Advanced Materials Research Vol. 795

Abstract: A novel stencil-printable silver-copper (Ag-Cu) nanopaste that serves as an alternative high temperature die attach material was introduced in this study. The nanopaste was made by mixing 50 nm-sized of Ag and Cu particles with an organic binder system. Sintering temperatures, up to 450°C, were used to sinter nanopaste in air and its post sintered properties were investigated. The viscosity of nanopaste was 350,000 cps and it demonstrated a shear thinning behavior. Scanning electron microscope revealed the change of grain structure with the change in the sintering temperature. Formations of Ag₉₇Cu₃ and Ag₁Cu₉₉ compounds after sintering were confirmed with X-ray diffraction; and the electrical conductivity of the sintered nanopaste was increased with the increase of the sintering temperature. The study concluded 380°C was the optimum sintering temperature to form a well sintered nanopaste.

Abstract: In this study, bio-glass 45S5 powder was added to pure magnesium powder to produce the magnesium/bio-glass composite by powder metallurgy method. The composite was synthesized based on 5 wt. %, 10 wt. % and 15 wt. % of bio-glass. The composite was investigated from the point of view of its microstructure, physical properties and in-vitro bioactivity. Microstructural analysis showed that bio-glass was agglomerated with increasing content of bio-glass. Density and hardness of composite increased as the content of bio-glass increased. During in-vitro test, corrosion resistance increased as the content of bio-glass increased.

Abstract: In this study, the effect of anodizing voltage on the current density versus time transient, oxide mass and the current efficiency of anodizing of aluminium manganese alloy was reported. It was found that the anodizing voltage facilitated the pore nucleation process and increased the steady state current density. However, when the anodizing voltage is 70V, dielectric breakdown occurred. The current density versus time transient for anodizing conducted at 30 to 60 V were typical while the shape was unusual for anodizing conducted at 70 V. The rate of oxide growth increased as a function of anodizing voltage. The current efficiency of anodizing increased as the anodizing increased from 30V to 70V.

Abstract: Electrostatic charges are potentially generated on a commercial vehicle through several ways, such as friction of its rubber tyres while rolling on the road and also from the rotating of its mechanical components (e.g. bearings shaft). If these accumulated electrostatic charges are not dissipated from the vehicle, interferences of electronic components within the vehicle may occur. Highly accumulated electrostatic charges may also lead to safety hazards (e.g. fires and explosions) for vehicles that transporting highly flammable materials or during the vehicles refueling process.

Abstract: Porosity of the fiber-reinforced polymer (FRP) is one of very important quality characteristics for the advanced use of the material in order to ensure full performance properties are attained. It was found that the porosity values of FRP in typical aircraft composite parts must be lower than 2.5 % to achieve the required mechanical properties. The most common method for measuring the void content is through acid digestion testing or burn-off method, since it provides the true values that could be used to generate the database properties of the materials. Thus, this paper discussed the detail of the acid digestion test procedures for the void content measurement of FRP, especially with regards to the suitable testing time and chemical volumetric quantity required to ensure the matrix of test sample has been completely extracted. In order to attain this, different test samples for different processing techniques were prepared. Subsequently, the findings were discussed within the context of void content in cured monolithic composite for different types of process, in which the samples from the VBO-oven curing process were compared with those of the autoclave-cured samples. In the VBO-oven curing process, the use of an intensifier during the curing provided higher void content of 15.52% in comparison with those achieved through the debulking process (10.91%). It has been clearly observed that the debulking produced a substantial effect towards the air evacuation mechanism within the laminate.

Abstract: Wear generated by the presence of friction on hip joint contact surfaces can cause debris, which may lead to loosening and failure of the hip prostheses. The objective of this study is to examine the limiting friction coefficient of the hip joint using Finite Element (FE) method. The hip joint model was developed to represent the contact surfaces between femoral head and inner socket, and the contact surfaces between inner socket and acetabular cup. The measured angle from 0° to 15° was applied to the inner socket for normal walking condition. The maximum contact pressure on the acetabular cup surface was found at the position angle of 10°. Therefore, further examination was carried out and the results showed that the highest friction coefficient of 0.4 was determined.

Abstract: Joining of stainless steel type 304 to mild steel was carried out using a gas tungsten arc welding (GTAW). Samples were welded using stainless steel welding electrode: (AWS: E308l-16) and mild steel welding electrode: (AWS: E6013). The mechanical properties of welded joint were investigated by tension test. It was observed that, the yield strength and tensile strength of welded samples using mild steel welding electrode were slightly lower than welded samples using stainless steel welding electrode. All welded samples fractured at mild steel base metal indicated that the regions of stainless steel base metal, fusion zone and heat affected zone are stronger than mild steel base metal.

Abstract: Porous F-75 (Co-Cr-Mo) was produced by powder metallurgy technique. F-75 powder was mixed with space holder and compacted using different pressures (300 MPa, 350 MPa, 400 MPa, 450 MPa). The green samples were sintered at 1150 °C in a tube furnace under argon atmosphere. Sintered samples were examined in terms of bulk density, porosity, hardness and pore size. Microstructural analysis was carried out using a scanning electron microscope (SEM). Microstructure analysis showed that pore sizes and pore shape were influenced by different compaction pressure. The hardness of the samples increased as compacting pressure increased. Density and porosity remained constant at certain level.

Abstract: The effect of space-holder content on the porosity of sintered copper that was fabricated by powder metallurgy technique has been investigated. Carbamide was used as space-holder and the content selected was 10 wt. %, 20 wt. % and 30 wt. %. A roll mill was used to mix the copper powder and the carbamide particles with rotation speed of 160 rpm for 2 hours. The mixture was compacted by hand press at 200-350MPa and sintered under argon atmosphere at 800°C. True density of the sample was determined by a gas pycnometer. Bulk density was determined using mass and volume of the sample. Result shows that the sintered porous copper with 30 wt. % of space-holder produced the highest porosity and the lowest density. Microstructure of pores was analyzed by a scanning electron microscope (SEM) which reveals the elongated pores interconnected to each other.

Abstract: Studies on the effects of welding current and cycles were carried on the galvanized steel sheets using spot welding. The welding currents used were 3 kA, 5 kA 6 kA and the welding cycles were 4, 6 and 8. Tensile shear and tensile peel load were determined on the joint of welded specimens. The results showed that the value of tensile shear load was lower than tensile peel load. The strength of the joint increased with the increasing of welding current and welding cycle used in the welding process.