Zhao Weimin1,WangYong2,Xue Jin1,Wu Kaiyuan2
(1.School of Material Science and Engineering,Xi'an Jiaotong University,Xi'an 710049, China; 2.School of Mechanical and Electrical Engineering, University of Petroleum, Dongying 257061,China)
Abstract:The NiCrBSi alloy powder was sprayed to a low carbon steel substrate using high velocity oxy-fuel (HVOF) spraying, and the corrosion tests were carried out by immersing the specimens in the 3.5% NaCl acidified with acetic acid to give a pH of 3. Techniques such as scanning electron microscopy (SEM) observing, high frequency plasma emission spectral analysis, electron probe micro-analysis (EPMA) and X-ray energy-dispersive analysis were employed to study the corrosion mechanism of the coating.It is found that the composition selective corrosion does not occur within the NiCrBSi coating,and the main reason is that electrolyte has penetrated into the inner part of coating.The corrosion first occurs on the surface of the coating around the particles that have not fused during spraying and the defects such as porosities, inclusions and micro cracks,and then develops along the paths formed by porosities, micro cracks,laminar structure,and so on.The main failure mechanism of the coating is exfoliating or laminar shell-off.Adjusting the thermal spraying parameters to reduce the electrochemical unevenness or sealing the porosities could improve the corrosion resistance of the coating.
Keywords: thermal-spraying; high velocity-oxy-fuel (HVOF); metallic coating; corrosion resistance