Crystallization of icosahedralAl86Mn14

Isothermal measurements of the crystallization kinetics of icosahedral ${\mathrm{Al}}_{86}$ ${\mathrm{Mn}}_{14}$ were made by differential scanning calorimetry and electrical resistivity in the temperature range 593–723 K. Transmission electron microscopy investigations of as-quenched samples showed that the icosahedral phase (i phase) occurs as dendritic nodules separated by α-Al. On crystallization, ${\mathrm{Al}}_6$Mn nucleates at the i-phase boundary and grows into the i phase, while consuming the α-Al. An effective-medium theory is used to relate resistance changes to the volume fraction transformed. A Johnson-Mehl-Avrami analysis for the kinetics of transformation indicates continuous nucleation with diffusion-limited growth. Nonisothermal differential scanning calorimetry measurements were made and analyzed using a numerical model that assumes simultaneous nucleation and growth. Crude estimates are given for the diffusion coefficient for growth of the crystal phase in the i phase and a lower bound for the i-phase ${\mathrm{Al}}_6$Mn interfacial energy.