Growth of semicoherent TiFe nanoparticles in β-Ti matrix in the Ti₇₃Fe₂₇ rapidly quenched ribbon

A thin Ti₇₃Fe₂₇ ribbon was prepared by rapid quenching from the melt. The as-quenched ribbon was in a metastable condition with a small amount of nanoparticles of TiFe, of a size of 138 ± 31 nm, embedded in the β-Ti matrix. The β-Ti matrix was supersaturated with Fe, and the fraction of the matrix was higher than that in the equilibrium state. High-resolution imaging of the interface of the TiFe/β-Ti showed that a periodic array of dislocations were present in the interface to accommodate the lattice mismatch. The spacing between the dislocations in the as-quenched specimen was 5.0 ± 0.5 nm. When the ribbon was heated to 700 °C, growth of the TiFe nanoparticles to a size of 228 ± 37 nm took place in the β-Ti matrix. The amount of β-Ti was reduced, as well as the Fe content in β-Ti. The interface between the TiFe and β-Ti remained semicoherent, except that the spacing between the interfacial dislocations was reduced to 3.5 ± 0.6 nm. The persistence of the semicoherent interface was ascribed to the same crystal structure and close lattice parameters shared by TiFe and β-Ti. The growth kinetics of the TiFe nanoparticles during heating was examined based on the modified theory of isothermal heating. It can be considered to be controlled by the diffusion of Fe atoms in the β-Ti matrix to the TiFe phase. Prolonged heating of the ribbon below the eutectoid temperature led to partial transformation of β-Ti to α-Ti.