Atomistic Modeling of Voiding Mechanisms at Oxide/Alloy Interfaces

Abstract

For the first time, voiding mechanisms resulting from the condensation of atomic vacancies injected at oxide/alloy interfaces by the growth of oxide layers have been studied by means of periodic density functional theory (DFT) calculations. Several interfaces were built by superimposing ultrathin films of alumina on the γ-TiAl(111) surface, and their relative stabilities were compared by calculating the interface energy variation. The formation energy of single Ti or Al vacancies and clustered and dispersed ensembles of 2Ti + 1Al or 2Al + 1Ti vacancies injected into the alloy were calculated. The results show that it is easier to inject the vacancies into the oxide/alloy interface than into the bare alloy surface and into the bulk alloy. The injected vacancies, trapped at the oxide/alloy interface, condense in the topmost plane of the alloy to form 2D clusters. The minimization of the coordination number of the vacancies with metal atoms of the alloy and O atoms of the overlaying oxide favors vacancy condensation and interfacial voiding. The data are relevant for a detailed understanding of the adherence and breakdown of protective oxide films and the lifetime of metallic materials.

Early and transient stages of Cu oxidation: Atomistic insights from theoretical simulations and in situ experiments

“…For such reasons, simulation on multiple component systems such as alloy is much more challenging than single component models. Theoretical studies of alloy system is either limited in the small scale at the framework of DFT calculations [146], or at the level of grain boundaries with less atomistic information [147,148]. Force field simulations of alloy models is still at its early stage [149].…”

Understanding the interaction of thiosulfate with Alloy 800 in aqueous chloride solutions using SECM

“…An advantage of SECM is its capability to probe charge transfer occurring nonuniformly at interfaces [13,14]. Scanning reference electrode technique (SRET) has been used for determination of the potential distribution on corroding surfaces [15][16][17][18][19][20] and scanning tunneling microscope (STM) is a technique to study corrosion at micro-and nano-scale [21][22][23][24]. Zhu et al [10] investigated the impact of tensile and compressive stress on reactivity of the Alloy 800 C-ring sample using SECM and found that both tension and compression increased the localized surface reactivity, indicating corrosion susceptibility of Alloy 800 under stress in thiosulfate-contained chemistries.…”

“…Mott-Schottky measurements were also used to investigate the electric properties as well as the susceptibility to the presence of chloride ions and tensile stress of passive films. Marcus et al investigated the passive film growth mechanism at nano scale using STM combined with molecular dynamics simulation [22,23,[26][27][28][29]. Limited studies of thiosulfate-chloride induced passivation degradation were performed using a combination of techniques [10].…”

Combined effects of surface oxidation and interfacial intermetallic compound growth on solderability degradation of electrodeposited tin thin films on copper substrate due to isothermal ageing

“…This is extensively accompanied by the nucleation and coarsening of oxide cavities as well as cracking, presenting potential weaknesses in the oxide microstructural integrity permitting liquid solder ingress into the metal/oxide interface. The evolution of the nanosized cavities into micron-sized, isolated voids imply a history of Ostwald ripening through the Kirkendall effect [30], where oxygen vacancies diffuse and supersaturate around existing void surfaces, subsequently into precipitation and further coalescence [31]. From 12 hr to 16 hr, the Sn thin film surface had attained full coverage of the rough 'oxide patch' morphology.…”