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and Vickers hardness tester were used to analyze the microstructure and mechanical properties of these coatings. The WC–CoCr coating presented the highest average microhardness of 1205 HV_0.3, and then followed by the WC–Cr₃C₂–Ni coating (1188 HV_0.3) and the WC–Ni coating (1105 HV_0.3). The abrasive wear behavior of the WC-based coatings under the conditions of different applied loads and sediment concentrations were studied by a wet sand-rubber wheel tester. The results indicated that the abrasive wear loss rates of all the coatings increased with the increment of applied load or sediment concentration. In addition, the coatings with higher microhardness appeared to have higher abrasive wear resistance. The abrasive wear resistance of the WC-based coatings was 4–90 times higher than that of AISI 304 stainless steel under the same testing condition. The abrasive wear mechanism of the WC-based coatings was deduced to be the extrusion and removal of binder phases, as well as the fragmentation and peel-off of hard phases.     

Selective area deposition of Tin–Nickel alloy coating – an alternative for decorative chromium plating

Sn–Ni alloy coatings on mild steel substrates produced by selective area deposition process with layer thickness of about 14 μm were investigated with regard to the structural and corrosion properties. X-ray diffraction analysis revealed that the selective area plated Sn–Ni alloy was heterogeneous and composed of NiSn, Ni₃Sn₂ and Ni₃Sn₄ phases. Uniform surface coverage of the substrate by granular morphology was observed from SEM and AFM. The alloy composition was determined by X-ray fluorescence (XRF). The corrosion protection performance of Sn–Ni alloy on mild steel was assessed using salt-water immersion and electrochemical corrosion tests. A sharp decrease in I _corr and high charge transfer resistance indicated improved corrosion resistant behavior of the selective area deposited Sn–Ni alloy.     

Preparation and investigation of pulse co-deposited duplex nanoparticles reinforced Ni-Mo coatings under different electrodeposition parameters

In this work, Ni–Mo–SiC–TiN nanocomposite coatings were deposited on aluminium alloy by pulse electrodeposition with various electrodeposition parameters. The influences of the pulse frequency and duty cycle on the phase structure, morphology, mechanical and corrosion performance of the coatings were systematically investigated. The results showed that with increasing pulse frequency and decreasing duty cycle, the content of embedded duplex nanoparticles increased, and the grains refined gradually. The nanocomposite coating that was prepared at 20% duty cycle and 1000 Hz pulse frequency exhibited compact, uniform, and fine microstructures with the maximum incorporation of nanoparticles (6.81 wt% TiN and 1.72 wt% SiC). The wear rate and average friction coefficient then declined to 4.812 × 10^?4 mm³/N·m and 0.13, respectively, with a maximum microhardness of 519 HV. Simultaneously, the corrosion current density was reduced to 3.11 μA/cm², and a maximum impedance of 34888 Ω cm² was exhibited. The uniformly distributed duplex nanoparticles acted as a hindrance, which consequently supported the enhancement of corrosion and wear resistance. By investigating the variation of the pulse diffusion layer with electrical parameters, it was discovered that when the crystallite size is equivalent to or smaller than the diffusion layer thickness, it would be easier to cross the diffusion layer to incorporate in the coating. Additionally, the effects of various duty cycles and pulse frequencies on the nucleation process of the grains were discussed.     

Chemical synthesis of TiO2 nanoparticles and their inclusion in Ni–P electroless coatings

The work addresses the preparation of Ni3P3TiO₂ nanocomposite coatings on mild steel substrate by the electroless technique. Nanosized TiO₂ particles were first synthesized by the precipitation method and then were codeposited (4 g/l) into the Ni3P matrix using alkaline hypophosphite reduced EL bath. The surface morphology, particle size, elemental composition and phase analysis of as-synthesized TiO₂ nanoparticles and the coatings were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD). Coatings with 20 µm thickness were heat treated at 400 °C for 1 h in argon atmosphere. The morphology, microhardness, wear resistance and friction coefficient characteristics (ball on disc) of electroless Ni3P3TiO₂ nanocomposite coatings were determined and compared with Ni3P coatings. The results show that as-synthesized TiO₂ nanoparticles are spherical in shape with a size of about12 nm. After heat treatment, the microhardness and wear resistance of the coatings are improved significantly. Superior microhardness and wear resistance are observed for Ni3P3TiO₂ nanocomposite coatings over Ni3P coatings.     

