Papers by Author: K.H. Kim

Abstract: The influence of annealing conditions on the crystallization and wear properties of bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 (BAZ) alloys was investigated. Nanocrystalline phases were precipitated from the bulk amorphous alloy matrix after an annealing treatment at both 670 K and at 780 K. The Vickers hardness (Hv) increased with the volume fraction (Vf) of the nanocrystalline phases with increasing annealing temperature. The friction coefficient and the wear loss showed a somewhat different trend with the volume fraction of the nanocrystalline phases. The friction coefficient had a minimum value of 0.46 at 670 K and a maximum value of 0.96 at 780 K. The wear loss of the BAZ showed a very similar trend of friction coefficient. The improved wear and hardness properties can be attributed to the formation of nanocrystalline precipitates in the Zr-based amorphous matrix.

Abstract: This paper investigates the effect of bubble on the primary Si size in Al-18wt.%Si alloy. The primary Si size observed was varied with bubble size and bubbling time in bubble process. The effect of the holding temperature of the melt in bubbling process was also investigated. In water model, as the injecting bubble size decreases, the residual bubble size in the water decreases and the residual bubble conservation time in the water increases. Also in the experiment of Al melt, the primary Si size decreases, as the injecting bubble size decreases and as the bubble processing time increases. Pore was observed at the center of primary Si. This pore was observed at many Si phases. So, this experiment suggests that the bubble can be used as nucleation sites of primary Si.