Abstract: Centrifugal casting method was used to fabricate composites with graded structures in alumina-zirconia system. The composition profiles of the graded composites showed three distinct regions, with a greater part of the specimen showing nearly linear variation of compositions. The composition profile can be varied by using zirconia powder of different size ranges. The top of the specimens showed nano-scaled microstructures. The composition profiles can also be varied by altering zirconia content in the starting suspension. It was found that the composites with graded structures showed higher bending strength than that of uniform composites. On the other hand, the specimens fractured with the lower zirconia content region being the crack initiate plane showed higher bending strength than that of fractured form higher zirconia content region.
Abstract: Cu-Ti and Cu-B alloys were separately cast in vacuum arc melting furnace for alloying. These alloys were added to the copper melt of 1500K in the induction furnace and performed electromagnetic stirring at 1000rpm. The cast ingot(dia : 70mm, length : 100mm) was hot extruded with the extrusion ratio of 13:1 after heating at 1073K for 1 hour. The TiB 2 precipitates were observed in the extruded materials and the mean size of TiB 2 precipitates was found to be about 1.5µm. The volume fraction of TiB 2 varies due to the density difference between the TiB2 and the
copper melt. With the increasing of TiB2 contents from 3 to 8 vol.%, the hardness and the tensile strength increased from 951 to 140Hv and from 248 to 278MPa, respectively, and the electrical conductivity decreased from 82 to 70%IACS. However, the mean size of TiB 2 particle was not increased despite increasing an annealing temperature.
Abstract: BN/Al(-Mg) metal matrix composite (MMC) was fabricated by the pressureless
infiltration technique. The phase characterizations of the composites were analyzed using the SEM, TEM, EDS and EPMA on reaction products after the electrochemical dissolution of the matrix. It is confirmed that aluminum nitride (AlN) was formed by the reaction of Mg 3N 2 and Al alloy melt. Plate type AlN and polyhedral type Mg(-Al) boride were formed by the reaction between Mg 2N 2, BN and molten Al in the composite. The reaction mechanism in the fabrication of BN/Al(-Mg)MMC was derived from the phase analysis results and the thermodynamic investigation.
Abstract: Tensile test at loading velocities up to 10 m·s-1 (strain rate up to 3.2x102 s-1) was carried out forr SiCp/AC4CH composite and AC4CH alloy. The microstructure of the composite before and after tensile deformation was carefully examined with both optical microscope and SEM. The experimental results demonstrated that the ultimate tensile strength (UTS) and yield strength (YS) increase with increasing loading velocity up to 10 m·s-1. Comparing with AC4CH alloy, the fracture elongation of the composite is sensitivity with the increasing strain rate. The YS of both the composite and AC4CH alloy shows more sensitive than that of the UTS with the increasing strain rate, especially in the range of strain rate higher than 102 s-1.
Abstract: Dense WC-base W-C-B composites were prepared by the reaction sintering of B4C-WWC (mole ratio 1 : x : 80 or 130, x = 1-9) powder mixtures using resistance-heated hot pressing. Sintered bodies were composed of different products depending on x both in B4C-xW-80WC and - 130WC: WC + WB when x ≤ 3, WC + W2B + WB when x = 5, and WC + W2B + W2C when x ≥7. They had the highest Young's modulus values 706 and 705 GPa for -80WC and -130WC at x = 3, respectively. The hardness was increased with x, depending on a decrease in the grain size of WC. Its highest value was 24.5 GPa both for -80WC and -130WC at x = 9. For the fracture toughness, the highest value 6.1 MPa m1/2 was obtained for -130WC at x = 5.
Abstract: Plasma arc cutting sound has close relation with cutting conditions, so it contains useful information about this cutting process. In order to analyze the relationship between the plasma arc cutting acoustic signal and cut quality (including top and bottom kerf widths, bevel angle and dross attached level), a number of experiments under various cutting speeds have been carried out. It is shown that SPL (sound pressure level) of cutting acoustic signal shows mountain-shaped distribution with an increase of bottom kerf width. Experimental results also suggest the possibility
to make an acoustic-based quality monitoring system for plasma arc cutting process.
Abstract: The optimized extrusion conditions from the present research were the extrusion
temperature of 573~623K and the extrusion ratio(A0/A) of 21.39. Above the extrusion temperature of 623K, the fracture of sheath material was observed. It is due to the difference of flow stress between the sheath material and the core material during extrusion process. The bonding strength increased with increasing the extrusion temperature and the extrusion ratio. The bonding strength increased with increasing the annealing temperature. However, over 573K, it decreased abruptly since the thick and brittle intermetallic compounds of larger than 3µm were formed. The electricalconductivity of copper clad aluminum wire was about 70%IACS without annealing.
Abstract: Semi-solid forming usually requires feed stock material in form of cylindrical billets with a uniform, globular and fine grain microstructure. These billets are commonly being produced by continuous casting involving agitation of the solidifying melt. The paper will present the development of a horizontal continuous casting machine using circumferential electromagnetic stirring to generate melt flow and shear rate in the continuous casting mould. The machine has been used to study the influence of various process parameters such as electromagnetic stirring strength and casting speed in the production of Al billet with a diameter of 76mm. In order to establish the quantitative relationship between microstructure and the process parameters, the morphology and primary crystal size of billet were observed according to the casting speed and electromagnetic stirring strength. A depth and distance of surface defect on the billet was decreased with increasing a casting speed and a very good smooth surface without any surface defect appeared on the billet produced at a casting speed of 600mm/min. A thickness of the solidifying shell was decreased with increasing the casting speed and the maximum casting speed without a break-out was 600mm/min in horizontal continuous caster designed in this study. Both the size and the aspect ratio of primary crystal were decreased with increasing the casting speed and electromagnetic stirring strength in the range of this study.
Abstract: Barrier ribs of plasma display panel (PDP) were prepared via injection molding of
thermally curable paste. The paste composition was optimized by considering the effects of powder content, binder type and content on the viscosity of paste. Various types of molds including stripe, honeycomb, and meander were prepared using UV lithography. In this study, main causes ofdimensional change during sintering of meander type barrier ribs produced by injection molding process were investigated by changing powder content in the paste. The results indicated that sintering stress generated in the barrier rib is not balanced at the points where the ribs are curved,
causing dimensional change in the ribs.
Abstract: A method for preheating steel scraps using waste heat in a continuous casting process was proposed. Experiment and numerical analysis were carried out to examine the ability of scrap preheating and to determine the factors affecting the rise in scrap temperature. Coupled natural convection-radiation heat transfer was solved by three-dimensional FEM. The distance and the constant were found to influence the sample's temperature rise greatly. The overall Nusset number can be obtained as