Materials Science Forum Vols. 510-511

Abstract: Change in mass and gas concentration during oxidation of carbon matrix composite added with B4C and SiC particles as an inhibiter for oxidation were measured continuously and accurately using a thermogravimetric analyzer, a couple of zirconia type oxygen sensors and infrared CO-CO2 gas analyzer. Total amount of oxygen consumed, the amount of oxygen consumed for matrix carbon oxidation, the amount of oxygen incorporated in CO and CO2 gases, total oxygen consumption rate during oxidation of the composite were obtained. The amount of glass phase formed from the inhibiter and the amount of matrix carbon oxidized could be estimated from calculation of a mole balance between the total oxygen consumption and the amount of oxygen incorporated in CO and CO2 gases. Oxidation behavior and oxidation mechanism of the C-B4C-SiC composites were clarified.

Abstract: The high temperature oxidation behavior of the TiAl(La)N coating, which was deposited on a steel substrate by the arc-ion plating method, was investigated at 700, 800 and 900oC in atmospheric air. The oxidation kinetics of the coating were mainly governed by the inward diffusion of oxygen and outward transport of nitrogen. The oxide scale was porous, nonadherent, and prone to cracking, indicating the oxidation resistance above 700oC is poor.

Abstract: The high-temperature oxidation behavior of WC-ZrN superhard nanocomposite film was studied in air between 500 and 700oC. The WC-ZrN film displayed poor high-temperature oxidation resistance, because of the formation of the nonprotective W-oxide scale and the less-protective, nonstoichiometric ZrO2-x oxide scale. The scale was prone to cracking and spallation. During oxidation, C and N escaped from the film into the air, while oxygen from the air diffused into the film.

Abstract: The oxidation of Cr-12.7 at.%C coatings electrodeposited on steel was studied at 700 and 800oC in air. The coatings, which consisted of nodular grains having microcracks and pits, had either an amorphous or a microcrystalline structure. They changed to crystalline Cr during oxidation. The oxidation resulted in the formation of Cr2O3, which provided good oxidation resistance to the coating. However, the presence of microcracks and pits in the coating was harmful to oxidation resistance.

Abstract: Using the hot pressing method, the Ti3SiC2 materials having fine and coarse grains were synthesized from TiC0.6 and Si powders, and the Ti3AlC2 materials having fine and coarse grains were also synthesized from TiC0.6 and Al powders. The cyclic oxidation between 900 and 1200oC for 40 hr in air resulted in the formation of an outer TiO2 layer and an inner (TiO2+ amorphous SiO2) mixed layer for Ti3SiC2, and the formation of an outer TiO2 layer and an inner (TiO2+ Al2O3) mixed layer for Ti3AlC2. The effect of the grain size on the cyclic oxidation resistance was not significant.

Abstract: ~100 nm-sized BaTiO3 powders were prepared by hydro-thermal techniques, and the structural features of the powders were investigated as a function of synthesis temperature and time. The spectral features of (200) XRD peaks and FT-Raman peaks at frequencies of 305 and 710 cm-1, which are sensitive to the presence of tetragonal BaTiO3, indicate that the nano-sized BaTiO3 powders are dominantly of a cubic phase, but the tetragonal phase is also exhibited at room temperature. The tetragonal and cubic phases exist in the core and shell regions in the powder, respectively; the difference in lattice spacing between the core and the shell regions is 0.061 Å, and the thickness of the cubic-phased shell region of the powders prepared at 180°C for 24 hrs is 3 nm.

Abstract: Deformation characteristics of a newly developed wave-typed heat sink during mechanical assembly of fin-base were analyzed by using the Ansys program. The original points a and b marked in the fin and base moved to the opposite y direction with increasing pressure, while their movements to x direction were relatively small. It was evident that at least 207㎫ must be applied to well bond the fin with the base. Under a constant pressure, the smaller the pressured area was, the better the bonding between fin and base was, despite a small uniform deformation in the base area as the pressured area increased.

Abstract: Surface Nanocrystallization(SNC) is a new method of fabricating nanostructured materials while thermal stability is an important problem for the application of nanostructured materials. A nanostructured layer was fabricated on the surface of 40Cr steel by Supersonic Particles Bombarding method, and the variation of microstructure and microhardness of nanostructured layer was studied. Nanostructured surface layer showed high thermal stability.

Abstract: Al or Zn content of AZ31 alloy was reduced and small amounts of Sn were added to improve the formability of alloys. And the recystallization behaviors and mechanical properties of Sn added alloys were investigated. In all the investigated alloys, of which Al content was less than 3%, virtually no Mg17Al12 phase was found. Nor any Sn-containing phase was observed in either AZ21 or AM30 base alloys up to 0.75%Sn. The elongation of alloys at both room temperature and 300oC was significantly improved by the Sn additions possibly owing to increased uniformity of grain size (size difference between fine and coarse grains). Hindered recrystallization and reduced growth rate of recrystallized grains by the Sn additions are postulated to be the main reason for the enhanced grain size uniformity.