Iranian Journal of Materials Science and Engineering

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Abstracts:

nanoparticles. All the extracts were used separately for the synthesis of gold nanoparticles through the reduction of

aqueous AuCl

gold ions to gold nanoparticles. The ethanol extract of black tea and its tannin free ethanol extract produced gold

nanoparticles in the size ranges of 2.5-27.5 nm and 1.25-17.5 nm with an average size of 10 nm and 3 nm, respectively.

The prepared colloid gold nanoparticles, using the ethanol extract of black tea, did not show the appropriate stability

during storage time (24 hours) at 4

showed no particle aggregation during short and long storage times at the same conditions. To the best of our

knowledge, this is the first report on the rapid synthesis of gold nanoparticles using ethanol extract of black tea and

its tannin free fraction.

In this research the ethanol extract of black tea and its tannin free fraction used for green synthesis of gold4¯. Transmission electron microscopy and visible absorption spectroscopy confirmed the reduction ofoC. In contrast, gold colloids, which were synthesized by a tannin free fraction

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ABSTRACT Macrosegregation has been received high attention in the solidification modeling studies. In the present work, a numerical model was developed to predict the macrosegregation during the DC Casting of an Al-4.5wt%Cu billet. The mathematical model developed in this study consists of mass, momentum, energy and species conservation equations for a two-phase mixture of liquid and solid in an axisymmetric coordinates. The solution methodology is based on a standard Finite Volume Method. A new scheme called Semi-Implicit Method for Thermodynamically-Linked Equations (SIMTLE) was employed to link energy and species equations with phase diagram of the alloying system. The model was tested by experimental data extracted from an industrial scale DC caster and a relatively good agreement was obtained. It was concluded that a proper macrosegregation model needs two key features: a precise flow description in the two-phase regions and a capable efficient numerical scheme

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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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Influence of formation of surface nano/ultrafine structure using deep rolling on plasma nitriding and tribological properties of the AISI 316L stainless steel was investigated. Initially, the deep rolling process was carried out on the bar-shaped specimens at 15 cycles with 0.2 mm/s longitudinal rate and 22.4 rpm bar rotation. Then, plasma nitriding treatment was applied on the as-received and deep rolled kinds at 450 °C and H₂-25% Vol. N₂ gas mixture for 5_­ h. Surface micro-hardness and un-lubricated pin-on-ring sliding wear tests were carried out on the as-received, deep rolled, plasma nitrided and deep rolled-plasma nitrided kinds. Results revealed that deep rolled-plasma nitrided kind is shown the highest wear resistance than the others, due to the further increased surface hardness achieved via the combined process.

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Spread extrusion is a capable method to produce different samples with a wider cross-section from the smaller billets in a single processing pass. In this study, dish-shaped samples are successfully produced from the as-cast cylindrical AM60 magnesium alloy at 300 °C, the mechanical properties and microstructural changes of the final specimens are precisely evaluated. Due to the high amount of plastic strain, which is applied to the initial billet during the material flow in the expansion process, grain refinement occurred as a result of recrystallization and subsequently good mechanical properties achieved. Therefore, mean grain size reduced from 160 µm to 14 µm and initial equiaxed grains changed to the elongated ones surrounded by fine grains. Also, microhardness measurements indicate that hardness increased from 51 Hv to 70 Hv. Some fluctuations were also observed in the hardness profile of the sample which was mainly related to the bimodal structure of the final microstructure. Good mechanical properties, fine microstructure, and also the ability to produce samples with higher cross-section make the spread extrusion process a promising type of extrusion.

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In the present work, accumulative roll bonding (ARB) was used as an effective method for processed of nano/ultrafine grained AA6063 alloy. Microstructural characteristics indicate considerable grain refinement leading to an average grain size of less than 200 nm after 7 ARB cycles. Texture analysis showed that 1-cycle ARB formed a strong texture near Copper component ({112}<111>). However, texture transition appeared by increasing the number of ARB cycles and after 7-cycle of ARB, the texture was mainly developed close to Rotated Cube component ({100}<110>). The results originated from mechanical properties indicated a substantial increment in strength and microhardness besides a meaningful drop of ductility after 7 ARB cycles.

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In this study, aluminum matrix composites reinforced with Al₂O₃ and SiC nanoparticles, and graphene nanoplatelets produced by Spark Plasma Sintering (SPS) were studied. The microstructural and mechanical properties of the composites were evaluated by changing the amounts of the reinforcing materials. The SEM images showed that the reinforcing particles were more distributed in the grain boundary regions. According to the results, the addition of alumina and SiC to the matrix caused an increase in the composite density whereas the composite density decreased by adding graphene nanoplatelets. The highest relative density of 96.3% was obtained for the composite containing 2 wt% Al₂O₃. The presence of the reinforcing particles increased the hardness of all the samples compared to the pure aluminum (39 HV). The composite containing 1 wt.% Al₂O₃, 0.7 wt.% SiC, and 0.3 wt.% graphene showed the highest hardness of 79 HV. Moreover, the plastic deformation of the specimens decreased and the slope of the plastic region increased by adding the reinforcing particles to the matrix.

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In this work, the addition of a combination of Graphene Oxide Nanoplatelets (GONPs) and Ground
Granulated Blast Furnace Slag (GGBFS) was studied as admixture in concrete. Tests on physical and mechanical
properties and chloride permeability were conducted. GGBFS was replaced with Ordinary Portland Cement (OPC)
and it was determined that GGBFS Up to 50% by weight improves the physical and mechanical properties of
concrete. GONPs with an optimal amount of 50% by weight of GGBFS were added to the concrete and the physical
and mechanical properties of the samples were determined. It was observed that the addition of GONPs was effective
in improving the mechanical strength and physical properties of specimens. The results indicated that addition of
0.1 wt.% GO and 50 wt.% GGBFS would increase the compressive strength of the concrete sample up to 42.7%
during 28 days and 46% during 90 days compared to OPC. Concrete with a combination of 0.1 wt.% GONPs and
50 wt.% GGBFS witnessed an increase in its flexural strength up to 58.5% during 28 days and 59.2% during 90
days. The results indicated that by adding 0.1 wt.% GO and 50 wt.%, concrete chloride permeability decreased
substantially 72% for 90 day cured samples compared to OPC. GONPs as an alternative to cement up to 0.1% by
weight can accelerate the formation of C-S-H gel, thereby increasing the strength and improving the resistance of
water absorption and chloride permeability. The effects of pozolanic reaction in the concrete leading to the filling
of the pores were significant factors in the proposed curtailment mechanism