Localized Corrosion of Al-Based Amorphous-Nanocrystalline Alloys with Solute-Lean Nanocrystals: Pit Stabilization

Abstract

The localized corrosion resistance of several partially nanocrystalline Al-based metallic glasses was examined in fully amorphous, partially nanocrystalline, and fully crystalline microstructures. In all of the alloys examined, Al90Fe5Gd5 , Al85Fe7Gd8 , Al90Co3Ce7 , and Al87Ni7Gd6 , the pitting potential remained elevated relative to pure Al in all partially nanocrystalline states. The pit growth kinetics of the alloys, which were examined using an artificial pit technique, showed that the anodic kinetics were ennobled and the cathodic kinetics were faster than those of pure Al. The pit stability product was also found to be lower for Al than for the fully amorphous alloys. Artificial pit growth experiments also showed that the difference in the repassivation potential between pure Al and the amorphous alloys is not due to the differences in the potential dependence of the transition to tunneling. There was no significant difference between the pit growth kinetics of the fully amorphous and partially nanocrystalline states of the alloys. Because the nanocrystals do not affect the growth kinetics of large ( d≫nanocrystal radius) artificial pits, it is concluded that any effects nanocrystals have on the pitting resistance of alloys must be related to pit initiation or early growth.

Nanocrystals in Metallic Glasses

“…The resistance to pitting can be determined quantitatively from measurements of the pitting and repassivation potentials in anodic polarization scans. The pitting potential reflects a resistance to pit initiation and stabilization (Lucente and Scully, 2008). For all four amorphous alloys the repassivation potential remained unchanged when the fully amorphous alloys were partially devitrified.…”

“…The chemical inhomogeneities are not limited to the nanocrystal/amorphous matrix interface, but extend into the amorphous matrix due to gradients in solute concentrations that exist at least during the g r o w s t a g e s o f n a n o c r y s t a l s t h a t f o r m n o n-polymorphically. Studies on the corrosion behavior of nanocrystal-containing metallic glasses have been conducted so far for Fe-based, Gd 6 were exposed to 0.6 M NaCl electrolyte in an electrolytic cell to test the resistance to micrometer-scale pitting (Lucente and Scully, 2008). The resistance to pitting can be determined quantitatively from measurements of the pitting and repassivation potentials in anodic polarization scans.…”

Effect of prior laser microstructural refinement on the formation of amorphous layer in an Al86Co7.6Ce6.4 alloy

“…The Al-TM (transition metal)-RE (rare earth) family of amorphous alloys is particularly promising for corrosion resistant applications [1]. Due to their wide range of glass forming compositions and tuneable corrosion resistance, Al-Co-Ce alloys have attracted attention from corrosion protection engineers and scientists [2].…”

Amorphous layer formation in Al86.0Co7.6Ce6.4 glass-forming alloy by large-area electron beam irradiation

“…The Al-TM (transition metal) -RE (rare earth) family of amorphous alloys has been shown to be particularly promising for corrosion resistant applications [4] has attracted much attention from corrosion scientists and engineers alike. Recently, several researchers have investigated the corrosion behaviour of several Al-TM-RE amorphous alloys including Al-Fe-Gd, Al-NiGd, Al-Ni-Y and Al-Co-Ce [4][5][6].…”

“…Recently, several researchers have investigated the corrosion behaviour of several Al-TM-RE amorphous alloys including Al-Fe-Gd, Al-NiGd, Al-Ni-Y and Al-Co-Ce [4][5][6]. The critical pitting potential and pit growth behaviour of this family of amorphous alloys were shown to be improved compared to high purity, polycrystalline Al.…”