Iranian Journal of Materials Science and Engineering

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Several extensive researches are being carried out in the field of 3D printing. Polymer matrices, such as High-Density Polyethylene (HDPE), are less explored in particular on the microstructure and mechanical properties of HDPE composites developed via Fused Deposition Modelling (FDM) process. Very scarce amount of works is devoted to study HDPE’s reinforced with carbon nano-tubes (CNT’s) . In the present work, we report on the mechanical properties of  HDPE composites prepared via FDM process. Varying proportions of CNTs ( 0.5, 1, 1.5 and 2%) are used as reinforcements. It is found that increasing CNT content enhances impact and tensile strength, with HDPE/2.0%CNT outperforming pure HDPE by approximately 71.6% and 25.4%, respectively. HDPE/2.0%CNT composite also showed Young's modulus approximately 49.2% higher than pure HDPE. According to fracture analysis, pure HDPE failed near ductile, whereas composites failed brittle. CNTs occupy the free positions in the polymeric chains, and their tendency to restrict chain mobility causes HDPE to lose ductility and begin to behave brittle. The use of CNTs as reinforcement successfully improved the mechanical properties of HDPE.

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In this study, the potential of calcined montmorillonite as a primary precursor for one-part alkali-activated cement incorporated with high percentage of limestone, is evaluated. Comparative studies on the properties of the sodium silicate activated metakaolin-limestone and metamontmorillonite-limestone fresh and hardened cement pastes depending on several formulation and processing parameters (precursor nature, dosages of limestone and alkali reactant, curing conditions) showed that metamontmorillonite exhibits reactivity comparable to that of metakaolin in the studied cement systems. The mechanical performance of optimal alkali-activated cement formulations consisted of 20-30% of metamontmorillonite and 70-80% of limestone is provided by both reactivity of metamontmorillomite under sodium silicate activation and the filler, nucleation, and chemical effects of the raw limestone. The reaction products and microstructures of alkali-activated metamontmorillonite-limestone cement-based hardened pastes were investigated using thermal, XRD, and SEM/EDS analyses.   
 

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Phase transformations and the evolution of hardness during elevated-temperature annealing of Inconel 718 superalloy manufactured by the laser powder bed fusion (L-PBF) were investigated. The microstructural evolution, elemental analysis, phase formation, and hardening were characterized by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and Vickers indentation test, respectively. It was observed that the effect of annealing treatments is directly governed by the annealing parameters (i.e. time and temperature), for which the hardness measurement as a fruitful and convenient tool can reveal this effect. The increase of the hardness, which was obtained by the annealing (aging) treatments at the temperature range of 800-900 °C, indicated precipitation of the Ni₃Nb γ˝ strengthening phase; while owing to the coarsening of precipitates as a results of overaging at this temperature range, the hardness decreased. For instance the length and aspect ratio of precipitates in the aged sample at 800 °C for 1 h is 67.14 nm and 0.32, respectively; while these values in the aged sample at 800 °C for 8 h is 78.34 nm and 0.44, respectively. On the other hand, the decrease of the hardness at temperatures of 950 and 1000 °C was attributed to the decrease of dislocation density in conjunction with the Ni₂Nb Laves phase dissolution. Hence, it is crucial to determine the annealing parameters according to the required microstructure and properties.

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In the present investigation, an attempt was made to evaluate the dissolution behavior of Ti in molten KCl-LiCl. The X-ray diffraction (XRD) pattern of heated Ti plate at 800 oC for 4 h without carbon black in molten salt revealed that TiCl3 formation was feasible. For more assurance, Ti plate was heated at 950 oC for 4 h in the presence of carbon black to identify synthesized TiC. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images from precursors and the final product showed that nano-crystalline TiC formation from coarse Ti particles was almost impossible without Ti dissolution. Thermodynamics calculations using Factsage software proved that it was possible to form various TiClx compounds. The TiC formation mechanism can be discussed in two possible ways: a reaction between Ti ion and carbon black for synthesizing TiC (direct) and a reaction between TiCl4 and carbon black led to indirect TiC synthesis. Elemental mapping using energy dispersive X-ray spectroscope (EDS) indicated that up to 815 oC, chlorine existed in the map. 

