Metastable microstructures in rapidly solidified zirconium alloys

Zirconium alloys exhibit a wide variety of phase transformations. The present review outlines some aspects of phase transformations, which are encountered in rapidly solidified zirconium alloys. The possibility of solidification of unalloyed zirconium directly into the low temperature phase is examined and the role that solidification microstructure plays in modifying the β to α martensitic transformation in rapidly solidified material is discussed. Zirconium alloys undergo two types of displacive transformations, namely, the martensitic transformation and the ω transformation. The influence of rapid solidification on the transition from the martensitic to the ω transformation is also discussed. Addition of transition metals are known to depress the melting point of zirconium alloys very drastically. As a consequence, glass forming abilities of a number of binary and ternary zirconium alloys are quite strong. A number of zirconium based metal-metal amorphous alloys have been synthesized using rapid solidification. In recent years, this work has been extended to bulk metallic glasses, which usually contain a larger number of alloying elements. Crystallization of these glasses and quasi-crystalline phase formation in these systems is also discussed.