Materials Science Forum Vols. 544-545

Abstract: A study was carried out to understand the relationship between the pore structure’s evolution of Al alloy melt foam and its preparation variables, which include decomposition properties of titanium hydride, the stirring foaming time and the holding foaming time. The results show that the foaming process of Al alloy melt can be inferred by the relation curves of decomposition quantity of titanium hydride and time at a specific temperature. The porosity of Al alloy melt during stirring foaming period is kept constant while the pore number increases and pore diameter decreases, which is a new method of fabricating Al alloy foam with a relatively low porosity and small pore size.

Abstract: The present study discussed extrudability improvement for 7000 series Al wrought alloys by thixoextrusion, with emphasis on controlling thixoextrusion parameters, such as initial ram speed, die bearing length and extrusion temperature of billet in semisolid state. The results of thixoextrusion experiments about microstructures and extrusion pressures were compared with conventional hot extrusion results. The maximum extrusion pressure for thixoextrusion was greatly decreased than that of conventional hot extrusion. This will contribute to extrudability in terms of extrusion pressure, which in turn means that shorter process time is required and smaller extrusion machine can be applied for the same operation. It is also possible to make complex shape components of 7000 series Al wrought alloys, which is not possible by conventional hot extrusion processes. The elongated grains to extrusion direction were generally observed during conventional hot extrusion, while the thixoextruded microstructures were isotropic.

Abstract: Lotus-type porous Ni- (15, 28 and 31) at.% Al alloys whose long cylindrical pores are aligned in one direction were fabricated by continuous zone melting technique under high-pressure gas of hydrogen of 2.5 MPa. A part of 5-10 mm in length of the rod in the vicinity of the coil was melted by high frequency induction heating, and was moved downwards by electric motors at a constant velocity of 330 μms-1 to 500 μms-1 for unidirectional solidification. The pores are formed as a result of precipitation from the supersaturated hydrogen gas when the liquid metals dissolved with gas atoms is solidified. The porosity and the pore size decrease with increasing aluminum content. An increase of solidification velocity from 330 μms-1 to 500 μms-1 leads to a decrease of pore diameter and an increase of pore number in the porous Ni-28at%Al.

Abstract: Forging process is one of the most basic metal forming processes. In this study a new forging process is applied to fabricate a precision forging product uniting parking and driven gears in order to obtain lightweight and cost effectiveness of an automobile. Since the united product using the precision forging process needs high quality and new manufacturing process, 3D computer simulation by FEM has been used to reduce some trial and errors in experiment and obtain the deformation, strain, stress and load of the workpiece and die. The study has tried to find out an optimal process including preform design putting emphasis on tooth filling by DEFORM-3D, a 3-dimensional rigid-plastic finite element code.

Abstract: The behavior of boride formation has been examined with solidification rates and boron contents by observing the solid/liquid interface using directional solidification in Mod. 12Cr-1Mo alloys. The phase transformation temperatures of liquidus, solidus, eutectic formation, and final solidification were analyzed by DTA. In order to analyze the crystallographic structure of the boride, extractive method, extracting the boride from the matrix, was used. The boride was proved as M3B2, and this boride phase expected to be formed by eutectic reaction. It has been also found that the boride formation depends on contents of born as well as the other alloying elements, such as C and W. As increasing boron contents, the amount of boride eutectic increased. Also, the alloying element W was shown to enhance the formation of the boride.

Abstract: This paper reports a low-cost microthermostat that is able to maintain a constant temperature necessary for restriction enzyme digestion. Polydimethylsiloxane (PDMS) and Pyrex glass were used to make the microthermostat, because PDMS is a cheap and mass-producible material and both PDMS and glass have very good biocompatibility compared to the more commonly used silicon. A heater made of Au wiring patterned on Pyrex glass was used to control the temperature. A PDMS replica molding technique was used to fabricate a reaction chamber with 3.6 μl capacity. Restriction enzyme digestion was performed by using the fabricated microthermostat and by a conventional method. Then, using gel electrophoresis, we compared results between the microthermostat and conventional methods. It was found that restriction enzyme digestion using the microthermostat required 5 min of heating.

Abstract: Highly porous Si3N4 ceramics in service are usually subjected to continuous impact of solid particles which may give rise to localized damage and consequently to strength degradation. Hertzian indentation and three-point bending tests were conducted to investigate the contact damage behavior of highly porous Si3N4 ceramics in this paper. The Hertzian indentation damage morphologies were examined by using a bonded-interface technique. As a result of intragranular microfracture under Hertzian indentation, a distributed subsurface damage region is developed beneath the indenter. It was shown that, with increasing indentation load, the damage region extends progressively and a quasi-plastic stress-strain response exhibits. Failure sources were observed to be Hertzian indentation sites in three-point bending tests, leading to a gradual strength degradation.

Abstract: The layered, machinable ternary compound, Ti3AlC2, was corrosion-tested at 800, 900, and 1000oC under an Ar-1% SO2 gas atmosphere. The scale formed consisted primarily of TiO2 and α-Al2O3. As the corrosion progressed, the scale became thicker and developed into an outer TiO2 layer and an inner (TiO2,Al2O3)-mixed layer.

Abstract: Formation of hollow structure through oxidation of Al nanoparticles was studied by applying transmission electron microscopy. Al nanoparticles 6~8 nm in diameter were observed to become hollow particles after having been exposed to air at 295 K for a few minutes. An analysis of the Debye-Sherrer rings in the selected area diffraction patterns before and after oxidation showed that hollow oxide nanoparticles are amorphous. The formation mechanisms of hollow oxide are discussed based on the low-temperature oxidation mechanism of Al and on the comparison with our previous results of hollow ZnO formation via oxidation of Zn nanoparticles.

Abstract: Getting to the market first” is extremely critical in this competitive business environment. The speed at which products are developed and released to the market is tightly linked to profitability and market share. Many companies that have been very skeptical of Rapid Tooling technologies developed so far are now working on hybrid tooling (HT) that can really meet the market standards. This paper describes how the HT process has been successfully established and effectively applied with ceramic filled SLA (StereoLithography Apparatuses) technologies.