Iranian Journal of Materials Science and Engineering

Drug resistant pathogenic microbes have been causing serious health issues resulting in the substantial increase of death rates and morbidity paving the way for nanoparticles to be utilized as antimicrobial agents. This study was performed to evaluate the effectiveness of CuNPs on the growth of drug resistant clinical isolates of Streptococcus pyogenes, Enterococcus faecium and Enterococcus faecalis. Minimum inhibitory concentration of CuNPs against Streptococcus pyogenes, Enterococcus faecium and Enterococcus faecalis was found to be 1.25. 1.25 and 0.625 mg/ml and minimum bactericidal concentration against the same isolates was found to be 2.5, 2.5 and 5 mg/ml respectively. The ratio of MBC/MIC, referred to as tolerance level, was calculated for all the isolates which signifies the bactericidal or bacteriostatic effect of any antimicrobial agent. For Streptococcus pyogenes and Enterococcus faecium, the tolerance level was 2 while as for Enterococcus faecalis, it was 8. Antibiotic susceptibility results were calculated which showed that the isolates were resistant to Ampicillin (10 µg), Amoxycillin (30 µg) and Aztreonam (30 µg). Susceptibility results were followed by calculating multiple antibiotic resistance indices (MARI). MARI is an important tool which gives an idea about the bacterial resistance in a given population. For all the three isolates, MARI results were equivalent to 1 because of their resistance towards all the three antibiotics used. Antimicrobial activity through well-plate method was carried out and inhibitory effect of CuNPs on biofilm formation was evaluated.
 

Thin films of SnS₂ were prepared, as the absorber layer in solar cells, using an aqueous solution of SnCl₄ and thiourea by spray pyrolysis technique. Effect of the Substrate temperature on the properties of these thin films was studied. Investigation via XRD showed the formation of polycrystalline SnS₂ along (001) in all layers; there was no sign of other unwanted phases. With increasing of substrate temperature from 325 to 400 ⁰C, the crystallinity of the sample was improved, after that, it deteriorated the crystallinity. Layers had granular morphology and Valley- Hills topography. UV-VIS spectra revealed that the transmittance of all layers was lower than 40% in the visible region and the band gap reduced from 2.8 to 2.55 eV with increment in temperature from 350 to 400 ⁰C. Photoluminescence spectra of the prepared film, which was formed at 400 ⁰C showed a dominant peak at 530 nm, caused recombination of excitons. The least electrical resistivity of the SnS₂ thin film prepared at 400 ⁰C in dark and light environment were 4.6 ×10 ^-3 Ωcm and 0.65×10 ^-3 Ωcm, respectively; which demonstrated 400 ⁰C was the optimum temperature in point of optoelectrical properties in the SnS₂ thin film.
 

In this research, the objective was to investigate the stabilized retained austenite in the microstructure resulting from the Q&P heat treatment since the primary goal in Q&P is to create a microstructure consists of stabilized retained austenite and martensite. For this purpose, a low-alloy steel with 0.4wt. % carbon was treated by quench and partitioning (Q&P) process. The Q&P was conducted at different quench temperatures to obtain a considerable amount of retained austenite, while partitioning temperature and time were kept constant. Through analysis of the XRD profiles, volume percent, carbon concentration, and lattice parameters of retained austenite and martensite were calculated. At quench temperature equal to 160°C, 12vol.% austenite was stabilized to the room temperature, which was the highest amount achieved. The microstructural observations carried out on selected samples, revealed that retained austenite has a nanoscale particle size, about 200nm. Distinguishing retained austenite in the SEM micrographs became possible by utilizing SE2 signals via the difference in phases contrast. Two types of morphology, film-like and blocky type, were identified by means of TEM and TKD and a schematic model was proposed in order to explain these morphologies

