Materials Science Forum Vols. 638-642

Abstract: Miniature specimen testing to evaluate mechanical properties, presents a novel opportunity to undertake structural integrity assessments of in-service power generation components, by removing only a very small volume of material. In this study, high temperature fatigue testing of P22 steel was undertaken and a number of fatigue properties determined using a miniature specimen testing methodology. Good comparisons were observed between fatigue properties determined by miniature specimens and the more established standard-sized specimen testing reported in literature.

Abstract: A gate insulator film with a wide bandgap and a high dielectric constants required to achieve high power field effect transistor (FET) using wide bandgap semiconductors such as SiC and diamond. We can achieve to suppress the gate leakage current and the charge shifts by using the AlSiO film. We found that the leakage current of Nitrogen-doped AlSiO film can be suppressed in high temperature region compared with AlSiO film. In addition, we attempted to study Yttrium aluminate (YAlO) and Lanthanum aluminate (LaAlO) as a gate insulator film. Since the Y (+3) and La(+3) have the same valence as Al (+3), it is expected that there is an advantage that Y, La doping generates less dangling bonds in the Al2O3 film. We can achieve to form aluminum based oxide film with higher dielectric constant by doping Lanthanoid atoms such as Y and La. The optimized YAlO and LaAlO films were applied to SiC-MIS structure. The Lanthanoid and Aluminum based oxide films can readily be applicable to wide bandgap semiconductor devices.

Abstract: Al-Mg based alloys have special attention due to the lightness of the material and certain mechanical properties and recyclability. Normally classified as non-heat-treatable these alloys obtain higher strength either by strain-hardening or by solid solution. The P/M process in the Al-Mg alloys in study leading to fine grain structure after the thermal treatment. The direct observation were made in a JEOL 200C and 2010 TEM combined with mechanical characterization utilizing Vickers microhardness measurements. The samples preparation followed the usual route of metallographic specimen preparation. The understanding of the observed phenomena depends of the fact that materials produced by powder metallurgy present complex interface reactions in a great amount of nucleation sites and a subtle change in the structure of the material causes an important variation in your properties. Alloys in study presented interesting values of properties, with evident technological potential.

Abstract: Experimental and numerical investigations have been performed in order to study the effect of welding parameters on properties of FSW-ed AZ31 magnesium alloy sheets. The results, presented in terms of tensile strength and numerical field variables distributions, allow to understand the behaviour of such material when FSW-ed using different rotational and welding speeds for a given tool geometry.

Abstract: A356 alloy is one of the wide used casting aluminum alloys and intense research activities of worldwide on casting process or refinement agent and procedure. In this study, we attempted refinement on Al primary phase and eutectic phase of A356 alloy by ultrasonic injection into the melts. The effect of ultrasonic injection into the melts could be summarized as follows: the morphology of the Al primary phase was refined and changed shape from dendritic to nondendritic and the eutectic phase of A356 was also refined and changed morphology from dendritic to plate shape.

Abstract: A new Temperature Gradient System has been designed for practical use when quenching real workpieces in any kind of liquid quenchants. The main hardware component of the system is a cylindrical probe of 50 mm Dia. × 200 mm assembled with three thermocouples, and the tem-perature data acquisition unit for automatic drawing of cooling curves. The accompanying software-package consists of three modules: The first one for calculation of the heat transfer coefficient, the second one for quenching process analysis by graphical presentation of different thermodynamic functions, and the third one for hardness distribution prediction on the axial section of axially-symmetrical workpieces of any complex shape. The hardness prediction 2-D program is based on a Finite Volume Method, by which cooling curves in every particular point of the axial workpiece section are calculated, and cooling times from 800 °C to 500 °C (t8/5) determined. Using the known relation between the cooling time (t8/5) and the distance from the quenched end of the Jominy spe-cimen, for the relevant steel, the hardness can be predicted, at once, in every particular point of the axial workpiece section, which is the unique feature of this system. The system itself is designed to: record, evaluate and compare real quenching intensities during the whole quenching process, when different liquid quenchants with different conditions are used, and different quenching techniques have been applied.