Iranian Journal of Materials Science and Engineering

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Metal matrix composite coatings reinforced with nano-particles have attracted scientific and technological interest due to the enhanced properties exhibited by these coatings. Cobalt/hexagonal boron nitride nano-composite coatings were prepared by means of the pulse current electroplating from a chloride electrolyte on copper substrates and a comparison was made with the pure cobalt in terms of structure and tribological properties. Effects of particles concentration (5-20 gL-1) and current density (50-200 mA cm-2) on the characterization of electroplated coatings were investigated via X-ray diffraction analysis, energy dispersive spectroscopy and Vickers micro-hardness. Moreover, the tribological behavior was studied using pin-on-disc method. The results showed that cobalt/hexagonal boron nitride nano-composite coatings have higher hardness, wear resistance and lower friction coefficient than pure cobalt and the plating parameters strongly affect the coating’s properties

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Metakaolinite-based geopolymer has been synthesized at about 25 °C from metakaolin which has been calcined in different temperatures (600-900 °C) and different Na2O/SiO2 ratio activator (0.3-1.1). Compressive strength and microstructure of cement pastes after 7-28 days curing at ambient temperature were measured. Compressive strength tests on the samples showed that the sample made with calcined kaolin at 700 °C and molar ratio of 0.6 has highest average compressive strength of 32 MPa after 28 days of curing. Evaluation of infrared spectroscopy (FTIR) and microstructure showed that geopolymer cement developed and new molecular structure established

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Abstract:Some types of glass and glass ceramics have a great potential for making bone tissue engineering scaffolds, drug carrier and bone cements as they can bond to host bone, stimulate bone cells toward osteogenesis, and resorb at the same time as the bone is repaired. Calcium phosphate glass ceramics have very attractive properties that allow them to use in bone tissue engineering. Calcium phosphate glasses could be used for the fabrication of resorbable constructs, with controlled biodegradability. This work was investigated crystallization and sinterability of biodegradable glass ceramics in the CaO–P2O5–Na2O–TiO2 system using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Sinterability of the glasses also was investigated by measurement of sintering parameters. Different thermal treatments were applied to control the degree of devitrification of glasses. In the developed glass ceramics Ca2P2O7 were the first phase to precipitate in the mother glass structure, followed by Ca(PO3)2 and TiP2O7 at elevated temperature. Ca2P2O7 and Ca(PO3)2 seem to have a very positive effect in bone formation in vivo. It is therefore expected that glass ceramics understudy have good potential to be used for bone regeneration applications

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Abstract: Mg2Ni alloy and Mg2Ni–x wt% TiO2 (x = 3, 5 and 10 wt %) composites are prepared by mechanical alloying. The produced alloy and composites are characterized as the particles with nanocrystalline/amorphous structure. The effects of TiO2 on hydrogen storage properties are investigated using anodic polarization and electrochemical impedance spectroscopy. It is demonstrated that the initial discharge capacity and exchange current density of hydrogen are increased by adding 5wt% TiO2, while the cycle stability and bulk hydrogen diffusivity don’t change. It is found that the charge transfer resistance of Mg2Ni–5wt% TiO2 composite is lower than that of Mg2Ni alloy. On the other hand, the hydrogen oxidation during the discharge process proceeds more easily on the electrode surface containing TiO2 additive.

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Abstract:In the present research, SiO2–TiO2 nanostructure films were successfully prepared on windshields using the sol–gel technique for photocatalytic applications. To prevent the thermal diffusion of the sodium ions from the glass to TiO2 films, the SiO2 layer was pre-coated on the glass by the sol–gel method. The substrates were dipped in the sol and withdrawn with the speed of 6cm/min-1 to make a gel coating film. The coated films were dried for 2 days at 27 °C to allow slow solvent evaporation and condensation reactions due to rapid sol–gel reaction of Titania precursor. Then, the films were annealed at 100 °C for 30min and at the final temperature (500, 700 °C) for 30 min continuously. The structure and surface morphology properties, which are as a function of annealing temperature, have been studied by SEM FE-SEM and XRD. The FE-SEM surface morphology results indicate that the particle size increases from 19 to 42 nm by increasing the annealing temperature from 500 °C to 700 °C. Likewise, XRD illustrate the crystal anatase and rutile as main phases for TiO2-SiO2 films annealed at 500 °C and 700 °C respectively. This procedure resulted in transparent, crack-free SiO2–TiO2 films.