An attempt has been focused to develop a new aluminum ion conducting non aqueous polymer electrolyte for high power rechargeable batteries having applications in rapidly growing markets, such as laptops, handy tele communication equipments, electric vehicles, camcorders, etc. These features have given a thrust to develop a suitable Nano composite GPE based on  PAN as polymer host and Sodium fluoride (NaF) as dopant salt and Al₂O₃ as nano filler in the form of thin films through solution casting technique consuming N,N-dimethyl formamide (DMF) as a common solvent. NCGPE films have been prepared by solution casting technique. The XRD pattern of 70PAN-30NaF with addition of wt% Al₂O₃ ceramic filler indicates reducing degree of crystallinity. Using IR studies revealed that the complexation of the polymer poly (acrylonitrle) with NaF. The conductivity of the GPEs was studied with enhancement of nano fillers. The sample containing 3% of Al₂O₃ exhibits the highest conductivity of 4.82x10^-3S cm^-1 at room temperature (303K) and 5.96x10^-3S cm^-1 at 378K. With the help of Wagner’s polarization technique electronic (t_e) and ionic (t_i) values can be determined.To determine profiles of discharge characteristics (70PAN-30NaF-3wt% Al₂O₃) NCGPE solid-state electrochemical cell was fabricated and various cell profiles were evaluated

The effects of rare earth element, erbium (Er) additions on the microstructure and mechanical properties of Al-15Zn-2.5Mg-2.5Cu alloy have been investigated. This new high strength alloy with erbium additions (0.5, 1.0, 1.5 and 2.0 wt%) was synthesized by liquid metallurgy route followed by hot extrusion. Microstructural characterization was performed using scanning electron microscope and electron probe microanalysis. Significant amount of grain refinement was observed with erbium addition in the hot extruded and heat treated alloy. Tensile test was performed to investigate the effect rare earth on mechanical behavior of alloy in as cast and hot extruded condition before and after T6 heat treatment. The combined effect of erbium addition, hot extrusion and heat treatment significantly enhanced the tensile strength of alloy (602 MPa) when compared to the as cast alloy without erbium addition (225 MPa). The strengthening of the alloy was attributed to grain refinement caused by erbium along with hot extrusion and formation of precipitates after T6 heat treatment. Fractograhic investigations revealed that the hot extruded alloy with erbium addition after heat treatment showed uniformly distributed deep dimples exhibiting ductile behavior. 
 

Centrifugal casting process, in both horizontal and vertical mode, is considered as an efficient method to produce bimetallic components. Al/Cu₆₅Zn₃₅ couples were prepared by the vertical centrifugal casting process. In this study, different volume of molten aluminum having melt-to-solid (m/s) volume ratios (VR) of 1.5 and 2.5, were cast into preheated brass bush rotating at 800, 1600, and 2000 (rpm), respectively. The thickness of the interface, which is composed of three different zones, is depended on the rotational speed and the (VR) and was at least 490µm (at VR=1.5 and 2000 rpm) and at most 1480 µm (at VR=2.5 and 800 rpm). The results of optical microscopy, energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction analysis showed that the interface layers are composed of Al₂Cu₅Zn₄, Al₃Cu₃Zn, Al₂Cu precipitates dispersed in the matrix and finally α-Al/Al₂Cu anomalous eutectic structure near the aluminum side. Gas pore entrapment and oxide film entrainment defect was detected within the interface next to the aluminum base metal.

In this study, the microstructure, hardness, and dry sliding wear behavior of the hardfaced layers made by a cored wire Fe-B-C-Ti alloy were investigated. St37 steel was used as the substrate and the deposition of the hardfaced layers was conducted by the flux cored arc welding (FCAW) process under single-, two-, and three-pass conditions. Dry sliding wear tests were performed by a pin-on-disk apparatus, based on ASTM-G99, at room temperature (25⁰C) at the normal applied loads of 50, 100, and 150 N with a constant speed of 0.08 m/s for a sliding distance of 1000 m. The microstructural and phase analyses were carried out by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), respectively. The results showed that the hardfaced layer produced by the single-pass process contains TiC rectangular phase distributed within a matrix containing ferrite and the eutectic of (α-Fe₂B). But, the hardfaced layers produced by the two- and three-pass process contain TiB₂ hexagonal phase in addition to TiC, which prevents the formation of detrimental FeB phase around Fe₂B and reduces the number of micro-cracks. Moreover, the sample hardfaced by the three-pass process had the best wear resistance due to the greater hardness resulted from the higher amounts of TiC and TiB₂ phases. In addition, increasing the number of passes has led to the reduction of wear rate at all the three applied loads. At the applied load of 100 N, the wear mechanism for the all three hardfaced samples was an oxidation wear. However, at the applied load of 150 N, the wear mechanism was a combination of oxidation and delamination.
 

