Numerical simulation of iron whisker growth with changing oxygen content in iron oxide using phase-field method

Abstract

Phase-field method is used to simulate the growth of iron whiskers on a gas–solid interface by changing the oxygen content in iron oxide. Results show that oxygen content significantly influences not only the crystal lattice but also the diffusion direction of iron ion vacancies and iron ions, wherein iron ions diffuse to low-oxygen-content areas and iron ion vacancies diffuse to high-oxygen-content areas. The catastrophic swelling of the micro-area volume and the growth of iron whiskers are caused by the enrichment of iron ions in low-oxygen-content areas. The simulation revealed the effects of the reduction rate and the oxygen potential of gas. Iron whiskers are longer and stronger when the oxygen potential of reducing gas decreases from −133.96kJ·mol−1 to −160.01kJ·mol−1 or when the reduction rate increases from 6.3×10−3mol·s−1 to 7.3×10−3mol·s−1. Iron whiskers can appear earlier with a low oxygen potential or a high reduction rate. Both oxygen potential and reduction rate promote the nucleation and growth of iron whiskers.