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Deformation-induced α΄-martensite generally forms at shear bands in the coarse-grained austenite, while it nucleates at grain boundaries in the ultrafine-grained (UFG) austenite. The available kinetics models are related to the nucleation on the shear band intersections, and hence, their application to investigating the kinetics of α΄-martensite formation for the UFG regime cannot be justified. Accordingly, in the present work, the general Johnson–Mehl–Avrami–Kolmogorov (JMAK-type) model was implemented for comparing the kinetics of α΄-martensite formation in the UFG and coarse-grained regimes using an AISI 304L stainless steel. On the experimental front, the X-ray diffraction (XRD) patterns and the electron backscattered diffraction (EBSD) maps were used for phase and microstructural analyses, respectively. It was revealed that the simple JMAK-type model, by considering the dependency of the volume fraction of α΄-martensite on the strain, is useful for modeling the experimental data, predicting the nucleation sites based on the theoretical Avrami exponents, and characterizing the transformation kinetics at low and high strains.

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Two-dimensional molybdenum disulfide (MoS₂) is used as a promising flame retardant and smoke suppressant nano additive in polymer composites due to its high thermal stability and layered structure. In this study, thermoplastic polyurethane (TPU) was melt-blended with MoS2 (1wt. %) and a halogen-free intumescent flame retardant (IFR) system. The IFR system consisted of ammonium polyphosphate (APP), Melamine polyphosphate (MPP), and pentaerythritol (PER), with a total amount of 25 wt. %. The TPU/IFR/MoS2 composite exhibited outstanding flame-retardant properties, achieving a UL-94 V-0 rating and a limiting oxygen index (LOI) value of 34%. Reaction-to-fire performance of the TPU/IFR/MoS2 composite was evaluated by cone calorimeter test (CCT). The CCT results indicated high flame-retardant efficiency and considerable smoke suppression performance, along with a significant decrease in the peak heat release rate (PHRR: 65.9%), peak smoke production rate (PSPR: 65.6%), and peak CO production (PCOP: 60.7%) compared to the neat TPU. The significant improvement in fire performance of TPU composite was mainly attributed to the effects of the physical barrier of MoS2 and catalytic carbonization of the IFR system. These resulted in forming an intumescent compact carbonized layer during the combustion, effectively restricting dripping. The continuous structure of the residual char was revealed by FESEM. Thermogravimetric analysis (TGA) indicated improved thermal behavior of the TPU composite in high temperatures. This work provides an effective method to improve the reaction to fire of TPU composites by incorporating traditional IFRs and MoS2, resulting in enhanced fire safety.

 
 

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The coated β-tricalcium phosphate (β-TCP) with dicalcium phosphate dihydrate (DCPD) has attracted much attention in the biomaterials field due to the increase in its osteoconductivity. Besides, the porous bioceramic scaffolds with controlled pore sizes are significant in stimulating bone-like cell activity. In this study, the effect of the setting-time process and acidic-calcium phosphate (CaP) concentrations on the fabrication and properties of porous DCPD/ β-TCP scaffolds were studied. Subsequently, the specimens were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), compression strength and Fourier transforms infrared (FTIR). The study results revealed that the porous DCPD/ β-TCP scaffolds with macro- and micropore sizes were successfully obtained after the 300-600 µm of porous β-TCP granules were exposed to an acidic-CaP solution. Furthermore, the setting-time process and acidic-CaP concentrations increased the DCPD interlocking between granules, and the mechanical strengths of scaffolds increased up to 0.5 MPa. Meanwhile, the porosity levels were changed based on the formation of DCPD crystals. This study was expected to provide novel insights to researchers in the field of bioceramics through its investigation on the creation of porous DCPD/ β-TCP scaffolds.

 

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The Nickel tungsten (Ni-W) alloy was electrodeposited on stainless steel (SS) substrate using potentiostatic mode at room temperature. Potentiostatic electrodeposition was carried out by varying the deposition time. The physicochemical properties of Ni-W alloys were studied using X-Ray diffraction (XRD), Electron Microscopy and micro-Raman spectroscopy. Recorded XRD spectra was compared with standard JCPDS card and the presence of Ni was confirmed, no such peaks for W were observed. Further study was extended for micro-Raman analysis. From Raman spectroscopy study the appearance of Ni-O and W⁶⁺=O bonds confirms that the Ni-W present in amorphous phase. Several cracks were observed in SEM images along with nanoparticles distributed over the electrode surface. The appearance of cracks may be correlated with the in-plane tensile stresses, lattice strains and stacking faults and may be related to the substrate confinements.
 

