Influence of temperature gradient to solidification velocity ratio on the structure transformation in pulsed- and CW-laser surface treatment

The temperature gradient G, the solidification velocity R, and the G/R ratio are used in solid-liquid interface analysis. The critical G/R values characterizing the transitions from a planar front to a cellular structure, and from a cellular to cellular-dendritic structure during solidification are determined. The regularities of the rapid solidification process are shown on the example of the titanium alloy subjected to boriding with a CW-laser. The G/R ratio and cooling rate values versus molted zone depth are analyzed. The dependence of the relative transition depth from cellular to cellular-dendritic structure on laser beam velocity is determined.