Surface Review and Letters

Effects of copper surface roughness $R_{\mathrm{\text{a}}}$ on the properties of Ni–Co–Fe alloy coatings were studied by the measurement of coating roughness, thickness, hardness, substrate/coating bonding force and the potentiodynamic polarization curve. Results showed that at the current density of 4A/dm², the coating roughness increased with the increase of the value of substrate $R_{\mathrm{\text{a}}}$ in the range 0.1–1.1$\mu$m. The coating thickness and hardness increased with the decrease of substrate $R_{\mathrm{\text{a}}}$. When substrate $R_{\mathrm{\text{a}}}$ was 0.4$\mu$m, the substrate/coating bonding force reached the maximum level. When substrate $R_{\mathrm{\text{a}}}$ was 0.1$\mu$m, the coating exhibited the best corrosion resistance. The comprehensive properties of the Ni–Co–Fe coatings can be effectively improved by controlling the surface roughness of copper substrate properly.

TiC particles/Ag composite films were successfully prepared through co-electrodeposition, using the Ag plating solutions with minor addition of TiC particles, followed by heat treatment in vacuum. The X-ray diffractometer (XRD), scanning electron microscope (SEM), nanoindentation tester and four-point probes were used to characterize phase composition, morphologies, mechanical properties and electrical properties of as-fabricated films, respectively. Experimental results show that only TiC and Ag phases are identified for the TiC particles/Ag composite films. TiC particles are incorporated tightly and evenly on the surface of the composite films without obvious agglomeration. TiC particles/Ag composite films maintain good electrical conductivity. Meanwhile, compared to pure silver film without the addition of TiC particles, the indentation hardness ($H_{\mathrm{\text{IT}}}$) of the TiC/Ag composite film electrodeposited from the plating bath containing 6g/L of TiC particles can be improved from 600 $H_{\mathrm{\text{IT}}}$ to 11,000 $H_{\mathrm{\text{IT}}}$.

This study considers high temperature tribological behavior of Al-TiB₂ aluminum matrix composites (AMCs) fabricated through stir cast method. Effect of operating temperature on wear and friction behavior is studied for four different weight percentages of reinforcements using a high-temperature tribo-tester over a temperature range of 50${}^{\circ }$C–250${}^{\circ }$C under normal load in the range of 25–75N. Surface morphology and wear debris are studied through scanning electron microscopy (SEM) images. Energy dispersive X-ray (EDAX) and X-ray diffraction (XRD) studies are performed to observe the wear mechanism at high temperature. Increase in the amount of reinforcement improves wear resistance of composites at all temperatures. Friction and rate of wear are found to increase with operating temperature. Formation of oxide layers and softening of the surface are found to play crucial role in controlling the tribological behavior of stir cast Al–TiB₂ composites at high operating temperatures.

The present work reports the deposition of a quaternary Ni-B-W-Mo coating on AISI 1040 medium carbon steel and its characterization. Quaternary deposits are obtained by suitably modifying existing electroless Ni-B bath. Composition of the as-deposited coating is analyzed by energy dispersive X-ray spectroscopy. The structural aspects of the as-deposited and coatings heat treated at 300${}^{\circ }$C, 350${}^{\circ }$C, 400${}^{\circ }$C, 450${}^{\circ }$C and 500${}^{\circ }$C are determined using X-ray diffraction technique. Surface of the as-deposited and heat-treated coatings is examined using a scanning electron microscope. Very high W deposition could be observed when sodium molybdate is present in the borohydride-based bath along with sodium tungstate. The coatings in their as-deposited condition are amorphous while crystallization takes place on heat treatment. A nodulated surface morphology of the deposits is also observed. Vickers’ microhardness and crystallite size measurement reveal inclusion of W and Mo results in enhanced thermal stability of the coatings. Solid solution strengthening of the electroless coatings by W and Mo is also observed. The applicability of kinetic strength theory to the hardening of the coatings on heat treatment is also investigated. Corrosion resistance of Ni-B-W-Mo coatings and effect of heat treatment on the same are also determined by electrochemical techniques.

