Finite Element Model for Coupled Diffusion and Elastoplastic Deformation during High-Temperature Oxidation of Fe to FeO

Abstract

Solid-oxide iron-air batteries are an emerging technology for large-scale energy storage, but mechanical degradation of Fe-based storage materials limits battery lifetime. Experimental studies have revealed cycling degradation due to large volume changes during oxidation/reduction (via H2O/H2 at 800 °C), but degradation has not yet been correlated with the microstructural stress and strain evolution. Here, we implement a finite element model for oxidation of a Fe lamella to FeO (74% volumetric expansion), in a lamellar Fe foam designed for battery applications. Growth of FeO at the Fe/gas interface is coupled, via an oxidation reaction and solid-state diffusion, with the shrinkage rate of the Fe lamellar core. Using isotropic linear elasticity and plastic hardening, the model simulates deformation of a continuously growing FeO layer by dynamically switching “gas” elements into new “FeO” elements along a sharp FeO/gas interface. As oxidation progresses, the effective plastic strain and von Mises stress increase in FeO. Distribution of tensile and compressive stresses along the Fe/FeO interface are validated by oxidation theory and explain interface delamination, as observed during in operando X-ray tomography experiments. The model explains the superior stability of lamellar vs dendritic foam architectures and the improved redox lifetime of Fe-Ni foams.

An integrated analysis of transport, oxidation, and creep during oxidation of interior pores in SiC

“…It should be noted that the present simulation framework and analyses have similarities with previous works, which provide additional insights regarding the impact of oxide growth in various material systems 9–16 . The most extensive body of the literature that couples diffusion, growth, and mechanics pertains to oxide growth in thermal barrier coating systems 12–15 .…”

“…Thus, while numerical aspects of these analysis have commonality with the present approach, the underlying physics (and frequently, the geometry) is quite different from that presented here. Arguably, the most directly relevant work from the literature on oxidation of metals is that of Wilke and Durand 16 , who used a framework similar to that presented here to examine internal oxidation of an iron tube; the evolution of domain shape and resulting stress bear strong similarities to that presented here.…”

“…It should be noted that the present simulation framework and analyses have similarities with previous works, which provide additional insights regarding the impact of oxide growth in various material systems. [9][10][11][12][13][14][15][16] The most extensive body of the literature that couples diffusion, growth, and mechanics pertains to oxide growth in thermal barrier coating systems. [12][13][14][15] These analyses generally focus on the evolution of waviness in the oxide layer (i.e., rumpling, enabled by plasticity in the underlying metal) and disregard oxide creep.…”

Study on the growth mechanism of the internal oxide layer in 9% Ni cryogenic steel

“…This can be explained by the reasons as follows: volume expansion was inevitable during the oxidation process. Fe 3 O 4 and FeO were mainly oxides in the Ni-rich layer, as stated in Section 3.2, which had large oxidation volume expansion with 110% expansion from Fe to Fe 3 O 4 and 74% expansion from Fe to FeO, leading to the significant compressive stress during the oxidation process (Wilke and Dunand, 2020). However, the area fraction of Ni-Fe particles increased sharply from 65 to 90 min (Figure 8A), taking the place of the iron oxide matrix and decreasing the amount of iron oxide.…”

Prediction of Anisotropic Elastoplastic Instability with Rice’s Criterion in Plane Compression

“…Polymers, especially transverse anisotropic fiberreinforced polymers (7) , are sensitive to that form of instability. Even materials such as oxide layers that grow from a foam of iron in batteries offer analogous phenomena (8) .…”