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<p>Laser-directed energy deposition (L-DED) is known for its high cooling and solidification rates in the molten pool, which is influenced by the self-quenching effect. This rapid cooling, combined with the layer-by-layer deposition approach, results in highly directional grain growth and anisotropy in the deposited components. This study examines how modulating the laser in pulse mode affects anisotropy in two deposition strategies: overlaying (thin wall deposition with single tracks) and overlapping plus overlaying (thick wall deposition with overlapping tracks and overlaying layers). By varying the duty cycle (DC) from 40 to 100% in 20% increments, while maintaining a laser frequency of 100 Hz, the impact on the molten pool's state was analyzed. An IR pyrometer, operating at 1 kHz, monitored the transition between liquid and solid states. For a 40% DC with pulse durations of 4 ms on-time and 6 ms off-time, the molten pool was found to change its state completely from liquid to solid, creating multiple solidification fronts and columnar dendrites with varied orientations while continuous wave mode exhibited directional grain growth. Modulated mode, with intermittent cooling, also led to finer microstructures and enhanced hardness. The mechanical strength and ductility improved, and anisotropy was found to reduce with deposition in laser-modulated mode. Digital image correlation (DIC) analysis of tensile tests revealed that strain localization was more uniform in modulated mode at 40% DC across all orientations, whereas continuous wave mode showed pronounced strain localization mainly at 0°, with broader zones at 45° and 90°, reflecting the impact of fusion lines on anisotropy.</p>

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Assessing the efficacy of laser modulation in controlling the anisotropy through monitoring of molten pool state using pyrometer in laser-directed energy deposition

  • 期刊论文

  • 发表日期：

    2025年1月9日

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  • Arkajyoti Jha,
  • M. Ramji,
  • Muvvala Gopinath

摘要

Laser-directed energy deposition (L-DED) is known for its high cooling and solidification rates in the molten pool, which is influenced by the self-quenching effect. This rapid cooling, combined with the layer-by-layer deposition approach, results in highly directional grain growth and anisotropy in the deposited components. This study examines how modulating the laser in pulse mode affects anisotropy in two deposition strategies: overlaying (thin wall deposition with single tracks) and overlapping plus overlaying (thick wall deposition with overlapping tracks and overlaying layers). By varying the duty cycle (DC) from 40 to 100% in 20% increments, while maintaining a laser frequency of 100 Hz, the impact on the molten pool's state was analyzed. An IR pyrometer, operating at 1 kHz, monitored the transition between liquid and solid states. For a 40% DC with pulse durations of 4 ms on-time and 6 ms off-time, the molten pool was found to change its state completely from liquid to solid, creating multiple solidification fronts and columnar dendrites with varied orientations while continuous wave mode exhibited directional grain growth. Modulated mode, with intermittent cooling, also led to finer microstructures and enhanced hardness. The mechanical strength and ductility improved, and anisotropy was found to reduce with deposition in laser-modulated mode. Digital image correlation (DIC) analysis of tensile tests revealed that strain localization was more uniform in modulated mode at 40% DC across all orientations, whereas continuous wave mode showed pronounced strain localization mainly at 0°, with broader zones at 45° and 90°, reflecting the impact of fusion lines on anisotropy.