Corrosion of high‐velocity oxy‐fuel (HVOF) sprayed iron‐based amorphous metallic coatings for marine pump in sodium chloride solutions

Abstract

FeCrMoMnWBCSi amorphous metallic coatings (AMCs) were deposited onto the 304 stainless steel (base material of pump impeller operated in sand‐containing seawater) by high‐velocity oxygen‐fuel (HVOF) thermal spray. The preparation, microstructural characteristics, and static corrosion behavior of the AMCs were presented. The microstructure and corrosion behavior of the AMCs were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and electrochemical methods. Melt‐spun ribbon and 304 stainless steel were also used for comparison purposes. The results indicated that the AMCs can spontaneously passivate with a wide passive region, and much higher ability to withstand pitting corrosion than that of the 304 stainless steel for the high pitting resistance equivalent value. The passive current density of the AMCs was at least two orders of magnitude higher than the counterpart ribbon, which showed a slightly decreased uniform corrosion resistance of the AMCs due to the incompact structure and porosity. The corrosion resistance of the AMCs increased with the coating thickness and decreased with the concentration of NaCl solution. A stable passivation ability held in the AMCs endowed them suitably used in marine environments.

Interfacial bonding of low-pressure plasma-sprayed Fe-based amorphous coating on 8090 Al–Li alloy

“…Chromium is the main element in the formation of passivation film, and Mo is the element that promotes the re-formation of soluble passivation film [38]. However, owing to crystallization and elemental segregation at the boundary of the coating particles during the bonding process, no Mo is involved in the subsequent passivation process at the boundary resulting in a slower passivation film generation rate, causing pitting in this area as well as the nearby passivation area [39]. After the pits are formed, Cl− accumulates in them, resulting in an autocatalytic effect that further accelerates the expansion of corrosion [40].…”

Effect of Oxidation and Crystallization on Pitting Initiation Behavior of Fe-Based Amorphous Coatings

“…In HVOF spraying, insufficient heat will lead to poor coating formation, leaving more pores to destroy the structure uniformity of the coating (loose structure as shown in Figure 2a), while excessive heat will induce oxidation and crystallization of the coating and destroy the uniform composition of the coating [39][40][41][42]. It is generally believed that the nanocrystals on the coating surface form potential pitting sites after galvanic coupling with the passivation film [43]. Moreover, Cl − tends to be enriched in the pores or pits, forming a concentration galvanic cell with the solution outside the pits.…”

“…This is called the self-catalytic effect and accelerates the formation and expansion of pits [44]. With the increase in the porosity of the amorphous coating layer, corrosion resistance in the chloride solution decreases notably [43,45].…”

Fe-based metallic glass coatings by thermal spraying: a focused review on corrosion properties and related degradation mechanisms

“…Porosity. One of the major aspects of Fe-based MGCs to have a considerable effect on corrosion properties is the porosity of the coatings [119,128,137,140,[231][232][233]. It is well known that porosity is an inevitable structural attribute of thermal sprayed Fe-based MGCs, which disturbs the structural homogeneity.…”