In-situ nanoscopic observations of dealloying-driven local corrosion from surface initiation to in-depth propagation

A Kosari,H Zandbergen,F Tichelaar,P Visser,P Taheri,H Terryn,J.M.C Mol

doi:10.1016/j.corsci.2020.108912

Abstract

Dealloying is involved in materials science responsible for fabrication of nanoscale structures beneficially but for corrosion degradations detrimentally. Detailed understanding related to the latter is critical for designing corrosion-resistance alloys and dedicated inhibition systems. Thus, direct nanoscopic observations of nano-structural and compositional evolutions during the process are essential. Here using liquid phase-transmission electron microscopy (LP-TEM), for the first time, we show dynamic evolution of intricate site-specific local corrosion linked to intermetallic particles (IMPs) in aerospace aluminium alloys. To thoroughly probe degradation events, oxidation direction is controlled by purposefully masking thin specimens, allowing for observing top-view surface initiation to cross-sectional depth propagation of local degradations. Real-time capturing validated and supported by post-mortem examinations shows a dealloying-driven process that initiates at IMPs and penetrates into the depth of the alloy, establishing macroscopic corrosion pits. Besides, controversial mechanisms of noble-metal redistribution are finally elucidated.

Highlights

High-strength-to-weight ratio in aluminium alloys (AAs) is key to many transport industries like aerospace as it reduces dead-weight and energy consumption and beneficially increases loading capacity [1]
High angle annular dark field-scanning TEM (HAADF-STEM), taken at 0 min in the absence of the electrolyte, shows a large bright particle of Al2CuMg embedded in the alloy matrix
The digitally-magnified view of the rectangular region shown in Fig. 2b reveals that the initially-corroded zone (Region I) is finely porous in morphology whereas Region II has coarser porosities (15 nm < pore size < 20 nm)

Summary

Introduction

High-strength-to-weight ratio in aluminium alloys (AAs) is key to many transport industries like aerospace as it reduces dead-weight and energy consumption and beneficially increases loading capacity [1]. The main contributors to mechanical properties are nano-to microscale intermetallic compounds that are introduced to the aluminium-based systems by specific alloying followed by precipitation hardening processes [2,3,4,5,6] (Fig. 1 and Movie S1), but they are typically undesirably detrimental to the corrosion resistance [7]. Contemporary aerospace AAs benefit from a comprehensive metallurgical knowledge of tuning the microstructure towards desirable mechanical properties [8]. Complicated site-specific local degradation events that predominantly take place at surface intermetallic particles (IMPs) dispersed in the AAs matrix eventually lead to progressive pitting and intergranular corrosion [9].

Methods

Results

Conclusion