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<p>In situ synchrotron high-energy X-ray diffraction was employed to track the phase-fraction evolution and lattice-parameter variation of Fe11Cr8Ni5Co3Mo steel during laser-directed energy deposition. The results reveal that both quantities vary significantly with deposition layer and local thermal history. Interlayer analysis from the fifth to the 15th layer reveals austenite declines from 7.45 to 3.20 wt.% due to reduced heat accumulation, accompanied by progressive lattice contraction in both martensite and austenite from residual compressive stresses. This layer-dependent trend reflects the strong influence of local thermal history on phase stability during deposition. In the tenth layer, thermal cycling induces reversible phase changes: Martensite fluctuates (97.9 → 92.2 → 94.5 wt.%) while austenite inversely shifts (2.1 → 7.8 → 5.5 wt.%). Thermal gradients near the melt pool transiently expand lattice parameters, followed by cooling-induced contraction. Corresponding nanoindentation measurements show layer-dependent hardness variations, with the fifth layer exhibiting the highest hardness of 5.72&#xa0;GPa, attributed to the combined effects of thermal gradients and phase transformations. Overall, the phase stability, lattice evolution, and layer-dependent hardness are closely related to cyclic thermal history during laser-directed energy deposition.</p>

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In situ synchrotron XRD tracking of cyclic phase transformations and stress evolution of Fe11Cr8Ni5Co3Mo steel during L-DED

  • 期刊论文

  • 发表日期：

    2026年6月2日

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  • Ling-Zhi Wu,
  • Wei Gao,
  • Sen Chen,
  • Dong-Sheng Zhang,
  • Cai-Juan Shi,
  • Cong Zhang,
  • Bing-Bing Zhang,
  • Hai-Qing Yin,
  • Geng Liu,
  • Jie Su

摘要

In situ synchrotron high-energy X-ray diffraction was employed to track the phase-fraction evolution and lattice-parameter variation of Fe11Cr8Ni5Co3Mo steel during laser-directed energy deposition. The results reveal that both quantities vary significantly with deposition layer and local thermal history. Interlayer analysis from the fifth to the 15th layer reveals austenite declines from 7.45 to 3.20 wt.% due to reduced heat accumulation, accompanied by progressive lattice contraction in both martensite and austenite from residual compressive stresses. This layer-dependent trend reflects the strong influence of local thermal history on phase stability during deposition. In the tenth layer, thermal cycling induces reversible phase changes: Martensite fluctuates (97.9 → 92.2 → 94.5 wt.%) while austenite inversely shifts (2.1 → 7.8 → 5.5 wt.%). Thermal gradients near the melt pool transiently expand lattice parameters, followed by cooling-induced contraction. Corresponding nanoindentation measurements show layer-dependent hardness variations, with the fifth layer exhibiting the highest hardness of 5.72 GPa, attributed to the combined effects of thermal gradients and phase transformations. Overall, the phase stability, lattice evolution, and layer-dependent hardness are closely related to cyclic thermal history during laser-directed energy deposition.