نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 65 (تابستان 1402)

Application of YSZ nanoceramic in liquid phase suspension as raw material in plasma coating process leads to thermal barrier coatings with more desirable properties. The key is to achieve a stable aqueous suspension containing these ceramic nanoparticles. In this research, the rheological properties and stability of YSZ nanoparticles in aqueous medium have been investigated. The type of dispersants added to the suspension and the chemical properties of the aqueous medium were studied as influential factors in the stability of the suspension containing by 30 weight percent. In order to characterize the properties, viscosity, zeta potential, NTU and TSI factor and sedimentation rate were performed and also the aging properties of different suspensions were studied over time. The results showed that the use of alpha terpineol dispersant with a concentration of 0.1 wt% in aqueous medium with a pH of 2.5 has led to an optimal suspension with optimum viscosity and stability conditions, defined as viscosities at 1.5 cp, zeta potential at 56 mV and Nephelometric turbidity units (NTU) 3680 were obtained. Microstructural study of the thermal barrier coating created by plasma spraying of the optimal suspension indicates the formation of a columnar structure that will have higher stability and strength properties in this type of coating.

In this research, a steel specimen with the new chemical compositions of 0.3 C, 2.5 Si, 1.8 Mn, and 0.5 Cr (wt. percent) was cast. Intercritical annealing (IA) heat treatment was performed at three temperatures(i.e., 825, 850, 875°C) on these samples in 26 minutes to achieve the dual-phase steel. To determine the effect of intercritical annealing (IA) temperature, optical (OM) and scanning electron microscopy (SEM) microstructures were studied, as well as mechanical properties via hardness, micro-hardness, and tensile testing. The results indicated that intercritical annealing temperature increased, martensite volume, hardness, and yield strength increased. Also, the tensile strength initially increased and then decreased. However, the sample intercritical annealed at 850°C showed maximum tensile strength (1532 MPa), and the sample intercritical annealed at 825°C showed maximum elongation (18.52 %), and strength–elongation balance (UTS×UE). This dual-phase steel showed two stages of hardening, with the increase of martensite, the slope of the second stage decreased, and the strain at the beginning of the second stage of hardening was transferred to lower strains.

The use of environmentally friendly energy storage systems is known as the best solution to reduce the fossil fuels consumption. Supercapacitors have received more attention than other energy storage devices (batteries and fuel cells) due to their high power density, high cycling stability and optimal energy density. The use of inexpensive and available electrode material is the key to the development of supercapacitors in the industrial and commercial scales. Nickel and manganese oxides have a high theoretical specific capacity, in addition to their availability and lower price. A type of morphology with many electrochemically active sites can be achieved by using these two metal oxides, together. In this research, nickel manganese oxide electrode material (NiMnO3) was synthesized using hydrothermal method. Then, the characterization tests of XRD, FT-IR and SEM were used to determine the crystallographic and morphological properties. Characterization analyses showed that the rhombohedral NiMnO3 nanoparticles with mesoporous structure were obtained. The electrochemical tests of CV, GCD and EIS showed that the NiMnO3 electrode has an excellent supercapacitive performance with the specific capacity of 444 F/g at a current density of 1 A/g. The great performance of NiMnO3 electrode can be related to the abundant and available electrochemical active sites of NiMnO3 electrode with appropriate mesoporous structure which led to the charge storage reactions.

