Application of the large angle convergent beam electron diffraction technique to the characterisation of martensitic phases in Cu–Zn–Al alloys

Martensitic phases in Cu–Zn–Al alloys have close packed structures which can be described as a face centred tetragonal (fct) lattice into which stacking faults are periodically inserted every second or third close packed plane. The tetragonality c/a of the fct cell is an important parameter which is related to the martensitic transformation temperature to the parent B2 or L21 phase. When diffusion is allowed in the martensitic phases, a process of stabilisation takes place. This process results in an increase of the transformation temperature to the parent phase and involves changes in the tetragonality of the fct cell. In order to study the tetragonality of the martensitic phases in Cu–Zn–Al alloys, the large-angle convergent beam electron diffraction (LACBED) technique is used. Different LACBED patterns are obtained to find an adequate orientation for the determination of the tetragonality, and its evolution during stabilisation. The results are compared with X-ray measurements available in the literature. The accuracy of the method and its applicability to the study of stabilisation processes are discussed.