Cavitation erosion mechanisms in Co-based coatings exposed to seawater

Guoliang Hou; Yi Ren; Xiaoliang Zhang; Fengxia Dong; Yulong An; Xiaoqin Zhao; Huidi Zhou; Jianmin Chen

doi:10.1016/j.ultsonch.2019.104799

Cavitation erosion mechanisms in Co-based coatings exposed to seawater

Ultrason Sonochem. 2020 Jan:60:104799. doi: 10.1016/j.ultsonch.2019.104799. Epub 2019 Sep 16.

Authors

Guoliang Hou¹, Yi Ren², Xiaoliang Zhang³, Fengxia Dong¹, Yulong An⁴, Xiaoqin Zhao¹, Huidi Zhou⁵, Jianmin Chen⁶

Affiliations

¹ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
² State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China; School of Materials Science and Engineering, Hebei University of Engineering, Handan 056038, China.
³ School of Materials Science and Engineering, Hebei University of Engineering, Handan 056038, China.
⁴ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China; Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: csuayl@sohu.com.
⁵ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China; Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: hdzhou@licp.cas.cn.
⁶ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China; Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.

PMID: 31563793
DOI: 10.1016/j.ultsonch.2019.104799

Abstract

The cavitation erosion (CE) of most materials in seawater is more serious than in fresh water due to the onset of corrosion; however, in a previous study we reported results that contradict this widely accepted trend. In this research our objective is to provide fundamental insight into the mechanisms that may be responsible for these earlier results. To accomplish this objective, two types of Co-based coatings, prepared by high velocity oxygen fuel (HVOF) spraying system, were used to further investigate the underlying corrosion-mitigating CE mechanism in seawater. Accordingly, the influence of spraying parameters on microstructure, composition and mechanical properties of the coatings was analyzed on the basis of SEM, XRD, Raman spectroscopy, Vicker's hardness and nano-indentation results. Electrochemical corrosion tests were used to evaluate the corrosion behavior of the Co-based coatings. Their CE performances in seawater and deionized water were comparatively studied by a vibratory apparatus. Results demonstrated that a higher flame temperature facilitated the oxides formation with associated improvements in compactness, hardness and toughness of the coatings. The presence of alumina in combination with the oxides formed in-situ facilitated the formation of an oxidation film on surfaces, and effectively enhanced the charge transfer resistance of the coating, thereby significantly improving the corrosion resistance in seawater. Metallic Co was not only more easily oxidized but also more readily corroded than the alloyed Co. Compactness was identified as an important factor affecting CE resistance of coatings in deionized water, because defects facilitate the nucleation and eventual collapse of bubbles. Moreover, bubble collapse produced a transient high temperature spike in excess of 600 °C that also caused Co and Cr elements to oxidize. Because the CE tests were carried out in seawater, additional Co₃O₄ and Cr₂O₃ were generated owing to corrosion that more effectively increased the surface compactness and mechanical properties of the coatings. This behavior was particular notable for coatings with metallic Co and Cr, which should be why seawater corrosion could weaken the CE of Co-based coatings.

Keywords: Cavitation erosion; Co-based coating; Corrosion; Mechanical properties; Oxidation.