Advanced Materials Research Vol. 856

Abstract: The steady state measurements in Liquid crystalline polyurethane (LCPU) have been investigated for different fields (4 - 45 kV/cm) and temperatures (50°-220°C). The nature of conduction processes has been determined by estimating ion jump distances (a) and Schottky coefficients. The order of magnitude of a in the temperature region 150°C and below does not seem to support an ionic conduction. However the magnitude of a at higher temperatures (180°C and above) indicates the possibility of ionic conduction. There is a definite possibility of a Schottky type conduction at lower temperature and a Poole Frankel type conduction at higher temperature (100°C). The activation energy associated with the high temperature region lies between 0.26 eV and 0.65 eV depending on the field whereas in the low temperature region the activation energy lies between 0.82 eV and 0.95 eV depending on the applied electric field. The dual slopes in the log I versus 1/T curves indicate the presence of more than one type of trapping levels.

Abstract: Single-phase Cu₂O films with p-type semiconducting properties were successfully deposited by reactive DC magnetron sputtering at room temperature followed by post annealing process at 200°C. Subsequently, such films were used to fabricate bottom gate p-channel Cu₂O thin film transistors (TFTs). The effect of using high-κ SrTiO₃ (STO) as a gate dielectric on the Cu₂O TFT performance was investigated. The results were then compared to our baseline process which uses a 220 nm aluminum titanium oxide (ATO) dielectric deposited on a glass substrate coated with a 200 nm indium tin oxide (ITO) gate electrode. We found that with a 150 nm thick STO, the Cu₂O TFTs exhibited a p-type behavior with a field-effect mobility of 0.54 cm².V^-1.s^-1, an on/off ratio of around 44, threshold voltage equaling-0.62 V and a sub threshold swing of 1.64 V/dec. These values were obtained at a low operating voltage of-2V. The advantages of using STO as a gate dielectric relative to ATO are discussed.

Abstract: A numerical analysis of the role of the gas friction force on the shape of the melt surface in laser cutting process is carried out. The liquid film shape is analyzed in the central plane of cutting for both cases with the pressure gradient force only and for the case of gas friction force contribution. It is shown that, the gas friction force has a significant role in the formation of humps in the central kerf zone and the transition from the smooth melt ejection regime to a wavy structure characterized by humps formation.

Abstract: The role of suspended particles on Ti-6Al-4V surface in Powder Mixed Electrical Discharge Machining (PMEDM) is studied using SiC powder mixing in water dielectric liquid. Surface modifications due to the additives in dielectric liquid are investigated by means of optical, scanning electron microscopy and energy dispersive spectroscopy. The attachment of added powders and surface topographies interrelated with powder suspension concentration, particle size and electrical parameters such as pulse on duration and current. The influence on discharge transitivity with respect to SiC additives is noticed with pock like features on the surface. The geometry and size of these features indicated a robust dependency with respect to operational parameters and indicated the role of secondary discharges during PMEDM. SiC particles severely transferred from di-electric liquid to machined surface at critical operational parameters and implied that the process could be also used as a surface alloying technique.

Abstract: Automotive industry makes wide scale use of cast aluminium alloy 354 in the production of crucial components, such as compressor wheels for turbochargers. The compressor wheels undergo T61 heat treatment, involving artificial ageing at 188°C. This study focuses on the possible improvement of the mechanical behaviour of the components by subjecting them to modified heat treatments involving usage of lower artificial ageing temperatures (160, 171 and 177°C). A comparative analysis of tensile properties and strain hardening behaviour has been carried out with different artificial ageing temperatures. Results showed that the heat treatment routinely employed by the industry (aged at 188°C) leads to overageing, thereby resulting in relatively inferior mechanical properties and lower strain hardening rates as compared to the samples heat treated at lower artificial ageing temperatures. It is concluded that lowering of the artificial ageing temperature can lead to a superior state of components with respect to mechanical behaviour.

Abstract: The results of microstructure investigation of eutectic alloys Sn Bi and Sn Pb, obtained at cooling rates of the melt 10^-2 K/s, 1 K/s and 10⁵ K/s are represented. Various cooling rates are achieved by graphite mold casting and by ultra fast quenching from the melt. Microstructure and grain structure are investigated by scanning electron microscopy and the electron backscatter diffraction technique. It has found that the melt cooling rate increasing at rapid quenching leads to microcrystalline structure and to a change of the solidification mechanism. The reasons for the transition from lamellar to the microcrystalline structure are discussed.

Abstract: Deoxidized High Phosphorus (DHP) Copper tubes are frequently used in numerous industrial and household applications. To ensure the acceptability of DHP copper tubes prepared by various industrial processes, the quality of the DHP copper tubes must be evaluated and one of the best ways to do so is to examine the microstructure and metallography and quantify grain size. In this paper the authors considered the average grain size of copper tube samples made traditionally as well as by the planetary rolling and CastTube process. Because of the small thickness of the CastTube samples, in certain circumstances traditional methods of grain counting were not plausible and a new procedure for grain counting needed developed. This paper is about the development and evaluation of grain sizes in continuously cast tube samples using both the planimetric procedure (ASTM E112) and a new method, which will be herby, referred to as the total grain counting method. This paper also concludes that there is a large difference in the grain size of tubes with different manufacturing methods.

Abstract: Biomaterials such as acrylic bone cements are widely applied in orthopaedic surgery for the fixation of artificial joints. Therefore, the mechanical behavior of such materials under external stresses is of special interest in order to achieve long-term in vivo performance. Fracture process can be attributed to diverse random microscopic damage modes. As the load increases, new damage modes appear and the existing ones can transition into others depending on the nature of the material. However, limitation exists in detailing the understanding of the micromanage initiation and development, and, consequently, in optimizing biomaterials performance. This paper focuses in the study of the emission of acoustic signals from bone cements in order to monitor the evolution of the internal defects that are believed to dominate in vivo failure.

Abstract: The effect of intercritical deformation on development of microstructure in low-silicon contents multiphase TRIP-assisted steels were investigated by laboratory simulation of controlled-thermomechanical processing in an automated hot compression testing machine. A typical multiple cooling stages TMP program was applied and samples were deformed in intercritical region to different strains. Microstructures of samples were characterized by optical and scanning electron microscopy, XRD and Mössbauer. The result indicated that intercritical straining increases volume fraction of polygonal ferrite and granular-type retained austenite particles, but reduces fraction of bainite. The increase in retained austenite volume fraction is attributed to strain-assisted diffusion of carbon and to refinement of retained austenite particles.

Abstract: This present study has evaluated the physical and mechanical properties of ceramic tiles processed from steel slag. The chemical compositions of both samples were conducted using atomic absorption spectrophotometer (AAS). Steel slag in the range of 0-100wt% was added to kaolinite clay. The blended samples were hydraulic pressed into rectangular moulds, oven dried and sintered within the temperature range of 1100°C - 1200°C. Surface appearance and colouration of sintered products were observed. Linear shrinkage, apparent porosity, water absorption, bulk density, apparent specific gravity and modulus of rupture of sintered samples were examined. Phases present were identified using X-ray diffraction (XRD), while microstructural examination was conducted using scanning electron microscopy (SEM). Phases like quartz, wollastonite, enstatite, were identified. SEM showed considerable degree of vetrification at both temperatures. Results obtained showed that samples containing 25-75wt% steel slag have very good usable ceramic tile properties.