نشریه مهندسی متالورژی و مواد
سال سی و چهارم شماره 1 (بهار 1402)

In this study, microstructure and wear properties of Al-8Zn-3Mg-2.5Cu nanocomposite reinforced with 1, 2, 3 and 5 wt.% SiC nanoparticles (SiCnp) produced by stir casting and ultrasonic treatment have been investigated. Ultrasound device equipped with a cooling system with 2000 W powers was used for mixing alloy and nanoparticles. Also scanning electron microscopy was used for microstructure studies. The microstructure of nanocomposite was investigated by scanning electron microscope.The microstructural studies of the nanocomposite revealed that SiCnp addition reduces the grain size, but adding higher SiCnp content (5 wt.%) does not change the grain size considerably. Further investigations on hardness revealed that the addition of SiCnp increases hardness and wear resistance. At higher SiCnp contents (5 wt.%), the presence of SiCnp agglomerate on grain boundaries was found that causes decrease the hardness and wear resistance. The optimum amount of nanoparticles before and after heat treatment is 3 wt.% SiCnp that nanocomposite exhibits best wear resistance.

The high temperature self-progressive combustion synthesis method, especially for aluminothermic systems, is a new method for making all kinds of intermetallic compounds, ceramics and composites with high melting point and hardness. In this study, first the homogenized powder mixtures in the desired ratio in alumino-thermic systems of Al-Fe2O3-Cr2O3-NiO is subjected in differential thermal analysis process and then, the phase composition (X-ray diffraction) of the thermal analyzed samples has been investigated. The obtained results indicate the formation of intermetallic compounds of iron and chromium aluminide as secondary phases with the presence of excess aluminum over the stoichiometric values in the thermally analyzed samples. In addition, with the presence of silicon in the aluminothermic mixtures, chromium silicide compounds are formed instead of chromium aluminide. For the Al-Fe2O3-Cr2O3-NiO system, the metallic phase of stainless steel with a ratio of Fe0.7Cr0.19Ni0.11 and the ceramic phase of Al2O3.are formed. For the Fe2O3- NiO system, only nickel ferrite is formed.

In this research, aluminum matrix reinforced with continuous carbon and glass fibres composite were produced using A356 aluminum alloy as the matrix, and T300 carbon fiber and E-glass as the reinforcement during the squeeze casting process. Carbon fibers were first coated with a layer of nickel-phosphorus using the electroless method. Then, aluminum alloy 356 pipe and composite pipes with 30 weight percent of carbon fibers and 30,40,50 and 60 weight percent of glass fibers were cast at 75 MPa and 500 °C. After casting, the microstructure, and mechanical properties of composite samples were investigated. Nickel-phosphorus coating on carbon fibers has a significant effect on the wettability of carbon fibers with aluminum melt and thus the penetration of aluminum melt into carbon fibers. The hardness of composite pipes reached approximately 2 times that of alloy pipe and the density decreased to 9.5% with increasing weight percent of fibers. The highest bending strength was obtained at 340.82 MPa, which is related to the reinforced composite pipe with40 weight percent of glass fibers. Tensile strength was measured by the nol ring test, in which a composite tube with 30 weight percent of carbon fiber had the highest tensile strength with a 76% increase over the alloy pipe. The predominant mechanism in the failure of carbon fiber-reinforced composite pipe was fiber pull-out and in the failure of glass-fiber-reinforced composite pipes, the fibers were cut.

In this article, an attempt was made to investigate the effect of the addition of silicon on the titanium aluminide compound formation from TiO2 and Al raw materials. Silicon has a eutectic with aluminum and can reduce its melting temperature, which can have effective impact on the formation of titanium aluminide compounds. On the other hand, due to the production of Ti5Si3 compound, it can be effective in increasing the oxidation resistance of compounds and composites containing titanium aluminide. With this aim in mind, the present paper has strove to determine the impact of this element on the formation of titanium aluminides and the type of titanium silicide phases by adding different amounts of silicon to TiO2 and Al raw materials. The key findings emerged, showed that when silicon is added to the system in small amounts (0.1), it not only does not have a positive effect on the reactions, it also prevents the formation of titanium aluminide compounds, but with an increase in its percentage (0.28), it also causes the formation of these titanium aluminide compounds and leads to the formation of Ti5Si3 phase. This phase changes from a discrete morphology to a continuous state as the percentage of silicon increases (0.6). With a further increase in the amount of silicon (1), the TiSi2 phase is formed, which is dispersed throughout the sample with a string-like structure.

The present study investigates the oxidation behavior of GTD-111 nickel base superalloy at 1000 °C in air. To this aim, several techniques including thermal gravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), grazing incidence X-ray diffraction (GI-XRD) and glow discharge optical emission spectroscopy (GDOES) were employed. The oxidation kinetics of this superalloy alters from linear to parabolic after 10 h exposure which is accompanied by the formation of a uniform surface oxide layer. Based on the cross-sectional analysis of FE-SEM and GDOES, Ti can most probably be considered as the first species which enters the reaction front when oxidation begins. However, as a result of its oxidation, Ti is depleted just beneath the oxide scale, and conditions changes in favor of the formation of other oxides, namely, Cr2O3. Subsequently, due to the internal diffusion of O2- species, Al is internally oxidized, and islands of Al2O3 form underneath the oxide layer. After 100 h of oxidation, the chemical composition of the oxide film consists of an Al-rich inner region, a Ti-rich outer region, and a Cr-rich intermediate layer. GI-XRD results also confirmed the formation of mentioned oxide phases. No indication of oxide spallation and formation of nickel oxides were observed even after 100 h of oxidation.

This work aims to investigate the effect of fuel ratio (ϕ) on the synthesis of CuO nanoparticles via solution combustion and evaluation of its antibacterial properties. Hexamethylenetetramine was considered as fuel and used in different ratio. The final products were characterized by XRD, DLS, FE-SEM analysis. The XRD results indicated that the highest quantity of CuO was found in ϕ=1. Based on particle size analysis results, all particles were in the range of 21.7 to 42.2 nms. Also, the finest particle size (21.7nm) was attributed to ϕ=1. Since the FE-SEM image of this specimen showed a spherical fine morphology, this specimen was chosen for antibacterial tests. In order to trace the second aim of this study, chosen specimen was tested against Escherichia coli and Staphylococcus aureus bacterial strains while suspended in nutrient broth, water and DMSO. The results revealed higher inhibition of E. coli (gram-negative strain) comparing to S. aureus (gram-positive strain) in all cases. Also, the CuO-nutrient broth appeared to be the suspension with the highest inhibitory for both bacterial strains. The Minimum inhibitory concentration of nanoparticles in this suspension are 105 and 242 µg/mL for E. coli and S. aureus. This could be related to the better dispersion of nanoparticles in nutrient broth solution. Therefore, it could be suggested that adding surfactants to suspension, can enhance the inhibition of bacterial strains.