Effect of water and mercury quenching on microstructure and mechanical behavior of room temperature rolled Zircaloy-2

The present study investigates the effect of water and mercury quenching on the microstructural and mechanical behavior of room temperature rolled Zircaloy-2. Solution treatment of Zircaloy-2 at 1073 K followed by quenching in mercury and water has been performed prior to rolling. Different reduction from 25% to 85% of the quenched alloy and further characterization has been performed by tensile testing, Electron back scattered diffraction (EBSD) and Transmission Electron Microscopy (TEM). Enhanced tensile strength (745 MPa) after 85% rolling reduction was obtained compared to 389 MPa after water quenching. Rolling reduction results an increase in the dislocation density, thereby enhancing the mechanical strength. Initial deformation has been observed by the activation of extension twinning from EBSD microstructure. Twinning results the inclination of ‘c’ axis towards the normal direction which makes near basal grains orientation along the deformation direction. Due to hard orientation i.e. ‘c’ axis aligned along the loading direction, the grain fragmentation is heterogeneous. Grain fragmentation leads to improvement in the ductility with minimal loss in strength owing to rearrangement of dislocations after annealing at 400 o C for 30 minutes. By optimizing the annealing temperature (400 o C for 30 minutes), bulk ultrafine grained Zircaloy-2 have been produced in 85% room temperature rolled Zircaloy-2.