Materials Science Forum Vols. 544-545

Abstract: The Arc melting technique was employed to synthesize the type I clathrate of Ba8Al16Si30 compound. Phase transformations during synthesis and homogenization treatment were investigated using X-ray diffraction (XRD) and thermal analysis (TG/DSC). Thermoelectric properties as functions of temperature and homogenization treatment time were evaluated in this study. Maximum ZT was 0.14 at 590K for homogenized at 1173 K for 168hrs specimen and it is strongly expected to show higher value above 600K.

Abstract: Two-step isothermal heating and conventional one-step heating processes were used to produce the semi-solid slurry of Mg-5%Zn-0.5%Zr alloys with and without 1%RE. It was found that the slurry with better semi-solid characteristics could be fabricated by the two-step heating compared to the conventional process. Only the small amount of RE addition to the Mg-5%Zn- 0.5%Zr alloy was observed to reduce the solid particle size of slurry significantly and to improve the tensile strength at 150oC, probably owing to Mg-Zn-RE phase with a high thermal stability.

Abstract: A DSR processing with a roll speed ratio of 1.08 was carried out on an AZ31 alloys with Mn additions of 0, 0.2, 0.4 and 0.6 wt.% for investigating the effects of Mn on the microstructural evolution and mechanical properties. The amount of the Al-Mn compounds increased with increasing the Mn content. Compare with the DSR processed sheet without Mn addition with a homogeneous grain size, those with Mn additions exhibited an inhomogeneous microstructure due to the appearance of the shear bands comprising the small grains around 5 μm. The Mn addition exhibited a significant effect in grain refinement even for a low content of 0.2 wt.%, which reduced the average grain size from about 25 μm to 10 μm. The Mn addition resulted in the significant increases in the tensile strength and the 0.2% proof stress by about 25 MPa and 40 MPa, respectively.

Abstract: The role of the basic factors in the wet fiber winding process was investigated from the point of view of the actual wet-wound parameters and the property of composite material. In the present work, a PBO fiber-reinforced epoxy-matrix composite material was prepared by a wet fiber-winding process. The effects of processing factors such as the volume fraction of PBO fiber, the preheating temperature of mandrel, the infiltration temperature and time of epoxy resin, and winding tension, on the tensile strength and interlaminar shear strength (ILSS) of the unidirectional composite materials were investigated. To evaluate correctly how the above-mentioned parameters affect the mechanical performances of the composite materials, a pair of standardized pressure vessels with a diameter of 150 mm were fabricated via the winding method. The optimum conditions are obtained as follows: the preheating temperature of mandrel is 60-70 °C, winding tension is 30-40 N, and the penetration temperature and time of epoxy resin into PBO fiber are 45 °C and 1-2 s, respectively. Under the conditions, the ILSS and tensile strength of the composite materials are 30 MPa and 2980 MPa, respectively. The burst pressure and performance factor of the manufactured pressure vessels is as high as 34 MPa and 60.4 km, respectively. It is demonstrated that high quality rings and vessels can be efficiently manufactured by methods described in the paper.

Abstract: We studied the effects of solution RPM, bath temperature, and time in anodizing AZ91 under a constant current density of 750 mA/cm2 in a 1 M NaOH solution. In general, increasing the anodizing time, RPM, and temperature of the bath improved the corrosion resistance. The thickness of the anodic oxide film likely grew by increasing the time required to generate the active dissolution reaction. When anodizing at 750 mA/cm2, we evaluated a 300–3600-s range in anodizing time, 0–1500 RPM, and 296–373 K bath temperatures, and determined that 3600 s, 1500 RPM, and 373 K comprised the optimum conditions.

Abstract: As samarium addition was increased, α- Mg matrix morphology was changed from dendritic to equiaxed grains and average value of grain size was decreased from 101.6㎛ to 39.3㎛. Samarium addition to Mg-5Al-3Ca based alloys resulted in the formation of Mg-Al-Sm thernary intermetallic compounds at grain boundarys and α-Mg matrix grains. In these alloys, two kinds of eutectic structure were observed; coarse irregular-shape structure at grain boundary and fine needle-shape structure in the α-Mg matrix grain. It is found that the yield strength and ultimate strength showed the maximum value of 109.1MPa and 139.3 at Mg-5Al-3Ca-2Sm alloy, respectively.

Abstract: In order to achieve effectively high electromagnetic absorption in the radio frequency for the application of the electromagnetic absorber, we investigated annealing effect of microforged powders on electromagnetic absorption behaviors of ferromagnetic Fe-Cr alloy metal powder-polymer composites. The power loss in the far field regime was improved with increasing the microforging time in the frequency range from 50 MHz to near 1 GHz, because the magnetic permeability was slightly increased in the frequency range due to the high aspect ratio of the microforged metal powders. At higher frequency more than ~1 GHz, there was no further increased in power loss because of development of internal strain during microforging process. The magnetic permeability was significantly increased with annealing temperature due to the reduction of the lattice strain of the microforged powders. As a result, the electromagnetic absorption of ferromagnetic Fe-Cr alloy metal powder-polymer composites was highly improved.

Abstract: Effects of Ag2O doping on the electromagnetic properties in the BiSrCaCuO superconductors. The electromagnetic properties of Ag2O doped and undoped BiSrCaCuO superconductor were evaluated to investigate the contribution of the pinning centers to the magnetic effect. It was confirmed experimentally that a large amount of magnetic flux was trapped in the Ag2O doped sample than that in the undoped one, indicating that the pinning centers of magnetic flux are related closely to the occurrence of the magnetic effect. It is considered that the area where normal conduction takes place increases by adding Ag2O and the magnetic flux penetrating through the sample increases. The results suggested that Ag acts to increase pinning centers of magnetic flux, contributing to the occurrence of the electromagnetic properties.

Abstract: The indentation test has been in the spotlight due to easy and non-destructive testing characteristics. However, there are little studies for the indentation test of porous materials in the evaluation aspect of methodology. The goal of this study was to evaluate a spherical indentation test in the aspect of indenter-size and indentation depth by measuring elastic modulus of porous materials such as a cancellous bone using a FEM. We developed a microstructure-based FE model of cancellous bone with apparent density 0.2~0.8 g/cm3 in order to simulate uniaxial compression test and indentation test in the light of anatomical observation with a scanning electron microscope (SEM). We obtained a load-displacement curve through the indentation simulation and calculated the Young’s modulus of cancellous structure based on Pharr's hypothesis. The result indicated that indenter diameter has to be more than five times of pore size and indentation depth should be about 8% of indenter diameter at least to obtain the appropriate result of the indentation test. It is expected that this result may guide to the design and the simulation of indentation test for porous materials

Abstract: In order to fabricate high efficiency, light-weight hydrogen storage materials in an economical way, we have been made to propose a new mechanical alloying process by high-pressure hydrogen induced planetary ball milling(HIMA) using Mg and Ni chips. Microstructural evaluations of the Mg-Ni-H systems synthesized were investigated by scanning electron microscopy and the transmission electron microscopy. X-ray diffraction analysis was also made to characterize the lattice constant, crystallite size and misfit strain. The hydrogenation properties of the particles synthesized were evaluated by automatic PCI (pressure-composition-isotherm). Adopting 66:1 BCR (ball to chips mass ratio) for HIMA process, fully hydrogenated alloys were obtained after 96 hrs of milling, resulting in total hydrogen content of 2.25 mass%.