Cathode plasma electrolytic deposition of Al2O3 coatings doped with SiC particles

Semiconductor particles doped Al₂O₃ coatings were prepared by cathode plasma electrolytic deposition in Al(NO₃)₃ electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings.     

Vacuum thermal treated electroless NiP-TiO2 composite coatings

Composite NiP-TiO₂ layers were prepared by simultaneous electroless deposition of Ni-P and TiO₂ on steel substrate, from a solution in which TiO₂ particles were kept in suspension by stirring. Deposits were characterized for its structure, morphology and hardness. It was found that the chemical composition of Ni-P matrix has been influenced by the incorporation of TiO₂ particles. TiO₂ particle incorporation increases with increase in their bath concentrations (0.5-2.0 g/l). An improvement (up to 20%) in microhardness was observed in both as plated and vacuum heat-treated composite coatings compared to Ni-P coatings. Electroless deposited composite coatings exhibit an amorphous structure of the nickel matrix in which crystalline titanium oxide is incorporated. Vacuum heat treatment leads to the formation of a crystalline layer in which the Ni and Ni₃P crystallites appear apart from those of the TiO₂ (anatase). Potentiodynamic polarization measurements made on these deposits in 3.5 wt.% sodium chloride solution showed decrease in the corrosion resistance for the as-plated and heat-treated composite coatings.     

Joining of SiC ceramics using the Ni-Mo filler alloy for heat exchanger applications

In order to meet the sealing demands of SiC heat exchanger, the Ni-Mo filler alloy was designed, prepared and employed to braze SiC ceramics. Wetting behavior of the Ni-Mo filler alloy on SiC ceramics and interfacial microstructure of the brazed joints were systematically characterized using optical observation furnace and XRD, SEM, EDS, TEM, respectively. Flexural strengths of the brazed joints at room temperature and high temperature were measured with four-point flexural strength method. HCl immersion test was performed to evaluate the corrosion resistance of the joints. The Ni-Mo filler alloy exhibited excellent wettability on SiC ceramics. During the process of brazing, SiC reacted with element Ni of the Ni-Mo filler alloy, resulting in the formation of Ni₂Si + graphite reaction layer adjacent to the SiC substrate. Ni₃Mo₃C and Ni₂Si compounds were precipitated at the center of brazing seam. When the brazing temperature increased from 1250 ℃ to 1400 ℃, the thickness of Ni₂Si + graphite layer increased gradually. The maximum room-temperature flexural strength of 174 ± 33 MPa was obtained when brazed at 1300 ℃ for 40 min. The joints also exhibited stable high-temperature strength and acid corrosion resistance. When the test temperature was 700 ℃, 800 ℃, 900 ℃, the joints gave the strength retention rate of 92.5 %, 79.8 %, 67.2 %, respectively. It was believed that the formation of high melting point phases played an important role. Residual strength of the joints after HCl corrosion exceeded 130 MPa, revealing a good potential for applications in corrosion environment.     

Effect of SiC particle size on structures and properties of Ni–SiC nanocomposites deposited by magnetic pulse electrodeposition technology

