Journal of advanced materials and processing
Volume:9 Issue: 1, Winter 2021

In this research, microstructure and mechanical performance of dissimilar resistance spot welded DP780/DP980 dual-phase steels were studied utilizing optical microscope, microhardness, and tensile shear tests. Resistance spot welding (RSW) was performed in the current range of 7 to 12 kA, with 0.5 kA steps. At welding currents lower than 7 kA low amount of melting led to the very low strength of the joints due to small weld nugget diameter. The results showed that an increase in welding current from 7 kA up to 11 kA, result in an increase in weld nugget diameter. Further increase of welding current (higher than 11 kA), however decreased the weld nugget diameter due to severe melt expulsion. Microstructural studies showed that weld nugget was primarily comprised of martensite, and the heat-affected zone (HAZ) of both sides of the joint was comprised of three different microstructural zones; upper-critical HAZ (UCHAZ), inter-critical HAZ (ICHAZ), and sub-critical HAZ(SCHAZ). Microhardness test showed that at both sides, softening occurred at SCHAZ. The results of the tensile shear test showed that both peak load and fracture energy of the joints followed approximately the same trend as weld diameter with welding current. Two different fracture modes of interfacial failure (IF) and pullout failure (PF) were observed in the tensile-shear test. At welding currents lower than 10 kA, the failure occurred in IF mode, while at higher welding currents, PF was dominant. Weld nugget diameter at welding current of 10 kA; i.e., critical weld nugget diameter, was ~8.5 mm.

In this study, a new kind of crosslinking film of polyvinyl alcohol, starch, and chitosan was obtained by alternating freeze-thaw cycles, and its various properties such as swelling rate, water vapor transmission rate, mechanical properties, and morphology were checked using electron microscopy. The results of this study showed that the hydrogel, made by providing a damp environment and the ability to pass water vapor in the range 720-1680 g/m2, has acceptable mechanical properties so that the fracture stress in polyvinyl alcohol was equal to 0.642 kgf/ mm2, which reached 0.372 kgf/ mm2 with the introduction of starch and 0.2475 kgf/ mm2 with the addition of chitosan. When we add starch and chitosan to polyvinyl alcohol at the same time, the fracture stress reaches 0.261 kgf/ mm2. In the sample containing pure polyvinyl alcohol, the elastic strain is equal to 6.157 and with the addition of starch, this value reaches 4.625 and with the addition of chitosan, this value reaches 5.70. Adding starch and chitosan to polyvinyl alcohol increases the modulus and toughness and decreases the flexibility of the polyvinyl alcohol hydrogel membrane. Images of SEM from a cross-section of hydrogel membrane fracture show that hydrogel membranes containing polyvinyl alcohol are very smooth and monotonous; however, when starch and chitosan are added to polyvinyl alcohol, the porosity will increase.

Self-lubricant coatings are among the newly improved type of coatings to reduce the coefficient of friction and protect the substrate in various conditions. Magnetron sputtering is the best technology to fabricate coatings with good morphology. In this paper, the tribological properties of magnetron sputtered Ni3Al-MoS2 coating on 4340 steel are reported. For this purpose, five tablets of Ni3Al-30 wt.% MoS2 were prepared as the target material and were placed in a copper holder. At last, we have sputtered from the target using the best sputtering condition to get a good morphology and microstructure of the coating. The morphology and microstructure of the coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The tribological properties of Ni3Al-MoS2 coating were investigated using a ball-on-disc tribometer at atmospheric conditions at room temperature. SEM was used to examine the morphology of the wear track after the ball-on-disc test. The Ni3Al-MoS2 composite coating showed lower frictions coefficient and higher wear resistance because of the hard Ni3Al matrix and soft MoS2 particles.

In this paper, influence power-law distribution with pressure on frequencies of the supported functionally graded cylindrical shell is studied. This shell is constructed from a functionally graded material (FGM) with two constituent materials. FGMs are graded through the thickness direction, from one surface of the shell to the next. The supported FGM shell equations are created based on FSDT. The governing equations of the movement were utilized by the Ritz method. The boundary conditions are clamp-sliding and free-simply support. The influence of the various values of the power-law distribution with pressure supported and different conditions on the frequencies characteristics are studied. This study shows that the frequencies decreased with the increase in the amounts of the power-law distribution with pressure. Thus, the constituent power-law distribution with pressure effects on the frequencies. The results show the frequencies with different power-law distribution under pressures are various for different conditions.

In this study, nanostructured carbon spheres were fabricated from leather leaf via hydrothermal carbonization and chemically activated with KOH. Different hydrothermal carbonization temperatures were used. The microtopographic, compositional, and structural characteristics and the surface properties of the synthesized material were then investigated via scanning electron microscopy, transmission electron microscopy, X-ray diffraction, nitrogen adsorption-desorption, and Raman spectroscopy. Results indicated that the KOH-activated sample synthesized with hydrothermal procedure leads to spheroidal nano-porous amorphous carbon particles with an average size of 3-5 micrometers. The nano-porous carbon spheres exhibited remarkable material properties such as high specific surface area (1342 m2 g–1) and a well-developed porosity with a distribution of micropores 2 nm wide. These properties led to good electrochemical performance as supercapacitor electrodes. The electrochemical investigations through a three-electrode cell in an aqueous electrolyte have also confirmed the capability of the synthesized activated carbon nano-particles as promising candidates for supercapacitor applications. In particular, a specific capacitance of 374 F g-1 was achieved at a current density of 2 A g-1.

In this research, Al-SiC composites were produced using FSP tools with different pin shapes to investigate the distribution of reinforcing particles in the base metal. First, to obtain the optimal rotational and traverse speed and tilt angle, several tests were performed on different parameters. The results showed that the rotational speed of 1250 rpm and the traverse speed of 100 mm/min in all tools produced flawless samples. Then, tools with different tool pin profiles of triflate, cylindrical, threaded, triangular, square, and hexagonal were utilized in this study. The distribution of reinforcing particles in the base metal was studied using a light microscope. The results showed that the cylindrical tool was not able to distribute particles in the base metal even after four passes of the process and was not a suitable tool for composite production. Tools with flat surfaces, such as square and triangular tools, have performed better in distributing reinforcing particles in the base metal. The results showed that the presence of a kind of eccentricity and pulse production in these tools had improved the distribution of particles. Threaded and hexagonal tools have the best performance in the distribution of reinforcing particles in the base metal and can be introduced as a suitable tool for composite products in the FSP process. The results of this study also showed that the change in the direction of tool rotation improved the distribution of reinforcing particles in all tools.