Substrate-driven L-DED for crack-free and high-performance nonweldable Ni-based superalloys

High γ' fraction Ni-based superalloys are widely used in high-temperature applications but are prone to cracking during laser directed energy deposition (L-DED) due to high residual stresses and limited ductility. In this study, a novel custom-designed substrate is developed to eliminate cracking and enhance mechanical performance. Comparative experiments show that the custom substrate effectively suppresses residual stress accumulation, preventing crack formation, whereas standard substrates induce severe cracking. The substrate design promotes in-situ heat retention, enabling γ' phase coarsening appropriately during deposition, achieving precipitate sizes comparable to post-deposition aging. Consequently, the as-deposited builds exhibit excellent mechanical properties, with yield and ultimate tensile strengths of 1005.7 MPa and 1287.6 MPa, and elongation of 25.5% at room temperature, and 746.4 MPa and 794.3 MPa, and 23.0% at 900 °C, demonstrating a superior strength-ductility balance. Analysis of strengthening and fracture mechanisms highlights the role of γ' evolution and dislocation interactions. This strategy offers a practical route to fabricate crack-free, high-performance L-DED Ni-based superalloys.