In this paper, Ni–SiC nanocomposites were deposited on Q235 steel substrates by magnetic pulse electrodeposition (MPED) technique. Microstructures, compositions and microhardness values of obtained composites were determined by scanning electron microscopy (SEM), scanning probe microscopy (SPM), X-ray diffraction (XRD), and triboindenter in-situ nanomechanical testing. Results showed S-30 nanocomposites with fine, compact and uniform structures consisting of fine nickel grains (average size: 381.7 nm) and SiC nanoparticles (average size: 34.2 nm). For SiC particle size of 30 nm, diffraction peaks of Ni and SiC appeared wide with low intensity, indicating S-30 nanocomposites with small sized Ni grains and SiC nanoparticles. Largest TiN content reaching 10.59 wt% was embedded in S-30 nanocomposites prepared at SiC particle size of 30 nm. Final depths of S-30 and S-200 composites were estimated to 15.1 μm and 24.8 μm, respectively. Wear and corrosion properties of Ni–SiC nanocomposites were then investigated. After corrosion testing for 24 h, the weight losses of S-200, S-80 and S-30 composites were recorded as 1.67, 1.44 and 0.95 mg, respectively. Under the same wear experimental conditions, S-200 composite presented the highest mass loss while S-80 composites displayed the lowest mass loss. By comparison, wear mass loss of S-30 nanocomposites was only 37.1 mg.     

Corrosion resistance properties of electroless nickel composite coatings

Electroless nickel (EN) composite coatings incorporated with PTFE and/or SiC particles demonstrated significantly improved mechanical and tribological properties as well as low surface energy which are desired for anti-sticking and wear resistant applications. The corrosion resistance of these composite coatings, however, has not been systematically studied and compared. This work aimed to investigate the corrosion characteristics of EN composite coatings using electrochemical measurements which include open circuit potential (OCP), electrochemical impedance spectroscopy and potentiodynamic test. The effects of the co-deposited particles on corrosion behavior of the coatings in 1.0 N H₂SO₄ and 3% NaCl media were investigated. The surface autocatalytic properties and the post-heat-treatment on coating corrosion resistance were also discussed. The results showed that both EN and EN composite coatings demonstrated significant improvement of corrosion resistance in both acidic and salty atmosphere. Ni striking substantially enhanced the corrosion resistance due to the improvement of the surface autocatalytic properties and homogeneity. Proper post-heat-treatment significantly improves the coating density and structure, giving rise to enhanced corrosion resistance.     

Microstructure and performance of brazed diamond segments with NiCr–x(CuCe) composite alloys

Novel multi-layer brazed diamond segments were fabricated using NiCr–x(CuCe) composite alloys. Differential scanning calorimetry curves of the composite alloys were measured and analysed. The microstructures of the alloy segments and surface topographies of the brazed diamond segments were characterised. Performance tests of the alloy segments and brazed diamond segments were performed. The undercooling degree of the Ni–Cr alloy in the composite alloy increased with the Cu–Ce alloy addition, which led to coarse NiCu-rich regions and Ni₃Si phases. A brazed diamond segment with a 5% Cu–Ce alloy addition exhibited the highest wear resistance and machining performance and the best surface morphology after a wear test. An excessive Cu–Ce alloy addition led to a rapid decrease in wear resistance of the brazed diamond segment owing to the large number of coarse NiCu-rich phases falling off from the composite alloy. The mechanism of the reduction in thermal damage to diamonds by the Cu–Ce alloy is elucidated. Initially the Cu–Ce particles melted and mainly Ni atoms diffused into the Cu–Ce liquid, thereby leading to the formation of NiCu-rich regions and Ce₂Ni₇ and CeNi₂ phases, which in turn promoted the diffusion. The melting temperature of the Ni–Cr composite alloy was significantly reduced by the addition of the Cu–Ce alloy.     

Morphological, structural, microhardness and electrochemical characterisations of electrodeposited Cr and Ni-W coatings

