نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 59 (زمستان 1400)

In this research in order to disperse nano additives through the matrix of mag- chrome refractories, a novel approach by using the silanol surface group was reported. In this regard, the modified of nano MgCr2O4 particles have been done by functionalizing of MgCr2O4 by 3-(thriethoxsilyl)propyl amine (APTES) silanol group. Then 1% MgCr2O4 nano additives (with and without surface group) were added to mag- chrome matrix and pressed under a uniaxial press at 120 MPa pressure and then fired at 1600 ℃. XRD and TEM analysis were used to evaluate the synthesis of nano particles. FTIR and XRD analysis were carried out to investigate the presence of surface group of nano particles. Phase analysis and microstructure investigation have been done by XRD and SEM analysis.  The physical and mechanical properties, were determined according to the respective DIN standards. Also XRD and FTIR analysis confirmed the presence of functionalized groups on the surface of nano particles. DLS analysis of functionalize and not functionalized nanoparticles shows the the decrease of particle size in presence of silanol groups,  the UV analysis confirmed better dispersion of nano particles due to higher adsorption of functionalized nano particles.  XRD results of mag-chrome samples showed increasing of secondary spinel in presence of functionalized nano additives which could related to better dispersion of nano additives which caused to promote nucleation of spinel phases and result in solid state sintering and could effect on the physical and mechanical properties.

In this paper ZrC coating was prepared on SiC coated graphite as a substrate by atmospheric plasma spray (APS) and solid shielding/ shrouded plasma spray (SSPS) methods. Microstructure observation and phase identification of the coatings were performed by scanning electron microscopy and X-ray diffraction. The ablation behavior of the coating was evaluated under supersonic flame for 60s. The results showed that the ZrC coating enhance the ablation resistance of SiC coated graphite remarkably. The results of ablation test revealed that the linear and mass ablation rates of the ZrC coating applied by APS method were 3.7×10-3 mm.s-1 and 22×10-3 g.s-1, while those for SSPS coating were 2.2×10-3 mm.s-1 and 14×10-3 g.s-1, respectively. The excellent ablation resistance is attributed to the formation of continuous zirconia (ZrO2) layer on the surface during the oxidation of the ZrC coating. Moreover, the SPS-ZrC coated sample with lowest pores and cracks have better ablation resistance during the ablation test and can protected the graphite substrate against ablation sufficiently.

Due to the problems of metal implants, it is observed that one of the main techniques in solving these problems is to improve the properties of implant coatings. One of the coatings that has been considered in the last decade is biphasic calcium phosphate gradient coating. Plasma spraying method was used to coating the implants and three coating layers including HAp, TCP 50%-HAp 50% and TCP were applied gradient on the titanium substrate, respectively. X-ray diffraction test was used to identify the phases. Corrosion of the applied layers was performed using body simulation solution and open circuit potential electrochemical tests were used to evaluate the corrosion of coating. Field emission scanning electron microscopy was used to observe the morphology and thickness of the layers before and after being placed in the body simulation solution. According to the results of open circuit corrosion potential test, the corrosion voltage is -0.07, -0.09 and -0.19 V for the sample with one layer of HAp coating, the sample without coating and the sample with three layers of coating HAp, TCP 50%-HAp 50% and TCP were obtained respectively. By placing the three-layer coating in SBF solution, tricalcium phosphate in the third and second layers is completely dissolved and with the presence of calcium and phosphorus ions in the form of saturated secondary hydroxyapatite is formed inside the coating.

Prosciuttoes are compounds that have the general formula ABO3, such as YbMnO3. In this research, YbMnO3 nanostructure has been synthesized by electrochemical deposition technique which is the green simple and new method. Then, XRD, DSC, SEM and EDS characterization tests were performed on the synthetic sample and the obtained results were analyzed. In addition, the morphological and structural properties of the synthetic nanomaterial showed that the main product was YbMnO3, with a nanoscale agglomerated structure with a particle size estimated at 35.5 nm. Also, some mechanical quantities, such as stress, strain, lattice constants and particle size of the synthetic perovskite compound, are calculated using the Scherer equation and the Williamson-Hall method, and the results were obtained with the results (values) obtained from the XRD spectra. And SEM were compared. It is predicted that the result of this research can open new horizons in the low-cost synthesis of eco-friendly (green Chemistry) nanomaterials and nanoparticles.

