Microstructure and property of directionally solidified Ni–Si hypereutectic alloy

This paper investigates the influence of the solidification rate on the microstructure, solid/liquid interface, and micro-hardness of the directionally solidified Ni–Si hypereutectic alloy. Microstructure of the Ni–Si hypereutectic alloy is refined with the increase of the solidification rate. The Ni–Si hypereutectic composite is mainly composed of α-Ni matrix, Ni–Ni₃Si eutectic phase, and metastable Ni₃₁Si₁₂ phase. The solid/liquid interface always keeps planar interface no matter how high the solidification rate is increased. This is proved by the calculation in terms of M–S interface stability criterion. Moreover, the Ni–Si hypereutectic composites present higher micro-hardness as compared with that of the pure Ni₃Si compound. This is caused by the formation of the metastable Ni₃₁Si₁₂ phase and NiSi phase during the directional solidification process.