Iranian Journal of Materials science and Engineering
Volume:17 Issue: 4, Dec 2020

In the present investigation effects of time and temperature on plasma nitriding behavior of DIN 1.2344 (AISI H13) steel are studied. Pulsed plasma nitriding process with a gas mixture of N2 = 25% + H2 = 75% and duty cycle of 70% is applied to cylindrical samples of DIN 1.2344 hot work tool steel. X-ray diffraction, surface roughness, microhardness and ball on disc wear test are performed and behavior of plasma nitrided samples are compared. Scanning electron microscopy and optical microscopy are used in order to observe the microstructure of samples after nitriding. XRD results showed that the compound layer is dual phase. Hardness near the surface dropped by rising the process temperature and it rose in longer process durations. The comparison of µ results showed frictional properties in longer durations with lower temperatures is approximately the same in higher temperatures with shorter durations.

The field of nanomaterial has greatly advanced in the last decade following a wider range of applications in the fields of electronics, automobiles, construction, and healthcare due to its extraordinary and ever-evolving properties. Synthesis of the nanomaterial plays a crucial role in redefining the current engineering and science field. At the same time, procuring an environment-friendly end product through eco-friendly solutions and sustainable processes is the key to many global problems. Green synthesis of nanomaterials like graphene and its derivatives involves mild reaction conditions and nontoxic precursors because it is simple, cost-effective, relatively reproducible, and often results in more stable materials. This paper primarily focuses on the green synthesis of graphene and its derivatives (graphene oxide & reduced graphene oxide) and geopolymers; a green technology for preparing graphene reinforced geopolymer composites. Various methods used globally for green synthesis of graphene and geopolymer are briefly discussed and this paper tries to integrate these two areas for a green end product. Possible applications of these green composites are also discussed to provide insights on the current growth and developments.

Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO..Graphene oxide (GO) and reduced graphene oxide (rGO) is a semiconductor device which finds its many applications in the various electronic devices. In the present study GO and rGO thin sheets have been grown over Si wafers using Hummer’s and modified Hummer’s method and a comparison in the properties of the coatings have been carried out. The morphology of the sheets characterized by SEM revealed similar transparent sheet like structure for both the chemical synthesis. The diffraction pattern of GO and rGO prepared with modified Hummer’s method showed peak shift to lower diffraction angle from 9.96 o to 9.63 o and 26.4 o to 26.3 o respectively. The diffraction peaks were observed at diffraction phase of 001 and 002 crystal plane. FTIR spectra revealed presence of oxygen functional groups in GO thin sheets whereas peaks for oxygen functionalities are absent in rGO. The polarization curve indicated similar corrosion resistance of GO and rGO thin sheets grown under Hummer’s and modified Hummer’s. Capacitive property of rGO is better than GO as observed by the electrochemical analysis of GO and rGO.

In this work, the facile synthesis and identification of hexylmethylimidazolium bis(trifluoromethyl sulfonyl) amide ([HMIM] TFSA) and hexylmethylimidazolium triethyltrifluorophosphate ([HMIM]FAP) ionic liquids (ILs), as multifunctional and multipurpose gear oil additives, is introduced. The tribological tests indicated that both ([HMIM]TFSA) and ([HMIM]FAP) ILs demonstrate antiwear/extreme pressure properties (AW/EP) to the gear oils by preventing wear and scar of the lubricated system at low and high temperatures. [HMIM]TFSA provided superior performance in comparison to [HMIM]FAP. Because of the presence of heteroaromatic imidazole moiety in the ILs structure, the prepared ILs also imparted anticorrosion, antioxidant, and anti-rust properties to the lubricant. All these observations confirmed that the ILs are single component multifunctional and multipurpose oil additives. In addition, due to avoiding the use of toxic and harmful elements in the preparation of ILs make the fabricated oils potential candidates for green lubricants.

