Comparative study of microstructure evolution of directionally solidified nickel-based superalloys via selective Laser melting and Laser metal deposition

This study aims to evaluate the potential of selective laser melting (SLM) and laser metal deposition (LMD) for repair of single-crystal nickle-based superalloys, by comparing the morphologies, molten pool characteristics, and microstructural evolution of single tracks of directionally solidified AM900 nickel-based superalloys fabricated via these two laser additive manufacturing techniques. SLM requires linear energy densities above 0.15 J/mm to continuous regular tracks, while LMD achieves them across a broader range. Molten pool morphology transitions from keyhole to spheroidized types, with pools exhibiting optimal grain control corresponding to width-to-depth ratios from 2.8 to 3.3. Both techniques enable [001] epitaxial growth with minimal surface stray grains (∼1–2%), demonstrating SLM's potential for precision repair despite its narrower process window.