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Heterostructure photocatalyst of CuWO₄ modified SnO₂ (CuWO₄/SnO₂) was fabricated by in simple wet-impregnation process and evaluated via degradation of rose Bengal (RB) under visible light irradiation. The samples had been completely characterized by Ultraviolet-visible diffuse reflectance spectroscopy (UV-vis-DRS), X-ray diffraction (XRD), Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), High-resolution TEM (HR-TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett and Teller surface analysis (BET). The result divulged that amongst the catalysts, CuWO₄/SnO₂ displayed higher photocatalytic activity than CuWO₄ or SnO₂. The enhanced photocatalytic efficiencies are attributed to the charge transfer from SnO₂ to CuWO₄ nanoparticles, which efficiently decrease electron-hole recombination energy level. The time required for maximum degradation of rosebengal (RB) under visible light over CuWO₄/SnO₂ was 180 min. The other parameters such as pH (pH=8), photocatalyst dosage (0.2 g/L) and dye concentration (20 µM) were optimized to achieve high degradation efficiency (98.5%). The excellent photocatalytic activity of CuWO₄/SnO₂ is due to efficient separation of photogenerated electron-hole pairs. The holes (h⁺) and superoxide radicals (O₂^•-) are the reactive species involved in photocatalytic mechanism for gdegradation of RB.

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In this study, the hot deformation and dynamic recrystallization behavior of low carbon steel containing 21 ppm boron was investigated. After homogenizing the samples at 1250 ℃ for 1-hour, hot compression tests were conducted at temperatures ranging from 850 ℃ to 1150 ℃ and strain rates from 0.01 to 10 s⁻¹, resulting in strain-stress flow curves. Following corrections, calculations and modeling were performed based on Arrhenius equations. Among them, the hyperbolic sine relationship provided the most accurate estimate and was selected as the valid model for the applied strain range. According to this model, the deformation activation energy (Q), was determined to be 293.37 KJ/mol. Additionally, critical and peak stress and strain values were obtained for each temperature and strain rate, and power relationships were established to describe their variation with respect to the Zener-Hollomon parameter (Z). Recrystallization fractions were derived by comparing the hypothetical recovery curves with the material flow curves, and the results were successfully modeled using the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The Avrami exponent was measured at approximately 2, indicating that nucleation predominantly occurred at grain boundaries. Microstructural analysis revealed that at higher Z values, recrystallization occurred along with a fraction of elongated grains, while lower Z values resulted in a greater fraction of equiaxed dynamic recrystallization (DRX) grains. The average grain sizes after compression tests at 950 ℃, 1050 ℃, and 1150 ℃ were measured as 21.9 µm, 30.4 µm, and 33.6 µm respectively at a strain rate of 0.1 s⁻¹, and 17.7 µm, 28.7 µm, and 31.3 µm at 1 s⁻¹. The overall microstructure displayed a more uniform grain size distribution with increasing deformation temperature.

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ZrO₂ is commonly incorporated into ceramic glass substrates to enhance radiopacity, mechanical strength, and chemical durability. Experience has shown that the crystallization of tetragonal zirconia in glass will have a greater effect on the mechanical properties of ceramic glass. To achieve optimal properties in zirconia, stabilizing oxides are often added to enhance its structural and mechanical qualities. In this research, in order to stabilize the tetragonal phase of zirconia, MgO and CeO₂ were added to the glass ceramic composition of the Li₂O-SiO₂-ZrO₂ system and the desired dental substrate was synthesized through the sinter process. The behavior of sintering and crystallization of basic and optimized glass was investigated using HSM and DTA thermal analysis, respectively. The results showed that the optimal sinter temperature, heat press and heat treatment are equal to 730°C, 900°C and 825°C, respectively. Then, in order to determine the crystallization behavior of the prepared samples, X-ray diffraction and microstructure images were used. The results also showed that the presence of the main Li₂ZrSi₆O₁₅ phase crystallizes at a temperature of 825°C in the base sample and the sample containing ceria. Also, due to early formation of MgSiO₃ crystals, magnesia prevents sintering and formation of Li₂ZrSi₆O₁₅ phase and stability of tetragonal zirconia phase. In the sample containing ceria, during crystallization, ZrO₂ entered its crystal structure and led to the stability of the tetragonal zirconia phase at room temperature.