Effects of boron on the microstructure and thermal stability of directionally solidified NiAl–Mo eutectic

Microalloying with 0.01at.% B decreases the range of growth speeds over which a well-aligned fibrous eutectic microstructure can be obtained in directionally solidified NiAl–Mo. Compared to the undoped alloy, the size/spacing of the Mo fibers is larger, and the fiber density smaller, in the B-doped alloy. Annealing at 1400°C coarsens the fibers by a mechanism involving fault migration and annihilation driven by diffusion along the fiber–matrix interface. The coarsening kinetics, given by the decrease in Mo fiber density with time, is exponential, and microalloying with B decreases the coarsening rate.