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The objectives of this research were to find an economical way of reducing porosities in the microstructure of coatings deposited by flame spraying technique on CK45 steel and also trying to increase their cohesive strength to the substrate, so that the overall wear properties of this type of coating can be improved. So several specimens from this steel coated with NiCrBSi powder under specific conditions were subjected to various furnace heat treatment at 1000, 1025, 1050, 1075 and 1100 °C, each for periods of 5, 10 and 15 minute before cooling them in air. Tribological properties of treated coatings were evaluated by pin on disc method. The results show the highest wear resistance and microhardness values observed in one of the sample was due to lower amount of porosity and higher amount of very fine Cr2Ni3B6 particles precipitated homogeneously throughout its microstructure during specific heat treatment.

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The probable reasons for evolution of weld porosity and solidification cracking and the structure- property relationship in aluminium welds were investigated. Aluminium plates (1xxx series) were welded by Tungsten Inert Gas (TIG) welding process, 5356 filler metal was used and heat input was controlled by varying welding current (145A, 175A and 195A). The welded samples were examined under optical and scanning electron microscopes and mechanical tests were performed to determine tensile and impact strengths. Secondary phase, identified as globules of Mg2Al3 precipitates, was found to be formed. Solidification cracking appeared in the heat affected zone (HAZ) and porosities were found at the weld portion. The tendency for the formation of solidification cracking and weld porosities decreased with increased welding current.

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In this research, variant selection of martensite transformed from ultrafine-grained (UFG) austenite fabricated by accumulative roll bonding (ARB) process and subsequent annealing was investigated with respect tomorphology of parentaustenitic phase. The results show that the original shape of austenite grain is very effective factor in determiningthe preferred variants of martensite transformed from the elongated ultrafine-grained austenite fabricated by 6-cycles via the ARB process. Annealing treatment of the austenitic samples subjected to the 6-cycle ARB processed at 873 K for 1.8 ks suppressed the variant selection by changing the morphology of austenite grains from elongated ultrafine-grains to fully-recrystallized and equiaxed fine-grains

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In this study, the effect of different parameters such as time and temperature of calcination and milling on the formation of calcium aluminosilicates was investigated. Raw materials used in this study were calcium carbonate and kaolin in high purity. Powder X-ray diffraction patterns were obtained from all samples after heat treatment at various temperatures and times. To study the microstructure scanning electron microscope was used. Milling the samples contributed to the amorphous structure due to inducing defects in the structure. Moreover, increasing the milling time reduced crystallization temperature of anorthite. Uptake experiments were performed using solutions containing different concentrations of nickel. Samples were exposed to the solution for 24 h with stirring then the samples were filtered and the concentrations of the cations in the separated solutions were analyzed. FTIR analysis was conducted on the adsorbents before and after nickel uptake. Nevertheless, they hardly helped understand sorption mechanisms. Therefore, adsorption isotherms were studied instead. Three adsorption isotherms of Langmuir, Freundlich and DKR were used to model sorption data. Results suggested monolayer sorption occurs on the surface of the adsorbent and sorption energy calculated by DKR model was 22.36 kJ/mol which can be described as a strong chemical adsorption mechanism

