Revista de Ciências e Engenharia de Materiais

The use of polymer fiber reinforced composite materials is growing day by day in all types of engineering structures such as aerospace, automotive, aircraft, chemical, constructions etc. because of their tailorable properties. Through these materials are tailorable, improvement in tribological properties is demanded.

Energetic needs and environmental concern are causing the evolution of fuels. Biofuels have started to partially replace non-renewable fuels. Among them, Biodiesel has occupied an important place on automotive industry. In the other hand, polymeric materials have substituted metals in some automotive components. Sometimes they are in direct contact with fuels, and then compatibility between polymers and fuels is essential. In this study, the compatibility of three different engineering polymer families, POM, PPA and PPS, is assessed with diesel and SME biodiesel. Polymer samples were exposed to fuel for a 1008h period at 120°C, simulating automotive extreme conditions. Mechanical properties of the specimens were evaluated at different periods of time. Differences on effects of biodiesel and diesel were assessed for the different families and it was found that the effect of biodiesel and diesel over the analyzed polymers is the same for both cases: the mechanical properties are slightly modified.

The microstructure of (Mg0.95Ni0.05)4(Nb1-xTax)2O9 is analyzed using X-ray diffractometry and scanning electron microscopy. The Qxf values of (Mg0.95Ni0.05)4(Nb1-xTax)2O9 increases with increasing sintering temperature; and then up to a temperature of 1375°C significantly decreased. The maximum values of the electric permititivity and the quality factor (Qxf) can be obtained 12.76 and 442,000 GHz is obtained for (Mg0.95Ni0.05)4(Nb1-xTax)2O9 sintered at 1375°C for 4 h. The temperature coefficient of resonant frequency (τf) measured for (Mg0.95Ni0.05)4(Nb1-xTax)2O9 is −54 ppm/°C.

The band structure and density of states of the orthorhombic Ag3PS4 and Ag5PS4Cl2 compounds has been investigated. The calculations are derived from the total-energy calculations using the Full Potential-Linearized Augmented Plane Wave (FPLAPW) method. The exchange and correlation potential is treated by the Local Density Approximation (LDA), Generalized Gradient Approximation (GGA) and Engel Vosko GGA. From the study of the band structure we confirmed that the Valence Band Maximum (VBM) and Conduction Band Minimum (CBM) of Ag3PS4 compounds situated at Г point, indicating a direct band gap. While for Ag5PS4Cl2 compound the VBM occurs along the Z–S direction and CBM at Г point exhibiting indirect band gap. The partial density of states confirm that the lower part of the valence band is dominated by S-s orbital, the mid part by P-s orbital and the VBM by the Ag-d orbital. The conduction band consists the major contribution of Ag-s/p orbital. Furthermore, the thermoelectric properties of both compounds were investigated by means of BoltzTraP code. The electrical conductivity, electrical resistivity, the power factor and Seebeck coefficient were investigated in the temperature range from 300 to 800 K. The electrical conductivity was enhanced by increasing the temperature, which leads to a small electrical resistivity and a large Seebeck coefficient. Consequently, large values of about 3.75×1011 and 1.2×1011 W/m K2 for Ag3PS4 and Ag5PS4Cl2 compounds were obtained. Therefore, the thermoelectric property of Ag3PS4 is not as good as that of Ag5PS4Cl2. Therefore, it can be concluded that Ag5PS4Cl2 is suitable for high performance thermoelectric application than Ag3PS4 at higher temperature.

Sn96.5Ag3Cu0.5 (SAC305) is widely used as lead-free solder for surface mount technology (SMT) card assembly and for ball-grid-array (BGA) interconnection in the microelectronic packaging industry as solder balls and pastes. In this study the effects of Lanthanum (La) doping on SAC305 under thermal aging was investigated as function of intermetallic compounds (IMCs) growth and grain size evolution. The morphology of the microstructure was analyzed under Scanning Electron Microscope (SEM) and optical microscope, the elemental distribution was confirmed by Energy Dispersive Spectroscopy (EDS) and phase identification of the crystalline structure formed during thermal aging was confirmed by x-ray diffraction (XRD). It was found that the microstructure of SAC305 solder alloy changes significantly with addition of La. Quantitative analysis of grain size and intermetallic particle size was performed both for undoped and La-doped SAC305 alloys.

An experiment based thermal analysis has been performed to obtain the thermal histories, which can be applied to determine cooling rate of weldment. During fusion welding process it is possible to determine temperature at any point by using thermocouple and from such data it is possible to draw thermal histories for any point of interest, such thermal histories can be utilized to determine cooling rate. The temperature distribution and cooling rate during the welding process have significant effect on the mechanical and metallurgical properties of a weldment. The changes in microstructure, grain growth and hardness in a weldment are very dependent on the temperature distribution and cooling rate. These studies are utilized to investigate the micro-structure and microhardness of the heat affected zone (HAZ) and weldment. In present work, the influence of heat input and cooling rate on microhardness has been investigated. Full factorial design is used to conduct the experiment with three factors and two levels. Eight combinations and two set of heat input are designed with different combinations of SAW welding parameters. Temperature distribution curves and cooling rate have been drawn. The effect of selected welding parameters (Wire feed rate, Open circuit Voltage and welding Speed) on the microhardness have been investigated.

Recycled AlSi2.4Mg cast alloys can be used directly in new cast products such as textile machinery parts and for structural engineering such as aluminum sidings and window frames. In this work, the modification effect of antimony (Sb) on the microstructure and tensile strength of recycled AlSi2.4Mg cast alloy was systematically investigated. Aluminum Piston scraps was melted in a furnace to form a melt composition. The melt was adjusted to form the present composition, consisting essentially of 2, 4, 6, 8, 10 and 12 gr addition of Sb. However, its effect as a modifier is more pronounce at 8 gr addition of Sb and caused refinement of microstructure, which led to increase in mechanical properties. It was obvious that Sb modify the coarse Si platelets into a more fibrous one. An optimal tensile strength of 82.59 MN/m2 was obtained.
However, fractal analysis performed on the micrograph revealed that the formation and features of Si platelets in as-cast sample and samples treated with 2 to 4 gr of Sb can act as a seedbed for micro-crack initiation because of their irregularity in nature and their departure from perfect shape. The best platelet shape was observed in 8 gr addition of Sb having a weighted average value of fractal dimension D=0.5961 and sphericity β=0.8501 respectively.