Papers by Author: Yu Chan Kim

Abstract: The hydrogen permeation properties of the Pd-coated Ni37.5Nb27.5Zr25Co5Ta5 amorphous membranes have been investigated at 673 and 723K for 720 hours (1 month). Values of the hydrogen permeability during these long term tests were found to be reduced of about 50 and 30 % at 673 and 723K, respectively. The reduction in the hydrogen permeability could be correlated to the change in the composition of the coating as well as at the interface between Pd coating and Ni-based amorphous membrane.

Abstract: The compositional dependency of the glass forming ability (GFA), magnetic and mechanical properties of the Fe52Co20B20Si4Nb4 bulk metallic glass was investigated by means of the partial substitution of Co either by Al, V or Mo elements. A minor concentration of these elements enabled an increase of the GFA and fully amorphous rods of 4 mm diameter were successfully fabricated for the Fe52Co19B20Si4Nb4Al1, Fe52Co17B20Si4Nb4V3 and Fe52Co17B20Si4Nb4Mo3 alloys. While the addition of Al resulted in an increase of the magnetization saturation, V appeared as the most effective element to enhance the plastic deformation under compression.

Abstract: This works deals with the deposition of Ti-Zr-Ni icosahedral quasicrystalline powders by low vacuum plasma spray technique and the performances of the resulting coating layers. The microstructure of the coatings, as analyzed by X-ray diffraction and TEM techniques, consisted of nanometer-sized W-Ti50Zr35Ni15 1/1 cubic approximant and TiZrNi Laves phases as well as a low volume fraction of submicrometer-sized ZrO2 phase. The absence of the icosahedral phase in the coating layers was explained by the loss of Ti during plasma spraying. The shift in the composition and the presence of the ZrO2 phase within the coating layers are believed to be responsible for the reduced microhardness and corrosion performances evaluated by electrochemical tests in a Hanks’ Balance Salt Solution at 37oC.

Abstract: Zr50Ni27Nb18Co5 amorphous ribbons were hydrogenated using an electrochemical method. Under a current density of 30 mA/cm2, the thermal stability of the amorphous phase was found to increase with the charging time. Hardness and fracture strength were found to be independent of charging time, indicating that the Zr-Ni-Nb-Co amorphous alloys preserved its mechanical integrity.

Abstract: A composite microstructure consisted of µm-scale Ta-rich solid solution particles distributed in the bulk metallic glass matrix was successfully obtained by injection casting of the (Cu ₆₀Zr 30Ti ₁₀) ₉₅Ta ₅ alloy into a copper mold. The (Cu ₆₀Zr ₃₀Ti ₁₀) ₉₅Ta ₅ bulk metallic glass matrix composite shows compressive strength of 2320 MPa and, in particular, a significantly improved plastic strain to failure of about 14.5%. The remarkable ductility improvement in the (Cu ₆₀Zr ₃₀Ti ₁₀) ₉₅Ta ₅ composite could be explained by the presence of the highly ductile Tarich particles.