Microstructure evolution and room temperature fracture toughness of an integrally directionally solidified Nb–Ti–Si based ultrahigh temperature alloy

Integrally directional solidification of an Nb–Ti–Si based ultrahigh temperature alloy was performed at 2000 °C with withdrawal rates varying from 2.5 to 100 μm s−1. The directionally solidified microstructure was composed of primary silicides and eutectic colonies that distributed evenly and aligned erectly along the growth direction. Both the average diameter and the lamellar spacing of eutectic cells decreased with increasing withdrawal rate. The room temperature fracture toughness was improved significantly by integrally directional solidification.