In the present study, austempering heat treatment was performed on compacted graphite aluminum cast iron with the chemical composition of 4.8%wt Al, 3.2%wt C, 0.81%wt Ni, 0.37%wt Mn, and 0.02%wt Mg. This study aims to investigate the effect of aluminum additions and removal of silicon on the kinetics of austempering transformation of Fe-3.2%C alloy. The cast samples were austenitized at 900 °C for 120 min and the isothermal austempering heat treatment was performed at 200 °C, 300 °C and 400 °C for 5, 30, 60, 120 and 180 minutes, respectively. Kinetics of this transformation was studied by X-Ray diffraction (XRD) analysis. The effect of temperature and time on the microstructure and hardness of the austempered samples was investigated and discussed. The presence of Al was seen to prolonged formation of the carbides from high carbon austenite, and that expanded the process window in the austempering transformation. Besides, the lower bainitic ferrite phase was observed in the austempered samples at 200 °C and 300 °C. Increasing austempering temperature to 400 °C changed the lower bainite to upper bainite structure. The volume fraction of austenite reached its maximum level (34.6 %) after austempering the samples at 400 °C for 30 minutes.

The graphene oxide -TiO2 (GO-TiO2) and pre-reduced graphene oxide -TiO2 (rGO-TiO2) nanocomposites were fabricated successfully by hydrothermal method. The microstructure of synthesized nanocomposites was investigated using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS) analysis. Moreover, galvanostatic charge/discharge (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods in three electrode system were applied to evaluate electrochemical properties. The results revealed that nanoparticles distributed more uniformly on graphene sheets, at lower concentrations of TiO2. The rGO-TiO2 and GO-TiO2 nanocomposites showed 224 and 32 F/g specific capacitance at 5 mV s-1 scan rate in 1 M KOH aqueous electrolyte, respectively. The pre-reduction of graphene oxide is the main reason for the better electrochemical performance of rGO-TiO2 nanocomposite compared to GO-TiO2 nanocomposite.

In this article, a novel bio-nanocomposite consists of sodium alginate polymer-based graphene nanosheet enhanced incorporating wollastonite containing various amount of graphene nanosheet were produced using freeze-drying technique. The bio-nanocomposites were mechanically and biologically evaluated using tensile strength and biological test. The phase and topological characterization were conducted using scanning electron microscopy (SEM) and X-ray diffraction (XRD) technique. Subsequently, based upon Euler-Bernoulli and Timoshenko beam theories (EBT and TBT), the buckling responses of the porous bio-nanocomposite soft tissue are analyzed corresponding to various graphene amounts. In order to solve the governing equations a sufficient numerical solution is proposed. Elastic modulus and mass density of the porous bio-nanocomposite are extracted from the experimental tests. The obtained results indicated the sample with 1 wt% graphene sheet has shown proper mechanical and biological features. Therefore, the sample with 1 wt% graphene sheet can be used as potential case for light weight bone substitute applications.

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.

In this research, densification and shape distortion of the Al-Cu-Mg (Al2024) pre-alloyed powder compact in the supersolidus liquid phase sintering process (SLPS) were investigated. The effect of Sn on the sintering process was also studied. The powders were compacted at pressures ranging from 100 to 500 MPa in a cylindrical die. The sintering process was performed in a dry N2 atmosphere at various temperatures (580-620 ºC) for 30 min at a heating rate of 10 ºCmin-1. Results showed that the onset of densification process was observed at 600ºC and onset of distortion was occurred at 610ºC. Addition of 0.1 wt. %Sn to the alloy has increased the distortion of the samples produced from Al-Cu-Mg pre-alloyed powder, but their densification has been improved. The compact pressure of 200MPa caused the complete densification at the optimum sintering temperature and at the compact pressures greater than 200MPa; the sintered density was independent of green density.

Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm-1 and 50 to 200mA.mm-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.

Mechanical properties of metals are substantially dependent on the microstructure, which can be controlled by thermo-mechanical parameters such as the temperature, strain and strain rate. Hence, understanding the microstructural evolution of alloys during the hot deformation is crucial for engineering the metal forming processes. The main objective of this work is to present an overview of Cellular Automaton (CA) modeling for predicting the microstructure of alloys during the dynamic recrystallization (DRX) phenomenon. In this review paper, first, overall descriptions about the DRX phenomenon and CA modeling were presented. Then, the CA modeling procedure was compared with similar methods. Meanwhile, related studies in the field of the DRX simulation by using the CA modeling were evaluated. Four main stages of the model were analyzed in terms of the “nucleation”, “growth”, “topological changes” and “texture evaluation” steps. Most important limitations including the calibration sensitivity, limitations in continuous DRX modeling, ignoring microstructural effects on the deformation behavior, limited applications and database as well as repeated results were discussed and then objective suggestions for the further development were provided. Finally, future prospects in CA modeling of DRX were presented in the last section.

