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<p>This study investigates the impact of N<sub>2</sub> and He process gases, along with heat treatment, on the microstructure and mechanical properties of cold-sprayed 3D-printed pure Cu using a low-pressure system. Microstructural analysis was conducted using XRD, optical microscopy, and EBSD, while hardness and tensile tests assessed mechanical performance. He-assisted deposition achieved higher efficiency due to increased particle velocity. However, because N<sub>2</sub> processing required more passes to reach the same thickness, enhanced cumulative peening led to greater plastic deformation, higher dislocation density, reduced porosity, and increased microhardness (112.19 ± 6.3&#xa0;HV, compared to 87.17 ± 13.12&#xa0;HV for He). Thus, property differences reflect the combined effects of impact conditions and build strategy rather than a gas-only influence. Both as-sprayed deposits exhibited brittle behavior with limited ductility. Heat treatments at 500 and 700&#xa0;°C for 4&#xa0;h promoted recrystallization and grain growth, with more pronounced effects at 700&#xa0;°C. He-processed samples showed higher recrystallization temperatures and finer grain structures post-annealing. While 500&#xa0;°C treatment partially healed interfaces, 700&#xa0;°C eliminated most unbonded regions and introduced spheroidized voids. After heat treatment at 700&#xa0;°C, the ultimate tensile strength improved to 213 (N<sub>2</sub>) and 193&#xa0;MPa (He), and elongation increased to 28 and 25%, respectively, up from &lt; 0.2% in the as-sprayed condition. Notably, the heat-treated N<sub>2</sub> samples exhibited improved metallurgical bonding, slightly outperforming those processed with He. Despite the enhancements, the mechanical properties remained inferior to those of cold-rolled and annealed bulk copper. Nonetheless, the results highlight that N<sub>2</sub>, when used with optimized parameters and heat treatment, offers a cost-effective alternative to He for cold spray applications. To further emphasize the role of in-process densification induced by the peening effect, particle deposition using N<sub>2</sub> and He was simulated using the material point method. The results show that the accumulation of plastic strain is greater in the N<sub>2</sub>-deposited particles than in the He-deposited particles due to the enhanced peening effect associated with N<sub>2</sub> deposition.</p>

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Evolution of Microstructure, Strength, and Ductility in 3D-Printed Low-Pressure Cold Spray Copper: Effects of Process Gas, Build Strategy, and Post-Deposition Heat Treatment

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Niloofar Eftekhari,
  • Ali R. Shams,
  • Reza Hirmand,
  • Hamid Jahed

摘要

This study investigates the impact of N2 and He process gases, along with heat treatment, on the microstructure and mechanical properties of cold-sprayed 3D-printed pure Cu using a low-pressure system. Microstructural analysis was conducted using XRD, optical microscopy, and EBSD, while hardness and tensile tests assessed mechanical performance. He-assisted deposition achieved higher efficiency due to increased particle velocity. However, because N2 processing required more passes to reach the same thickness, enhanced cumulative peening led to greater plastic deformation, higher dislocation density, reduced porosity, and increased microhardness (112.19 ± 6.3 HV, compared to 87.17 ± 13.12 HV for He). Thus, property differences reflect the combined effects of impact conditions and build strategy rather than a gas-only influence. Both as-sprayed deposits exhibited brittle behavior with limited ductility. Heat treatments at 500 and 700 °C for 4 h promoted recrystallization and grain growth, with more pronounced effects at 700 °C. He-processed samples showed higher recrystallization temperatures and finer grain structures post-annealing. While 500 °C treatment partially healed interfaces, 700 °C eliminated most unbonded regions and introduced spheroidized voids. After heat treatment at 700 °C, the ultimate tensile strength improved to 213 (N2) and 193 MPa (He), and elongation increased to 28 and 25%, respectively, up from < 0.2% in the as-sprayed condition. Notably, the heat-treated N2 samples exhibited improved metallurgical bonding, slightly outperforming those processed with He. Despite the enhancements, the mechanical properties remained inferior to those of cold-rolled and annealed bulk copper. Nonetheless, the results highlight that N2, when used with optimized parameters and heat treatment, offers a cost-effective alternative to He for cold spray applications. To further emphasize the role of in-process densification induced by the peening effect, particle deposition using N2 and He was simulated using the material point method. The results show that the accumulation of plastic strain is greater in the N2-deposited particles than in the He-deposited particles due to the enhanced peening effect associated with N2 deposition.