The present study was focussed on investigating the corrosion properties of plasma-oxidized and -nitrided CoCrMo alloys under different conditions. The structural properties of untreated and treated samples were examined by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of samples was mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid solution. The results showed that corrosion resistance of the oxidized layers was better than that of the nitrided ones. The corrosion resistance of the alloys increased as the plasma oxidation process temperature and time increased. However, the corrosion resistance of the alloys reduced with increase in the process temperature and time after plasma nitriding process.

The deposition of Ni–Fe thin layers in boric acid and ionic liquid ([BuMePyr][Tf₂N]) baths were successfully prepared. The obtained materials have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX) and SEM. Meanwhile, these materials were carried out by chronoamperometry or chronopotentiometry by varying the intensity of the current and the deposition potential. The results indicate that the coatings of Ni–Fe alloys were successfully obtained by electroplating on the copper substrates, and the alloys composition shows irregular behavior with polarization. The nickel content in the samples is in the range of 55–90%, but the iron content ranges from 10–30%, when potential deposits were varied from $-$2V to $-$4V vs Ni electrode. The results also showed that the thin layers are monophased; they contain the Ni₃Fe phase. Further, SEM images of Ni–Fe alloys show the different shapes of particles.

The influence of oxygen atmosphere and substrate temperature on morphology and microstructure of the hydroxyapatite (HA) composite films prepared by pulsed laser deposition (PLD) was studied. According to the results of X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR), it was found that the phase compositions and the crystallinity of HA were affected by the oxygen pressure and substrate temperature. High oxygen pressure can increase the crystallinity of HA, and make random oriented HA gradually transform into $c$-axis orientation, and decrease the Ca/P atomic ratio of the film. High substrate temperature can increase the crystallinity of films and the degree of c-axis orientation of HA, but increase the Ca/P atomic ratio slightly. Changes of oxygen pressure or substrate temperature have little influence on the surface morphology and thickness of film. Valuable HA composite film could be obtained at 600${}^{\circ }$C under 5Pa O₂ atmosphere.

This study presents the tribological behavior of austenitic 316L Stainless Steel (SS) coated with nano Tungsten Carbide (WC). The nano WC particles were prepared by mechano chemical method. The tungsten and toluene have been ball milled for 40h led to the synthesis of WC nano particles. An average particles size of 48nm was achieved. The prepared nano WC particles were deposited on 316L SS substrate as a thin film using DC magnetron sputtering process. The thickness of the nano WC coating was 5$\mu$m. The synthesized nano WC particles and the thin nano WC film are characterized using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and Energy Dispersive X-ray Analysis (EDAX) technique. Vickers microhardness test was conducted to evaluate the microhardness of the thin film. A high microhardness value of 2242 HV${}_{10}$ was observed. The coated specimens are subjected to wear test using pin on disc setup and the tribological parameters such as friction and wear are analyzed. The results were compared with uncoated 316L SS specimen and micro WC particles coated 316L SS. The nano WC coated 316L SS possess high hardness and better wear resistance when compared with 316L SS and micro WC coated 316L SS specimen.

In the present investigation, Titanium Carbonitride (TiCN) coating was deposited on a cemented carbide substrate, by means of Plasma Enhanced Physical Vapour Deposition (PEPVD) process. The microstructure of the deposited film was characterized using the Scanning Electron Microscope (SEM). Highly dense, less porous and uniformly distributed TiCN coating was observed on the coated surface. X-Ray diffraction analysis was carried out to access the phases present in the coated layer. The scratch resistance and hardness were measured using the scratch tester and Nanoindenter, respectively. The TiCN coating gives higher hardness and superior scratch resistance when compared to the substrate. The surface morphology of the coated film was characterized using the Atomic Force Microscope (AFM) and was found that the surface roughness was lesser for TiCN coating when compared to cemented carbide substrate. The intensified TiCN coating on the substrate will be useful in improving the surface behavior of cemented carbide cutting tool.

