Orientation relationships, interface structures, and mechanical properties of directionally solidified MoSi2/Mo5Si3/Mo5Si3C composites

• DS MoSi2/Mo5Si3/Mo5Si3C composites exhibit a fine script lamellar microstructure.
• Mo5Si3C forms interconnected networks and divides MoSi2 matrix into small regions.
• The orientation relationship is selected to effectively accommodate lattice misfits.
• Three-phase composites have higher yield strength than two-phase counterpart.

The microstructures, orientation relationships, and high-temperature deformation behavior of directionally solidified (DS) ingots of MoSi2/Mo5Si3/Mo5Si3C three-phase eutectic composites were investigated. The DS three-phase composites exhibit a fine and homogeneous script lamellar microstructure. Mo5Si3 and Mo5Si3C individually form interconnected networks that extend in the growth direction (GD) of the MoSi2 matrix and maintain [11¯0]MoSi2, [001]Mo5Si3[001]Mo5Si3, and [0001]Mo5Si3C[0001]Mo5Si3C approximately parallel to the GD. High-temperature strength is higher in the DS three-phase composite than in the binary two-phase counterpart, especially below 1200 °C. This is mainly because of MoSi2 matrix refinement and the presence of the strengthening phase Mo5Si3C. The observed orientation relationship between component phases is discussed in relation to lattice misfits.