Iranian Journal of Materials Science and Engineering

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Abstract: In this study Al-5 (Vol) % SiCp nanocomposite powder has been successfully synthesized by high-energy planetary milling of Al and SiC powders for a period of 25 h at a ball-to-powder ratio of 15:1. The changes of the lattice strain, the crystallite size of the matrix phase, and the nanocomposite powder microstructure with time have been investigated by X-ray diffraction (XRD), X-ray mapping, and scanning electron microscopy (SEM) analyses. The morphologies of the nanocomposite powders obtained after 25 h of milling have also been studied by transmission electron microscopy (TEM). The results showed that nanocomposite powders were composed of near-spherical particles and, moreover, the SiC particles were uniformly distributed in the aluminum matrix.

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Abstract: SiC nano particles with mono dispersed distribution were synthesized by using of silicon alkoxides and phenolic resin as starting materials. After synthesis of sample, characterizations of the obtained powder were investigated via Fourier Transform Infrared Spectroscopy (FTIR) with 400-4000 cm-1, X-ray Diffractometry (XRD), Laser Particle Size Analyzing (LPSA), Si29 NMR analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). FTIR and Si29 NMR results of the gel powder indicated that Si-O-C bonds were formed due to hydrolysis and condensation reactions . FTIR results showed a very strong peak for heat treated powder at 1500°C after carbon removal which is corresponded to Si-C bond. Obtained pattern from X-ray diffractometry showed that the final products contain -SiC phase with poly crystalline planes and little amounts of residual carbon. PSA results showed that the average particles size were 50.6 nm with monosized distribution. Also microstructural studies showed that the SiC nano powders have semi spherical morphology with mean particles size of 30-50 nm and also there are some agglomerates with irregular shape.

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Abstract: Microwave processing is one of the novel methods for combustion synthesis of intermetallic compounds and
composites. This method brings about a lot of opportunities for processing of uniquely characterized materials. In this
study, the combustion synthesis of TiAl/Al2O3 composite via microwave heating has been investigated by the
development of a heat transfer model including a microwave heating source term. The model was tested and verified
by experiments available in the literature. Parametric studies were carried out by the model to evaluate the effects of
such parameters as input power, sample aspect ratio, and porosity on the rate of process. The results showed that
higher input powers and sample volumes, as well as the use of bigger susceptors made the reaction enhanced. It was
also shown that a decrease in the porosity and aspect ratio of sample leads to the enhancement of the process.

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The process of mullitization of kyanite concentrate was studied at different conditions of heat treatment (1400
– 1600 °C and 0.5 – 3.5 hours) and particle size of raw materials (38-300 ?m). Kyanite concentrate was obtained from
ore-dressing of kyanite deposits of Mishidowan-Bafgh region at 100 km northeastern part of Yazd. The results of
microstructure (shape, distribution and size of the grains) and phase evolution studies by SEM and XRD showed that
total transformation of kyanite to mullite takes place by heat treatment between 1500 –1550 °C during 2.5 hours.. At
temperatures below 1500 °C need-like mullite grains are always produced. At higher temperatures the mullite grains
reveal rounded and platelet morphology. At 1550 °C, the rate of mullitization and densification were improved by
increasing soaking time from 1h to 3h and decreasing particle size of materials from 300 to 38 m

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Microstructure and properties of the Al-6Si-0.3Mg alloys containing scandium (0.2 to 0.6wt %) were investigated. The microstructure was observed by optical microscopy, the hardness was determined by Vickers tester and phase transformation was investigated by differential scanning calorimetry (DSC) technique. The results showed that scandium can refine dendrites, enhance hardness in the aged alloys and suppress softening effect during prolonged ageing treatment.