Nano-crystalline copper oxide films were deposited on quartz substrates by RF-magnetron sputtering in argon gas environment. The XRD patterns show Cu₄O₃ phase for films deposited at 50 and 60W of RF power. The film deposited at 70W shows existence of Cu₄O₃ and CuO phases, whereas film deposited at 100W of RF power consists of only CuO phase. Raman spectra and transmission electron microscopy (TEM) also confirm these results. Field emission scanning electron microscopy (FESEM) shows morphological changes in the film as a function of RF power. The optical band gap estimated from the transmission spectra of the films are 2.3 and 1.7eV for Cu₄O₃ and CuO phase, respectively. The hydrothermal heat treatment of the film leads to transformation of Cu₄O₃ to CuO phase in the film.

With the rapid development of rail transit, the wear problem of track has become a serious challenge. Laser quenching is a new surface modification process, and it is expected to improve the service life of the track. Laser quenching was carried on the surface of rails by using 6kW fiber laser. The microstructure, hardness, wear resistance, and contact fatigue resistance (CFR) of the phase transformation hardening layer were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester, and wear tester. The results show that the microstructure of the hardened layer is composed of fine martensite and a small fraction of retained austenite. The microstructure of substrate is pearlite and ferrite. The hardness of rails quenched by the laser increased nearly two times than that of the un-treated track materials. When the laser power is 1000W, the depth of hardened layer reaches 0.8mm, and the wear resistance of hardened layer increases 167% than that of the substrate. The number, length, and depth of fatigue cracks decreased on the cross-section of worn rails after laser quenching, which indicates that laser quenching can improve the CFR of rails.

In recent years, photoelectrochemical (PEC) based devices have become attractive due to production of hydrogen by splitting water using photocatalyst alpha ($\alpha$)-hematite (Fe₂O₃) as an electrode material due to its bandgap, low cost, chemical stability and extreme abundance in nature. The $\alpha$-Fe₂O₃ is also related to low carrier diffusion due to higher resistivity, slow surface kinetics, low electron mobility and higher electro–hole combination. The carrier mobility and carrier diffusion properties of $\alpha$-Fe₂O₃ have been enhanced by doping as well as composite formation. Keeping in view the enhanced properties of $\alpha$-Fe₂O₃, attempt is being made to dope and form composite using trivalent “aluminum” ions. The Al–$\alpha$-Fe₂O₃ nanophotocatalytic materials were synthesized by varying the ratio of Al to $\alpha$-Fe₂O₃ using sol–gel technique. The nanomaterials “$\alpha$-Fe₂O₃ and Al–$\alpha$-Fe₂O₃” were physically characterized through X-ray diffraction, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and UV–visible techniques, respectively. The diffusion coefficient of nanomaterials at the electrode/electrolyte interface was analyzed using electrochemical analysis. Interestingly, the presence of aluminum causes the $\alpha$-Fe₂O₃ to change the structural, optical and morphological properties of nanomaterials. The bandgaps of $\alpha$-Fe₂O₃ vary from 2.2eV to 2.45eV due to presence of aluminum in the structure. The photocurrent studied on Al–$\alpha$-Fe₂O₃ based electrode clearly shows the enhanced hydrogen production under photoelectrochemical cell.

Although electroplated hard chromium coatings were extensively studied and applied in industry, the properties of the coatings after annealing at different temperatures were investigated insufficiently. In this work, the influence of heat treatment on the mechanical, tribological, and structural properties of chromium coating, electrochemically deposited on 38HN3MFA steel were investigated. A specific bath composition and deposition parameters were selected, which has been compared to the literature data. Parameter selections were based on data from military research industry and contain noticeably lower amount of sulfuric acid (1.2g/L), CrO₃ (180g/L) and lower current density (25A/dm${}^2)$. Coefficient of friction and coatings wear rate were measured by means of ball-on-disc method at the temperature of 30${}^{\circ }$C, 200${}^{\circ }$C, 500${}^{\circ }$C, and 700${}^{\circ }$C. The coefficient of friction has decreased from 0.71 for the temperature of 30${}^{\circ }$C to the value of 0.5 for 700${}^{\circ }$C due to the change of wear mechanism. Hardness of the as-received coating reaches the value of 11.4GPa and 9.5, 8.3, 6.4GPa for the samples after annealing in the temperature of 200${}^{\circ }$C, 500${}^{\circ }$C and 700${}^{\circ }$C, respectively. The influence of heat treatment on structural properties of electroplated Cr coatings was studied by X-ray diffraction. Scratch test showed that layer is characterized by excellent adhesion with no adhesive rupture. Cr-coated 38HN3MFA steel exhibits reduced susceptibility to high-temperature degradation by 25%, basing on the mass lost measured at 900${}^{\circ }$C.

