5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Powder bed fusion processes in additive manufacture (AM) of metals typically involve solidification in high thermal gradients, leading to unwanted anisotropic columnar growth and high residual stress in as-printed components. Equiaxed solidification can alleviate such problems but is difficult to achieve due to the thermal fields naturally evolving in typical AM processes. Pre-heating of the powder bed in electron beam-based processes can reduce the thermal gradient and, together with grain refinement of the alloys, this encourages equiaxed solidification. However there is a material-dependent possibility of sintering of loose powders if this approach is taken which makes it more difficult to recycle un-used powder after print runs. The process is quite complicated, experimental trials are expensive and can be carried out only within limited ranges of specific machine parameters, and in-process experimental measurements are difficult. Computer simulation and modelling is therefore a key tool in investigating possible ways of creating conditions suitable for equiaxed solidification. A multi-scale modelling approach is presented which will predict columnar and equiaxed solidification and the columnar-to-equiaxed transition, using front-tracking at the scale of grains to simulate the non-equilibrium growth of dendritic fronts and grain envelopes, with phase field formulations for the micro-scale physics of dendritic growth. Preliminary results are outlined.