In this work, we present the development of directional solidification for a novel high-temperature Mo-20Si-52.8Ti (at.%) alloy using a modified Bridgeman type apparatus. The resulting alloy exhibits a two-phase microstructure consisting of a body-centered cubic solid solution BCCss and a hexagonal silicide (Ti,Mo)5Si3 phase with approximate volume fractions of 50% for each phase. The phases exhibit a crystallographic orientation relationship with (123)BCCss // (0001) (Ti,Mo)5Si3 planes and [111]BCCss // [112 ̅0](Ti,Mo)5Si3 direction. Different solidification velocities were imposed which revealed an inverse relationship between lamellae spacing and solidification velocities consistent with the Jackson-Hunt theory.

Mechanical characterization using Vickers indentation at room temperature demonstrated that the BCCss phase accommodates plasticity through dislocation mediation, while the silicide phase exhibits high hardness and brittleness, serving as a crack initiation site. Interestingly, crack propagation was arrested and deflected at the interface of the BCCss phase. Fracture toughness measurements via indentation testing yielded a fracture toughness value of 3.7 MPa√m for the silicide phase, somewhat higher than previously reported fracture toughness for Si- and Cr-based intermetallics. The directionally solidified (DS) specimens showed an enhancement in fracture toughness attributed to the increase in the BCCss phase length scale; thus, combining the ductile and hard phases resulted in a ductile phase toughened intermetallic composite. The findings open up new possibilities for the design and development of advanced intermetallic composites with improved mechanical performance and high-temperature stability.