During Wire Arc Additive Manufacturing (WAAM), rapid cooling rates lead to high thermal gradients in the melt pool. In Ti alloys, this promotes the epitaxial, intra layer growth of large columnar grains. This, combined with the grains’ strong texture, causes anisotropy in mechanical properties. This anisotropy is unacceptable in safety critical applications, such as aerospace structural components. Therefore, for WAAM to be suitable for producing such components, the microstructure must be modified to consist of equiaxed grains.

To achieve this columnar to equiaxed transition (CET) in Ti-6Al-4V a low thermal gradient (G) and high growth velocity (v) is necessary. Unfortunately, the processing limitations on WAAM make achieving these conditions challenging, with Ti-6Al-4V. An alternate route to achieving CET is to change the alloy composition to increase the constitutional supercooling, which will promote nucleation in the melt pool. Whist empirical models can guide binary alloy selection , this is more difficult for multi-component alloys. Experimental studies to evaluate the large combination of potential alloys are impractical. We aim to use computer simulations of nucleation to offer guidance here. Our simulations are based on a phase field model, which calculates energy using the CALHPAD techniques. This enables us to, using a classical nucleation model, predict the processing conditions pertaining to CET for a particular alloy. Using this technique, we will be able to try different alloys, combined with Ti-6Al-4V, to gain insights into which will produce an epitaxial microstructure at higher G and/or lower v than with Ti-6Al-4V.

Using this technique, different alloys will be used, combined with Ti-6Al-4V, to gain insights into which will produce an epitaxial microstructure at higher G and/or lower v than with Ti-6Al-4V.