Journal of Advanced Materials in Engineering (Esteghlal)

In this investigation, the effect of grain size on the corrosion behavior of 304L stainless steel has been studied. Samples with grain sizes of 0.5, 3 and 12 micrometers were fabricated through formation of strain-induced martensite by 80% cold rolling of the stainless steel sheets at -15 ^°C and its reversion to austenite during annealing at 900 ^°C for 1, 5 and 180 min. The corrosion behavior of samples with different grain sizes was investigated by cyclic polarization experiments and  immersion tests in 0.1 M hydrochloric acid (HCl). The polarisation tests showed no differences in uniform corrosion rates of the samples. The results of the cyclic polarisation and immersion tests showed that decreasing the grain size improved the pitting corrosion resistance from 290 mV_Ag/Agcl for grain size of 12 micrometers to 420 mV_Ag/Agcl for grain size of 0.5 micrometers.

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.

In this study, NBG was successfully achieved through a sol-gel technique, and to further improve its dispersibility, a crylate coupling agent was coupled onto the surface of the NBG. The 3-(Trimethoxysilyl)Propylmethacrylate coupling agent was used to the surface modification of the synthesized NBG by a wet-chemical method in a dynamic inert nitrogen atmosphere. The surface properties of the biomaterials before and after modification were characterized and compared using FTIR and AFM techniques. The characteristic peaks in FTIR spectra indicated that –CH2, –CH3 and C=O groups appeared on the surface of modified NBG, and also, AFM analysis revealed that the dispersibility of surface modified NBG was improved, significantly. The above results proved that the desired groups of 3-(Trimethoxysilyl)Propyl methacrylate had been covalently bonded onto the surface of NBG. Besides, a nanocomposite scaffold was synthesized using the synthesized NBG and polyurethane foam as raw materials. The morphology of pores, porosity contents, compress strength and bioactivity of the scaffold were studied. The results showed that the biological scaffolds for use in bone tissue engineering with the basic requirements (90% porosity and 200-600 μm pore diameter) were successfully prepared. The polymer component had no effect on the relationship between the scaffold pores and bioactivity of bioglass nanoparticles. Improvement of compressive strength and proper bioactivity of the resulted scaffold showed that it is an acceptable candidate for biomaterials applications.

The aim of this study was to fabricate carbon nanotube (CNT) and bioactive glass nanoparticles (BG) (at levels of
5 and 10 wt%) incorporated electrospun chitosan (CS)/polyvinyl alcohol (PVA) nanofibers for potential neural tissue engineering applications.The morphology, structure, and mechanical properties of the formed electrospun fibrous mats were characterized using scanning electron microscopy (SEM) and mechanical testing, respectively. In vitro cell culture of embryonal carcinoma stem cells (P19) were seeded onto the electrospun scaffolds. The results showed that the incorporation of CNTs and BG nanoparticles did not appreciably affect the morphology of the CS/PVA nanofibers. The maximum tensile strength (7.9 MPa) was observed in the composite sample with 5 %wt bioactive glass nanoparticles. The results suggest that BG and CNT-incorporated CS/PVA nanofibrous scaffolds with small diameters, high porosity, and promoted mechanical properties can potentially provide many possibilities for applications in the fields of neural tissue engineering and regenerative medicine.

In the present research NdFeB thin films coupled with buffer and capping layer of W were formed on Si/SiO₂ substrate by means of RF magnetron sputtering. The system was annealed at vaccum at different temperatures of 450, 500, 550,. 600 and 650 °C Phase analysis was carried out by XRD and it was found that NdFeB was formed without the formation of any kind of secondary phase. The cross sectional and grain size of the thin films were measured by scanning electron microscopy. Morphological studies were performed by atomic force microscopy. Magnetic properties of thin films including coercivity, saturation of magnetization and hysteresis area were evcaluated by vibrating sample magnetometer. It was found that by annealing at 400 °C the amorphous layer was formed.The highest intensity of peaks was formed at 550 °C and with an increase in temperature the intensity was declined. The grain size was increased by temperature and had an impact on the coercivity. With an increase of temperature up to 600 °C, perpendicular coercivity was increased and then by further increase of temperatute, coercivity was reduced. Based on the obtained data the temperature of 600 °C was selected as the optimum annealing temperature for reaching enhanced structural and magnetic feature.

