Yong-Sheng Zhu, Xin-Yuan Dong, Xiao-Tao Luo, Yan Wang, Chang-Jiu Li
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引用次数: 0
Abstract
During metallic coating deposition by atmospheric plasma spraying (APS), air entrainment into the plasma jet inevitably leads to oxidation of the molten metallic droplets. The oxides formed in-flight accumulate within the metallic coating, which significantly degrades the performance of the coating compared to the bulk counterpart. It is widely believed that the in-flight oxidation behavior of metal droplets and the state of oxides on their surfaces are critical factors affecting the subsequent spreading behavior and bonding formation of the metal droplet on the substrate surface. In the present work, individual in-flight droplets were collected with liquid N2 to investigate their in-flight oxidation and the oxide state on the droplet surfaces. The effect of in-flight oxidation on the bonding formation of NiCrAlY splats with the superalloy substrate was examined by the focus ion beam (FIB) technique and high-resolution transmission electron microscopy (TEM). Results reveal that the oxides formed during flight within the plasma jet primarily exist in two forms, including small-sized oxide nodules inside the particles and an oxide cap covering the particle surface. SEM examination of splat morphology shows that the high-temperature molten oxide cap is located in the tail of the NiCrAlY metal droplet when the droplet travels through the plasma jet. This oxide distribution pattern results in the metal droplet impacting the substrate first, followed by the deposition of the oxide on the metal splat surface. FIB analysis reveals that the molten oxides deposit on the NiCrAlY splat surfaces without affecting the interfacial bonding at the impact center between splats and substrate. However, these oxides cause entrapment at the periphery of the splats and hinder the bonding between the splats and the substrate. TEM evidence confirms that metallurgical bonding forms at the impact center of the particle due to the absence of oxide film. Chemical bonding is locally achieved at oxide-containing interfaces, whereas delamination dominates most interfacial regions. The effect of high-temperature molten oxides on the bonding mechanism between NiCrAlY splat and substrate is addressed.
期刊介绍:
Surface and Coatings Technology is an international archival journal publishing scientific papers on significant developments in surface and interface engineering to modify and improve the surface properties of materials for protection in demanding contact conditions or aggressive environments, or for enhanced functional performance. Contributions range from original scientific articles concerned with fundamental and applied aspects of research or direct applications of metallic, inorganic, organic and composite coatings, to invited reviews of current technology in specific areas. Papers submitted to this journal are expected to be in line with the following aspects in processes, and properties/performance:
A. Processes: Physical and chemical vapour deposition techniques, thermal and plasma spraying, surface modification by directed energy techniques such as ion, electron and laser beams, thermo-chemical treatment, wet chemical and electrochemical processes such as plating, sol-gel coating, anodization, plasma electrolytic oxidation, etc., but excluding painting.
B. Properties/performance: friction performance, wear resistance (e.g., abrasion, erosion, fretting, etc), corrosion and oxidation resistance, thermal protection, diffusion resistance, hydrophilicity/hydrophobicity, and properties relevant to smart materials behaviour and enhanced multifunctional performance for environmental, energy and medical applications, but excluding device aspects.