Band 50, Heft 2

A Cu–8 %Ag alloy was directionally solidified at different growth velocities to investigate the relationship between the solute distribution and the electrical conductivity of the material. The temperature gradient was fixed at 6.1 K/mm, and the growth rate was varied from 1 µ m/s to 200 µ m/s The planar interface was not observed in this experimental range, although cellular and dendritic interface morphologies were observed. As the growth velocity was increased, the initial silver content decreased, while the silver content near the dendrite boundary increased. The lattice parameter of the Cu – Ag alloy increased with increases in the number of silver sites in the copper lattice as measured via a calculation using the VASP (Vienna Ab-initio Package Simulation) code. The lattice parameter also decreased with increases in the growth velocity due to the decrease in silver content in the matrix. Higher electrical conductivity was obtained with higher growth velocities.

The effect of chemical composition on the surface characteristics of the hot-dip galvannealed (GA) steel sheets with a carbon content as low as 15 ppm strengthened by Cu and/or Mn sulfides instead of Ti and/or Nb carbides has been studied. The most important goal for developing the new type of steel sheets is focused on the achievement of the extreme surface quality to fulfill the high aesthetical requirements for defect-free automotive outer panels. The shape and distribution of the surface enrichments of Cu, Mn, Al and O on the GA steel sheets were characterized by OM, SEM and TEM. Especially, formation mechanism of the narrow streaky mark with the width of 50–100 µ m occasionally observed on the surface of GA steel sheets will be presented.

The oxidation behaviors of Mo rich alloys have been investigated in the Mo-Si-B ternary system. Seven selected alloy systems composed of two phase alloys (Mo (solid solution) + T2 (Mo 5 SiB 2 ) and three phase alloys (Mo (solid solution) + T2 (Mo 5 SiB 2 ) + Mo 3 Si) have been fabricated by arc melting elemental components. Mechanical behaviors of the selected alloy systems have been investigated in order to identify the effect of composition on the ternary system. Also, oxidation tests have been performed in order to identify the oxidation behaviors at 1 073 and 1 373 K. When the alloy compositions move towards the Mo side, the oxidation reactions were accelerated for the two phase alloys due to the presence of Mo (s. s.), while the tendency of oxidation was not fast for the three phase alloys. The oxidation behaviors at above and below 1 273 K have been discussed in terms of microstructural observations during oxidation tests.

Y 2 BaCuO 5 (Y211) particle distribution within YBa 2 Cu 3 O 7-y (Y123) grains of YBCO samples melt growth (MG) processed was examined. To understand the processing variables on the Y211 distribution, a cooling rate ( R C =1 K/h to R C =20 K/h) through a peritectic temperature ( T p = 1010 °C), a precursor powder size and composition were changed. Two different Y211 distributions (a linear x-like track and planar butterfly-like pattern) were observed, depending on the processing variables. The linear x-like Y211 tracks were observed in the Y123 samples prepared using a stoichiometric Y123 precursor, whereas the planar butterfly-like Y211 patterns were observed in the Y 1.8 Ba 2.4 Cu 3.4 O 7-d (Y1.8) samples prepared using an Y211-excess composition precursor. The track and planar Y211 patterns were clearer at lower R C (slower growth rate of Y123 grains) and for the smaller Y211 particles. In contrast, the random Y211 distribution was dominant at the higher R C and for the larger Y211 particles. The Y211 distribution patterns in the Y123 grains were explained in terms of the interfacial energy difference among growing Y123 fronts.

In this paper, starting from the gas atomization powders, n-type Bi 2 Te 3 thermoelectric alloys prepared via high energy ball milling and subsequently consolidated by hot extrusion. The effect of ball milling on the microstructure of Bi 2 Te 3 alloys was studied. With increasing the milling time, from 3 min to 90 min, the particles were coarsening due to the agglomerated because of the high surface energy of the fine particles adhesive each other during the high energy ball milling. The preferential orientations of grains indicate that the extrusion process has the significant method to forcing the basal plane to orient preferentially in the extrusion direction were clearly observed by the TEM micrograph. The maximum electrical conductivity 6675.567 Ω −1 m −1 measured at 100 °C temperature owing to the increasing of carrier concentration due to the donor defect formation and contamination occurred during the high energy ball milling at longer milling time (90 min).