A Multi-Scale Model for Microstructure Evolution During a Multi-Material Additive Manufacturing Process

Abstract

Powder-based additive manufacturing (AM) technologies are commonly used to fabricate intricate-shape three-dimensional (3D) composite parts. The present study provides further insights into powder melt pool behavior and microstructure evolution during additive manufacturing of Hastelloy(HX)/WC composite using sequentially coupled multi-scale models. At the macro-scale, the heat transfer model is used to predict the temperature distribution and melts pool geometry formed during laser heating of multi-material powder bed. At the mesoscale, the phase-field and heat transfer models are coupled to predict the evolution of grains during the solidification of the powder melt. The computational results are reasonably comparable to that of the experiments. It is found that an ellipsoidal melt pool shape is formed around the irradiated zone. The temperature, thermal gradient and cooling rate changes across the melt pool dimensions. Due to epitaxial growth, columnar (elongated) grains are developed near the solid-liquid interface. In contrast, equiaxed grains are formed near the top regions of the melt pool due to higher cooling rates. The elongated grains become split into equiaxed ones due to the presence of the WC particles. The presence of the larger WC particles enhances the cooling rate; thereby, resulted in grain refinement. Reducing the WC particle size still results in grain refinement due to the pinning effect on grain boundaries; however, the grain size becomes affected by the WC particle size. The inclusion of foreign particles could be used to inhibit anisotropic behavior in 3D printed parts.