Abstract: Electrical conductivity plays an important role in the performance of thermoelectric semiconductor material. This study discusses the electrical conductivity measurements of Zinc Oxide (ZnO) doping Aluminium (Al) pellet as a material of thermoelectric using four-point probe method at high temperatures. Al-doped ZnO (2 wt%) pellet was sintered at the temperature of 1100°C, 1200°C, 1300°C, 1400°C, and 1500°C with the heating rate of 8°C/minute. SEM and XRD tests show that the higher sintering temperature effects to larger grain sizes, better crystallinity, and lower porosity. There is no electrical conductivity in the sintering sample at 1100°C due to the small grain sizes and high porosity. In the sintering sample at 1500°C, the phase of ZnAl2O4 erupted. The highest electrical conductivity of 5923.48S/m of Al-doped ZnO pellet was obtained at the sintering temperature of 1400°C with measurement temperature of 500°C.
Abstract: Highly oxidized iron powders were consolidated by means of the medium-frequency electrical resistance sintering technique (MF-ERS). In order to activate the powders and to disperse the oxides coating the particles, prior to the consolidation process, powders were milled in a high-energy mill for 7 minutes. Structural and mechanical characterisations of electrically consolidated compacts were carried out in order to study the effect of two main processing parameters (current intensity and heating time). The compact properties resulted to be very sensitive to these parameters, especially to the current intensity. A change from 5 kA to 10 kA in the current intensity makes the porosity to fall from 30% to 8%. Moreover, using a higher current intensity (10 kA) increases the mechanical properties of the final compacts: micro-hardness change in almost 50 HV, up to 104 HV 1, and compression resistance by around 500 MPa, up to 569 MPa.
Abstract: This paper focuses on the microstructural characterization of Al25Ti75, Al37Ti63, Al50Ti50, Al63Ti37 and Al75Ti25 powders mixtures prepared by mechanical alloying (MA). The high-energy ball-milling, up to 75 h, of aluminium and titanium powders leads to a nanocrystalline or an amorphous structure. It is showed that a stable amorphous Al–Ti phase with uniform elemental distribution forms after 50 h of milling in Al50Ti50 alloy. Heat treatment of the different alloys leads to the crystallization of AlTi3, AlTi, Al2Ti and Al3Ti intermetallic compounds. A comprehensive study by laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) was carried out on the structure, surface morphology and thermal behaviour of the MA Al-Ti mixtures, both of milled and heat treated powders.
Abstract: Compacts of iron powders were prepared by medium-frequency electrical resistance sintering (MF-ERS) and electrical discharge consolidation (EDC). Structural and mechanical characterization was carried out in order to study the effect of the main processing parameters (current intensity and sintering time in MF-ERS and voltage and capacity in EDC). The compact properties resulted to be quite sensitive to the consolidation method and parameters. Porosities around 8% and microhardness of about 120 HV were reached. It is concluded that the MF-ERS process can be a best option for the consolidation of cemented carbide composites with composition WC-6wt.%Co. MF-ERS compacts of this composite show a very low porosity and reasonable uniform microstructure, preserving the original ultrafine grain size and an adequate hardness with a very quick processing cycle of the order of one second.
Abstract: The application of underwater welding is for repairing the damage underwater structures and oil pipelines to extend the lifetime of the facilities. Generally, underwater welding studies were performed in shallow depth water. It is important to investigate the properties of the underwater welding joint based on the depth of water in meter scale. In this work, the shielded metal arc welding (SMAW) was used to conduct the welding process of SS400 low carbon steel. The water depth of 2.5 m, 5.0 m, and 10.0 m were evaluated, while the welding electric current were varied in the range from 80 A to 110 A. Underwater welding processes were carried out using the E7016 electrode. Non-destructive and destructive tests were conducted including the X-ray analysis, microstructure investigation, tensile, and hardness tests. The X-ray analysis showed that there were many defects for all underwater welding specimens. The water depth of 2.5 m joint specimens provided the highest tensile strength. It decreased as increasing of water depth level. Stability of welding arc due to the water pressure was the main reason. Tensile strength increased slightly as the welding current increasing due to deeper penetration. For all specimens, the highest hardness was found in the HAZ which was adjacent to the fusion zone.