One-step and two-step annealing techniques were used to examine the relationship between microstructure and mechanical properties during compression tests in iron-based ribbons and nanostructured 1- and 2.5mm cylindrical rods. The X-ray diffraction, microstructural, and mechanical results showed that substituting Nb for Fe had a minor effect on glass-forming ability but increased the formability index. The novel two-step annealing process resulted in a remarkable formability index of 16.62 GPa, yield stress of 2830 MPa, ultimate strength of 3866 MPa, and 4.3% plastic strain. A ductile nanosized α-Fe framework and boron-containing nano precipitations, which caused Zener pinning effect, were responsible for these novel mechanical properties.

This paper investigates premature failure of High Pressure (HP) PT6A-114A Compressor Turbine (CT) blades used for short-haul aircraft fleet at 6378 hours, contrary to 10000 hours pre-set by the manufacturer. The CT blades were sectioned both transversely and longitudinally and subjected to several microstructural examinations; X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Energy Dispersive Spectroscopy-Scanning Electron Microscopy (EDS-SEM) of the tips, airfoils, as well as the bases. It was observed that from repeated elevated heating, incomplete solutioning and recrystallization of the substrate material, brittle carbides were initiated and developed. The tips were more affected, followed by the airfoils and least at the bases. Impingement of heat from the combustors on the CT blades led to rapid graining and rafting with eventual cracking upon cooling. The results further suggested that pores which are typically manufacturing defects were pronounced at the bases than either at the airfoils and the tips. However, contrary to the expectation that the bases would degrade more and rapider, a more near uniform distribution of the cuboidal phase was evident relative to the tips and airfoils, confirming that degradation of the CT blades originated from creep and fatigue.

Composite structures are widely used in many applications ranging from, but not limited to, aerospace industry, automotive, and marine structures due to their attractive mechanical properties like high strength to weight ratios. However composite structures needs utmost care during structures manufacturing and working conditions should be assessed prior to installation. One of the important defect in composite structures is delamination. Present work is focused on investigation of delamination effects on the natural frequencies of composite plate using commercial finite element software, ABAQUS. Analytical results were also analyzed using MATLAB code. Different stacking sequences and boundary conditions are considered for study in both analytical formulation and finite element analysis. Finite element results are compared with analytical results to validate the perfect composite plate. The natural frequency of the composite plate reduced with an increase in delamination size. Additionally, all-sides clamped composite plate showed higher values of natural frequency than other constraints in lower modes for symmetrical laminates. Natural frequency in cross ply laminates are higher for the simply supported composite plates. On comparison, results from both the techniques, finite element analysis and analytical analysis, were in good agreement.

In this study nanosized TiO2coatings on the 316L stainless steel substrate were prepared by means of dip-coating technique in which thickness of the coating layer increased byrepeating the coating cycles in two different routes: (I) dipping and drying,respectively, were repeated one, three and five times and finally the dried coated sample was heat treated (single); (II) multiple heat treatment performed after each dipping and drying cycle, respectively.The structural, morphological and optical characterizations of coatings as well as thickness of coatings were systematically studied.The photocatalytic activity of the various TiO₂ coatings was investigated based on the degradation of an aqueous solution of Methyl orange.Moreover, thecorrosion protective properties of coatings were evaluated in both dark and UV illumination conditions based on the obtained polarization curves. The results indicated 1.75 times improvement in photocatalytic reaction rate constant, a two orders of magnitude decrease in corrosion current density in dark condition and about 140 mV electrode potential reduction under UV illumination with optimum coating preparation procedure, repeating the cycle from dipping to heat treatment three times, than the sample prepared with one time coating and heat treatment since this procedure provided not only high thickness and defect-free coating but also transparent one.