Microstructure and properties of Ni–Ni3Si composites by directional solidification

Ni–Ni 3 Si composites are prepared by the Bridgman directional solidification technology under different growth conditions, aiming to improve the ductility of the Ni 3 Si compound and investigate the relationship between solidification microstructure and the properties. Microstructure of the Ni–Ni 3 Si hypoeutectic in situ composites transforms from regular lamellar eutectic to cellular structure then to dendritic crystal with the increase of the solidification rate. Ni–Ni 3 Si eutectic composites display regular lamellar eutectic structure at the solidification rate R =6.0–40.0 μm/s and the lamellar spacing is decreased with the increase of the solidification rate. Moreover, the Ni–Ni 3 Si hypoeutectic composites present lower micro-hardness than pure Ni 3 Si, which indicate Ni–Ni 3 Si hypoeutectic composites have higher ductility, whereas the ductility of the Ni–Ni 3 Si eutectic composites has scarcely been improved. This is caused by the formation of the metastable Ni 31 Si 12 phase in the Ni–Ni 3 Si eutectic composites.