Abstract
Scanning Kelvin probe force microscopy was used to investigate the influence of microstructure on the corrosion behavior of nickel aluminum bronzes in ammoniacal and NaCl solutions as well as under potential control in Na2SO4. The results showed an inverse correlation between the measured Volta potential difference and the observed corrosion behavior. In other words, the phase with initially higher Volta potential was preferentially attacked whereas those with the lowest Volta potential difference values remained intact. This behavior suggests that Volta potential difference maps in air cannot be universally correlated with practical nobility or reactivity in solution, as proposed by other investigators. The implications of these findings are discussed.
Highlights
Nickel aluminum bronzes.—Nickel aluminum bronzes (NABs) are Cu-based alloys with a typical nominal composition of 10 wt% Al, 5 wt% Ni, and 5 wt% Fe.[1]
NABs solidify as a single body-centered cubic β-phase, at room temperature they consist of a Cu-rich face-centered cubic α-phase and several intermetallic compounds (IMCs) that some authors refer to collectively as κ-phase.[1]
The tensile strength (TS) and yield strength (YS) of the heat treated (HT) plate material approached those reported for cast NAB,[20] but with notably improved ductility
Summary
Nickel aluminum bronzes.—Nickel aluminum bronzes (NABs) are Cu-based alloys with a typical nominal composition of 10 wt% Al, 5 wt% Ni, and 5 wt% Fe.[1]. NABs solidify as a single body-centered cubic (bcc) β-phase, at room temperature they consist of a Cu-rich face-centered cubic (fcc) α-phase and several IMCs that some authors refer to collectively as κ-phase.[1] Ni, Fe, and Mn combine with aluminum to form the various κ-phases, extending the apparent stability range of the α field and retarding the formation of the deleterious γ2-phase from the decomposition of β.6 In this regard, β decomposes to α and γ2 during annealing or slow cooling below 565◦C, which has plagued binary α/β aluminum bronzes with more than 9.4% Al.[7]. Vasanth and Hays found that the presence of ammonia was especially detrimental, in agreement with the well-documented performance of Cu-based alloys in ammoniacal solutions.[21,22] Despite this evidence, there seems to be no consensus on a plausible SCC mechanism
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