過冷したニッケル系非共晶組成溶湯の擬共晶凝固

抄録

  The structures of Ni-Sn and Ni-Sb alloys of eutectic and near eutectic composition solidified from undercooled melts have been investigated. Specimens were undercooled by glass slag method. The undercooled melts were quenched into water before nucleation of the solid, in order to minimize the anticipated structural change during the recalescence.
  Study of the microstructures thus obtained showed that there exists a range of composition and temperature below the eutectic temperature within which a melt of off-eutectic composition solidifies as quasi-eutectic. The quasi-eutectic structure consists of regions of anomalous eutectic surrounded by regions of normal eutectic. As a general rule, the amount of anomalous eutectic increases with undercooling and the anomalous eutectic growth is associated with recalescence. The shape and position of the quasi-eutectic region are governed by the liquidus lines of the phase diagram just as in organic systems. Specimens outside the quasi-eutectic region solidify with dendrites with various degree of metamorphosis, depending on the amount of undercooling of the two primary phases.