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<p>This study reports the fabrication and comprehensive characterization of a thin-walled SS316L/Inconel 625 functionally graded material (FGM) produced by directed laser metal deposition (DLMD) using a continuous-wave fiber laser with a wavelength of 1070&#xa0;nm, at a laser power of approximately 220 W, scanning speed of 6&#xa0;mm/s, and powder feed rate of 18&#xa0;mg/s. A controlled compositional gradient was designed along the build direction, and x-ray computed tomography (XCT) was used to assess internal integrity. Complementary XRD and EBSD analyses confirmed the predominance of the γ-FCC phase throughout the graded region, with localized BCC ferrite mainly on the SS316L side, indicating crystallographic continuity without abrupt phase discontinuities. Microstructural analysis revealed a gradual transition from fine cellular austenite in the SS316L-rich region to columnar dendritic structures in the IN625-rich zone, accompanied by Nb and Mo segregation and possible Laves-related phase formation under non-equilibrium solidification. Elemental redistribution across the graded region was confirmed by EDS mapping and line-scan analysis, which correlated with a monotonic increase in hardness from 210 HV to 321 HV. Tensile testing demonstrated uniform deformation behavior, with ultimate tensile strength of 570-596&#xa0;MPa, yield strength of 327-355&#xa0;MPa, and elongation exceeding 30%. Fractographic and EDS analyses confirmed predominantly ductile failure through microvoid coalescence, localized entirely within the lower-strength SS316L-rich region. Wear resistance improved significantly toward the IN625-rich region, with the wear rate decreasing from 6.4 × 10<sup>−4</sup> to 4.5 × 10<sup>−4</sup> mm<sup>3</sup>/N.m. Overall, these results demonstrate that the controlled compositional gradient promotes a smooth microstructural transition while enhancing the mechanical integrity and tribological performance of the fabricated FGM, confirming that DLMD is a reliable approach for producing high-performance metallic FGMs intended for components subjected to combined structural and tribological loading.</p>

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SS316L/IN625 Functionally Graded Material Fabricated by Directed Laser Metal Deposition: Microstructure and Mechanical Performance of Thin-Walled Structures

  • 期刊论文

  • 发表日期：

    2026年5月28日

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  • Nguyen Van Quan,
  • Doan Tat Khoa,
  • Nguyen Van Hoang

摘要

This study reports the fabrication and comprehensive characterization of a thin-walled SS316L/Inconel 625 functionally graded material (FGM) produced by directed laser metal deposition (DLMD) using a continuous-wave fiber laser with a wavelength of 1070 nm, at a laser power of approximately 220 W, scanning speed of 6 mm/s, and powder feed rate of 18 mg/s. A controlled compositional gradient was designed along the build direction, and x-ray computed tomography (XCT) was used to assess internal integrity. Complementary XRD and EBSD analyses confirmed the predominance of the γ-FCC phase throughout the graded region, with localized BCC ferrite mainly on the SS316L side, indicating crystallographic continuity without abrupt phase discontinuities. Microstructural analysis revealed a gradual transition from fine cellular austenite in the SS316L-rich region to columnar dendritic structures in the IN625-rich zone, accompanied by Nb and Mo segregation and possible Laves-related phase formation under non-equilibrium solidification. Elemental redistribution across the graded region was confirmed by EDS mapping and line-scan analysis, which correlated with a monotonic increase in hardness from 210 HV to 321 HV. Tensile testing demonstrated uniform deformation behavior, with ultimate tensile strength of 570-596 MPa, yield strength of 327-355 MPa, and elongation exceeding 30%. Fractographic and EDS analyses confirmed predominantly ductile failure through microvoid coalescence, localized entirely within the lower-strength SS316L-rich region. Wear resistance improved significantly toward the IN625-rich region, with the wear rate decreasing from 6.4 × 10−4 to 4.5 × 10−4 mm3/N.m. Overall, these results demonstrate that the controlled compositional gradient promotes a smooth microstructural transition while enhancing the mechanical integrity and tribological performance of the fabricated FGM, confirming that DLMD is a reliable approach for producing high-performance metallic FGMs intended for components subjected to combined structural and tribological loading.