In this study, electrical wire explosion has been used to produce aluminum carbon nanotube (Al-CNT) nanocomposite particles in acetone medium. In order to synthesize Al-CNT nanocomposites, initially, CNTs were ultrasonically dispersed. Then, aluminum wire was exploded in this medium. Synthesized samples were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM) methods. The results exhibited formation of spherical nanoparticles in the medium. The average diameter of nanoparticles was 4 nm. Moreover, attained nanoparticles remained stable in acetone. Results revealed a good interaction between aluminum nanoparticles and CNTs in this medium. It is concluded that acetone is a suitable medium for synthesizing Al-CNT nanocomposite as appropriate dispersion of Al-CNT nanoparticles can be achieved in this medium.

In this research, Glass Form Ability (GFA) has been investigated in the new class of Fe-based amorphous
alloys. Indeed, the main purpose is to evaluate the effects of alloying with niobium on glass form ability of Fe_55-xCr₁₈Mo₇B₁₆C₄Nb_x (X=0, 3, 4, 5) alloys. Vacuum induction melting (VIM) was utilized for production of primary ingots and melt spinning process was used for production of thin ribbons required for kinetic and structural investigations. Kinetic analysis was done using
the data obtained from Differential Scanning Calorimetry (DSC) tests. Results showed that GFA and viscosity were enhanced by Nb alloying. It was also determined that devitrification transformation was accomplished in alloys by nucleation and growth mechanisms.

In this study, centrifugal casting process was used for producing Al/Mg bimetal. Molten Mg was poured at 700 ^oC, with 1.5 and 3 melt-to-solid volume ratio (Vm/Vs) into the 450 ^oC preheated solid Al rotating at 800, 1200, 1600 and 2000 rpm. Castings were kept inside the centrifuged casting machine and cooled down to 150 ^oC. Investigating the effect of melt-to-solid volume ratio showed that increasing volume ratio from 1.5 to 3 results in diminishing metallurgical bonding in Al/Mg interface, because the force of contraction overcomes the resultant force acted on the interface. The results of study by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) showed that bimetal compounds of Al₃Mg₂, Al₁₂Mg₁₇ and δ+Al₁₂Mg₁₇ eutectic structure (δ is the solid solution of Mg in Al) are formed in the interface. Atomic force microscopy (AFM) image of Al surface showed that the surface was rough in atomic dimentions, which can result in the formation of gas pores in the interface.

This study has examined the properties of Crofer 22APU stainless steel produced by mechanical alloying for using as interconnect plates in solid oxide fuel cells.This alloy was produced by mixing the source powders and mechanical alloying for 40 hours. For creating a sample with high density, spark-plasma sintering was applied at 1100 °C and 50 Mpa stress for
10 minutes. To achieve the desired properties such as low electrical resistance and high oxidation resistance, a number of samples were coated by manganese-cobalt using electrodiposition technique at current density of 150 mA/cm ² for 40 minutes. Then, considering the properties required for an interconnect plate of solid oxide fuel cell, oxidation resistance and electrical resistance of the coated and uncoated samples were investigated. Oxidation behavior of the coated and uncoated samples, after 100 hours oxidation in air at 800°C did not follow any rule and its curve was a sinus type. The electrical resistance of uncoated samples was in the range of 0.1-0.2 mOhm.cm², but the electrical resistance of the coated samples after 100 h oxidation reached to a less ammount  than that of the corresponding uncoated ones. The alloy produced by mechanical alloying method, compared with commercial ones produced by casting methods, showed similar oxidation behavior after 100 h oxidation, but it had a surface electrical resistance far less than its commercial ones.

The purpose of this article is to study the formation of intermetallic compounds (IMCs) at the interface of Al/Cu bimetal produced by compound casting of molten Al in solid copper tubes. The mechanism of the intermetallic compounds formations at the interface, the effects of molten aluminum pouring temperature and solid copper tubes preheating tempreture, were investigated on the IMCs type and thickness and Al/Cu interface microstructures were characterized by optical microscope (OM) and electron probe micro-analyzer (EPMA). Results show that the interface consists of three main layers, where Layer (I) is α-Al/Al₂Cu eutectic structure, layer (II) is intermetal of Al₂Cu and layer (III) constituites several intermetallic compounds such as AlCu, Al₃Cu₄, Al₂Cu₃ and Al₄Cu₉. Considering the components of hypereutectic melt at the interface, initially layer (II) was formed by θ phase nucleation and growth mechanism, then layer (I) was formed by Al and Cu dissolving and solidification. Finally layer (III) was formed by solid-state phase diffusion. Raising molten Al temperature and preheating solid Cu leads to increase of the intermetallic compounds thickness at interface which consequently increases the specific electrical resistance and decreases the Al/Cu bond strength. From experimental results it seems that the bond strength is affected by the thicknesses of layer II and III.

