Journal of Advanced Materials in Engineering (Esteghlal)

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Zinc-Nickel electrodeposits have been widely adopted for surface treatment of automobile steel sheet for high corrosion resistance. In this work the effect of pulse parameters on the Zn-Ni alloy electrodeposits was investigated. The hardness, thickness, corrosion resistance and composition of deposits thus produced were investigated. The surface topography of the deposits was also observed in SEM and results are reported. It has been shown that the thickness of the pulse electrodeposits was almost even. The hardness in the pulse electrodeposits increased by increasing the on-time period and by decreasing the current density. It was also noticed that increasing the on-time period increases the nickel content of the deposit. Pulse electrodposits had fine structure and the structure become finer by reducung the on-time period and pulse frequency. The corrosion dehaviors of the deposits were then investigated. The results showed that the corrosion resistance of the DC electrodeposits improves in their nickel content increases. Pulse electodeposits show the same behavior, but deposits with about 13% nickel show maximum corrosion resistance.

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Production of nickel-silver by mechanical alloying was investigated. Effects of parameters such as milling duration, ball to powder weight ratio, and chemical composition on mechanical alloying process, and alloy's color and microstructure were studied. The milled powders were characterized, using XRD and SEM. Results showed that nickel-silvers could be produced by mechanical alloying in a wide range of compositions. Alloyed powder with a bright silvery contrast and less than 15 nm grain size could be obtained by optimization of milling parameters. Zinc content of the powder mixture had a significant effect on the minimum alloying time. Ball to powder ratio up to 25 also reduced minimum alloying time but it had no significant effect above this value.

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Coherency elastic strain between γ and  is one of the effective factors which affect the morphology, spatial re-arrangement and coarsening kinetics of  precipitates in nickel-base superalloys. In this investigation, using X-ray diffraction (XRD) technique, the - constrained and unconstrained lattice misfits were calculated for different morphologies of the  precipitates in Inconel 738LC nickel-base superalloy. The constrained and unconstrained misfits, hence the coherency elastic strains of different morphologies of the  precipitates were calculated from the XRD patterns of the bulk sample and electrolytically extracted  precipitates, respectively. According to the results, as the sizes of the  particles increased the - coherency as well as the compressive strain of the  precipitates was reduced and consequently their morphology changed from spherical to cubic, then flower-like, and finally dendritic shapes.

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The effects of temperature, time and atmosphere on microstructure and magnetic properties of NiFe2O4 glassceramic were investigated utilizing differential thermal analysis, X-ray diffraction, vibrating sample magnetometer and scanning electron microscope techniques. Various compositions were studied in the Na2O-NiO-Fe2O3-B2O3-SiO2 system to obtain amorphous phase. The sample heat-treated in graphite bed at 510°C for 1 hr showed higher magnetization than the one heattreated in the air under the same condition. XRD analysis showed the presence of nickel ferrite and some non-magnetic phases such as sodium borate and silicate phases in the heat treated samples. The maximum magnetization of samples reduced by increasing the holding time from 1hr to 3 hr at 510°C. Increment of temperature to 700°C increased the amount of NiFe2O4 and maximum magnetization.

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Today, along with the advances in circuit printing technology it has become possible to fabricate band lines integrated with circuit elements. The band lines are known as microstrip lines and the whole packages are called microstrip antennas. The microstrip antennas have three layers, including conductive patch layer, dielectric sub layer, and ground conductive layer. One of the most important problems of prevalent antennas is their inflexibility, which was addressed in the current paper using textile based structure with proper flexibility and flexural stiffness. This was done using ink jet printing techniques followed by electrolytic plating to provide diverse antenna patterns based on nickel particles. The coated surface was characterized by scanning electron microscope, elemental analysis and optical microscope. Moreover, the washing fastness and the other physical and mechanical specifications were measured using standard techniques. The elemental analysis of metal-coated fabric clearly indicated a high level of nickel. Furthermore, the morphological investigation proved the formation of homogenous nickel nanoparticle in a diameter range of 100-500 nm with an evident boundary and semi-spherical shape. In addition, the cumulative presence of particles in a sequence followed a cabbage-like structure originating from metallic crystals. The washing fastness tests revealed a high stability in electrical resistance after several washing steps. In the meantime, the antenna gain and the corresponding bandwidth were measured using spectrum analyzer. The results indicated a 1 kHz increase in bandwidth and 11 dB decrease in antenna gain for a large size compared to a small one. Meanwhile, the bandwidth of rectangular pattern showed a 0.2 kHz increase and 2.5 kHz decrease compared to spiral pattern. Finally, the four-probe electrical conductivity test demonstrated a high level of conductivity around 2632 S/cm.

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Nickel ferrite based cermets and their relevant composites have been widely used as inert anodes for aluminum electrolysis due to their good combination of chemical resistance, thermal stability and mechanical properties. In this study, various NiO/NiFe2O4 composites consisting of 5, 10 and 15% NiO in conjunction with Cu/NiFe2O4 cermets containing 0.5, 10 and 15% Cu were prepared by powder metallurgy method. The degradation resistance of the developed inert composites was examined under hot corrosion condition by plunging samples in to the molten electrolyte at 1000ºC. The strength, toughness, hardness, relative density, microstructural observation, phase analysis and electrical resistivity were evaluated by 3-points bending tests, Vickers method, Archimedes method, scanning electron microscope, x-ray diffraction and conventional direct current four-probe techniques, respectively. The experimental results for NiO/NiFe2O4 composites showed that a significant improvement of toughness and degradation resistance continuously occurred with a moderate decrease in strength by increasing NiO content, while the relative density was increased only up to 5%NiO content. By increasing the Cu content in the cermet samples, all the properties such as strength, toughness and electrical conductivity were improved considerably but the degradation resistance decreased.

