Phase separated characteristics affected by cooling rate of immiscible Cu-Cr alloy by laser surface melting

The effect of cooling rates on the solidified microstructure of Cu-50Cr (wt. %) produced by laser surface melting (LSM) was studied. Layered structure transformed into a dispersed structure when the cooling rate increased from ∼105 K/s to ∼106 K/s. The average diameter of the Cr-rich spheroids in the homogenous layer was reduced to less than 1 μm, and the migration velocity by Marangoni motion was ∼103 times higher than the velocity by Stokes sedimentation, suggesting that the movements of α-Cr droplets containing supersaturated Cu phase during liquid phase separation (LPS) were dominated by Marangoni motion. Although the collisions and coagulations between Cr droplets couldn't be eliminated, the growth was suppressed by high cooling rate. The melt layer presented improved homogenous microhardness and the well-dispersed melt layer exhibited higher withstanding voltage than that of the untreated.