Rapid directional solidification with ultra-high temperature gradient and cellular spacing selection of Cu-Mn alloy

The detailed laser surface remelting experiments of Cu-31.4 wt pct Mn alloy and Cu-26.6 wt pct Mn alloy on a 5 kW CO₂ laser were carried out to study the effects of processing parameters (scanning velocity, output power of laser) on the growth direction of microstructure in the molten pool and the cellular spacing selection under the condition of ultra-high temperature gradient and rapid directional solidification. The experimental results show that the growth direction of microstructure is strongly affected by laser processing parameters. The ultra-high temperature gradient directional solidification can be realized on the surface of samples during laser surface remelting by controlling laser processing parameters, the temperature gradient and growth velocity can reach 10⁶ K/m and 24.1 mm/s, respectively, and the solidification microstructure in the center of the molten pool grows along the laser beam scanning direction. There exists a distribution range of cellular spacings under the laser raid solidification condition, and the average spacing decreases with the increase of growth rate. The maximum primary spacing, λ_max, the minimum primary spacing, λ_min, and the average primary spacing, λ, as functions of growth rate, V_b, can be given by using the following formulas: λ_max=12.54 V_b^-0.61, λ_min=4.47 V_b^-0.52, λ=9.09 V_b^-0.62, respectively. The experimental results are compared with the calculation results obtained with the current Hunt Lu model for rapid cellular/dendritic growth, and a good agreement is found.