Abstract
This paper presents the advances in wire arc additive manufacturing (WAAM) processes and efforts in grain tailoring during the process for desired size and shape. WAAM can cause fabrication and post-processing time reduction in comparison with traditional processes. However, the high cooling rates and thermal gradient of the fusion-based metal additive manufacturing process often leads to an almost exclusively columnar grains microstructure (especially in titanium-based alloys), which can result in anisotropic mechanical properties and are, in consequence, undesirable. The issue of large directional grains can be addressed either with the addition of potent nuclei, a solute that promotes constitutional supercooling or a combination of the two. Nuclei are naturally present in liquid metals and are the starting point of every grain. Introducing additional potent nucleant particles by inoculation would facilitate grain refinement by increasing the total number of grains and therefore reducing the average grain size. To study the importance of solutes like Cr. and/or nuclei phases like TiB on final grains size and topology of the printed Ti-6Al-V titanium alloy with WAAM method, coupled thermal and microstructure simulations conducted. Simulation results show that the final microstructure of Ti-6Al-4V alloy at points without adding nucleants (solute and nuclei phase) will be columnar. By adding some solutes (Cr), the final microstructure is finer but still remains columnar. Although the final microstructure is equiaxed for all scenarios, adding solute and nuclei phases will change the final average size of the grains and hence achieve grain refinement.
