Mechanism of creep deformation with evolution of microstructure and texture of Zr-2.5Nb alloy

The creep behavior of Zr-2.5Nb alloy has been studied in the temperature range of 350-450 degrees C and stress range of 82-283 MPa using constant load creep tests. The creep parameters such as creep activation energy WO, and stress exponent (n) have been determined following the temperature-compensated power law, and are found to be 247 +/- 5.0 kJ/mol and 5.5 +/- 0.27, respectively. The value of threshold stress was obtained by varying the stress exponent. This subsequently led to evaluation of the true stress exponent (similar to 4.02 +/- 0.19) and true activation energy (similar to 116 kJ/mol), which is dose to that for lattice-self diffusion of zirconium alloys. The results of creep data suggest that rate-controlling mechanism of creep is dislocation climb. Basal component (0002) along transverse direction was observed in the as-received condition, whereas in the sample creep tested at 450 degrees C, the components are (0002) and (10 (1) over bar0). Similar type of microtexture evolution has been observed in the samples subjected to creep failure or interrupted creep tests at 450 degrees C under a constant stress of 82 MPa. The microtexture components observed in the creep tested samples were {0002} <11<(2)over bar>0> and <11<(2)over bar>0> fiber. As such, there is no change in microtexture components for interrupted creep tests performed at different stages of creep. Microstrucutral observations of the creep tested samples were characterized by using the transmission electron microscopy (TEM) to reveal the dislocation substructures, and niobium rich precipitate particle of beta-(Nb, Zr) in the alloy.