In this work we investigate the effect of metal layer in the Al-doped ZnO (AZO)/Al/AZO structure. AZO and Al thin films are deposed successively at room temperature using DC magnetron sputtering by rotating the substrate holder without breaking the vacuum. The optical characterization of AZO/Al/AZO structure was performed by the spectroscopic ellipsometry under different incidence angles (55${}^{\circ }$, 65${}^{\circ }$ and 75${}^{\circ }$). For the AZO monolayer structure, it was found that the complex refractive index and the complex permittivity coefficient varied differently according to the incidence angle. The addition of Al layer (5nm thicknesses) in this monostructure reduces significantly this influence on the measurement, homogenizes the real refractive index variation and significantly reduces the real electrical coefficient permittivity in the visible range. In addition, the obtained depolarization values confirm the results of the AFM roughness revealing that the Al layer addition makes the surface smoother so that it meets the required conditions as the bottom electrode of organic light emitting diodes. The photoluminescence (PL) measurements indicate that the Al layer alters the PL emission. Actually, the Al layer enhances subsequently the PL emission and promotes the blue and red emission.

The Q235 steel was covered by Fe–Al–Nb alloyed coating to improve the mechanical properties of the Q235 steel. This double glow plasma surface metallurgy (DGPSM) surface modification technique was carried out at 1023K and pressure of 38Pa for 4.5h. The surface morphology represented the typical Volmer–Weber mode, an island structure which was accumulated by numerous small particles, and most of the angles formed between three islands were about 120${}^{\circ }$ where there was no appreciable defect. Meanwhile, in the cross-sectional morphology of the Fe–Al–Nb coating, there was a deposition layer, a diffusion layer and two transition regions between the different adjacent interfaces, and the coating approximate 17$\mu$m was found to be metallurgically adhered to the Q235 steel. The basic mechanical properties of the Fe–Al–Nb coating and Q235 steel including the hardness, elastic modulus and friction performance were measured and compared. The results showed that the formation of Fe₃Al, FeAl, and Fe₂Nb intermetallic compounds and Nb carbides in the coating can enhance the mechanical properties of the treated sample. The nanoindentation tests indicated that the hardness and elastic modulus of Fe–Al–Nb coating were 8.08GPa and 260.03GPa which were much higher than Q235 steel. The sliding friction tests showed that Fe–Al–Nb coating significantly improved the friction performance of Q235 steel at the speed of 300, 600 and 900rpm with load 320g for 15min.

Titanium alloys have been used for variety of engineering applications but their relatively low hardness and low thermal conductivity are shortcomings that have reduced their potential use. In this work, attempts have been made to study the effects of laser scanning speed and admixed fraction of reinforced Ni–Co powders on clad layer formation and its corresponding properties on Ti–6Al–4V. Laser power of 750W, beam size of 3mm with argon shield gas flow rate of 1.2L/min was made constant, while the powders were premixed and deposited on Ti–6Al–4V with varying compositions at different scanning speeds of 0.6 and 1.2m/min. The microstructural analysis, phase constituents and hardness properties of Ni–Co intermetallics reinforced clads were also examined. The morphology of the resultant coatings was analyzed using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). The research results showed that laser cladding coatings displayed enhanced properties such as fine microstructure and good metallurgical bonding with the substrate containing minimal pores with respect to the substrate. Furthermore, the microstructure revealed the formation of various fractions of interdendritic compounds/intermetallics dispersed within the coating matrix which could be responsible for the increased hardness obtained. The average hardness of the coating was about 856HV ${}_{0.1}$, which was about 2.5 times that of the substrate.