An examination of the use of the Modified Jogged-Screw model for predicting creep behavior in Zircaloy-4

The alloy Zircaloy-4 is used primarily as a structural material in nuclear reactors. A thorough understanding of the thermal creep response of such materials is essential to enable accurate forecasting of material behavior during both service and long-term storage. To this end, the Modified Jogged-Screw model, originally developed to predict steady-state creep rates in γ-TiAl, has been applied to Zircaloy-4. This work provides a more complete database for model validation through creep testing of several Zircaloy-4 specimens over a range of stress and temperature conditions. Bright-field scanning transmission electron microscopy was used to observe the substructure and quantify the model parameters important to the Modified Jogged-Screw model. These observations were used to confirm the applicability of the proposed model and assess the sensitivity of the model parameters to test conditions. The increased availability of statistics for model parameters as a result of substructural observation will elucidate the strengths and weaknesses of the model as previously proposed.