A numerical modelling for laser Powder-bed fusion of Ti-alloy with a hybrid heat Source: An investigation on solidification and microstructure formation
Mahyar Hasanabadi, Shahriar Imani Shahabad, Ali Keshavarzkermani, Roger Eybel, A.P. Gerlich, Ehsan Toyserkani
Abstract
Among metal Additive Manufacturing (AM) methods, Laser Powder-bed Fusion (LPBF), is a proven fabrication method to produce complex-shaped parts with tailored properties. To achieve the desired properties, proper LPBF modelling facilitates the understanding of the correlation between input process parameters and output microstructure. In this paper, a numerical heat transfer modelling with a novel hybrid volumetric heat source has been proposed to simulate the LPBF of metastable beta titanium alloy (Ti-5553). The developed hybrid model provides a reliable estimation of temperature distribution and thermal variables (e.g., temperature gradient G and solidification rate R), for any location of the melt pools, during solidification. For the process parameters which provide conduction melting mode, the simulated results agree well with experimentally measured melt pool dimensions where the verified model can also predict grain morphology, grain growth direction, and dendrite size. An in-depth analysis of predicted G/R values at the solidification front reveals that the center of the melt pool has a higher preference for equiaxed grain structure formation, while columnar grains are always dominant at melt pool boundaries. In addition, the scanning speed parameter was found to have a stronger influence on thermal conditions compared to laser power.