Primary spacing selection of Cu-Mn alloy under laser rapid solidification condition

In order to investigate the primary spacing selection under rapid solidification conditions, laser surface rapid resolidification experiments have been performed on Cu-26.6 wt.% Mn alloy. By taking transverse and then longitudinal sections of the directional growth dendrites/cells in the laser traces, the average primary spacing, spacing distribution range as well as the corresponding growth rate are quantitatively measured by SEM and image analyser. It has been found that there exists a wide distribution range in primary spacing under rapid solidification condition. As the growth rate increases, both the distribution range and the average spacing decrease. The maximum, λ_1max, minimum, λ_1min, and average primary spacing, λ̄₁, as functions of growth rate, V_s, can be given by λ_1max = 10.68V^-0.28_s, λ_1min = 2.42V^-0.22_s, and λ̄₁ = 510V^-0.33_s, respectively. Our experimental results are compared with the current KGT model for rapid dendritic growth, and a good agreement is found.