Hiroshi Kogure

Effects of the SiC/Al interface reaction on fracture behavior of a composite conductor using SiC fiber reinforced aluminum for next generation power equipment

Electrical power demands are increasing every year, meaning that lightweight electric cable is needed which has high transmission capacity, high thermal resistance and low sag. Tokyo Electric Power Co., Chubu Electric Power Co. and Hitachi Cable Ltd. have been breaking new ground in the field of electric cable through the development of a SiC fiber reinforced aluminum conductor. In this work, the SiC/Al interface reaction during the manufacturing process and the electricity transmission temperature were studied by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and field emission-Auger electron spectroscopy (FE-AES) for long-term reliability assessment. No reaction products were detected at the SiC/Al interface of elemental wire consisting of 7 SiC/Al preformed wires, indicating that the wire manufacturing process was reliable. An Al4C3 product was detected locally at the SiC/Al interface of the wire which had been thermally treated in molten Al under unfavorable conditions. The activation energy, Q, of Al4C3 growth at the SiC/Al interface was about 190 kJ/mol. In the temperature range of electricity transmission, Al atoms diffused into SiC fiber during heat treatment, and the amount of the diffused Al increased with increasing treatment temperature and holding time. The activation energy of Al diffusion through the SiC/Al interface to SiC fiber was about 78 kJ/mol. Strength deterioration was not induced by Al diffusion into SiC fiber, but strength strongly depended on the formation of Al2SiO5 compound at the SiC/Al interface above 400°C transmission temperatures. Kinetics calculations indicated that the rate of strength deterioration of the composite cable, held at 300°C for 36 years, was about 5%, so that practical use of SiC/Al composite cable should not be far in the future.

Influences of Fe-impurity on the production process of SiC fiber reinforced Al for electric cables

As electrical power demands increase every year, the need becomes stronger for light weight electric cables which have high transmission capacity, high thermal resistance and low sag. We have developed a SiC fiber reinforced aluminum electrical cable to meet this need. Mechanical properties of the SiC/Al composite conductor are very susceptible to iron impurity which becomes mixed in the Al matrix during manufacture of the composite conductor. In this work, we studied the effects of Fe impurity in Al on fracture behavior of the composite conductor. A preformed wire was prepared by dipping a bundle of 1500 pieces of SiC fiber (Si: 63.7, C: 35.8, O: 12.3 mass %) into molten Al in which 0.36 mass % Fe and 0.5 mass % Ti were mixed. The Ti was added to improve the wetting property. Test samples were prepared by bundling seven preformed wires together. A tensile test was carried out for the composite conductor, and pull-out behavior of SiC fiber at the fracture surface was observed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and electron probe micro analysis (EPMA). Pull-out of SiC fiber was observed at the fracture surface of the composite conductor using Fe-free Al. However, pull-out of SiC fiber was not observed at the fracture surface of the composite conductor using Fe-containing Al since Al was combined inseparably with the SiC and Fe. The fracture origin of the Fe-containing sample was a precipitated Fe-compound at the SiC/Al interface. Tensile strength of the Fe-containing sample was a half of that of the Fe-free sample. We propose the following the precipitation mechanism for the Fe compound. In manufacturing of the preformed wire, molten Al solidifies from the surface to the SiC/Al interface because of the low thermal conductivity of the SiC fiber. In the cooling process, Fe-free Ti-compound precipitates in the molten Al by a peritectic reaction. This leads to a higher concentration of Fe in the molten Al near the interface, and finally, FeAl3 compound precipitates at the SiC/Al interface.

Magnetic Properties and Microstructure of CoCrTa/Cr Magnetic Recording Media

High-density recording requires longitudinal magnetic recording media with high coercivity and low noise. We report our studies of magnetic and microstructural properties of high-coersivity CoCrTa films. A coercivity of 2450 Oe has been obtained by applying a high bias voltage to the substrate. Microstructural analysis by TEM and electron diffraction studies revealed that in high-coercivity film c-axes are strongly oriented in the film plane.

Interfacial reactions in aluminum/SiC fibre composite electric power cable using low oxygen SiC fibre reinforcement

We have evaluated the interfacial reactions of SiC fibre reinforced Al electrical power cable using low oxygen SiC fibre (Si : 62.4, C : 37.1, 0 : 0.5 mass%), and determined the relationship between the tensile strength and the amount of reaction products at the interface. The following are occurring at the SiC/Al interface: i) diffusion of Al atoms into the SiC fibre, ii) formation of needle–shape Al4C3 compounds, and iii) formation of Al9Si compounds. Formation of Al4C3 and Al9Si compounds at the interface causes the strength of SiC/Al composite electric power cable to deteriorate.