skip to main content

Title: Surface Film Formation on Al-V Alloys with Far-From-Equilibrium Microstructure

Nanocrystalline supersaturated Al-V alloys produced by high-energy ball milling have been reported to exhibit enhanced corrosion resistance and mechanical properties compared to commercial Al alloys. Corrosion of passive alloys such as Al-V alloy relies on the characteristics of the surface film, which is studied using scanning/transmission electron microscopy and time-of-flight secondary ion mass spectrometry. The effect of microstructure and composition on the surface film has been investigated after different immersion periods (30 min, 2 h, and 1 day) in 0.1 M NaCl. The surface film was complex and composed of oxidized Al and V. The heterogeneous surface film was observed due to the presence of secondary phases and initiation of localized corrosion. The void formation was observed beneath the surface film that would potentially cause pitting corrosion. The generation of nano-sized voids was dependent on grain orientation. Compared to pure Al, the chloride penetration is suppressed in Al-V alloys. The effect of composition and microstructure on surface film formation and attendant corrosion behavior is discussed herein.

more » « less
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
The Electrochemical Society
Date Published:
Journal Name:
Journal of The Electrochemical Society
Page Range / eLocation ID:
Article No. 031508
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Al-V alloys produced via high-energy ball milling have been reported to show simultaneous improvement of corrosion resistance and mechanical properties compared to traditional Al alloys. In these alloys, V content plays a crucial role in increasing or decreasing corrosion resistance. Therefore, the effect of V and microstructure on corrosion of high-energy ball milled and subsequently spark plasma sintered Al-xV alloys (x = 2, 5, 10 at.%) has been studied. Cyclic potentiodynamic polarization tests and electrochemical impedance spectroscopic analysis revealed that increments of V content up to 5 at. % enhanced the corrosion resistance of the alloy. However, highly heterogeneous microstructure in Al-10 at.%V resulted in significant localized corrosion over the immersion time. The electrochemical impedance spectroscopy studies over 14 days of immersion revealed underlying corrosion mechanisms.

    more » « less
  2. Al x CoCrFeNi High Entropy Alloys (HEAs), also referred to as multiprincipal element alloys, have attracted significant interest due to their promising mechanical and structural properties. Despite these attributes, Al x CoCrFeNi HEAs are susceptible to phase separation, forming a wide range of secondary phases upon aging, including NiAl–B2 and Cr-rich phases. Controlling the formation of these phases will enable the design of age-hardenable alloys with optimized corrosion resistance. In this study, we examine the critical role of Al additions and their concentration on the stability of the CoCrFeNi base alloy, uncovering the connections between Al composition and the resulting microstructure. Addition of 0.1 mol fraction of Al destabilizes the single-phase microstructure and results in the formation of Cr-rich body-centered-cubic (bcc) phases. Increasing the composition of Al (0.3–0.5 mol fraction) results in the formation of more complex coprecipitates, NiAl–B2 and Cr-rich bcc. Interestingly, we find that the increase of the Al content stimulates the formation of NiAl–B2 phases, increases the overall density of secondary phases, and influences the content of Cr in Cr-rich bcc phases. Density functional theory calculations of simple decomposition reactions of Al x CoCrFeNi HEAs corroborate the tendency for precipitate formation of these phases upon increased Al composition. Additionally, these calculations support previous results, indicating the base CoCrFeNi alloy to be unstable at low temperature. This work provides a foundation for predictive understanding of phase evolution, opening the window toward designing innovative alloys for targeted applications. 
    more » « less
  3. Abstract

    Supersaturated solid solutions of Al and corrosion-resistant alloying elements (M: V, Mo, Cr, Ti, Nb), produced by non-equilibrium processing techniques, have been reported to exhibit high corrosion resistance and strength. The corrosion mechanism for such improved corrosion performance has not been well understood. We present a fundamental understanding of the role of V in corrosion of an Al-V alloy, which will provide a theoretical background for developing corrosion-resistant Al alloys. High-energy ball milling of the elemental powder of Al and V produced an in situ consolidated Al-V alloy, which exhibited high solid solubility of V. The corrosion resistance of Al-V alloy was significantly higher than that of pure Al, which was attributed to the (1) enrichment of V at the passive film/substrate interface, (2) incorporation of V into the passive film, and (3) deposition of V on the iron-containing cathodic particles and therefore, retardation of cathodic reaction.

    more » « less
  4. Abstract

    Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al51Ge35Ni14as the best glass forming composition with a critical cooling rate of 104 K/s.

    more » « less
  5. Abstract

    Ion-beam irradiation of an amorphizable material such as Si or Ge may lead to spontaneous pattern formation, rather than flat surfaces, for irradiation beyond some critical angle against the surface normal. It is observed experimentally that this critical angle varies according to many factors, including beam energy, ion species and target material. However, many theoretical analyses predict a critical angleθcof 45independent of energy, ion and target, disagreeing with experiment. Previous work on this topic has suggested that isotropic swelling due to ion-irradiation may act as a stabilization mechanism, potentially offering a theoretical explanation for the elevated value ofθcin Ge compared to Si for the same projectiles. In the present work, we consider a composite model of stress-free strain and isotropic swelling with a generalized treatment of stress modification along idealized ion tracks. We obtain a highly-general linear stability result with a careful treatment of arbitrary spatial variation functions for each of the stress-free strain-rate tensor, a source of deviatoric stress modification, and isotropic swelling, a source of isotropic stress. Comparison with experimental stress measurements suggests that the presence of angle-independent isotropic stress may not be a strong influence onθcfor the 250 eV Ar+Si system. At the same time, plausible parameter values suggest that the swelling mechanism may, indeed, be important for irradiated Ge. As secondary results, we show the unexpected importance forθcof the relationship between free and amorphous-crystalline interfaces in the thin film model. We also show that under simple idealizations used elsewhere, spatial variation of stress may not contribute toθcselection. These findings prompt modeling refinements which will be the focus of future work.

    more » « less