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<p>This study systematically investigates the effects of <i>in situ</i> remelting (ISR) on the microstructural evolution and mechanical properties of DD432 single-crystal (SX) Ni-based superalloys fabricated by laser-directed energy deposition (L-DED). Through orthogonal experiments and multi-scale characterization (SEM-EDS, EBSD, hardness analysis), we demonstrate that ISR significantly refines the primary dendrite arm spacing (PDAS) by 26 pct, suppresses elemental segregation (particularly for elements Al, W, Re, and Ta with low diffusivity), and enhances <i>γ′</i>-phase precipitation. Notably, ISR induces a dramatic contrast in <i>γ-</i> phase evolution: Remelted samples exhibit a progressive increase in <i>γ′</i> volume fraction ~ 46 pct with cladding height, while non-remelted counterparts show a reverse trend (40 pct to 33 pct). Finite element simulations reveal that ISR elevates thermal gradients (<i>G</i>) while maintaining dendrite tip velocity (<i>V</i>), synergistically reducing PDAS via the Brody-Flemings model. The refined microstructure correlates with enhanced mechanical performance, achieving a 58 pct hardness increase (1100 HV vs. 700 HV in non-ISR samples) through three mechanisms: (1) solute redistribution via melt pool homogenization, (2) PDAS-driven shortened diffusion paths, and (3) thermal field optimization for stabilized γ′ nucleation. This work establishes ISR as a transformative strategy for SX blade repair, addressing critical challenges in defect suppression, elemental uniformity, and high-temperature strength retention.</p>

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In Situ Remelting Enhances Dendritic Refinement and γ′ Strengthening in L-DED Repaired DD432 Single-Crystal Superalloys

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • Gengshuo Liu,
  • Shujie Liu

摘要

This study systematically investigates the effects of in situ remelting (ISR) on the microstructural evolution and mechanical properties of DD432 single-crystal (SX) Ni-based superalloys fabricated by laser-directed energy deposition (L-DED). Through orthogonal experiments and multi-scale characterization (SEM-EDS, EBSD, hardness analysis), we demonstrate that ISR significantly refines the primary dendrite arm spacing (PDAS) by 26 pct, suppresses elemental segregation (particularly for elements Al, W, Re, and Ta with low diffusivity), and enhances γ′-phase precipitation. Notably, ISR induces a dramatic contrast in γ- phase evolution: Remelted samples exhibit a progressive increase in γ′ volume fraction ~ 46 pct with cladding height, while non-remelted counterparts show a reverse trend (40 pct to 33 pct). Finite element simulations reveal that ISR elevates thermal gradients (G) while maintaining dendrite tip velocity (V), synergistically reducing PDAS via the Brody-Flemings model. The refined microstructure correlates with enhanced mechanical performance, achieving a 58 pct hardness increase (1100 HV vs. 700 HV in non-ISR samples) through three mechanisms: (1) solute redistribution via melt pool homogenization, (2) PDAS-driven shortened diffusion paths, and (3) thermal field optimization for stabilized γ′ nucleation. This work establishes ISR as a transformative strategy for SX blade repair, addressing critical challenges in defect suppression, elemental uniformity, and high-temperature strength retention.