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The influences of age hardening and HIP (Hot Isostatic Pressing) on the mechanical properties of A356 (Al 7Si 0.6 Mg) casting alloys were studied. Cast bars were homogenized, heated and maintained at a temperature of 540°C for a duration of 2 hours, followed by rapid cooling in a polymeric solution. The castings were age hardened at 180°C for a duration of 4 hours before being subjected to HIP process at pressure of 104 MPa for 2 hours. The results indicated that the age hardening process used improved the tensile properties of A356. The HIP process removed the internal surface-connected porosities and improved the ductility of the samples significantly. Additionally, HIP reduced scattering in the tensile test data

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The wear mechanism of plasma electrolytic nitrocarburised (PEN/C) 316L stainless steel samples was studied after a pin on disc wear test. The surface morphology of samples after application of PEN/C process was studied using scanning electron microscope technique. The sliding tracks resulting from the wear tests on the treated specimens indicated no signs of plastic deformation and adhesive wear, but the slider wear particles were trapped in the micro-craters of the counterface. The results showed that this mechanism may further improve the tribological performance of the system by increasing the wear resistance and lowering friction. PEN/C treated surfaces are therefore believed to have the potential to limit metal-to-metal wear mechanisms on a microscale, if contact pressures are sufficiently low

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Ni and Cu elemental powder mixtures containing 25, 50, and 75% at Cu were subjected to mechanical alloying in a planetary ball mill under various milling times. Structural evolution was analyzed by means of X-ray diffraction and scanning electron microscopy. Experimental results indicated that nanostructured solid solution alloy powders having homogeneous distribution of Ni and Cu were formed by milling-induced interdiffusion of the elements. Average crystallite size of the as-milled powders was decreased with increasing Ni content and milling duration, and found to be in the order of 15-40 nm after 30 h of milling for all powder compositions. Moreover, lattice parameter and lattice strain of solid solutions were increased with the time of MA, which was more intense for nickel-rich alloys

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Precipitation behaviour of wrought Al-6Mg alloys with ternary scandium and quaternary zirconium and titanium has been studied. Hardness measurements and resistivity studies are employed to assess the precipitation behaviour of scandium doped Al-6Mg alloy without or with quaternary additions of zirconium and titanium. Further, the kinetics of precipitations are studied by differential scanning calorimetric technique. Scandium has been observed to form fine coherent Al3Sc precipitates during ageing and these are responsible for strengthening of the alloys. The precipitation kinetics of Al3Sc depends on the diffusion of scandium in aluminium. Presence of fine coherent precipitates of Al3Sc impedes the migration of dislocations and increase the recovery temperature. The kinetics of recrystallisation is also delayed.

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In the present study NiCrAlY bond coating layer was produced by electroplating against common atmospheric plasma spraying (APS). Both types of the bond coats were applied on IN738LC base metal then, the YSZ (ZrO2-8% Y2O3) thermal barrier top layer was coated by atmospheric plasma spray technique. Hot corrosion is one of the main destructive factors in thermal barrier coatings (TBCs) which come as a result of molten salt effect on the coating–gas interface. In this investigation the hot corrosion behavior of coatings was tested in the furnace which was contain Na2SO4-55% V2O5 and mixed salts environment at 900°C up to 15 hr. dwell time. Optical microscopy, scanning electron microscopy (SEM / EDS) and X-ray diffraction analysis (XRD) was used to determine the crystallographic structure and phase transformation of the coatings before and after the hot corrosion tests. The transformation of tetragonal Zirconia to monoclinic ZrO2 and formation of YVO4 crystals as hot corrosion products caused the degradation of mentioned TBCs. The results showed NiCrAlY coated by economical electroplating method a viable alternative for common thermals sprayed bond coats in hot corrosive environments with same corrosion behavior

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In order to evaluate the sintering behavior of lithium meta titanate (Li2TiO3) powder, the shrinkage of powder compact was measured under constant rates of heating. Densification curves for Li2TiO3 have been constructed with the help of shrinkage powder measured at different heating rates. The activation energy at the initial stage of sintering was determined by analyzing the densification curves and the value of Q=377 kJ/mol was obtained. The diffusion mechanism at the initial sintering stage was determined by the analytical method applied to the constant rates of heating data. This analysis exhibited that the dominant mechanism for initial sintering stage of Li2TiO3 is volume diffusion from grain boundary and surfaces.

