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<p>In laser-based directed energy deposition (DED), achieving stable melt pool behaviour and consistent clad quality is challenging due to sensitivity to spatial energy distribution at the laser-material interface. Laser spot diameter governs this distribution, yet its mechanistic influence on plasma plume behaviour and melt pool thermophysics remains insufficiently understood, as prior studies have mainly emphasized laser power and scanning speed. This study demonstrates the role of spot diameter as a design relevant control parameter in SS 316&#xa0;L DED by linking plasma plume dynamics to melt pool behaviour and clad morphology. An integrated in-situ diagnostic approach combining optical emission spectroscopy (OES), CMOS imaging, two-colour pyrometry, and high-speed melt pool imaging was applied across four spot diameters (0.8, 1.3, 2.1 and 3.5&#xa0;mm) under constant processing conditions. OES measurements revealed a non-monotonic dependence of plasma-plume intensity fluctuation on spot diameter, reflecting changes in vaporization intensity and melt pool stability. A small spot diameter (0.8&#xa0;mm) produced high plume fluctuations (~ 42.5%) and melt- pool instability, while a large diameter (3.5&#xa0;mm) resulted in weak plasma plume activity and poor bonding. An intermediate diameter (1.3&#xa0;mm) yielded a stable plasma plume with reduced fluctuation (~ 21.5%), uniform clad morphology and favourable microstructural-characteristics. Complementary CMOS imaging, high-speed melt pool visualization, and pyrometry measurements consistently supported the OES-derived trends, revealing surface oscillation behaviour and temperature variations with surface tension aligned with the measured plasma plume fluctuations. OES-derived plasma plume intensity and fluctuation provide a physics-based, in-situ measure of spot-diameter-induced melt pool stability in DED.</p>

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Mechanistic influence of laser spot diameter on SS 316 L directed energy deposition revealed by in-situ plasma plume diagnostics

  • 期刊论文

  • 发表日期：

    2026年4月9日

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  • Mohit Singh,
  • Misba Amin,
  • J. Manoj,
  • K. R. Ravi

摘要

In laser-based directed energy deposition (DED), achieving stable melt pool behaviour and consistent clad quality is challenging due to sensitivity to spatial energy distribution at the laser-material interface. Laser spot diameter governs this distribution, yet its mechanistic influence on plasma plume behaviour and melt pool thermophysics remains insufficiently understood, as prior studies have mainly emphasized laser power and scanning speed. This study demonstrates the role of spot diameter as a design relevant control parameter in SS 316 L DED by linking plasma plume dynamics to melt pool behaviour and clad morphology. An integrated in-situ diagnostic approach combining optical emission spectroscopy (OES), CMOS imaging, two-colour pyrometry, and high-speed melt pool imaging was applied across four spot diameters (0.8, 1.3, 2.1 and 3.5 mm) under constant processing conditions. OES measurements revealed a non-monotonic dependence of plasma-plume intensity fluctuation on spot diameter, reflecting changes in vaporization intensity and melt pool stability. A small spot diameter (0.8 mm) produced high plume fluctuations (~ 42.5%) and melt- pool instability, while a large diameter (3.5 mm) resulted in weak plasma plume activity and poor bonding. An intermediate diameter (1.3 mm) yielded a stable plasma plume with reduced fluctuation (~ 21.5%), uniform clad morphology and favourable microstructural-characteristics. Complementary CMOS imaging, high-speed melt pool visualization, and pyrometry measurements consistently supported the OES-derived trends, revealing surface oscillation behaviour and temperature variations with surface tension aligned with the measured plasma plume fluctuations. OES-derived plasma plume intensity and fluctuation provide a physics-based, in-situ measure of spot-diameter-induced melt pool stability in DED.