Development of microstructures in laser surface remelting of DD2 single crystal

Detailed experiments were carried out to investigate the effects of crystallography on the microstructure evolution during the solidification of the laser molten pool with a DD2 single crystal specimen using a 5 kW CO₂ laser. The experimental results showed that crystallographic effects can influence dendrite growth by favoring growth along a preferred crystallographic direction, and crystallographic effects are greater than that of heat flux during dendrite growth. On the same crystal face, the microstructures in the molten pool are very different when laser beam scanning along different crystal orientation. The same conclusions can be obtained by laser beam scanning along a fixed direction on different crystallographic surface. A growth velocity analysis was carried out during laser surface remelting processing based on a minimum velocity or minimum undercooling criterion and the relationships between dendrite growth velocities in the three 〈100〉 directions, moving velocities of the solid/liquid interface and laser scanning velocities for the different crystallographic orientations were also set up. According to this analysis, the reconstructed and predicted molten pools concurred with the experimental results very well.