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 ra pidly 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-p hase has undergone the initial stages of beta-->omega transformation, as indicated by circular diffuse scattering in SAD patterns. After agi ng at room temperature, the crystalline omega-phase is formed in the b eta-matrix, and the omega particle size increases with increasing agin g time. With prolonged aging, the equilibrium alpha-phase can be obser ved 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 neve r an ideal hexagonal structure.