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<p>The coexistence of B19′ martensite and geometrically necessary dislocation (GND) in LPBF-fabricated NiTi alloys introduces competing effects on cyclic superelastic stability and corrosion resistance. However, the relationship among hatch spacing, thermal history, microstructural evolution, and functional performance remains insufficiently understood. In this work, hatch spacing (h, 70–90&#xa0;μm) was systematically varied to investigate the process–microstructure–performance relationship in LPBF-fabricated NiTi alloys. Mesoscale simulations suggest that decreasing h increases peak melt pool temperature from ~ 2850&#xa0;K to above 3300&#xa0;K and enhances inter-track thermal cycling, thereby promoting selective Ni evaporation and GND accumulation. ICP-OES and DSC analyses revealed continuous Ni depletion (50.23→50.01 at%) and a corresponding increase in Ms (–3.31→17.92 °C), accompanied by a significant increase in B19′ phase fraction (4.04→22.75%) as Ms approached room temperature in the h = 80–75&#xa0;μm interval. The martensitic transformation interval also broadened from 37.97 to 71.33&#xa0;K, indicating increased transformation heterogeneity associated with defect accumulation. Cyclic compression tests showed a non-monotonic variation in cyclic strain degradation ratio, reaching a minimum value of 1.40% at h = 80&#xa0;μm, where a relatively balanced microstructural state promoted reversible martensitic transformation while suppressing excessive irreversible deformation. In contrast, corrosion resistance deteriorated progressively with decreasing hatch spacing. XPS and EIS analyses indicated reduced passive film stability in samples with h ≤ 75&#xa0;μm, accompanied by Ti<sup>0</sup> exposure, increased Ni(OH)<sub>2</sub> content, and a significant decrease in film resistance. Based on the combined microstructural and functional responses, three processing regimes were identified: a corrosion-dominant regime at h = 90&#xa0;μm, a balanced optimization regime at h = 85–80&#xa0;μm, and a degradation regime at h = 75–70&#xa0;μm where both cyclic stability and corrosion resistance deteriorated simultaneously. Among the investigated conditions, h = 80&#xa0;μm provided the best overall combination of densification, cyclic stability, and corrosion resistance.</p>

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Hatch spacing controlled thermal history governs microstructural and defect evolution and functional stability in LPBF fabricated NiTi alloys

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Quan Li,
  • Yongjun Shi,
  • Xuejin Zhao,
  • Ying Li,
  • Kaijun Fan,
  • Xinyu Yan,
  • Mingjun Tian

摘要

The coexistence of B19′ martensite and geometrically necessary dislocation (GND) in LPBF-fabricated NiTi alloys introduces competing effects on cyclic superelastic stability and corrosion resistance. However, the relationship among hatch spacing, thermal history, microstructural evolution, and functional performance remains insufficiently understood. In this work, hatch spacing (h, 70–90 μm) was systematically varied to investigate the process–microstructure–performance relationship in LPBF-fabricated NiTi alloys. Mesoscale simulations suggest that decreasing h increases peak melt pool temperature from ~ 2850 K to above 3300 K and enhances inter-track thermal cycling, thereby promoting selective Ni evaporation and GND accumulation. ICP-OES and DSC analyses revealed continuous Ni depletion (50.23→50.01 at%) and a corresponding increase in Ms (–3.31→17.92 °C), accompanied by a significant increase in B19′ phase fraction (4.04→22.75%) as Ms approached room temperature in the h = 80–75 μm interval. The martensitic transformation interval also broadened from 37.97 to 71.33 K, indicating increased transformation heterogeneity associated with defect accumulation. Cyclic compression tests showed a non-monotonic variation in cyclic strain degradation ratio, reaching a minimum value of 1.40% at h = 80 μm, where a relatively balanced microstructural state promoted reversible martensitic transformation while suppressing excessive irreversible deformation. In contrast, corrosion resistance deteriorated progressively with decreasing hatch spacing. XPS and EIS analyses indicated reduced passive film stability in samples with h ≤ 75 μm, accompanied by Ti0 exposure, increased Ni(OH)2 content, and a significant decrease in film resistance. Based on the combined microstructural and functional responses, three processing regimes were identified: a corrosion-dominant regime at h = 90 μm, a balanced optimization regime at h = 85–80 μm, and a degradation regime at h = 75–70 μm where both cyclic stability and corrosion resistance deteriorated simultaneously. Among the investigated conditions, h = 80 μm provided the best overall combination of densification, cyclic stability, and corrosion resistance.