Organic–inorganic hybrid coatings were prepared by sol–gel method and deposited on aluminum alloy 6061. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) were used for structural study of the hybrid coatings. Adhesive strength of sol–gel coatings to the substrate was evaluated quantitatively and qualitatively. Corrosion behavior of the samples was studied by cyclic potentiodynamic and linear polarization tests. Results showed that adhesion strength of the coatings to the substrates was increased with increasing tetrapropoxide of zirconium (TPOZ) and cerium content. Corrosion tests showed that corrosion current density of coated samples were decreased three to seven orders of magnitude in comparison with uncoated aluminum alloy 6061. Decreasing in corrosion current density and increasing in polarization resistance was observed by increasing zirconia and cerium content. Unlike the uncoated aluminum alloy 6061, the crack-free coatings did not show pitting tendency. 

In recent years the use of nanomaterials in bone tissue engineering scaffold has been considered due to its imitating the structure of natural bone tissue which contains a nanocomposite structure mixed with a three-dimensional matrix. In the meantime, Polycaprol actone has been used as a bio-polymer in bone tissue engineering applications as a scaffold. The aim of this study is to develop porous scaffolds made of polycaprol actone/layered double hydroxide biocomposite, with appropriate mechanical, bioactive and biological properties, for bone tissue engineering application. The nanocomposite scaffolds were fabricated by the particulate leaching method and freeze-drying method. In this study, MG63 cells (osteosarcoma) was investigated for cellular study. Energy dispersive X-ray analysis confirmed uniform distribution of ceramic phase in polycaprol actone matrix. The results of mechanical tests showed the increase in young’s modulus after addition of ceramic phase. The microscopic investigations demonstrated that the pores generated after addition of ceramic phase and the average size of pores was as large as 100-600μm. Also by the addition of LDH, the hydrophilicity of PCL increased but the rate of hydroxyapatite formation was delayed due to presence of magnesium ions. The cell culture experiments confirmed the attachment and proliferation of cells on the scaffolds. The results showed that the fabricated scaffolds have the potential to be used in cancellous bone tissue engineering.

Magnesium-manganese ferrite nanopowders (Mg_xMn_1-xFe₂O₄, x=0.0 up to 1 with step 0.2) were prepared by coprecipitation method. The as-prepared samples were pressed with hydrolic press to form a pellet and were sintered in 900, 1050 and 1250˚C. Scanning Tunneling Microscope (STM) images showed the particle size of powders about 17 nm. The X-ray patterns confirmed the formation of cubic single phase spinel structure in samples sintered at 1250˚C. Substituting Mg²⁺ with Mn²⁺ in these samples, the lattice parameter decreased from 8.49 to 8.35Å and magnetization saturation decreased from 74.7 to 21.2emu/g. Also, coercity (H_C ) increased from 5 to 23Oe and Curie temperature (T_C ) increased from 269 to 392˚C. Samples with x= 0.2, 0.4, 0.6 sintered at 1250 ˚C, because of their magnetic properties, can be recommended for hyperthermia applications and for phase shifters.

In this research, the nanopowders of lanthanum and neodymium co-doped yttria were synthesized by sol-gel combustion method. Citric acid and glycine were used as the gel maker and fuel respectively. The effect of molar ratio of citric acid to glycine on the grain size and morphology was evaluated. The optimized products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), UV–visible (UV–Vis), thermal gravimetric-differential thermal analysis (TG/DTA), and Fourier transform infrared spectrometer (FTIR). The optimized products which are synthesized with a molar ratio citric acid to glycine 1.06:1.06 have an average grain size of 30-40nm with spherical morphology, and without agglomeration. Also, their band gap is 3.29eV.

In this study, aluminium composite foams reinforced by different volume fractions of SiC particles as reinforcement and stabilizing agent were fabricated with the direct foaming route of melt using different contents of CaCO₃ as foaming agent. The density of produced foams were measured to be from 0.38 to 0.68 g/cm³. The microstructural features and compressive properties of the AA356/SiC_p composite foams were investigated. The relation between plateau stress, density and, weight percentage of CaCO₃ and SiC_p volume fraction with a given particle size was also investigated. The results showed that compressive stress-strain curves of the products were not smooth and exhibit some serrations. Also, it was shown that in the same density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiC particles and decreasing weight percentage of CaCO₃.

