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<p>The industrial integration of duplex stainless steels fabricated via Wire-Arc Directed Energy Deposition (WA-DED) remains severely hindered by unpredictable microstructural heterogeneities. Due to the layer-wise deposition process, the material undergoes repetitive solid-state thermal cycles (SSTCs) that critically disrupt the essential ferrite–austenite phase balance. To decode the real-time physical mechanisms governing these cyclic phase transformations, a comprehensive cross-scale methodology is introduced. Initial WA-DED experiments utilizing ER2209 wire were conducted to capture the process-induced thermal histories. These thermal profiles were subsequently replicated via in situ heating within a scanning electron microscope using micro-electromechanical systems, and the findings were validated through precipitation-kinetics modeling based on the CALPHAD framework. The findings reveal a significant vertical phase gradient driven by SSTCs. The austenite fraction surges from approximately 57% in newly deposited layers to 80% after merely two reheating cycles, with no additional phase transformation triggered by subsequent SSTCs. Both in situ observations and kinetic modeling indicate that this rapid ferrite-to-austenite conversion proceeds mainly by diffusion-controlled growth of pre-existing austenite along ferrite–austenite interfaces, rather than by nucleation of new austenite grains. Crucially, phase evolution is dictated by the integrated thermal history within specific cooling intervals (t<sub>12/8</sub> and t<sub>8/5</sub>), rather than the absolute peak reheating temperatures. Despite these phase shifts, macroscopic hardness remains remarkably uniform, as strict interpass temperature control effectively mitigates excessive and uncontrolled heat accumulation. By quantitatively linking localized thermal histories to real-time phase kinetics, this work establishes a robust predictive framework that forms the mechanistic basis for optimizing deposition strategies and ensuring the reliable performance of industrial WA-DED components.</p> Graphical abstract <p></p>

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Cyclic heating effects on microstructure development in duplex stainless steel manufactured via wire-arc directed energy deposition

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月9日

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  • T. Reindl,
  • C. Koenig,
  • A. Aslam,
  • J. Vincic,
  • J. R. Jinschek,
  • A. Bastos Fanta,
  • P. Mayr

摘要

The industrial integration of duplex stainless steels fabricated via Wire-Arc Directed Energy Deposition (WA-DED) remains severely hindered by unpredictable microstructural heterogeneities. Due to the layer-wise deposition process, the material undergoes repetitive solid-state thermal cycles (SSTCs) that critically disrupt the essential ferrite–austenite phase balance. To decode the real-time physical mechanisms governing these cyclic phase transformations, a comprehensive cross-scale methodology is introduced. Initial WA-DED experiments utilizing ER2209 wire were conducted to capture the process-induced thermal histories. These thermal profiles were subsequently replicated via in situ heating within a scanning electron microscope using micro-electromechanical systems, and the findings were validated through precipitation-kinetics modeling based on the CALPHAD framework. The findings reveal a significant vertical phase gradient driven by SSTCs. The austenite fraction surges from approximately 57% in newly deposited layers to 80% after merely two reheating cycles, with no additional phase transformation triggered by subsequent SSTCs. Both in situ observations and kinetic modeling indicate that this rapid ferrite-to-austenite conversion proceeds mainly by diffusion-controlled growth of pre-existing austenite along ferrite–austenite interfaces, rather than by nucleation of new austenite grains. Crucially, phase evolution is dictated by the integrated thermal history within specific cooling intervals (t12/8 and t8/5), rather than the absolute peak reheating temperatures. Despite these phase shifts, macroscopic hardness remains remarkably uniform, as strict interpass temperature control effectively mitigates excessive and uncontrolled heat accumulation. By quantitatively linking localized thermal histories to real-time phase kinetics, this work establishes a robust predictive framework that forms the mechanistic basis for optimizing deposition strategies and ensuring the reliable performance of industrial WA-DED components.

Graphical abstract