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<p>With plasma spraying of metal coatings, severe in-flight oxidation leads to coatings with high content of oxide inclusions and, subsequently, limited interlamellar bonding. Recently, the strategy has been proposed to generate oxide-free molten droplets by air plasma spraying (APS) in ambient atmosphere through designing metal powders with specific deoxidizer. However, achieving super-hot in-flight particles is essential to ensure effective in-flight in situ deoxidization. In this study, the effect of nozzle geometry with changing diameters and lengths on in-flight particle temperature was investigated to find the parameter windows to fulfill the temperature requirements both for in situ deoxidization kinetics and spray-fusing self-bonding mechanism. The particle temperatures were measured by the DPV-2000 thermal spray in-flight particle diagnostic system. The double effects both to generate oxide-free metal droplets and initiate spread-fusing self-bonding mechanism during APS using deoxidizer-containing powders by super-hot molten droplets were examined. Results show that the modified anode nozzle with a diameter of 8&#xa0;mm and the internal heating length of 10&#xa0;mm can ensure the generation of molten droplets with a temperature higher than 2400&#xa0;°C, which fulfills the requirements for in situ in-flight deoxidizing and spread-fusing mechanisms. It was confirmed that with Ni-based materials, boron can be used as deoxidizer effectively, while with Al-containing alloys such as MCrAlY carbon can be used instead. The oxide-free molten metal droplets can be achieved for NiCrB and NiCrAlY spray particles. The examination into splats deposited on Ni-based alloy substrate reveals that sufficient metallurgical bonding was achieved at splat–substrate interface. Therefore, with spray metal powders design and generation of super-hot droplets, dense metal coatings with high cohesion and low oxide inclusions can be deposited by APS.</p>

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Double Effect of Super-Hot Molten Droplets on the Formation of Oxide-Free Metal Droplets and Intersplat Bonding during APS Using Deoxidizer-Containing Powders

  • 期刊论文

  • 发表日期：

    2025年11月7日

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  • Chang-Jiu Li,
  • Yong-Sheng Zhu,
  • Xiao-Tao Luo,
  • Xin-Yuan Dong,
  • Xuan Xue

摘要

With plasma spraying of metal coatings, severe in-flight oxidation leads to coatings with high content of oxide inclusions and, subsequently, limited interlamellar bonding. Recently, the strategy has been proposed to generate oxide-free molten droplets by air plasma spraying (APS) in ambient atmosphere through designing metal powders with specific deoxidizer. However, achieving super-hot in-flight particles is essential to ensure effective in-flight in situ deoxidization. In this study, the effect of nozzle geometry with changing diameters and lengths on in-flight particle temperature was investigated to find the parameter windows to fulfill the temperature requirements both for in situ deoxidization kinetics and spray-fusing self-bonding mechanism. The particle temperatures were measured by the DPV-2000 thermal spray in-flight particle diagnostic system. The double effects both to generate oxide-free metal droplets and initiate spread-fusing self-bonding mechanism during APS using deoxidizer-containing powders by super-hot molten droplets were examined. Results show that the modified anode nozzle with a diameter of 8 mm and the internal heating length of 10 mm can ensure the generation of molten droplets with a temperature higher than 2400 °C, which fulfills the requirements for in situ in-flight deoxidizing and spread-fusing mechanisms. It was confirmed that with Ni-based materials, boron can be used as deoxidizer effectively, while with Al-containing alloys such as MCrAlY carbon can be used instead. The oxide-free molten metal droplets can be achieved for NiCrB and NiCrAlY spray particles. The examination into splats deposited on Ni-based alloy substrate reveals that sufficient metallurgical bonding was achieved at splat–substrate interface. Therefore, with spray metal powders design and generation of super-hot droplets, dense metal coatings with high cohesion and low oxide inclusions can be deposited by APS.