Numerical simulation of multi-component evaporation during selective electron beam melting of TiAl

Powder-based additive manufacturing technologies such as selective laser melting (SLM) and selective electron beam melting (SEBM) hold great promise for producing high-value metal components with customized geometries. Development of scanning strategies and prediction of optimal process parameters thereby remain key factors for the fabrication of high-quality products without local inhomogeneities in alloy composition or porosity. In this contribution, the relation between energy input, evaporation and residual porosity is numerically investigated on the titanium aluminide alloy Ti-48A1-2Cr-2Nb. The numerical model is based on a lattice Boltzmann method and includes hydrodynamics, thermodynamics and multi-component evaporation. Simulation results show that the spatial distribution of alloying elements within the final part is dominated by the advection of melt which is driven by surface tension and evaporative recoil and influenced by the random arrangement of powder particles. Regarding evaporation losses, the line energy appears to be of central importance, as it strongly affects peak temperatures during processing. For a given melt strategy there is a trade-off between porosity and loss of aluminum due to evaporation. It is demonstrated that significant reductions in evaporation losses can be achieved by application of a suitable beam scanning strategy. The presented numerical findings are consistent with experimental data.