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The effect of Y2O3, CeO2, P2O5, ZrO2 and TiO2 in single, double and triple form on crystallization mechanism of Li2OAl2O3- SiO2(LAS) glass-ceramic system was investigated .The nucleation and crystallization peak temperatures of optimized samples in each group were determined by Ray & Day method .The crystalline phase was determined by the X-ray diffractometery .The micro-structure of the samples was studied by SEM techniqe .Crystallization activation energy ,E, and kinetic constants(n ,m) were determined by differential thermal analysis (DTA) through Marotta and Augis-Bennet methods .According to the results ,the Avrami constants(m ,n) derived from the Marotta and Augis- Bennett, glasses containing both ZrO2 and TiO2 nuclei were showed bulk crystallization .The crystallization mechanism of specimens containing ZrO2, TiO2 and CeO2 in the triple nuclei series represent two-dimensional bulk crystallization .By comparison of Avrami constants and activation energy of crystallization of optimized samples with other results they gave much lower value of E(255.5 kJ/mol) and higher value of n in 4.38.The lattice constants of the main phase( -eucryptite solid solution)in samples were determined according to the XRD results

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TiO2/SiO2 nanocomposite with molar ratio 1:1 was synthesized by a free calcination sol-gel method using titanium tetra chloride and tetraethylorthosilicate as raw materials. In the composite, TiO2 nanocrystals are highly dispersed in the amorphous SiO2 matrix and the mater showed size quantization effect arising from the presence of extremely small titanium oxide species having a low coordination number. Thermal phase transformation studies of the as-prepared composite were carried out by means of X-ray diffraction (XRD) patterns and thermogravimetry–differential scanning calorimetry (TG–DSC) analyses. The studies showed existence of anatase phase in all the tested temperatures. When temperature exceeds 400°C, brookite phase was formed beside anatase phase. At 950°C amorphous silica matrix was transformed to crystobalite and brookite phase disappeared. Finally, small peaks of rutile phase were detectable at 1100°C.

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The wide-gap aluminothermic rail welds with root opening of 50-70 mm were produced using plain carbon steel rail and non-alloy aluminothermic charge. Mechanical properties and micro-structure of the weld metal and HAZ as well as the impact energy and the fracture toughness of the welds were investigated. The yield and tensile strength of wide-gap welds were about 98% and 95% of the base metal, respectively. Both minimum and maximum hardnesses of the joint were seen in HAZ which were related to the grain coarsening and normalizing, respectively. The mean value of wide-gap weld fracture toughness is more than narrow-gap weld. Moreover, trans-granular cleavage indicated the brittle fracture mode of the weld metal.

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Abstract: A thermodynamic model was used to find out the optimum temperature for the growth of ZnS single crystals in closed ampoules by chemical vapor transport technique. Based on this model 1002 °C was found to be optimum temperature for 2 mg/cm3 concentration of transporting agent (iodine). ZnS Crystals were grown in optimum (1002 °C) and non-optimum (902 °C and 1102 °C) temperatures. The composition structure and microstructure of the grown crystals were studied by Atomic absorption spectroscopy, X-ray diffraction and Scanning electron microscopy measurements. Properties of the grown crystals were correlated to the growth conditions especially a stability in mass transport along the closed tube length.

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Abstract: Nickel was electrodeposited onto copper substrates with high {111} and {400} peak intensities. The grain size of coatings deposited onto the copper substrate with a higher {111} peak intensity was finer. Spheroidized pyramid morphology was obtained at low current densities on both copper substrates. By increasing the deposition current density, grain size of the coating was increased for both substrates and eventually a mixed morphology of pyramids and blocks was appeared without further increase in grain size. This decreased the anodic exchange current density probably due to the decrease of surface roughness and led to a lower corrosion rate.

