Journal of advanced materials and processing
Volume:2 Issue: 4, Autumn 2014

In this study, the effects of mould materials on microstructure and mechanical properties of cast A356 Al alloy were investigated. The alloy was poured into three different moulds. Then the samples were homogenised and applied T6 heat treatment. The optical, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) studies were made. Secondary dendrite arm spacing (SDAS) was measured by image analysis systems. Hardness and tensile tests were also performed. The ultimate tensile strength (UTS) values were evaluated by Weibull statistical analysis As a result of the studies, the highest values of SDAS were measured for the samples obtained using ceramic mould, which led to the slowest cooling rate, the lowest values of SDAS were measured for the samples obtained using chromite sand mould, which led to the highest cooling rate. The hardness values were increased about 2.5 times which samples were applied T6 heat treatment. The highest tensile strength was observed for the samples obtained using sand mould.

Several characteristics of a novel PLGA/Merwinite scaffold were examined in the present study to evaluate the possible applications in bone tissue regeneration. Physical and mechanical properties, as well as degradation behavior and in vitro bioactivity of porous scaffolds produced by solvent casting and particle leaching technique were also characterized. Results showed that incorporation of merwinite particles into the porous polymer structure had a significant effect on cell viability in such a way that cell densities increased by increasing the merwinite content in the scaffolds after 3 and 7 days of culture. In contrast, mechanical analysis showed that the presence of merwinite had an adverse effect on the compressive strength of porous structures, due to the lack of formation of a chemical bond at the polymer-ceramic interface and non-homogenous distribution of the ceramic particulates through the matrix. Incorporation of the merwinite particles caused about 35% decrease in the compressive strength in samples containing 30 wt% merwinite, compared to pure PLGA porous scaffolds.

In this research, BaTiO3 thick deposit has been successfully sprayed by air plasma spray. The microstructure and dielectric properties of thick films were investigated by secondary electron microscopy (SEM) and LCR meter respectively. XRD measurement was carried out on plasma sprayed BaTiO3. The results illustrate differences in the crystal structure between plasma sprayed coatings and feed stock powders. The as deposited films were mainly crystalline with small amount of an amorphous second phase. The amount of crystalline to amorphous phases was found to be critically dependent upon the degree of melting of feed stock powders. The as-deposited BaTiO3 films had maximum dielectric constant as high as 85 at room temperature. Upon annealing in air at 1050 oC, the dielectric constant increased to165. Increasing in dielectric constant was attributed to the crystallization of the amorphous phase. The dielectric constant of BaTiO3 thick films produced by plasma spray was lower than that of sintering ceramic. Reduction in dielectric properties of deposited films was related to splats interface and lamellar structure of plasma sprayed coatings.

There are various methods to produce iron based nano crystalline magnetic alloys. Among these methods, mechanical alloying is one of the most important. In this research, nano crystalline Fe85Si10Ni5 soft magnetic alloy was synthesized by mechanical alloying. The effect of alloying time on phase constituents and magnetic properties of the produced powders was investigated, by X-ray diffraction (XRD) and alternating gradient force magnetometer (AGFM). The XRD results showed that alloy formation started after 2 hours of milling. Further milling resulted in the reduction of the grain size and lattice parameter. After 60 hours of milling, the grain size was reduced to 8 nm. AGFM results showed that magnetic saturation and coercivity depends on the alloying time. Increasing the alloying time, causes the increase of magnetic saturation and decrease of coercivity.Abstract There are various methods to produce iron based nano crystalline magnetic alloys. Among these methods, mechanical alloying is one of the most important. In this research, nano crystalline Fe85Si10Ni5 soft magnetic alloy was synthesized by mechanical alloying. The effect of alloying time on phase constituents and magnetic properties of the produced powders was investigated, by X-ray diffraction (XRD) and alternating gradient force magnetometer (AGFM). The XRD results showed that alloy formation started after 2 hours of milling. Further milling resulted in the reduction of the grain size and lattice parameter. After 60 hours of milling, the grain size was reduced to 8 nm. AGFM results showed that magnetic saturation and coercivity depends on the alloying time.

This paper investigates the dynamic behavior of Gas Metal Arc Welding (GMAW) process for two types of power supplies –inverter and rectifier- for short circuit transfer mode. The large ripples on the rectifier power source are able to perturb the metal transfer mode. In this experimental work some operating points in the short circuit mode have been selected using an automatic pipeline welding system -, and then both rectifier and inverter effects (as the power supplies) on the process are illustrated. For the small voltage and currents, the two power supplies effects are similar in the short circuit transfer mode. On the other hand, for larger voltage and current values, the responses will be different as the rectifier power supply produces more perturbations on the metal transfer. However the process with the inverter has a more regular behavior and more stable detachment. finally, the results have been evaluated by implementing on the real industrial GMAW system.

In recent years, a lot of research has been done in the field of producing soft magnetic nano composites by means of mechanical alloying. These materials indicate more electrical resistance and permeability in comparison with soft magnetic composites (SMCs). In this research, reduction of silicothermal mixed powder (Nickel-oxide, Silicon and Iron) was carried out by mechanical alloying to form soft nano composites of FeSiNi/SiO2. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were used to detect physical characterization and finding the effect of milling time on micro structural properties. It is determined that initiation of forming the homogenous alloy was in 4 hour milling, increasing the time of milling to 40 hours caused decreasing grain size to 13 nm and formation of homogenous alloy. Magnetic properties of milled powder were studied by alternating gradient force magnetometer (AGFM) and it was observed that increasing milling time will cause improvement in soft magnetic properties (decreasing magnetic coercivity and increasing magnetic saturation).

Duplex stainless steels (DSSS) have a microstructure composed of ferrite and austenite phases that gives them a very good combination of mechanical and corrosion properties. These steels are desirable for many applications in the chemical and petrochemical industries. In the present study, a type of stainless steel was cast, solution annealed at 1200°C for 60 min and then quenched in water. Initial microstructure was composed of about 51.8% ferrite and 48.1% austenite. The steel was then cold rolled about 90% and subsequent annealing at 800,850 and 900°C for different time were performed. Results showed that tensile strength of steel have been significantly improved. Austenite grain size of cast steel was refined through static recrystallization of the austenite occurred during post cold deformation annealing. Results show that yield strength of as-cast steel is increased from 552 to 1800 and its tensile strength increased from 672 to 2350 MPa as a result of large cold deformation. With increasing annealing time, sigma phase increases and this leads to decrease of elongation. Thus sigma phase can be expected to embitter the alloy.

Structural features of La(1-x)SrxMn0.5Co0.5O3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nano-particles were investigated using X-ray powder diffraction and FT-IR spectroscopy. The characterization of compounds by X-ray powder diffraction and using Fullprof program show a cubic structure (Pm3m space group) for x = 0.0 and a rhombohedra structure (R-3c space group) for the Sr substituted La(1-x)SrxMn0.5Co0.5O3 samples. Crystallite size and unit cell parameters decrease with Sr substitution. The electrical conductivity of the samples in oxidizing (air) and reducing atmosphere (6%CO in nitrogen) and also band gap of the samples has been investigated to interpret the performance of samples. Results show that their behavior increases non-uniformly with increase in Sr substitution. An increase of Sr substitution up to 0.5 increases the performance of the samples and an optimal catalytic activity in the low-temperature conversion of CO to CO2. It is mainly attributed to a decrease of the crystallite size.