Iranian Journal of Materials Science and Engineering

---

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

---

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.

---

Shrinkage behavior of a geopolymer cement paste prepared from pumice-type natural pozzolan was studied
by changing parameters of chemical composition including SiO2/Na2O molar ratio of activator and total molar ratios
of Na2O/Al2O3, and H2O/Al2O3. For investigating the effect of curing conditions on shrinkage, hydrothermal curing
was also applied. The obtained results clearly revealed the governing effect of chemical composition on shrinkage.
Mixes with different Na2O/Al2O3 molar ratios exhibited different shrinkage behavior due to variations made in
SiO2/Na2O molar ratio. Application of hydrothermal curing after a 7-day period of precuring in humid atmosphere
also showed strong effect on shrinkage reduction.

---

Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.

---

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

---

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

---

This article addresses the interplay between heat of hydration and physico-mechanical properties of calcium sulfate hemi-hydrate in the presence of retarding additives such as citric and malic acids and sodium citrate. The heat of hydration was measured using a semi-isothermal calorimeter. Results proved that citric and malic acids had superior impact on hydration and mechanical properties. While the concentration of additives was increasing, the maximum heat of hydration was decreasing from 56.15 cal/g.min for blank sample to 33 cal/g.min for high concentrations of citric and malic acids. Consequently, the measured time to this maximum heat of hydration and thus the induction period were increased significantly from 5 to 105 min. Mechanical results indicated that the increase in the amounts of additive led to the reduction of the compressive strength from 16.25 MPa in the blank sample up to 74% for the highest concentration of malic acid

---

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.

---

---

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.

---

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.

---

Modification of MnFe₂O₄@SiO₂ core-shell nanoparticles with (3-aminopropyl) triethoxysilane (APTES) was investigated. The magnetite MnFe₂O₄ nanoparticles with an average size of ~33 nm were synthesized through a simple co-precipitation method followed by coating with silica shell using tetraethoxysilane (TEOS); that has resulted in a high density of hydroxyl groups loaded on nanoparticles. The prepared MnFe₂O₄@SiO₂ nanoparticles were further functionalized with APTES via silanization reaction. For having suitable surface coverage of APTES, controlled hydrodynamic size of nanoparticles with a high density of amine groups on the outer surface, the APTES silanization reaction was investigated under different reaction temperatures and reaction times. Based on dynamic light scattering (DLS) and zeta potential results, the best conditions for the formation of APTES-functionalized MnFe₂O₄@SiO₂ nanoparticles were defined at a reaction temperature of 70 °C and the reaction time of 90 min. The effectiveness of our surface modification was established by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). The prepared magnetite nanostructure can be utilized as precursors for synthesizing multilayered core-shell nanocomposite particles for numerous applications such as medical diagnostics, drug, and enzyme immobilization, as well as molecular and cell separation.

---

Microscopic studies has shown that adjacent to the interface between cement paste and aggregate, there exists an area with high porosity and low binding compounds that is referred to as interfacial transition zone (ITZ). ITZ in concrete and mortar imposes a number of negative effects, including flexural and compressive strengths reduction and permeability enhancement. That’s why many research attempts have been devoted to limit ITZ and its negative effects. The present study investigates the possibility of utilizing fine Portland cement (PC) clinker as a reactive aggregate in mortar for the same purpose. For this, natural quartz sand in normal mortar (NM) was totally replaced with PC clinker of the same particle size distribution and the most important engineering properties of the new mortar referred to as Reactive Aggregate Mortar (RAM) were measured and compared with NM as control. The results of compressive strengths measurements represented 65% and 21% increases at curing ages of 7 and 90 days, respectively, for RAM compared to NM. Chloride penetration depth in RAM displayed reductions by about 33% and 26% after 14 and 28 days of exposure, respectively. The effect of PC clinker reactivity on the microstructure and size of ITZ was studied by using scanning electron microscopy.

---

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.

---

Quaternary ammonium compounds (QACs) are among the most commonly used antibacterial agents. The aim of this study was to synthesize a dimethacrylate monomer functionalized with a QAC and to study its effect on the properties of an orthodontic adhesive primer. Urethane dimethacrylate monomer functionalized with a QAC (UDMAQAC) was synthesized and then characterized by nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). 5, 10, 15 and 20 wt% of UDMAQAC was added to an orthodontic adhesive primer (control group). FTIR analysis was used to measure the degree of conversion (DC). The bond strength of dental brackets was measured by shear bond strength (SBS) test and adhesive remaining index (ARI) was evaluated by stereomicroscope. Agar diffusion test and MTT assay were used to evaluate the antibacterial property and cell viability, respectively. Statistical analysis included one-way ANOVA with Tukey’s post hoc test and Kruskal-Wallis nonparametric test (P˂0.05). Although the obtained data did not show significant differences between the SBS and DC of different groups, but the highest values were obtained by adding 10 wt% monomer. Adding more than 10 wt% UDMAQAC resulted in significant increase in antibacterial property. The 15 and 20 wt% groups showed significantly lower cell viability