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C-SiC composites with carbon-based mesocarbon microbeads (MCMB) preforms are new type of highpreformance and high-temperature structural materials for aerospace applications. In this study MCMB-SiC composites with high density (2.41 g.cm-3) and high bending strength (210 MPa,) was prepared by cold isostatic press of mixed mesophase carbon powder derived from mesophase pitch with different amount (0, 2.5, 5%) nano SiC particles. All samples were carbonized under graphite bed until 1000 °C and finally liquid silicon infiltration (LSI). Microstructure observations resultant samples were performed by scanning electron microscopy and transition electron microscopy (SEM & TEM). Density, porosity and bending strength of final samples were also measured and calculated. Results indicates that the density of samples with nano additive increased significantly in compare to the free nano additives samples.

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In this study the effect of Al–5Ti–1B grain refiner on the structural characteristics and wear properties of Al–12Zn–3Mg–2.5Cu alloy was investigated. The optimum amount for Ti containing grain refiners was selected as 2 wt.%. T6 heat treatment, (i.e. heating at 460 °C for 1 h before water quenching to room temperature and then aging at 120 °C for 24 h) was applied for all specimens before wear testing. Dry sliding wear resistant of the alloy was performed under normal atmospheric conditions. The experimental results showed that the T6 heat treatment considerably improved the resistance of Al–12Zn–3Mg–2.5Cu alloy to dry sliding wear.

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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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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 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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The microstructure and mechanical properties of 7075 wrought aluminum alloy produced by strain induced melt activation (SIMA) route were investigated.Also liquid volume fraction measurement was studied by three procedures. Remelting process was carried out in the range of 560 to 610 °C for 20 min holding. The microstructure in the semi-solid state consists of fine spherical solid grains surrounded byliquid.The mechanical properties of the alloy vary with the grain size and weak mechanical properties of globular samples would appear if an alloy reheated at a high temperature. Thermodynamic simulation is a fast and efficient tool for the selection of alloys suitable for semi-solid processing

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Mono dispersed nano SiC particles with spherical morphology were synthesized in this project by hydrolysis and condensation mechanism during sol gel processing. pH, temperature and precursor’s ratio considered as the main parameters which could influence particles size. According to DLS test results, the smallest size of particles in the sol (<5nm) was obtained at pH<4. It can be observed from rheology test results optimum temperature for achieving nanometeric gel is about 60 ˚C. The optimum pH values for sol stabilization was (2-5) determined by zeta potentiometery. Si 29NMR analysis was used in order to get more details on final structure of gel powders resulted from initial sol. X-ray diffraction studies showed sythesized powder consists of β-SiC phase. Scanning electron microscopy indicated agglomerates size in β-SiC synthesis is less than 100 nm. Finally, TEM studies revealed morphology of β-SiC particles treated in 1500˚C and after 1hr aging is spherical with (20-30) nm size

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Microstructure and corrosion performance of admiralty brass (ADB) and aluminum brass (ALB) alloys after passing different annealing heat treatments were investigated using optical and scanning electron microscope, energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), DC polarization measurements and electrochemical impedance spectroscopy (EIS). The results showed that heat treating of ALB caused gradient in aluminum concentration across the grains whose increased with increasing of annealing temperature. On the other hand, corrosion current density (i corr) of ADB in 3.5%NaCl media decreased with increasing of recrystallization, while ALB showed corrosion behavior inconsistent with ADB. The impedance measurements showed that corrosion rate of ADB decreased with increasing of exposure time from 0 to 15 days which could be related to the formation of SnO 2 surface film and the Sn-rich phases. While polarization resistance of ALB decreased by passing days in the corrosive media which could be associated to establishing of differential aluminum concentration cells.

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This article examines the Weibull statistical analysis that was used for investigating the effect of melt filtration on tensile properties and defects formed inside the casting. Forming and entrapping of double oxide films have been explained by using the context of critical velocity of melt in the runner. SutCast software results were used to examine the amounts of the velocity of melt as such. SEM/EDX analysis is used to observe the presence of double oxide films in the fracture surfaces of the tensile specimens. The article goes on to propose that castings made with foam filters with smaller pores show higher mechanical properties and reliability due to higher Weibull modulus and fewer defects