Advances in nano-inoculant grain refinement for fusion-based additive manufacturing of Al and Ti alloys

Metal additive manufacturing (AM) has rapidly progressed, particularly in the use of lightweight alloys such as aluminium (Al) and titanium (Ti), attracting increasing industrial interest. Despite this growth, a critical issue persists: the formation of coarse columnar grains during solidification. These grains can extend across the entire build height, leading to defects including hot cracking, distortion, and anisotropic mechanical properties, all of which degrade the component’s quality. Although several thermo-mechanical strategies have been explored to refine grains, they are often impractical for large-scale or complex AM parts. In response, attention has shifted to a more traditional approach—grain refinement via the addition of inoculant particles. This method has shown promising results in Al alloys but remains less developed in Ti systems. This paper reviews recent advancements in the use of nano-sized inoculants for AM of Al alloys, examining the mechanisms driving grain refinement and their effectiveness. It also explores the potential for applying similar strategies to Ti alloys. Finally, the review identifies current knowledge gaps and offers clear recommendations for future research. These insights aim to advance the understanding and implementation of inoculant-based grain refinement in AM, enabling the fabrication of high-performance Al and Ti components with improved microstructural control.