Study of the role of B addition on the microstructure of the Nb-24Ti-18Si-8B alloy

The effects of B on the microstructure and hardness of the as cast and heat treated Nb-24Ti-18Si-8B (at%) alloy (TT1) were studied. There was macrosegregation of B, Si and Ti. The microstructure of the alloy in the as cast and heat treated conditions consisted of the (Nb,Ti)ss, (Nb,Ti)3Si and the tetragonal T2 silicide. The Ti and B exhibited opposite partitioning behaviour in the (Nb,Ti)ss, and the (Nb,Ti)3Si and T2 silicides and the solubility of B in T2 was higher than that in (Nb,Ti)3Si. The addition of B stabilised the T2 silicide as the primary phase and the (Nb,Ti)ss + T2 eutectic. The synergy of B and Ti contributed to the retention of the hardness of the (Nb,Ti)ss. The hardness of the T2 silicide in TT1-AC was the same as that of the unalloyed Nb5Si3.