Measurement and investigation of mechanical properties of a partial oxide dispersion strengthened Zircaloy-4 tube via an instrumented indentation test

The formation of a partial oxide dispersion strengthened (here denoted as P-ODS) layer on the surface of a Zircaloy-4 (Zry-4) tube is regarded as one of the effective ways to increase the strength of the Zry-4 tube at a bulk scale. This consequently enhances the resistance to ballooning and rupture under accident conditions. In this study, the mechanical properties such as the yield strength of a P-ODS Zry-4 tube at local scale were investigated by micro instrumented indentation testing (IIT). The P-ODS layer was formed on the surface of the Zry-4 tube by a laser beam scanning (LBS) method that uses Y2O3 particles. The IIT was performed at a cross-sectional plane of the P-ODS Zry-4 tube using a spherical indenter. Several regions, including the base Zry-4 tube and P-ODS layer, were considered as indentation points. As a result, the mechanical properties of the P-ODS Zry-4 tube at the local scale were effectively obtained from the IIT. Considerable strength enhancement of the P-ODS layer was observed by comparing with the base Zry-4 tube. Furthermore, the strength enhancement was studied using microstructure-based strengthening models such as Orowan and Hall-Petch to predict the amount of strengthening theoretically. From the suggested strengthening models, the strengthening of the P-ODS layer was effectively investigated, and the results can be useful for both fabricating and simulating the P-ODS Zry-4 tube.