Primary dendrite arm spacing and preferential orientations of the Ni–Si hypereutectic composites at different solidification rates

Abstract

A hypereutectic alloy is a metallic alloy which has a composition beyond the eutectic point. As the temperature of a non-eutectic composition is lowered, the liquid mixture will precipitate one component of the mixture before the other. In the present paper, Ni–Si hypereutectic composites at the different solidification rates were prepared by a modified Bridgman directional solidification technique. Primary dendrite arm spacings of the Ni–Si hypereutectic composites were calculated at the different solidification rates according to Kurz–Fisher model, Hunt–Lu model and Trivedi model, respectively. Relation between micro-hardness and primary dendrite arm spacing was obtained. The selected area electron diffraction was adopted to confirm the preferential orientation of Ni–Si hypereutectic composites. It is found that primary dendrite arm spacing of the experimental results are very close to Kurz–Fisher model, while deviating from that predicted from Hunt–Lu model and Trivedi model. Therefore, Kurz–Fisher model is much more suitable to describe primary dendrite arm spacing of Ni–Si hypereutectic.