Computational analysis of thermal cycling phenomena during multilayer laser powder bed fusion process for Ti6Al4V

Abstract

During laser powder bed fusion (LPBF) process, single tracks overlap to form layers and layers merge to form the complete 3D object. Because of this, a recurring temperature rise and fall happens, which is called thermal cycling phenomenon. It affects the microstructure and mechanical properties of the manufactured component via multiple reheating (and remelting) cycles, resulting in an intrinsic aging type heat treatment process that invokes an additional anisotropy along the build direction. To date, this phenomenon has been rarely studied due to the computational resource constraints and difficulties in experimental temperature measurement. Hence, in this study, a computationally efficient thermal model has been developed and applied to study the multilayer LPBF process for Ti6Al4V. The model was validated against the single track single layer experimental data and then used to simulate multilayer LPBF till a height of 3 layers to study the temperature field evolution and thermal cycling phenomenon. The average temperature of the computational domain is plotted against time to show the origin of intrinsic heat treatment. It is observed that while with each next layer the temperature rises, the maximum temperature value remains constant due to material evaporation taking place. The results suggest that thermal buildup also happens in the process as the average temperature of the computational domain as well as the melt pool volume increases with each layer.