Decoupling the role of stress and corrosion in the intergranular cracking of noble-metal alloys

Abstract

Intergranular stress-corrosion cracking (IGSCC) is a form of environmentally induced crack propagation causing premature failure of elemental metals and alloys. It is believed to require the simultaneous presence of tensile stress and corrosion; however, the exact nature of this synergy has eluded experimental identification. For noble metal alloys such as Ag-Au, IGSCC is a consequence of dealloying corrosion, forming a nanoporous gold layer that is believed to have the ability to transmit cracks into grain boundaries in un-dealloyed parent phase via a pure mechanical process. Here using atomic-scale techniques and statistical characterizations for this alloy system, we show that the separate roles of stress and anodic dissolution can be decoupled and that the apparent synergy exists owing to rapid time-dependent morphology changes at the dealloyed layer/parent phase interface. We discuss the applicability of our findings to the IGSCC of important engineering Fe- and Ni-based alloys in critical applications.

Computational modeling of pitting corrosion

“…The model captures changes in structural (damage) and mechanical properties (different elastic modulus, and porosity) taking place at the electrolyte-bulk interface and their influence on corrosion evolution and stress corrosion cracking. This type of nonlocal model leads to a diffuse layer at the pit boundary which happens to match well the experimentally observed microstructure in several alloys (Li et al, 2016(Li et al, , 2018Badwe et al, 2018;Vallabhaneni et al, 2018;Yavas et al, 2018). PF models of pitting corrosion (Mai et al, 2016;Ansari et al, 2018;Chadwick et al, 2018;Mai and Soghrati, 2018;Nguyen et al, 2018;Tsuyuki et al, 2018) also use a diffuse region instead of a mathematically sharp transition between the electrolyte and the metal, and the governing equations in this case consist of two coupled PDEs in which the "thickness" of the diffuse layer introduces a length scale in the model.…”

“…Corrosion is a type of damage that progresses in the material by dissolution, and it influences the mechanical behavior in some significant ways (Pantelakis et al, 2000;Chen et al, 2005;Song et al, 2005;Liu et al, 2008b;Zhong et al, 2017;Li et al, 2018). Recent experiments report a small-scale distributed damage in a thin (micrometer-scale) layer near the corrosion front referred to as the "diffuse corrosion layer" (DCL), with degraded mechanical properties and gradual changes in chemical composition (Li et al, 2016(Li et al, , 2018Badwe et al, 2018;Vallabhaneni et al, 2018;Yavas et al, 2018). The nonlocality of PD models allows to easily capture the distributed damage in the DCL and its evolution (Chen and Bobaru, 2015;Jafarzadeh et al, 2018b).…”

Topology evolution during coarsening of nanoscale metal network structures

“…Nanoscale metal network materials made by dealloying, and notably nanoporous gold (NPG), are under investigation as model systems for fundamental studies of small-scale plasticity [1]. These studies have provided insights into the impact of size [2][3][4][5][6][7] and of surface effects [8][9][10] on small-scale plasticity and they highlight the role of nanoporosity in stress corrosion cracking [11,12]. The discussion tends to focus on the ligament size, L, and on the solid (volume) fraction, ϕ, as the defining microstructural parameters.…”

Deciphering atomistic mechanisms of the gas-solid interfacial reaction during alloy oxidation

“…While substantial efforts have been exerted to decouple the mechanical and chemical factors in macroscale corrosion phenomena (16), little is known about their initial entanglement at the nanoscale to atomic scale. For the technologically important Ni-Al alloys, attempts have been made to determine the atomic structure of ultrathin surface layer formed on -NiAl under ideal conditions (17,18).…”