Abstract
In this work, the corrosion behavior and surface reactivity of as-cast and heat-treated nickel aluminum bronze casting alloy (UNS C95800) in 3.5 wt% NaCl solution is investigated under stagnant and flow conditions. Increasing flow rate conditions are simulated using a rotating disk electrode from 0 to 9000 revolutions per minute (rpm). Optical micrographs confirm the decrease in the phase fraction of corrosion-sensitive β phase in the microstructure of C95800 after annealing, which, in turn, enhances the corrosion resistance of the alloy. Electrochemical studies including open circuit potentiometry, potentiodynamic polarization, and electrochemical impedance spectroscopy are performed to assess the effect of flow rate and heat treatment on the corrosion of samples at 25 and 40 °C in 3.5 wt% NaCl solution. For both as-cast and heat-treated samples, increasing the flow rate (i.e., electrode rotating rate) linearly reduces the corrosion resistance, indicating that the metal dissolution rate is significantly affected by hydrodynamic flow. Increasing the solution temperature negatively impacts the corrosion behavior of the as-cast and heat-treated samples at all flow conditions.
Highlights
Copper alloys containing nickel and aluminum are referred to as nickel-aluminum bronze (NAB) and often contain 5–11 wt% aluminum [1]
The mechanical and corrosion behaviors of NABs are largely dependent on its chemical composition as well as the post-casting heat treatment of these alloys; many studies have been performed to assess the mechanical strength [5,6], wear resistance [7], fatigue [8], and corrosion behavior [9] of NABs as a function of their chemical composition and microstructure
The microstructure of the as-cast C95800 alloy is comprised of alpha (α) and beta (β) phases as well as a small fraction of intermetallic kappa (κ) phases, the fraction and distribution of which are highly dependent on the cooling rate after casting and the subsequent heat treatment
Summary
Copper alloys containing nickel and aluminum are referred to as nickel-aluminum bronze (NAB) and often contain 5–11 wt% aluminum [1]. Due to their mechanical and corrosion resistance properties, NABs have found many industrial applications, especially in the marine environment [2,3]. The mechanical and corrosion behaviors of NABs are largely dependent on its chemical composition as well as the post-casting heat treatment of these alloys; many studies have been performed to assess the mechanical strength [5,6], wear resistance [7], fatigue [8], and corrosion behavior [9] of NABs as a function of their chemical composition and microstructure. The phase distribution and microstructure of C95800 affect the corrosion performance of the alloy during its exposure to certain corrosive environments
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