Microstructure evolution in laser surface remelting of Ni-33 wt.%Sn alloy

Laser surface remelting experiments have been performed on a Ni-33 wt.%Sn hypereutectic alloy. The microstructure characteristic, grain orientation and microhardness were investigated. The lamellar eutectic spacing decreased with increasing the scanning velocity, and the lamellar eutectic spacing is reduced significantly after laser rapid solidification. The anomalous eutectic was obtained in the bottom of the molten pool when the sample was melted thoroughly with the low scanning velocity of 0.1 mm/s. It is found that the free nucleation and rapid growth of two eutectic phases should be a necessary condition for the formation of anomalous eutectic. The EBSD maps and pole figures indicated that the grain orientations of anomalous eutectic obtained by laser remelting are analogous to that obtained by high undercooling solidification. The microhardness of anomalous eutectic is lower than that of regular lamellar eutectic.