Microstructural evolution in rapidly solidified Ti-7.5 Mn-0.5 B alloy

A Ti-7.5 Mn-0.5 B (wt%) alloy has been prepared by consolidation of rapidly solidified alloy fibres. A homogeneous distribution of fine TiB particles has been obtained in the consolidated alloy. TEM examination of the microstructure of the consolidated alloy shows that the beta-phase has undergone the initial stages of beta-->omega transformation, as indicated by circular diffuse scattering in SAD patterns. After aging at room temperature, the crystalline omega-phase is formed in the beta-matrix, and the omega particle size increases with increasing aging time. With prolonged aging, the equilibrium alpha-phase can be observed at the TiB/beta interface. The formation of metastable omega-phase at room temperature has been discussed with respect to thermodynamics and anomalous diffusion in b.c.c. titanium. In addition, the diffuse scattering exhibited by the b.c.c. beta-phase indicates that the omega-phase formed in b.c.c. alloys is possibly always trigonal and is never an ideal hexagonal structure.