---

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

---

The introduction of the 2D materials in recent years has resulted in an emerging type of the constructed structures called van der Waals heterostructures (vdWHs) that take advantage of the 2D materials in forming atomically thin components and devices. The vdWHs are constructed by the stacking of 2D materials by van der Waals interactions or edge covalent boning. The electron orbitals of the 2D layers in vdWHs extend to each other and influence the electronic band structures of the constituent layers. The tunable optical response over a wide range of the wavelengths (NIR to visible) can be obtained by assembling vdWHs through combining of the monolayers. By application of 2D layers in vdWHs, p-n heterojunctions without lattice mismatch can be formed. The photodiodes based on the van der Waals interactions could be considered as promising candidates for future optoelectronic devices. Furthermore, on-chip quantum optoelectronics can move to the next generation by using 2D materials in vdWHs. In this review, the vdWHs are introduced and their properties and applications in light-emitting diodes (LEDs) have been discussed. The vdWHs allow bandgap engineering, and hence, LEDs working in a range of the wavelengths can be realized. The applications of vdWHs in forming atomically thin components in optoelectronic devices and LEDs have been addressed.
 

---

Amorphous calcium phosphate (ACP) which is a transient phase in natural bio-mineralization process has recently gained the spotlight. This study aimed to assess the effect of incorporation of nano-ACP (NACP) in a dental adhesive with/without surface treatment with silane coupling agent on bond strength. NACP was synthesized by the wet chemical precipitation technique. To characterize the structure of NACP, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used. Forty molars were randomized into 4 groups of 10. The teeth were restored with composite resin and the bonding agent (one of the four groups). Adper Single Bond 2 was used as the control group. In 4wt% NACP group, NACP fillers were added to the bonding agent. In 0.4wt% and 4wt% SNACP groups, silanized NACP fillers were added to the bonding agent. Finally, the mode of failure of specimens was determined. Data were analyzed by one-way ANOVA and Tukey's post-hoc tests. P<0.05 was considered statistically significant. Addition of 4wt% non-silanized NACP decreased the bond strength compared with the control group (P<0.05). The bond strength of the groups with silanized fillers was not significantly different from that of the control group. Addition of silanized NACP to dental adhesive had no significant adverse effect on bond strength, which is a promising finding to pave the way for the synthesis of bonding agents containing bioactive fillers.

---

This study investigates the microstructural evolution and variations in the mechanical properties of pre-cold worked Nimonic 80A superalloy, subjected to two levels of deformation (25% and 50%) and welded via Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques using ER309L filler wire. The objective is to evaluate the effect of the initial microstructure on the welding behavior of Nimonic 80A and compare the weldments produced using GTAW and PCGTAW. Microstructural characterization was conducted using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). XRD analysis demonstrated that the welding pulsed current mode, compared to the continuous current mode and at equal heat input, led to a refined microstructure, suggesting improved welded mechanical properties of the weld. It also showed a potential reduction in grain refinement with a higher level of cold work. Tensile testing demonstrated that fractures consistently occurred within the weld zone (WZ), with the PCGTAW sample achieving the highest tensile strength (766 MPa). Microhardness analysis indicated a notable reduction in hardness within the heat-affected zone (HAZ) and WZ, particularly in the 50% pre-cold worked sample. However, PCGTAW retained higher hardness due to its refined microstructure. The weld metal primarily consisted of an austenitic microstructure characterized by dendrites and interdendritic precipitates. Microstructural analysis revealed that welding induced significant changes in the weldment, with the PCGTAW sample exhibiting a more uniform microstructure and smoother transitions at the weld interface. Fractography confirmed ductile fracture in all specimens, with smoother and more uniformly distributed dimples in the PCGTAW sample. These findings highlight the advantages of pulsed current welding in optimizing the mechanical performance of Nimonic 80A welds and suggest its potential application in industries requiring superior weld quality.

---

This work reports the influence of Cu dopant and annealing temperature on CdO_x thin films deposited on glass substrates by spray-pyrolysis method. The Cu doping concentrations were 0, 0.46, and 1.51 at% with respect to the CdO_x undoped material. Then, the fabricated films were subjected to annealing process at temperature of 450°C. X-ray diffraction (XRD) examination confirms that the as-deposited films show a cubic crystallographic structure with high purity of CdO in the annealed films. It was found that the (111) peak is the most predominant diffraction orientation in the surveyed samples. At the microscopic scale, AFM machine was operated to quantify the three important parameters of the mean roughness (Ra), rms value (Rq), and z scale. These parameters hold highest values for the sample with 0.46 at% of Cu. Finally, reflectance, absorbance, transmittance and other optical parameters dielectric measurements were comprehensively analyzed. Our evaluation of optical band gaps for the studied samples reveals that the synthesized films have direct band gap character with the fact that the rise in the Cu contents in the as-deposited films lead to lessen the band gap values. In contrast, annealing process results in raising the band gap.