Microstructure and Pitting Corrosion Behavior of Plasma-Sprayed Fe-Si Nanocomposite Coating
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Technical Note
Microstructure and Pitting Corrosion Behavior of Plasma-Sprayed Fe-Si Nanocomposite Coating Xi Shi, Xinjing Meng, Qingdong Zhong, Jian Yang, Mingyong Shu, Hongbo Han, and QuocBinh Bui (Submitted December 25, 2015; in revised form March 25, 2016) In this study, Fe-Si nanoparticle composite coating (FSN) and Fe-Si microparticle composite coating (FSM) were prepared via atmospheric plasma spraying, and FSN was thermally treated under hydrogen atmosphere at 1120 °C for holding time of 2.5 h (TFSN). Under transmission electron microscopy, many unmelted nanoscale particles were observed in FSN, while no substantial particles were found in TFSN. On scanning electron microscopy analysis, pores and cracks were observed in FSM and FSN, while no defects were found in TFSN. Scanning electrochemical microscopy testing in 3.5 wt.% NaCl for 5 h revealed that FSM underwent severe pitting corrosion, FSN showed relatively minor pitting corrosion, and TFSN had no pitting corrosion.
Keywords
corrosion resistance, Fe-Si nanocomposite coating, plasma spray, SECM
1. Introduction Atmospheric plasma spraying (APS) is an effective and environmentally friendly method for rapid deposition of high-quality coatings (Ref 1). Because of the features of conventional thermal spray processes, the coating microstructure is often characterized by the presence of pores and cracks (Ref 2, 3). In the 1980s, attention gradually shifted from study of conventional microscale materials towards the characteristics of nanoscale materials, due to the appearance of nanoscale science and technology (Ref 4). Recently, there has been great interest in such nanostructured materials, because of their excellent properties, which differ from conventional bulk materials (Ref 5). In earlier-stage work, plasma-sprayed nanocomposite coatings were manufactured and thermally treated. This work revealed that the nanoparticles grew as well as close combination and uniform arrangement of particles after thermal treatment (Ref 6). Fe-Si alloy is an important soft-magnetic alloy, being highly corrosion resistant. Intermetallic compounds are formed in Fe-Si alloy, such as Fe3Si or FeSi, which have
good corrosion and oxidation resistance (Ref 7). In FeSibased alloys, addition of silicon improves the corrosion resistance of the protective film formed, where the composition of the oxide layer formed is rich in SiO2 (Ref 8). In this work, plasma-sprayed nanocoatings were researched much further, using FeSi as spray material. Fe-Si nanoparticle composite coating (FSN) and Fe-Si microparticle composite coating (FSM) with nominal composition of 14.2 wt.% Si and 85.8 wt.% Fe were prepared via APS on Q235 low-carbon steel, and subsequently FSN was thermally treated under hydrogen atmosphere (TFSN).
2. Experimental Procedures 2.1 Reconstitution and Spraying The equipment and process used for reconstitution and spraying were similar to in earlier work on FeCr plasmasprayed nanocomposite coating (Ref 6). The key parameters are presented in Tables 1 and 2, and Fe-Si nanoag
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