The effect of cooling rate after annealing at 900 °C on the microstructure and hardness of high entropy alloys was investigated using two typical samples with the chemical composition of Co16Cr14.5Fe29Mn11.5Ni29 and Co11.5Cr7Fe27Mn27Ni27(Nb0.08C0.5) (at%). The microstructural characterisation and hardness measurements were carried out by optical microscopy, scanning electron microscopy, wavelength-dispersive X-ray spectroscopy, electron back scattered diffraction, X-ray diffraction technique and Vickers hardness testing. A face centred cubic crystal structure matrix was observed in both alloys before and after annealing and regardless of cooling conditions. SEM analyses revealed an extensive precipitation in Co11.5Cr7Fe27Mn27Ni27(Nb0.08C0.5) alloy after annealing. It was also found that air/furnace cooling can enhance grain growth-coarsening just in Co16Cr14.5Fe29Mn11.5Ni29. However, the hardness results generally showed insignificant hardness variations in both alloys after water-quenching, air-cooling and furnace-cooling. The results suggested that the hardness is mainly controlled by solid solution strengthening.

The aim of this study is to establish the correlation between the impact strength and texture, fractal dimensions of fractures , fractal dimensions  obtained from load-time diagrams  reflecting the applied load (P) dependence on time (τ) during the Charpy impact test of 20K steel at various temperatures as well as the comparison of abovementioned fractal dimensions. The tests were carried out on a vertical impact testing machine with a multi-channel system for high-speed registration of forces and strains, as well as a heating and cooling system for samples in a wide temperature range. The load vs. time (load dependence on time) diagrams were obtained at an impact velocity of  = 4.4 m/s at temperatures of -50, +20, + 50°С. The Charpy standard samples of 20K steel (analogue to DIN17175, class St45.8) were cut in various directions out of a 12 mm thick the destroyed tank shell of a distillation column for oil refining. It was established that the behavior of both abovementioned fractal dimensions depending on the cutting direction and test temperature coincides qualitatively. The trend of decreasing in fractal dimension with a more viscous nature of fracture was found. The effect of texture is discussed.

Sago hampas was chemically modified through esterification process to adsorb both laboratory and commercial synthesized ZnO nanoparticles from water in a batch adsorption studies. The esterified sago hampas (ECSH) as a biosorbent w:as char:acterized using Energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) technique s. Investigating the effect of pH, contact time, initial sorbate ion concentration, temperature and sorbent mass were carried out where adsorption parameters were analyzed using Langmuir, Freundlich and Temkin models. The correlation between kinetics of adsorption and tgr rate order of ZnO nanoparticles on ECSH were also determined. The adsorption of the ZnO nanoparticles was found to increase with increasing contact time with the attainment of equilibrium at 100th minutes with maximum removal efficiency of 85.5% (0.036 mg/g) and 89.6% (0.106 mg/g)  ZnO nanoparticles for laboratory and commercial synthesized ZnO from aqueous solution. An optimum pH of 8 with adsorbent dose of 2.0 g at a temperature of 50 oC gave good results of  ZnO nanoparticles removal. The equilibrium data for both sorbate solution fitted well for both Langmuir and Freundlich isotherm models. From the Langmuir model, ECSH recorded greater sorption capacity of 0.2 mg/g and 0.6 mg/g for both laboratory and commercial synthesized ZnO nanoparticles respectively. The kinetic studies showed pseudo-second order model as the best fitted for the sorption of ZnO nanoparticles for both synthesized samples.

Graphene oxide thin layers, graphene oxide:silver nano-composite, graphene oxide:zinc oxide nano-composite and graphene oxide:zinc oxide/graphene oxide:silver bilayer were deposited by spray pyrolysis method. The synthesized thin layers were characterized using X-ray diffraction spectroscopy, field emission scanning electron microscope, energy dispersive x-ray spectroscopy and Raman spectroscopy. The optical properties and the band gap of the thin layers were also studied and calculated using the Tauc equation. Gram-negative bacterium of Escherichia coli was used to study the antibacterial properties of thin layers. The results showed that among the thin layers investigated, GO:ZnO/GO:Ag bilayer had the greatest effect on the inhibition of E. coli growth and was able to control the growth of bacterium after 2 hours.