Corrosion and Cavitation Erosion Behaviours of Cast Nickel Aluminium Bronze in 3.5% NaCl Solution with Different Sulphide Concentrations

Abstract

The effect of sulphide (Na 2 S) concentration (SC) on the corrosion and cavitation erosion behaviours of a cast nickel aluminium bronze (NAB) in 3.5% NaCl solution is investigated in this study. The results show that when the SC exceeds 50 ppm, the hydrogen evolution reaction dominates the cathodic process, and a limiting current region appears in the anodic branch of the polarisation curve due to the formation of a copper sulphide film, which is a diffusion-controlled process. After longterm immersion, the increased mass loss rate of NAB with the sulphide additions of 20 and 50 ppm is attributed to the less protective films, which contains a mixture of copper oxides and sulphides. Moreover, NAB undergoes severe localised corrosion (selective phase corrosion, SPC) at the β′ phases and eutectoid microstructure α + κ III . By comparison, NAB undergoes general corrosion and a copper sulphide film is formed in 100 and 200 ppm sulphide solutions. Cavitation erosion greatly increases the corrosion rate of NAB in all solutions and causes a negative potential shift in 3.5% NaCl solution due to the film destruction. However, a positive potential shift occurs in the solutions with SC higher than 50 ppm due to the accelerated mass transfer of the cathodic process. The cavitation erosion mass loss rate of NAB increases with the increase of SC. The occurrence of severe SPC decreases the phase boundary cohesion and causes brittle fracture under the cavitation impact. The corrosion-enhanced erosion is the most predominant factor for the cavitation erosion damage when the SC exceeds 50 ppm.

A review of the corrosion behavior of conventional and additively manufactured nickel–aluminum bronze (NAB) alloys: current status and future challenges

“…Furthermore, increasing sulphide concentration in the range of 20 to 100 ppm led to deterioration of corrosion properties. 114 Cu + HS − → Cu(HS) ads + e − Cu + Cu(HS) ads + HS − → Cu 2 S + H 2 S + e − These findings emphasized the profound effect of solution type on the corrosion behavior of NAB. 86,113,114 A recent comparative study, conducted in simulated seawater (SSW) and simulated freshwater (SFW) revealed that NAB alloy experienced localized attack in SFW due to the presence of sulphate and bicarbonate in the environment, which hindered the attainment of equilibrium.…”

“…114 Cu + HS − → Cu(HS) ads + e − Cu + Cu(HS) ads + HS − → Cu 2 S + H 2 S + e − These findings emphasized the profound effect of solution type on the corrosion behavior of NAB. 86,113,114 A recent comparative study, conducted in simulated seawater (SSW) and simulated freshwater (SFW) revealed that NAB alloy experienced localized attack in SFW due to the presence of sulphate and bicarbonate in the environment, which hindered the attainment of equilibrium. 87 On the other hand, when exposed to SSW, it rapidly formed a relatively protective film on the surface.…”

“…The corrosion characteristics of NAB in 3.5 wt% NaCl solution with different levels of sulphide was investigated using electrochemical testing and immersion test methods. 114 It was revealed that increasing sulphide concentration led to decreased corrosion resistance due to adsorption of HS − on NAB surface (see eqn (12) and (13)). 114 Gravimetric measurements also indicated that in all sulphide-polluted media, the corrosion resistance of the alloy was lower than that in non-polluted solution, but the formation of a homogenous corrosion product film (mainly Cu 2 S) in the electrolyte containing 200 ppm sulphide could beneficially affect the corrosion resistance of the alloy.…”

“…114 It was revealed that increasing sulphide concentration led to decreased corrosion resistance due to adsorption of HS − on NAB surface (see eqn (12) and (13)). 114 Gravimetric measurements also indicated that in all sulphide-polluted media, the corrosion resistance of the alloy was lower than that in non-polluted solution, but the formation of a homogenous corrosion product film (mainly Cu 2 S) in the electrolyte containing 200 ppm sulphide could beneficially affect the corrosion resistance of the alloy. Furthermore, increasing sulphide concentration in the range of 20 to 100 ppm led to deterioration of corrosion properties.…”

“…114 It was reported that an increase in sulphide concentration was accompanied by a higher cavitation erosion mass loss rate, primarily due to mechanical damage promoting cavitation erosion deterioration. 114 Notably, corrosion-enhanced erosion was identified as the major cause of cavitation erosion damage, as selective phase attack of corrosion-sensitive phases (β′ and eutectoid microstructure of α + κ III ) was aggravated in solutions with sulphide concentration higher than 50 ppm, leading to considerable damage due to a brittle fracture mode. 114 This view was further supported by another report.…”