Effect of beam width on melt characteristics in large-area laser surface alloying

This article presents an investigation of the convection behavior of the melt pool for laser surface alloying with a wide beam. A line beam source with a dimension of 6 mm x 0.7 mm from a 3 kW cw Nd-YAG laser was used. The work concentrated on studies of the influence of various laser operating conditions, especially the melt width of the tracks and the substrate thermal properties, on the convection behavior during the laser surface alloying process. Three different substrates precoated with a Ni layer were selected on the basis of their different thermal properties. An investigation of the relationships between the laser beam dimension, the structure of melt flow, and concentration fields of the alloying elements was carried out. It was found that the beam width had a significant effect on the alloying patterns on solidification. It was also found that a wider beam width (varied with a mask aperture) produced a greater melt depth. A three-dimensional mathematical model was applied to numerically simulate the temperature field and convection flow of the melt pool. Some specific alloying patterns were found favorable for coinage applications.