Directional solidification of hypereutectic Nb-Si-Ti alloy: Influence of drawing velocity change on microstructures

In this study, the microstructural characteristics of directionally solidified (DS) hypereutectic Nb-Si based alloys were investigated. The abrupt acceleration and deceleration of directional solidification were designed to explore the influence of drawing velocity change on microstructure. Results show that the microstructure can be changed by abrupt deceleration, which provides a new possibility to control the properties of DS Nb-Si based materials. The abrupt decelerated solidification for the 17 at.% Si composition is able to scatter the primary silicide slabs, and irregular octahedral primary silicides are finally formed. For the 16 at.% Si composition, the solidification with a constant velocity of 100 mm/min, pseudo-eutectic can be obtained, in which the primary silicides can be eliminated within a certain distance of 4 mm. However, due to the inheritance of the microstructure, the pseudo-eutectic can not be obtained at the same drawing velocity by acceleration from 10 mm/s to 100 mm/s. The directionally solidified microstructure of hypereutectic Nb-Si alloy consists of eutectic and halo microstructures (primary silicides and Nbss shell). Two different growth modes of halo microstructures were identified by EBSD investigations. (C) 2020 Elsevier B.V. All rights reserved.