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In the present investigation, spherical nanoparticles of nickel ferrite with uniform structure were successfully produced by hydrothermal method in the presence of polyethylene glycol (PEG) as a polymeric surfactant at 180°C for 12 hour aging time and the effects of the synthesis time, temperature and surfactant were investigated. According to the X-ray analysis, conversion of nickel oxide and hematite to nickel ferrite was a way to produce NiFe2O4. At 140‌°C, agglomerated particles without specific shape were formed, but at 180°C particles were homogenous with spherical shape. Saturation magnetization increased by increasing the hydrothermal process aging time.

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Super-hydrophobic nickel and nickel-cobalt alloy coatings with micro-nano structure were successfully electrodeposited on copper substrates with one and two steps electrodeposition. Surface morphology, wettability and corrosion 

resistance were characterized by scanning electron microscopy, water contact angle measurements, electrochemical impedanc spectroscopy (EIS) and potentiodynamic polarization curves. The results showed that the wettability of the micro-nano Ni and Ni-Co films varied from super-hydrophilicity to super-hydrophobicity by exposure of the surface to air at room temperature. The corrosion results revealed the positive effect of hydrophobicity on corrosion resistance of Ni coating (~10 times) and Ni-Co coating (~100 times) in comparison with their fresh coatings. The results showed that super-hydrophobic nickel coating had higher corrosion resistance than super-hydrophobic nickel-cobalt coating.

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In this study, Ni-Mo nanocrystalline alloys were prepared on steel substrates by electrodeposition method from citrate-ammonia bath by applying current densities 30, 60 and 100 mA/cm². Results indicated that the obtained coatings were uniform and compact. Moreover, molybdenum content in the alloy and current efficiency decreased with increasing electrodeposition current density. X-ray diffraction analyses indicated that all coatings were composed of face-centered cubic solid solution of molybdenum in nickel with grain size of 9-5 nanometer. Moreover, the most intensive plane in X-ray diffragtogram was (111). On the othe hand, roughness measurements indicated that surface roughness escalated with increasing current density. Corrosion behavior study showed decrease in corrosion current density of substrate with applying Ni-Mo alloy coatings. In addition, corrosion current density reduced with increasing molybdenum content of the coating and the minimum amount was related to the coating with 13 atomic percent molybdenum.

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In this study, creation of a silicon aluminide coating on IN738LC nickel-based superalloy has been investigated, using co-deposition process. Thermochemical calculations indicated the possibility of obtaining a silicon aluminide with NH₄Cl activated pack powder at 900°C, in order to achieve coating with desirable structures. Two powder mixtures with nominal compositions of 7Si-14Al-(1-3) NH₄Cl-Al₂O₃ (wt. %) and 16Si-4Al-(1-3) NH₄Cl-Al₂O₃ (4 and 0.5 Si/Al ratios, respectively) were used. According to the results, both coatings showed multi-layered structures containing AlNi₂Si as dominant phase. In coating created by pack powder with Si/Al ratio of 0.5, a porous and brittle layer of NiSi was formed on the surface which deteriorated the mechanical properties of coating to some extent. It was found that inward diffusion of Al was dominant at the first stage, while afterward, inward diffusion of Si led to conversion of NiAl phase to AlNi₂Si and, finally, to NiSi phase. Eventually, the sample coated by Si/Al=4, showed superior microstructural characteristics, containing desirable AlNi₂Si phase without undesirable brittle NiSi phase.

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In this research, nickel ferrite nanoparticles were synthesized by sol-gel auto-combustion route, and the effect of calcination temperature on phase constituents, magnetic properties and microstructure of the synthesized nanoparticles was evaluated using X-ray Diffraction (XRD), Vibrating Sample Magnetometer (VSM) and Scanning Electron Microscopy (SEM). XRD results were submitted to quantitative analysis. Microstructural studies and crystallite size calculations showed formation of nanoparticles. XRD results showed that the combustion product consisted of NiFe₂O₄, α-Fe₂O₃, NiO, and FeNi₃ phases. FeNi₃ was eliminated by calcination, and the amounts of NiO and α-Fe₂O₃ were modvlated by changing in calcination temperature. Saturation magnetization changed from 37emu/g in combustion product to 30emu/g by calcination at 600°C, due to decomposition of FeNi₃ magnetic phase and formation of higher amount of antiferromagnetic hematite phase. Also, the coercivity values increased, that could be due to increasing the amount of nickel ferrite phase and eliminating FeNi₃ phase. Saturation magnetization reached to 43emu/g in calcinated sample at 1000°C due to the reaction between hematite and NiO phases that led to formation of higher amount of nickel ferrite to 43emu/g. Coercivity value dropped out to 127Oe by calcination at 1000°C, the reason of which could be incresing of particle size and formation of multi domain magnetic particles.
 

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In the present study, the mechanical alloying process was used to produce the Ni-Nb-Si amorphous alloy. X-ray diffraction (XRD)analysis and high-resolution transmission electron microscopy (HRTEM) were used to approve the amorphous phase formation after 12 hours of mechanical alloying. The results obtained from the SEM morphological images of powder particles during mechanical alloying showed that increasing the milling time caused the reduction  of the powder particles size and uniformity in the shape of the particles. Enhancing the embrittlement and fracturing rate caused brittleness and the  increase in the  failure rate; these were followed by a decrease in the powder particle size to 1-5μm. Cold welding and flattening of the pure elemental powders after mechanical alloying for 2 hours formed a lamellar structure of the alternative layers of different elements lying over each other. SEM image of cross-section of powder particles showed that by increasing the milling time, the interlamellar spacing was decreased, the elements were distributed more uniformly, and finally, a uniform structure of theamorphous phase was completed.

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