In this research, the surface hardening of SKS3 cold work tool steel has been performed by high power diode laser with a maximum power 1600 W. The applied powers of 1200 and 1450 W, the scanning speeds of 1.6 to 3 mm.s-1 and working distances of 55,, 70 and 75 mm were applied as test parameters. Microstructure and phase analysis and microhardness measurement were studied by optical microscopy, electron microscopy, X-ray diffraction and microhardness testing methods, respectively. The microstructure and phase analysis showed that the hardening process led to the formation of martensite and retained austenite dual-phase structure. The use of laser, created all three states of surface hardening, surface melting and non-hardening. The best result in terms of depth and width of hardening was obtained for samples with energy density of 208-250 J/mm2. The calculation of retained austenite phase percentage and heat input, indicated that an increase in the heat input raised the residual austenite percentage, so that for the sample with maximum heat input, the retained austenite phase percentage was calculated to be approximately 37%. Also, for the sample with the highest heat input (906/J/mm2), the lowest hardness was obtained (653 Vickers) and the sample with lower heat input (725 J/mm2) was owned the highest hardness (760 Vickers). Investigations of the values of hardening efficiency showed that the hardening conditions are not improved only by increasing the laser energy density, but to obtain highest hardness and appropriate microstructure, the optimum amount of power and scanning speed is needed.

In this paper, three-types of metal-cations doped superparamagnetic iron oxide nanoparticles (IONs) including glucose-grafted Zn2+-doped MNPs (glucose/Zn-IONs), sucrose-grafted Zn2+-doped IONs (sucrose/Zn-IONs) and starch-grafted Zn2+-doped IONs (starch/Zn-IONs) are reported. These IONs are fabricated by OH– ions electrochemical generation through cathodic deposition method. The saccharide capped layer onto the surface of deposited IONs and also zinc cations doping into their crystal structure were confirmed via Fourier-transform infrared spectroscopy, Field-emission scanning electron microscopy and Energy Dispersive X-ray techniques. Figures of the Field-emission scanning electron microscopy showed that the morphology of particles synthesized is spherical. Analyses revealed magnetite crystal structure with about 10% doped zinc for all the prepared samples. The magnetic evaluations by sample vibrating magnetometer (VSM) technique specified the superparamagnetic behaviors for the prepared samples, where low coercivity and remanence values (i.e. Hci=8.9Oe and Mr=0.24 emu/g for glucose/Zn- IONs; Hci=3.6Oe and Mr=0.09 emu/g for sucrose/Zn- IONs; Hci=9.2Oe and Mr=0.28 emu/g for starch/Zn- IONs) were observed.

In this study, simulation of the effect of the second pulse current on temperature distribution and nugget size of TRIP1100 steel during resistant spot welding was performed by finite element method. Then, the effect of the second pulse current on the weld nugget size, weld nugget microstructure and mechanical properties of the resistant spot welds of the above-mentioned steel was experimentally investigated. Temperature distribution, weld nugget dimensions and heating and cooling cycles during resistant spot welding were predicted by simulation. Based on the simulated thermal cycles and continuous cooling transformation diagram of the TRIP1100 steel, a fully martensitic microstructure was predicted for the weld nugget in all currents. A good agreement was obtained between the simulated and experimental results. It was observed that the nugget diameter logarithmically increases with increasing the second pulse current. Furthermore, the microstructure of weld nugget in all samples was fully martensitic. Assessment of the mechanical properties of the welded samples by shear tension test demonstrated that the maximum load increases with increasing the weld nugget diameter. Nevertheless, the fracture energy decreased with increasing the nugget diameter.

In this research, X70 (API 5L grade X70)microalloyed steel of oil and gas transmission pipeline was used. In order to draw the temperature-time-transformation diagram, the classical heating and cooling thermal cycle was used. Analysis of the thermal cycles of the heat-affected zone was done based on practical conditions and a dilatometry device was used for simulation. By applying thermal cycles with peak temperatures of 950, 1150 and 1350 °C, the transformation behavior and microscopic structure of different heat-affected areas were studied. Analyzing the results of dilatometry, the kinetics of austenite formation (at different heating rates from 5 to 350 °C/s) and the kinetics of austenite decomposition (in two cases of constant austenite grain size with variable cooling and variable austenite grain size and constant cooling) were investigated. Modeling of austenite transformation was done using modified JMAK equation. It was observed that the “n” parameter does not have much dependence on temperature and is considered constant. The “k” parameter strongly depends on temperature, transformation amount and austenite grain size. Using the modified JMAK, a relationship was created that includes all these variables.