Advanced Materials Research Vol. 911

Abstract: In the present study, the impact strength of annealed Al-6063 alloy developed by equal channel angular extrusion (ECAE), up to 6 passes at a temperature of 200^°C following route A with a constant ram speed of 30 mm/min through a die angle of 90^° between the die channels was investigated. The impact strength of extruded specimens is evaluated for different passes at a strain rate of 1800 s^-1 using Split-Hopkinson pressure bar techniques. The results indicate that the major strength improvement occurs in the 5^th and 6^th passes while in primary passes, the strength improved but at a considerably lower rate. A total increasing in ultimate strength (UTS) and yield strength (YS) are 127% and 65% respectively and observed for the extruded material after 6 passes. Optical microscopic examinations show a grain refinement from 45 μm to 2.8 μm.

Abstract: Cold upsetting experiments were carried out on sintered Fe-0.8%C-1.0%Si-0.4%Cu preforms to evaluate their deformation characteristics.The sintered preforms are subjected to axial compressive deformation under nil and graphite lubricant condition in steps of 0.04MN until cracks began to appear on the free surfaces. Combined strain, has been considered to study the densification mechanism of the preforms. It was observed that overall,densification enhances against combined strain for both the friction conditions,however dry friction restricts the free deformation consequently facilitates faster densification as compared to its counterpart. Further,an attempt has been made to analyse various stresses against strain as well as against attained density. The calculation for Poissons ratio has been shown and its characteristics have been detailed against attained density.

Abstract: AZ31B Mg alloy and Cu were joined through diffusion bonding using a Zn interlayer film prepared. The element distribution, microstructure and hardness was studied by means of scanning electron microscope(SEM), Energy Dispersive Spectrdmeter (EDS) and Microhardness tester.The result show that SEM results indicate the diffusion zone of Mg/Cu diffusion bonded joint consists of intermetallic compounds. Via enhanced holding time,these intermetallic compounds go steady gradually. Thus the Mg/Cu diffusion bonded joint of strength can be improved. This work provides a theoretical reference and practical experience for Mg/Cu dissimilar metal connection.

Abstract: Mineralogical composition has a decisive influence on the durability of silica materials built into heating aggregates as well as their dense. This paper describes the influence of Fe aditives and the influence of firing temperatures on the physical and mechanical properties and on final mineralogical composition of silica materials. The paper compares the properties of silica prepared without Fe additives with that prepared using Fe additives of varied granulometry.

Abstract: The mechanical response of a hot rolled polycrystalline AZ31B Mg plate along its two directions is predicted using a visco-plastic self-consistent (VPSC) model coupled with a dislocation-based hardening scheme. The hardening response along the in-plane and through thickness directions of the plate was successfully predicted in tension and compression. The high flow stress anisotropy and tension/compression asymmetry of the alloy is attributed mainly to the directionality of the tensile twinning. The high hardening rate after twinning is also predicted successfully using the above mentioned hardening scheme.

Abstract: Ferroelectric barium strontium titanate (Ba_xSr_1-xTiO₃) thin films with different Ba content have been fabricated as MFM configuration using sol-gel technique. The effect of barium-to-strontium ratio on the leakage current mechanism of Ba_xSr_1-xTiO₃ thin films has been investigated. The results show that the leakage current density increases as Ba content increases, which attributed to the grain size effect. The leakage current for the tested films has been studied using log (J) vs log (E) plane, which shows three distinguished linear regions. These regions have been characterized using power law () to find that: the region at low electric fields (E < 20 KV/cm) is controlled by Ohmic conduction and the other two regions (E > 20 KV/cm) are due to space charge limited conduction, which is also confirmed via modified Langmuir-Child law. In addition, it is observed that at high electric fields region (E > 1.29×10⁵ V/m) the films show Schottky emission (SE) and PooleFrenkel (PF) emission mechanisms.

Abstract: This research work investigates the surface degradation of wind turbine blade surface insulator which is made from modified epoxy resin mixed with Zinc oxide (ZnO) and Aluminium oxide (Al₂O₃) in different percentage as a filler elements. Accelerated test with AC voltage of 4.5 kV 50 Hz with NH₄Cl saline solution using flow rate of contaminant equals to 0.6 ml/min according to IEC 60587 standard. It was found that, the solid insulators which has 30 % of Zinc oxide (ZnO) and 20% of Aluminium oxide (Al₂O₃) fillers prolong the process of surface tracking to the order of 5.41 for Zinc oxide (ZnO) filler and also to the order of 30.68 for Aluminium oxide (Al₂O₃) filler. On the other hand, if the amount of Aluminium oxide (Al₂O₃) filler is more than 20% by weight, it will lead to a rapid tracking phenomena.

Abstract: The effect of excess calcium and aging media on calcium phosphate biomaterials mechanical strength was studied. The variation of excess calcium and sample type has shown different performance when they are being aged in the moist environment (ME) and the simulated body fluid (SBF). The calcium phosphates were synthesized via low temperature hydrothermal method and sampled to two types of powder-water (3:2) mixture and paste for 90 days of the aging time. Two mechanical tests were applied, compression and diametrical tensile test, while XRD to evaluate phases. Scanning electron micrograph showed the paste samples that soaked in SBF was better entanglement of the particles, better compression strength but with degradation and diametrical tensile strength improvement by aging. Calcium hydroxide and ammonium di-hydrogen phosphoric was traced in all the samples along with calcium deficient hydroxyapatite as the main phase.

Abstract: Two starch/wax based binders were formulated for metal injection moulding of 316L stainless steel. The formulations difffer in term of the starch type which substitute the backbone polyethelene. Feedstock having powder loading of the stainless steel powder up to 65 vol.% can be injection moulded successfully. Solvent debinding was performed in water at a temperature of 60°C for 3 hours and followed by immersion n-heptane for duration of 2 hours to remove the residual wax. The remaining binder was thermally extracted at 450⁰ with heating rate of 3°C/min, with no defects. The parts were then sintered in vacuum atmosphere within a temperature range of 1300°C to 1380°C. Approximately, 6.8 g/cm³theoretical density, hardness of 188.8 HV and tensile strength of 229.3 MPawere achieved for cassava starch/wax based binder while rice starch/wax based binder possessed 8.6g/cm³theoretical density, hardness of 385 HV and tensile strength of 462.1 MPa.

Abstract: Depositions of BaZr_0.10Ti_0.90O₃ and BaZr_0.10Ti_0.90O₃ thin films doped with strontium (Sr) have been growth on Pt/Si substrate using the sol gel method prepared with spin coater. Mole percent of Sr is varied to 1%, 3% and 5%, repectively. The characterization of its micro structure showed that the diffraction angle is shifted to the right if the mole percent of the Sr doped is increased. We found that the particle size of BZT with Sr dopant is bigger than BZT without dopant Sr as shown in the morphological characterization result. The thickness of BaZr_0.10Ti_0.90O₃ and BaZr_0.10Ti_0.90O₃ thin films doped with Sr are about 400 nm. The obtained hysteresis curves of BaZr_0.10Ti_0.90O₃ and BaZr_0.10Ti_0.90O₃ thin films shown that the saturation values are similar to each other, however the remnant polarization and coercive field geting smaller along with the increasing of mole percent of Sr dopant.