Influence of annealing on crucible-free float zone melted LaB6-TiB2 composites

Polycrystalline and textured eutectics LaB6-TiB2 were obtained by the floating zone melting (FZM) method for powders using polycrystalline (PC) and (111) single crystalline (MC) seeds. The phase composition, microstructure, crystallographic orientation, residual stresses and mechanical characteristics in PC and MC composites after FZM process and their changes during annealing were studied. It is shown that the annealing temperature and the exposure time necessary to achieve the equilibrium eutectic phase and optimum mechanical properties in PC composites are lower than in the MC ones. Crack resistance and hardness in PC and MC composites after FZM process are smaller than the values in the equilibrium state and this difference is due in part to the residual stresses in both phases. It is established that under optimal annealing conditions, it is possible to substantially increase the mechanical characteristics of PС and MC eutectics. Fracture resistance rises in 1.5-1.6 times and hardness from 14 to 15 GPa to 25 and 27 GPa in MC and PC composites, respectively.