This study examines the corrosion of electrodeposited Cr and of two electrodeposited Ni-W coatings in 0.1 mol L⁻¹ NaCl solution, as well as the influence of heat treatment on the crystallographic structure and microhardness properties of these coatings. Physical characterisation is carried out using scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. Electrochemical characterisation is carried out using both the potentiodynamic linear polarization technique and open circuit measurements during long-term immersion tests. The corrosion products on the coating surfaces are characterised by ex situ Raman spectroscopy. As-electrodeposited Ni-W samples do not present defects, and the surface evolves from fine globular grains to rough polycrystalline morphology with decreasing electrodeposition current density. All the studied coatings corrode in the chloride medium and the corrosion is non-uniform for the Ni-W coatings. Raman analyses carried out after the immersion tests reveal Cr₂O₃ and Cr(OH)₂ corrosion products on the Cr coating surface, and Ni(OH)₂, NiO and WO₃ corrosion products on the Ni-W coating surfaces. Ni, Ni₄W and Ni-W phases are formed after heat treatment of the Ni₈₆W₁₄ coating at 600 °C. Although all the annealed Ni-W layers are cracked, their microhardness increases as the annealing temperature increases, suggesting that Ni-W coatings are potential substitutes for chromium in industrial applications in which good microhardness properties and stability at temperatures higher than 100 °C are required.     

Corrosion and wear resistant electrodeposited composite coatings

Composite electroplating is a method allowing to co-deposit fine particles of metallic or non metallic compounds into the plated layers in order to improve the surface properties. The aim of the present work was to compare the performance of pure nickel and Ni-SiC nano-structured composite coatings as far as corrosion, wear and abrasion resistance were concerned. The characteristics of the coatings were assessed by scanning electron microscopy, micro hardness test, Taber Abrader test, electrochemical impedance spectroscopy and wear corrosion measurements. Additionally accelerated salt spray tests were performed. The results obtained in this study indicate that the co-deposition of nickel and SiC nano-particles leads to uniform deposits possessing better abrasion, wear and corrosion properties.     

Fabricating eco-friendly nanocomposites of SiC with morphologically-different nano-carbonaceous phases

A route based on aqueous colloidal processing followed by liquid-phase assisted spark-plasma-sintering (SPS) is described for fabricating eco-friendly nanocomposites of SiC with nano-carbonaceous phases (nanotubes, nanoplatelets, or nanoparticles). To this end, the conditions optimizing the aqueous colloidal co-dispersion of SiC nanoparticles, Y₃Al₅O₁₂ nanoparticles (acting as sintering additives), and carbon nanotubes (CNTs), graphene oxide (GO) nanoplatelets, or carbon black (CB) nanoparticles were first identified. Next, homogeneous powder mixtures were prepared by freeze-drying, and densified by liquid-phase assisted SPS, thus obtaining nanocomposites of SiC with CNTs, reduced GO (rGO) nanoplatelets, or pyrolized?+?graphitized CB (p?+?gCB) nanoparticles. It is also shown that these nanocomposites are dense and have a high hardness of ～20?GPa regardless of the nano-carbonaceous phase chosen, but are markedly tougher with CNTs and rGO (i.e., with high aspect ratio nano-carbonaceous phases). Finally, arguments are provided for the appropriate choice of nano-carbonaceous phases for engineering ceramic nanocomposites.     

Corrosion- and wear-resistant properties of Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite coatings containing various forms of alumina

This article describes the effect of the addition of different phases of alumina particles on the properties of electrodeposited Ni–Al₂O₃ composite coatings. The corrosion- and wear-resistant properties of Ni–Al₂O₃ composite coatings electrodeposited from a nickel sulfamate bath containing (i) alpha-alumina particles (Ni–Al₂O₃-1), (ii) gamma-alumina particles (Ni–Al₂O₃-2), and (iii) mixture of alpha, gamma, and delta alumina particles (Ni–Al₂O₃-3) have been studied. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed superior corrosion resistance of Ni–Al₂O₃-2 composite coatings compared with other two coatings. The SEM images and EDAX spectra also corroborated well with the observed corrosion results. The pin-on-disk wear studies showed improved wear resistance of Ni–Al₂O₃-1 composite coating containing alpha alumina compared with other two coatings. The transfer of material from the pin onto the disk was evident from the optical microscopy images of the wear tracks and Raman spectra of the wear track. This study shows that the addition of pure gamma-alumina particles enhances the corrosion resistance, and that pure alpha-alumina particles enhance the wear resistance of Ni composite coatings to a greater extent.