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<p>Controlling prior-β grain morphology is crucial for achieving specific isotropic properties in Wire Arc Additive Manufacturing (WAAM). Arc oscillation has been proven effective in refining grain size during aluminum welding, primarily due to the dendrite fragmentation mechanism. However, its impact on the grain structure of Ti-6Al-4&#xa0;V remains underexplored. In this study, various arc oscillation amplitudes were applied to assess grain morphology evolution. In the stringer method (without oscillation), 100% equiaxed grains were observed in both the transverse and longitudinal directions due to lower heat input. As oscillation amplitude increased, the grain structure gradually transformed from equiaxed to columnar. At an amplitude of 6&#xa0;mm, 80% columnar grains were obtained. To understand these findings, numerical simulations were conducted to quantitatively analyze the thermal history. SYSWELD calculations showed that a larger oscillation amplitude (6&#xa0;mm) significantly influenced the weld pool shape (height and width), amplifying the temperature gradient (G) to nearly twice that of the specimen without oscillation during solidification. Furthermore, the dendrite fragmentation mechanism suggests that although thermal fluctuations caused by oscillation were observed in the molten region, they gradually dissipated after one or two remelting cycles. Controlling the frequency of these thermal fluctuations and the weld geometry presents a potential approach to modifying prior-β in Ti-6Al-4&#xa0;V using arc oscillation.</p>

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Oscillation-driven grain structure control and its mechanisms in Ti64 wire arc additive manufacturing

  • 期刊论文

  • 发表日期：

    2025年5月12日

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  • Guo Xian,
  • Muralimohan Cheepu,
  • Namhyun Kang

摘要

Controlling prior-β grain morphology is crucial for achieving specific isotropic properties in Wire Arc Additive Manufacturing (WAAM). Arc oscillation has been proven effective in refining grain size during aluminum welding, primarily due to the dendrite fragmentation mechanism. However, its impact on the grain structure of Ti-6Al-4 V remains underexplored. In this study, various arc oscillation amplitudes were applied to assess grain morphology evolution. In the stringer method (without oscillation), 100% equiaxed grains were observed in both the transverse and longitudinal directions due to lower heat input. As oscillation amplitude increased, the grain structure gradually transformed from equiaxed to columnar. At an amplitude of 6 mm, 80% columnar grains were obtained. To understand these findings, numerical simulations were conducted to quantitatively analyze the thermal history. SYSWELD calculations showed that a larger oscillation amplitude (6 mm) significantly influenced the weld pool shape (height and width), amplifying the temperature gradient (G) to nearly twice that of the specimen without oscillation during solidification. Furthermore, the dendrite fragmentation mechanism suggests that although thermal fluctuations caused by oscillation were observed in the molten region, they gradually dissipated after one or two remelting cycles. Controlling the frequency of these thermal fluctuations and the weld geometry presents a potential approach to modifying prior-β in Ti-6Al-4 V using arc oscillation.