Crystallization behavior of amorphous Cu48Ti52: Formation of an intermediate long-period superlattice phase

Amorphous Cu48Ti52 crystallizes during continuous heating by a two-step process involving initial polymorphic transformation to a long period superlattice structure followed by decomposition to the equilibrium phases. From TEM lattice fringe imaging and diffraction data, an antiphase boundary (APB) model for the superlattice structure based on the equilibrium CuTi phase is proposed. The antiphase boundaries have a structure related to the minority equilibrium phase CuTi2. During longer anneals, oriented precipitates of CuTi2 form in the CuTi matrix with an orientation relationship rotated 90° from that of the APB structure. The reorientation minimizes strain energy between the lattices.