Structure--Property Correlation of Zirconium-Base Alloys

Zirconium alloys, because of their unique combination of high strength, good corrosion resistance in water and low capture cross-section for thermal neutrons, have become attractive for use as structural materials in the nuclear industry. Presently, Zircaloy-2 and Zircaloy-4 find wide application as fuel and pressure tube materials for water cooled power reactors. To understand how the various alloying elements of Zircaloy, namely Sn, Fe, Cr and Ni, affect the mechanical properties, a programme has been initiated to evolve a correlation between chemistry, microstructure and mechanical properties of Zr-alloy containing various amounts of Sn, Fe and Cr. In the present investigation, mechanical properties of Zr-alloys with various addition of Sn, Fe and Cr have been determined at 300 and 573K in various metallurgical conditions such as recrystallised annealed, beta -quenched, tempered and alpha -annealed conditions. The study revealed that the reduced Sn content did not affect the mechanical properties as the reduced Sn leads to formation of fine precipitates. The mechanical properties were not altered drastically with the low level of Fe and Cr concentrations studied. Cold work and alpha -annealing after beta -quenching resulted in the growth and redistribution of second phase particles. Metallographic studies showed that particle distribution was not uniform. A TEM investigation of the alloys has also been undertaken to study the details of microstructure developed during various heat-treated conditions. It has been found that the beta -quenched samples exhibit the most uniform microstructure consisting of acicular alpha phase with lath boundary enriched by solute element and fine intermetallic particle formation. The observed microstructural features together with the mechanical properties data have been compared with the available mechanical properties and microstructure of Zircaloy. 26 ref.--AA