Effect of swaging feed rate and annealing phenomena on tensile, fracture toughness and microstructural evolution of Zr-4 alloy

Abstract

Zirconium alloys are primarily used in nuclear applications as a cladding material due to its low neutron absorption, excellent mechanical strength, ductility, oxidation, and corrosion resistance properties. The effect of rotary-swaging feed rates (0.7 m/min, 1.25 m/min, and 2 m/min) and material-conditions (As-Received, Swaged, and Swaged+Annealed, 732 °C-3 h) on tensile, fracture toughness, and microstructural evolution of Zr-4 alloy were studied. Significant improvement has been observed in tensile strength (∼42%), ductility (∼37%), and fracture toughness (∼21%), especially in higher swaging (30%, ε=0.38, feed rate = 1.25 m/min) conditions. The ductility and fracture toughness (J-integral) were found maximum in swaged + annealed samples. The microstructural inhomogeneities are observed at centre and edge locations of swaged and annealed samples, investigated through EBSD. The in-depth microstructural mechanisms were explored through a transmission electron microscope (TEM) and X-ray diffraction analysis. The vital characteristic features such as dislocation-precipitate, dislocations-twin/grain boundary interactions, and ultrafine grain (UFG) evolution through dynamic recrystallization influences the strengthening mechanisms.