In this study, the protective behavior of the biofilm produced on the surface of the API X42 micro-alloyed pipeline steel by the bacterium clostridium sp. as an anaerobic sulfate-reducing bacteria (SRB) is evaluated in a saline simulated soil solution in comparison with the sterile medium. Microstructure and surface morphology was examined by field emission scanning electron microscopy (FESEM) coupled with energy dispersive spectroscopy (EDS). Corrosion properties were investigated using linear polarization and electrochemical impedance spectroscopy (EIS). The results approve the formation of a biofilm consisting of bacterial cells, extracellular polymeric substance (EPS), and corrosion products. In this relatively dense biofilm, semiconductive iron sulfide which is destructive to the corrosion behavior of biofilm is not observed. In addition, the biofilm produced on the metal surface at immersion time of 21 days in the bacterial inoculated medium improves polarization resistance to 7330 Ω.cm2, while at this time the polarization resistance of the protective corrosion products layer created in the sterile condition is about 1421 Ω.cm2. This comparison shows a 5-fold improvement in corrosion resistance as a result of the biofilm's protective behavior.

In this paper, 50CrV4 steel wire with a diameter of 4 mm were subjected to pure Zn electroplating. The effect of shot peening before and baking after electroplating on tensile performance of steel was investigated. Bombardment was done before plating for 20 minutes with shots 0.5 mm and 58 RC. Baking was performeIn this paper, 50CrV4 steel wire with a diameter of 4 mm were subjected to pure Zn electroplating. The effect of shot peening before and baking after electroplating on tensile performance of steel was investigated. Bombardment was done before plating for 20 minutes with shots 0.5 mm and 58 RC. Baking was performed after plating for 24 hours at 200°C. Finally, the samples were subjected to slow strain rate test, microhardness test and SEM imaging. The results showed that the effect of baking on improving the mechanical life of the sample under tension alone is greater than the shot peening. The mean time to failure of plated and baked samples was 2.5 hours, but for shot and plated samples was 2.1 hours. The simultaneous effect of pre-plating shot peening and post-plating baking led to further improvement of the tensile performance of the wire and the mean failure time reached 3.55 hours in the slow strain rate test. The embrittlement susceptibility index is now reduced from 0.76 for only plated samples to 0.13 for shot peened and baked samples, which shows a very good improvement. The effect of shot peening on the tensile properties of steel can be attributed to the formation of a residual compressive stress layer on the substrate surface, which leads to a reduction in the growth rate of microcracks due to tensile stresses under working conditions. The results also showed that due to the baking, continuous microcracks are created in the coating / substrate interface, which provide suitable paths for hydrogen to leave the substrate. after plating for 24 hours at 200°C. Finally, the samples were subjected to slow strain rate test, microhardness test and SEM imaging. The results showed that the effect of baking on improving the mechanical life of the sample under tension alone is greater than the shot peening. The mean time to failure of plated and baked samples was 2.5 hours, but for shot and plated samples was 2.1 hours. The simultaneous effect of pre-plating shot peening and post-plating baking led to further improvement of the tensile performance of the wire and the mean failure time reached 3.55 hours in the slow strain rate test. The embrittlement susceptibility index is now reduced from 0.76 for only plated samples to 0.13 for shot peened and baked samples, which shows a very good improvement. The effect of shot peening on the tensile properties of steel can be attributed to the formation of a residual compressive stress layer on the substrate surface, which leads to a reduction in the growth rate of microcracks due to tensile stresses under working conditions.

Poly Lactic Acid implants are a good candidate for bone tissue engineering due to their favorable biodegradability and mechanical properties. In this study, after studying the structural and thermal properties of polymer by Fourier transform infrared spectroscopy (FTIR), differential calorimetery analysis (DSC), thermal gravimetery analysis (TG) and X-ray diffraction (XRD) tests, to determine the appropriate temperature range of 3D printing, rigid polylactic acid (PLA) implants were prepared by Fused Deposition Modeling FDM at three different temperatures of 200, 210 and 220 °C as standard tensile test specimens. The results of the tensile test showed that in this range, as the print temperature increased, the samples had higher strength and higher fracture stress. Also to further investigate the effect of the FDM temperature, scanning electron microscopy (SEM) images were taken from the surface of the printed samples. Microscopic images show that as the print temperature increases, the melt spray and diffusion are more severe and the sample surface is rough. The results show that 210 °C is the optimum temperature for PLA printing.