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The orthogonal array design has been used to determine the optimum conditions for gold recovery from Zarshuran refractory gold sulfide ore (Iran) by direct cyanidation and roasting-cyanidation. The Taguchi method was used as the experimental design to determine the optimum conditions of dissolution behavior of gold with cyanidation and roasting-cyanidation from Zarshuran refractory gold ore . The experimental conditions were studied in the range of 10–12 for pH, 20-40 for time(h), 400-1200 for cyanide content (g/ton) and 30 -40 for percent solid(%). Orthogonal array (OA) L9 (34) consisting of four parameters each with three levels, was chosen. From this study for direct cyanidation the total optimum gold dissolution (30.11%) obtained at pH (10), Time (40 h), Cyanide content (800g/ton) and Percent solid (30%). Also for roasting- cyanidation the total optimum gold dissolution (34.96%) obtained at pH (12), Time (40 h), Cyanide content (1200g/ton) and Percent solid (35%).

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In the present study, reduction of zinc oxide from the pellets made of steelmaking electric arc furnace dust has been investigated. Effects of such parameters as the type of carbon material (graphite, coke and charcoal) as well as time and temperature on the reduction reaction have been examined. The reduced (dimensionless) time method was applied to perform a kinetic analysis of the system. Experimental results showed that increasing the temperature in the range of 925-1150°C results in a remarkable increase in the reduction rate. It was also shown that the reduction process is controlled by chemical reaction. Meaningful difference in the activation energy values calculated for reduction with graphite (24.75 kcal/mol), coke (18.13 kcal/mol) and charcoal (11.52 kcal/mol) indicate the predominant role of chemical reaction (carbon gasification) in the overall reaction rate and its rate-controlling mechanism. Carbothermal reduction of pelletized EAF dust proved to be an efficient reduction method, so that above 90% reduction was achieved in about one hour at temperatures around 1100°C.

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The effects of H2SO4 concentration on the electrochemical behaviour of passive films formed on AISI 304 stainless steel were investigated using by potentiodynamic polarization, Mott–Schottky analysis and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization indicated that the corrosion potentials were found to shift towards negative direction with an increase in solution concentration. Also, the corrosion current densities increase with an increase in solution concentration. Mott–Schottky analysis revealed that the passive films behave as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott– Schottky analysis indicated that the donor and acceptor densities are in the range 1021 cm-3 and increased with solution concentration. EIS data showed that the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants is applicable.

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Weight loss technique has been used to study the corrosion inhibition efficiency of tin in HNO3 solution by using the leaves and stem extract of different varieties of Holy Basil viz. ocimum basilicum (EB), ocimum cannum (EC) and ocimum sanctum (ES). The results show that all the varieties under study are good corrosion inhibitors, among which leaves extract of EB is the most effective. Corrosion inhibition efficiency increases with increasing concentration of inhibitor and it also increases with increasing concentration of HNO3 solution. Inhibition efficiency was found maximum up to 95.83% for tin in 3.0 M HNO3 solution, with 0.6% leaves extract whereas it was 81.25% in same concentration of HNO3 solution for stem extract

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Metal matrix nano composite coatings possess enhanced properties such as corrosion and wear resistance. This paper aims to study the corrosion behavior of pure Co and Co-BN nano composite coatings deposited with different particles concentration (5-20 g L-1) on copper substrates using electroplating technique. Morphology and elemental compositions of the coatings were investigated by means of scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The corrosion behavior was analyzed in a 3.5 wt% NaCl via polarization and impedance techniques. The results obtained in this study indicate that the co-deposition of BN nano particles improved corrosion resistance of electrodeposited cobalt coatings.