Silveira, Antonio Carlos

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Silveira, Antonio Carlos
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antoniofigueiredosilveira@gmail.com
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57225962065

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    Item type:Publication,
    Microstructure evolution during laser directed energy deposition of a hardenable tool steel
    (2026-06-16)
    Silveira, Antonio Carlos
    ;
    Fechte-Heinen, Rainer
    ;
    Niendorf, Thomas
    ;
    Fechte-Heinen, Rainer
    This work used in situ high-energy synchrotron X-ray diffraction (HEXRD) at the P07-EH3 beamline at DESY-Petra III to investigate microstructural evolution in X40CrMoV5-1 tool steel during laser-based directed energy deposition (DED-LB/M) of thin walls. The synchrotron beam was fixed at five wall-height positions (0%, 25%, 50%, 75%, and 100%), and diffraction data were processed with PyFAI and refined via a custom Rietveld script in TOPAS-Academic V6, alongside additional dilatometric HEXRD experiments to improve the estimation of temperature based on the lattice parameter of the main phases. Results show peak temperatures exceeding 1400 °C near the deposition zone, with solidification rates up to 2000 K/s, followed by martensitic transformation. Thermal accumulation increased with wall height, altering heat treatment (IHT) and creating a heterogeneous microstructure. IHT was decomposed into five cycles: full melting, partial melting, austenitization, partial austenitization, and tempering. Rietveld analysis revealed high dislocation density and martensite tetragonality early in the process, decreasing with heat accumulation (auto-tempering). Repeated austenitizing cycles caused dislocation accumulation in austenite. Metallographic characterization (optical/electron microscopy, microhardness, EBSD, EPMA) showed light tempering at the bottom, severe tempering mid-height, and quenched martensite at the top, with a hardness transition between 50–75%. APT and TEM identified carbide/carbonitride precipitation: V-rich MC/MCN formed during partial melting cycles, with MC dissolving during austenitization while MCN persisted. V-rich M8C7 and Fe-Cr-rich M3C/M7C3 formed during partial austenitizing and tempering cycles, respectively. Tempering severity affected precipitate distribution/composition rather than total phase fraction, with less-tempered regions showing more Fe-rich, non-equilibrium carbide compositions. The work establishes a methodology for tracking fast phase transformations, temperature, lattice defects, and precipitation behavior in tool steel during AM, providing a knowledge base for future processability, simulation, and synchrotron studies.
    doctoral thesis
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