External cooling condition effects on formation of anomalous eutectic in Ni-Sn alloy by laser remelting

Microstructure evolution of Ni-33%Sn (mass fractiion, similarly hereinafter) alloys during laser remelting is investigated by placing on the copper plate, titanium plate and refractory brick, respectively. The result shows that the microstructure of samples on three different cooling plates is quite similar as for thoroughly melting of Ni-33%Sn alloy and the anomalous eutectic structure can be obtained at the bottom of the molten pool. The area of anomalous eutectic on copper plate is significantly larger than those on the other two cooling plates. Free nucleation at the bottom of the molten pool and rapid growth lead to the generation of anomalous eutectic. The epitaxial growth behavior on both sides of the molten pool and the epitaxial growth conditions after high speed free nucleation and growth at the bottom of the molten pool lead to the small area of the anomalous eutectic at the bottom of the pool. The greater thermal conductivity of copper plate makes faster cooling rate and larger nucleation region at the bottom of the sample, which leads to larger area of anomalous eutectic than those of the other two cooling plates.