Journal of Metallurgical and Materials Engineering
Year:2016 | Volume:27 | Issue:2|Papers Count:10

In this study, GTAW process and cored wires were used to coat Al/Al3Ti wear resistant composite on a commercial pure Al substrate. Wire drawing process was utilized to produce the cored wires from aluminum strips and a mixture of titanium and aluminum powders. The microstructures and the present phases were investigated by metallographic, SEM equipped with EDS and XRD analysis. Moreover, the hardness and wear resistance of the samples were evaluated. A maximum micro hardness value of about 300HV was measured which is 13 times higher than the hardness of the substrate material. The results showed that the coating was composed of Al, Ti as well as Al3Ti. The presence of Al3Ti led to increase in the wear resistance of the coating.

The effect of iron on the structure and absorbed energy in thin-walled brass tubes filled with Al-Si-SiCxFe foams, produced through powder metallurgy rout, during uniaxial compressive loading was evaluated. Results showed that by increasing the iron content up to 3 wt.% will increase the sphericity of the cells, foam density and homogeneity of the structure. However, the formation of Al4Fe2Si intermetallic and micro-shrinkage in the cell walls and edges resulted in a decrease in the magnitude of the absorbed energy. Moreover, according to experimental data, a model was developed based on the relative density of the foam along with the geometry of the foam and tube. This model was used to predict the energy absorption of foam filled tubes.

In this research, the effect of synthesis temperature on the phase composition, crystal size, morphology and photocatalytic activity of titanium dioxide nanoparticles prepared by solvothermal method was investigated. The results showed that the crystallinity of the particles occurs within the gel-like matrix and the particles size increases from 4 to 8 nm by increasing the synthesis temperature. All samples showed suitable photo degradiation up to 94% yield. Nano-particles synthesized at 120°C showed the highest photo catalytic activity.

The microstructural evolution of dissimilar joining of austenitic stainless steel AISI 316 and low carbon steel St37 by friction stir welding has been investigated. Friction stir welding was carried out using a rotational speed of 600 rpm and a linear speed of 50 mm/min. The microstructure was characterized using a scanning electron microscope and optical microscopy. Also, possible phase transformations were determined using X-ray diffraction technique & electron diffraction spectroscopy. The results of phase investigations showed that no carbides and brittle phases were detected at the joined boundary. Microstructural investigations showed that the highest decrease in grain size occurred in the stir zone of the austenitic stainless steel which was attributed to discontinuous dynamic recrystallization caused by severe deformation imposed at high temperatures in this region.

In this study, Ti-6A1-4V alloy was coated with a 200 nm thick tantalum nanolayer using physical vapor deposition method with electron beam in order to improve its surface and corrosion properties. The surface hardness and roughness of the control sample (Ti-6A1-4V) and those with tantalum coating (Ti- 6Al-4V/Ta) were assessed. After coating, the surface hardness and roughness of the samples increased from 345 HV to 371 HV and from 0.055 mm to 0.107 μm, respectively. Moreover, the corrosion test in Hank's solution revealed that the corrosion current density of Ti-6Al-4V/Ta decreased from 1.9 mA/cm2 vs.0.7 μA/cm2 for control sample. Following the corrosion test, the release rate of V, Al and Ti ions was examined. The results showed that the concentration of the released elements was halved after coating. Finally, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDS) were conducted to determine the phases, microstructures, and percentage of elements in the samples, respectively. The test results indicated that tantalum-coated Ti-6A1-4V alloy has desirable corrosion resistance and excellent mechanical properties and can thus be employed in dental and orthopedic implants.

In this study, it is tried to use an inexpensive and new method for fabrication of aluminum matrix nanocomposites reinforced with SiO2 nano-sized ceramic particles. In this method, ultrasonic device was used for increasing wettability and dispersion of reinforcement nanoparticles within the aluminum melt. After producing aluminum nanocomosites reinforced with 0.25, 0.5, 0.75 and 1.0 wt. % SiO2, microstructure study of matrix were carried out with an optical microscope and SEM equipped with energy dispersive spectroscopy (EDS). At the end, compression test were taken on produced nanocomposites. The results show that adding SiO2 nanoparticles will improve structure and properties of the final product by creating nucleation center for intermetallic compounds and also increase compressive strength of produced nanocomposites than the pure Al alloy.

In this study, an aluminum matrix nanocomposite reinforced with oxide nanoparticles as well as intermetallic particles in the Al-Zr system was produced and optimized through mechanical milling.  Results revealed that even long milling times of the powder mixture would not lead to the production of intermetallic phases in the Al-Zr system. This is while Al3Zr and Al2O3 phases form during subsequent heat treatment after milling by the implementation of the relevant reactions between the powder mixture components. After cold pressing and sintering, the hardness increased to 98 HV due to the presence of Al3Zr and Al2O3 phases. In addition, the wear resistance of the bulk samples decreased significantly.

Hydroxyapatite due to its biocompatibility and chemical and biological affinity with bone tissue is used for orthopedic implant, dental implant, oral and maxillofacial surgery and as a coating film on metal or alloy implants. In this study, hydroxyapatite powders were synthesized with three different ratios of Ca/P =1.6, Ca/P=1.5 and Ca/P=1.67 using sol-gel method and utilizing P2O5 and Ca (NO3)2.4H2O as starting materials. The X-ray diffraction (XRD) results reveal that the highest peak of hydroxyapatite and b-TCP, a biphasic bioceramic with high ability of ossification, are found for the hydroxyapatite powder synthesized with Ca/P=1.6. Microstructural studies at high magnifications reveal a uniform distribution of hydroxyapatite nanoparticles (10-400 nm) while at low magnifications only clusters of nano - particles could be detected. The peak intensity of the b-TCP phase is increased after applying the sintering heat treatment for all three ratios of Ca/P. By increasing the Ca/P ratio from 1.5 to 1.6, the grain size of the sintered samples increased and the morphology of the microstructure became coarser. The biocompatibility evaluation of the synthesized hydroxyapatite indicate that increasing the ratio of Ca/P will increase the volume and rate of apatite formation on the surface of the sintered samples.

The hot ductility of IMI834 alloy in two conditions of first hot rolling and second hot rolling has been studied by conducting tensile tests with a strain rate of 0.1 s−1 and temperature range of 800–1000°C. In first hot rolling condition, IMI834 alloy showed little hot ductility in the temperature range 800–900°C and ductility loss occurred at 850°C. In second hot rolling condition, hot ductility increased at all temperatures and ductility loss is not occurred. Especially at 900°C, hot ductility increased from 31% in first hot rolling to 95% in second hot rolling.

Ionic polymer metal composites have recently been extensively used in various industries. These are a new generation of smart materials for fabrication of actuators. IPMC is a layered polymer-metal composite processed using advanced technology. The objective of this project is the production and processing of polypyrrole-gold-polyvinylidene fluoride (PVDF) composite. The porous PVDF membranes were first sputtered with gold as a conductive layer. The solution of propylene carbonate, pyrrole and lithium triflouromethane sulfonamide salt was employed as an electrolyte for electroplating of poly pyrrole on the gold layer under controlled conditions. The composite layers along with the influence of temperature, current and time of electroplating, electrolyte concentration and thickness of the gold layer on the characteristics of the IPMC were investigated using SEM and FTIR techniques. The results indicated that the thickness of poly pyrrole layer increased with an increase in the thickness of the gold layer and electroplating duration. Meanwhile, the optimum condition of electroplating was obtained in the sample containing 0.1 molar of pyrrole and lithium triflouromethane sulfonamide salt temperature of -25°C.