Zirconium alloys: an ideal system for studying phase transformations

A wide variety of phase transformations of zirconium alloys has been reviewed in this paper. Some of the important general issues in the phase transformations research have been identified. The manner in which studies in zirconium alloys have contributed to the understanding of these issues have been discussed in this paper. The crystallography of martensitic transformations in this system has been briefly described and the observed morphological and substructural changes in the zirconium martensites have been rationalised. The influence of substructure on the strengthening contribution has also been examined. Morphological and crystallographic features of diffusional and mixed mode transformations have been studied with a view to examining whether the transformation mechanisms have characteristic imprints on these experimental observables. A brief account of the methodology of phase diagram analyses for predicting the transformation sequences has been included. The mechanism of the displacive ω transformation has been described and it has been shown that formation of ordered ω phases involve coupling of displacive and replacive ordering. The last section of this paper deals with amorphization and crystallization processes in zirconium alloys. (author)