HASEGAWA Hajime Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Research Associate, 多元物質科学研究所, 助手 (70323102)
MIZOGUCHI Shozo Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Professor, 多元物質科学研究所, 教授 (90311555)
|Budget Amount *help
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2002: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2001: ¥2,100,000 (Direct Cost: ¥2,100,000)
In order to elucidate the nature of the heterogeneous nucleation, a differential sacanning calorimetry (DSC) thermal analysis of pure Fe, Fe-Ni alloys (Ni content : 1 to 30 mass%) and Fe-Cr-Ni alloys (Cr + Ni content : 1 to 30 mass%) containing TiN, Al_2O_3, and Ti_2O_3 was conducted. Then, special attention was paid to the difference in the phase of the primary crystal nucleated by the triggering effect of a catalyst (nucleating agent). Thus some important features on the heterogeneous nucleation were found in a series of DSC thermal analysis.
1. The solidification and transformation modes appearing during cooling in these alloys is classified into three cases : F mode, FA mode and A mode. The change of modes and the critical undercooling. ΔT, depend on the kind and the amount of catalyst used as well as the chemical composition. In addition, in spite of the kind of primary crystal the value of ΔT is always small in the order of TiN, Al_2O_3 and Ti_2O_3. That is, the catalytic potency of TiN is greatest.
2. The most significant factor for the heterogeneous nucleation is cosθ, that is, the interface free energy ratio, (γ_<CL>-γ_<SC>)/γ_<LS>. The greater catalytic potency indicates a smaller critical undercooling, that is, a cosθ close to unity. The approximately optimum condition is γ_<CL> 【approximately equal】 γ_<LS> and γ_<SC> 【approximately equal】 O. This condition means that there is a close similarity in the crystal structure between the catalyst and the primary crystal. Therefore the lattice disregistry becomes also small. Thus, Bramfit's relation can be qualitatively explained.