Abstract:The microstructures of  Ti-45%Al(molar fraction) alloy directionally solidified at different growth rates in alumina tube by electromagnetic heating zone melting were studied. The measured temperature gradient of the system is about 10⁴K/m. The microstructures show that the primary solidified phase is β phase at different growth rates. The growth at low rates from 1.94×10^-6m/s to 4.16×10^-6m/s results in a transient solid/liquid interface structure from planar to shallow cellular. This transient rate is larger than the theoretical value of  v_c=6.94×10^-7m/s. Compared with v_t=v_c/k=1.01×10^-6m/s, the cellular-dendritic transient rate of experiment is observed in the range of 1.67×10^-5-2.50×10^-5m/s. The primary arm spacing decreases with increasing growth rate. 

Key words: Ti-45Al alloy; directional solidification; growth rate; interface structure