Tailoring microstructure using pulsed electromagnetic field-assisted directed energy deposition

Despite the advancements in laser directed energy deposition, challenges such as micro-segregation, formation of hard and brittle phases, and poor controllability over solidification microstructures persist due to the rapid melting-solidification transience, complexity of multi-physics metallurgical processes, and instability of multiple processing parameters. These issues impair the performance of deposited layers and hinder further development and broad application of the technology. Recently, electromagnetic field-assisted solidification has emerged as a promising method to tailor solidification structures and suppress defects. In this study, a novel pulsed electromagnetic field (PEMF) assisted laser directed energy deposition was investigated to tailor the microstructure of IN718 superalloy. Comprehensive analysis revealed that PEMF treatment significantly refined grain structures, reducing average grain size by 60.3% from 310 μm to 123 μm through enhanced columnar-to-equiaxed transition. Simultaneously, chain-like Laves phase was transformed into fine granular particles with reduced volume fraction under optimal parameters. The mechanical properties of the deposits were synergistically enhanced at room temperature, with yield strength and ultimate tensile strength increasing by 21.1% and 17.3%, respectively, due to combined strengthening from grain refinement, solid solution effects, and elevated dislocation density. High-temperature tensile tests also confirmed a significant improvement in strength. The high-fidelity simulation results indicate that PEMF application effectively reduced thermal gradients from 3.5 × 10 5 to 2.1 × 10 5 K/m while amplifying solidification rate fluctuations, thereby promoting equiaxed grain nucleation via enhanced constitutional undercooling. These microstructural alternations is achieved by the PEMF assisted laser directed energy deposition as a transformative approach for the IN718 superalloy additive manufacturing. • A novel PEMF-assisted L-DED technique achieved 60.3% grain refinement and transformed chain-like Laves phase into fine granular particles. • The treated specimens showed 21.1% and 17.3% increases in yield and ultimate tensile strength, respectively, due to combined strengthening. • The PEMF promoted equiaxed grain refinement by reducing thermal gradient and amplifying solidification rate fluctuations.