Effect of layer thickness on the melt pool behavior and pore defects evolution of selective laser melting CuCrZr alloy

Abstract

Despite the great potential of selective laser melting technology, the low build rate has become a major reason limiting its large-scale use. Thick layer thickness can significantly increase the build rate, but an unlimited increase in layer thickness can easily lead to defects which can seriously affect the mechanical properties of the part. To date, the correlation between powder layer thickness and melt pool dynamics behavior and its influence on defect evolution in the production of copper-based alloys by selective laser melting remains unclear. Therefore, in this paper, a high-fidelity computational fluid dynamics (CFD) model combined with a ray-tracing algorithm is developed to investigate the effect of layer thickness on melt pool dynamics and the evolution of pore defects. The results show that as the powder layer thickness increases, the melt track width and depth rise, reaching a maximum of 169.8 µm and 177.2 µm at 60 µm layer thickness, which is probably attributed to the growth of global absorptivity. Besides, the increased instability of melt flow under thick layer thickness resulted in undulations in the solidification track surface and accompanying slag phenomena. It is worth noting that the generation of pores was observed at 45 µm and 60 µm layer thickness. Both the number and dimension of pores increase with thicker layer thickness, which are caused by the multiple reflection behavior of the laser rays in the keyhole. In addition, the elimination of pore defects under thick layer thickness was also explored, and it was found that remelting could effectively reduce the pores generated by previous layers.