Abstract:Ni-45.5Al-9Mo (mole fraction, %) alloy was directionally solidified with a constant temperature gradient (G_L=334 K/cm) and growth rates ranging from 2 to 300 μm/s using a Bridgman type crystal growing facility with liquid metal cooling (LMC) technique. The effect of growth rate (v) on the solidified microstructures such as rod spacing (λ), rod size (d) and rod volume fraction was experimentally investigated. Two types of the solidified interfaces, planar and cellular, were identified. On the condition of both planar and cellular eutectic microstructures, the relationships between λ, d and v were given as: λv^1/2=5.90 μm·μm^1/2·s^1/2 and dv^1/2=2.18 μm·μm^1/2·s^1/2, respectively. It was observed that the volume fraction of Mo phase could be adjusted in a certain range. The variation of phase volume fraction was attributed to undercooling increase and the growth characteristics of the individual constituent phases during the eutectic growth.

Key words: NiAl-9Mo; directional solidification; intermetallics; crystal growth; microstructure