Comprehensive Phase Field Study on Directionally-Solidified MoSi<sub>2</sub>/Mo<sub>5</sub>Si<sub>3</sub> Eutectic Alloy

Abstract

MoSi2/Mo5Si3 eutectic composites have been considered as one of the promising candidates for ultra-high temperature structural applications owing to their high melting point, good oxidation resistance, and low mass density. Their mechanical properties can be improved by controlling the eutectic structure (i.e. script lamellar structure) in directional solidification. It is important to elucidate the dominant factors underlining the unique pattern formation. We conducted a comprehensive phase field study to examine the influence of various factors on the MoSi2/Mo5Si3 eutectic microstructure with complicated morphology. First, the inclined lamellae have been attributed to the minimization of elastic strain energy due to the lattice mismatch between MoSi2 and Mo5Si3, which are partially relaxed by forming semi-coherent phase boundaries. Second, the maze-like pattern on the horizontal cross-section appeared when a two-fold anisotropy of interfacial energy is superimposed on the MoSi2/Mo5Si3 boundary. Third, the random and intersected lamellae have been obtained by assuming the instability of the solid-liquid interface and introducing successive nucleation of Mo5Si3 phase. These findings provide guidance for manipulating the eutectic structure and act as footsteps for further theoretical investigation.