Band 114, Heft 9

In this study, a quaternary composite of graphite, polyaniline, cobalt ferrite, and thermoplastic polyurethane as a shielding material was prepared. The composite materials were analyzed with X-ray diffraction, field emission scanning electron microscopy, vibrating-sample magnetometer and thermogravimetric analysis. The electromagnetic characterization of the samples was achieved using a Vector Network Analyzer in the X-band. The composites’ conductivity was analyzed by using the four-point probe method. For the investigation of water absorption, the ASTM D570-98 Standard Method was used. Design-Expert software applied design optimization for broadband electromagnetic shielding of the composite film. Ultimately, we introduced a composite film as an efficient microwave absorbent that had a weight percentage of cobalt ferrite 6.95 %, polyaniline 20.04 %, graphite 12.13 %, and thermoplastic polyurethane 60.88 % in a thickness of 1.26 mm, which had shielding effectiveness higher than 30 dB, which was suitable for commercial purposes. The results showed that graphite played an essential role in increasing the composite’s electrical conductivity and thermal stability but was unsuitable for water absorption resistance.

Though good qualities of graphene have been prepared by the electrochemical method, the quality in terms of grain boundaries which has a consequential impact on its electrical properties has not yet been investigated in detail. In this work, grain boundaries and their electrical properties in graphene prepared by the electrochemical method have been investigated. The grain boundary in graphene has been examined from images obtained by a high-resolution transmission electron microscope. The finding reveals no grain boundaries in the graphene sheet prepared by the electrochemical method. As a result, a high current value has been obtained which may be attributed to the smooth passage of charge careers due to the absence of grain boundaries in graphene. The finding suggests that the prepared graphene sheets using the above-mentioned method are excellent in qualities that can be potentially used in various electronic devices, such as field-effect transistors, solar cells, transparent electrodes, interconnects, etc.

The present study focuses on the wear behaviour of a Al 2 O 3 -13 wt.% TiO 2 composite coating deposited by a flame spray method for high temperature applications. The microstructural characterisation and mechanical properties, such as microhardness and surface roughness were studied. In addition, the porosity characterisation of the coating was studied through quantitative image analysis using the software Image_J. The tribological testing of the deposited coating was performed at four different temperatures, i.e., 25 °C, 100 °C, 200 °C and 400 °C, using a high temperature pin-on-disk tribometer. The specific wear rate decreases with an increase in temperature of upto 200 °C and then increases slightly at 400 °C, whereas the coefficient of friction declines with temperature rise. The dominant wear mechanism is three-body abrasion and brittle fracture followed by erosion and oxidation wear at high temperatures.

This paper is focused on evaluating the surface properties of protective coating prepared by plasma electrolytic oxidation on magnesium alloy EV31. Plasma electrolytic oxidation was performed in DC mode with a constant current density of 0.05 A cm −2 for 14 min. Evolution of voltage was measured and depicted graphically in order to describe the growth of the plasma electrolytic oxidation coating. Morphology and thickness of the plasma electrolytic oxidation coating were examined together with corrosion resistance of the coating by measurements of electrochemical characteristics using electrochemical impedance spectroscopy and potentiodynamic polarization after 1 h in 0.1 M NaCl. Results from potentiodynamic polarization showed decrease in corrosion current density i corr from 10.50 μA cm −2 (substrate) to 1.02 μA cm −2 (plasma electrolytic oxidation coated) and results from electrochemical impedance spectroscopy showed increase in R p by one order of magnitude for plasma electrolytic oxidation coated sample after both 1 h and 168 h exposure times.

Using a thermal simulation testing machine, hot compression experiments were carried out on extruded homogenized AZ31 magnesium alloy, and the hot deformation behavior was analyzed. Based on this, the constitutive equation of the alloy is constructed to explore the evolution law of microstructure during hot deformation of the alloy, which could provide theoretical guidance for the reasonable selection of parameter ranges during hot compression of extruded homogenized AZ31 magnesium alloy. The experimental result indicated that the flow stress of the alloy during the hot deformation decreases with increasing temperature, increases with the strain rate increasing, and the real stress–strain curves during deformation show dynamic recrystallization curves. According to the experimental results, the deformation activation energy Q is 126.882 kJ mol −1 and the stress exponent n is 4.36 calculated by the constitutive equation under the given parameters, which confirmed that the glide and climb of dislocations in the climb-controlled regime is the deformation mechanism in this work. Decreasing the compression temperature and increasing the strain rate are helpful to reduce the Zener–Hollomon parameter, control the dynamic recrystallization occurring, and refine grain size to improve the mechanical properties effectively. Moreover, the dynamic recrystallization model of the alloy was constructed using the work hardening rate method and regression method, including dynamic recrystallization critical condition model, dynamic model and grain size model.

The present investigation studies the solid-state joining of difficult-to-weld aerospace materials such as titanium alloy (Ti6Al4V, ELI) and pure aluminum. Due to the wide difference in thermo-mechanical properties, it was a challenging task to establish a dissimilar metal joint. The friction stir welding process with a conically shaped tungsten carbide tool was used in the present investigation to join the dissimilar titanium alloy and aluminum in the lap joint configuration. After a series of pilot experiments, the optimum test conditions to produce the defect-free joint are spindle speed of 1200 rpm, feed rate of 40 mm min −1 , tool tilt angle of 1°, and 1 mm tool offset towards the aluminum side. The results show that a good joint was achieved with a maximum joint strength of 89 MPa. The dissimilar joints are characterized by macrostructure, microstructure, microhardness, and scanning electron microscopic analysis.