In this study, fabrication of an in-situ composite through aluminothermic combustion synthesis in An Al–V₂O₅-NiO system was investigated. Therefore, Al, V₂O₅ and NiO powders with stoichiometric ratio of 11:1:1, respectively, were milled for an  hour and finally the mixtures were compressed. In order to investigate the temperatures of phase transformations, Differential Thermal Analysis (DTA) was utilized. Heat treatment was applied on the raw samples according to their peak temperatures treated in DTA. X Ray Diffraction (XRD) analysis for the samples shows formation of phases such as Al₃V and Al₃Ni₂ at different sintering temperatures. Microstructure and phase analysis showed that during sintering of this sample, Al₃V phase was not formed below 700 °C, at 880 °C Al₃Ni₂ it was formed and after 950 °C, it was transformed to Al₄Ni₃ phase. In addition, after 950°C, Al₃V transformed into Al₂₃V₄ phase. Analysis of samples density and hardness showed that, due to increase of volume fraction percentages of reinforcing phase, these two parameters increase as well.

In this work, cobalt ferrite nanocrystallites were synthesized by air annealing of milled Co-Fe compound. Effect of annealing temperature on phase formation of cobalt ferrite and structural and magnetic properties of the product was studied. Analysis of annealed sample in 450 ^oC showed that around 46 weight percent of the specimen was changed to Co₂FeO₄. This value increased to 95 and 90% for 800 ^oC and 900 ^oC annealed samples respectively. Reduction of saturation magnetization under annealing was related to transformation of Co-Fe to cobalt ferrite. Increasing the value of saturation magnetization in 900 ^oC annealed sample compared to 800 ^oC one was attributed to decreased surface to volume ratio and crystallite size. The main reason of occurrence of maximum coercivity in 800  ^oC annealed sample was its low crystallite size.

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.

In this research, the wear behavior of commercial grades of WC-10wt%Co (H10F), WC-40vol%Co and WC-40vol%FeAl-B composites with different amounts of boron from zero to 1000 ppm has been investigated by the pin on disk test  method at high temperature. The wear tests were done under load of 40 N, a distance of 100 m and at ambient temperature, 200 ̊C and 300 ̊C. Wear surfaces were examined by scanning electron microscopy. The results showed that the wear resistance of all composites decreased with increasing temperature. The boron free WC-40vol%FeAl composite showed the lowest wear resistance at all ranges of temperature. In the presence of boron up to 500 ppm in iron-aluminide matrix, the high temperature wear resistance of these composites improves and the wear mechanisms changes from particle pullout into abrasive state. The toughness enhancement of these composites and plasticity enhancement of iron aluminide in the presence of boron, leads to better link of the interface of FeAl matrix and tungsten carbide particles, and thus increases the wear resistance of these composites. WC-40vol% FeAl-500ppmB composite has a higher wear resistance at high temperature than WC-40vol% Co and commercial WC-10wt% Co.
 

The aim of this investigation is obtaining WC-Co composite powder from WO₃ and Co₃O₄ by in-situ and carbothermic reduction method using activated carbon as a reducing agent. In this study, cobalt and tungsten oxide powders with 17% carbon (30% more than stoichiometric value) were mixed by ball-milling under atmosphere of argon for 20 hours. Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA) results on powder mixture show complete reducing of oxides at 1050°C and forming cobalt carbide and tungsten carbide. Compact samples underwent carbothermic reduction at 1050 °C for different times of 1, 2 and 4 hours with protective layer of alumina and carbon powder mixture with ratio of 1:1. Based on X-Ray Diffraction (XRD) analyses, the best holding time in furnace is 4 hours, in which tungsten reduction and carbonization is completed. XRD evaluation of reduced compacted samples in three conditions of atmosphere protective layer of alumina and carbon powder mixture with ratio of 1:1, protective foil of refractory steel and argon, shows that unreduced oxides and extra phases are present in argon atmosphere and protective foil of steel but not in alumina and carbon mixture layer. The measurement results of physical and mechanical properties on the sintered composite sample in heating rate of 5 °C /min to temperature 1500 °C and the holding time of 2 hours under a shielding layer of alumina and carbon shows obtaining the optimal properties (P_r=80%, K_IC=8.1 MPa , MHV=15.67GPa) comparable to that of advanced and costly methods.