Iranian Journal of Materials Science and Engineering

Friction stir welding (FSW) is a promising technique to join aluminum alloys without having problems encountered during fusion welding processes. In the present work, the evolution of microstructure and texture in friction stir welded thin AA2024 aluminum alloy are examined by electron backscattered diffraction (EBSD) technique. The sheets with 0.8 mm thickness were successfully welded by friction stir welding at the tool rotational speeds of 500, 750, and 1000 rpm with a constant traverse speed of 160 mm/min. EBSD revealed that stir zones exhibited equiaxed recrystallized grains and the grain size increased with increasing the tool rotation rate. The fraction of high angle grain boundaries and mean misorientation angle of the boundaries in the FSW joints at 500 rpm were 63.6% and 24.96°, respectively, which were higher than those of the sample welded at 1000 rpm (53.6% and 17.37°). Crystallographic texture results indicated that the Cube {001}<100> and S {123}<634> textures in base metal gradually transformed in to Copper {112}<111> shear texture. It was found that with increasing the tool rotation rate, the intensity of Cube {001}<100>, Y {111}<112>, S {123}<634>, and Dillamore {4 4 11}<11 11 8> texture orientations increased and the intensity of Brass {011}<211> texture orientation decreased. 

An efficient solid-state approach was established to synthesize (K_0.5Na_0.5) NbO₃ ceramics using calcination kinetics and microwave assisted sintering. Milling of carbonate and oxide raw materials were carried out for 15h to obtain homogeneous nano particles. The crystallite size of 5.30 nm was obtained for the KNN system after calcination through optimized parameters and observed to be stoichiometric in nature. The obtained nano particles showed phase transition from orthorhombic to tetragonal crystal structure without any secondary phases. The high relative density and tetragonality ratio of KNN ceramics obtained through optimized sintering parameters yielded with significant piezoelectric and ferroelectric properties.
 

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.
 

Repairing a crack in a structure consists in reducing crack’s tips stresses by transferring loads trough a bridge made of the composite patch and the adhesive. This operation is impacted by four factors: shear modulus of the adhesive, the composite patch’s Young module and the thicknesses of these two materials. The design of experiments method allowed us to determine, the weight of each of the four factors and their interactions as well their best combination to obtain an efficient and lasting repair. The constraints relative to the stiffness ratio and the shear strain were taken into consideration in order to determine the best configuration that allowed the minimization of K.

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. 
 

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.

 In this study, high-carbon, chromium alloy steel (100Cr6) having the initial spheroidized microstructure was welded using the rotary friction welding method. The effects of process parameters such as friction time and friction force were experimentally investigated. The friction welded joints were produced of two 100Cr6 steel rods. In order to examine the microstructure and mechanical properties of the friction welded 100cr6 steel joints, tensile and hardness tests were conducted. The microstructure of weld zone was examined by optical microscopy. It was found that after cooling, martensitic structure is obtained at the core and periphery of the weld joint. It was found that the tensile strength of friction welded samples is increased with increasing time and force of friction up to a certain level and then decreases again. Hardness measurements show a higher hardness at the centre of the weld joint in comparison with its periphery.

In this paper, the effects of solutioning and various aging heat treatment processes on the microstructure, the hardness and electrochemical properties of a duplex stainless steel (DSS) were studied. The evaluation of the microstructure and phase compositions were carried out by the optical microscopy (OM) and the X-ray diffraction (XRD), respectively. Electrochemical behaviors of specimens were evaluated by both potentiodynamic polarization and electrochemical impedance spectra (EIS) tests at temperatures of 25 and 60 ºC. The obtained results showed that the solutioning heat treatment increased corrosion rates with respect to the blank specimen. The aging process at 490 ºC for 20 hrs increased the volume percent of the carbide phase to the highest value (25.1%) which resulted in an increase of the hardness value to 170 VHN. The specimen which was aged at 540 ºC for 10 hrs with the Cr₇C₃ size of 22.8 µm, exhibited the higher corrosion resistance at both temperatures of 25 and 60 ºC with respect to other aged specimens. In addition, the temperature of 60 ºC promoted the anodic reactions in 3.5 wt% NaCl solution which decreased impedance modulus values significantly. Consequently, the carbide size was more effective parameter than the carbide content in predicting electrochemical behaviors of such alloys. 

In this study an effort has been made for the plasma ion nitriding (PIN) of Inconel 600 and 601 alloys at low temperatures. After plasma ion nitriding, microstructure study, growth kinetics of nitrided layer formation and wear properties were investigated by various characterization techniques such as; scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, micro-hardness measurement and wear test by pin on disk technique. It was found that, surface micro-hardness increases after PIN process. A mix peak of epsilon (ε) phase with fcc (γ) phase was detected for all temperature range (350 ⁰C to 450 ⁰C), while the chromium nitride (CrN) phase was detected at elevated temperature range ~450 ⁰C in inconel 601 alloy. The calculated values of diffusion coefficient and activation energy for diffusion of nitrogen are in accordance with the literature. Volume loss and wear rate of the plasma nitrided samples decreases, but it increases as PIN process temperature increases.