Materials design for grain refinement using inoculants in additive manufacturing

Durga Ananthanarayanan, Niklas Holländer Pettersson, Greta Lindwall

KTH Royal Institute of Technology, Stockholm, Sweden

In powder-bed fusion based additive manufacturing, columnar grain structures are typically formed, directed by the heat flow. To obtain a more equiaxed, finer grain structure, inoculants have been used to create effective heterogeneous nucleating sites. Though this has been demonstrated for several alloy systems, it is still a challenge to use inoculation for grain refinement in additive manufacturing, given the complexity of the process and its implications on the solidification process. In this study, we present computational methods to design alloy systems with inoculants for grain refinement during additive manufacturing. Starting from the selection of inoculant and the method of incorporation to predicting the final structure, we discuss various models based on computational thermodynamics and kinetics including the effect of rapid soldification. These models are validated and compared with experimental data for different alloy systems such as steels and aluminium alloys. In particular, we highlight the role of the size distribution of inoculants and the thermal conditions at the meltpool scale on the final grain structure. The integration of computational methods into the design of alloy systems with inoculants is essential in expanding the application of this technology to a wider range of alloys.