Abstract
Ni–43Ti–7Al (at-%) alloy was directionally solidified at different withdrawal rates (2, 20 and 100 μm s−1) and a constant temperature of 1550°C by liquid metal cooling method. Results show that as the withdrawal rate decreases from 100 to 2 μm s−1, the cellular arm spacing increases from 39·5 to 126 μm, the size of Ti2Ni and the stability of the liquid/solid interface also increase, while the volume fraction of Ti2Ni decreases from 3·1 to 0·9%. Moreover, microstructural analysis reveals that a NiTi+Ti2Ni anomalous eutectic structure is formed in intercellular regions of directionally solidified samples withdrawn at 20 and 100 μm s−1. However, in the sample withdrawn at 2 μm s−1, Ti2Ni phases represent strip and liquid droplet morphologies in the intercellular region. Finally, the possible explanation to the change of microstructure is discussed.