Effect of hydriding on the creep behavior of HANA-4 Zirconium alloy
2019
Abstract HANA-4 (High Temperature Alloys for Nuclear Applications) is Zr-1.5 Nb alloy developed by the Korea Atomic Energy Research Institute for advanced nuclear fuel cladding applications. In this work, the effect of hydriding on the biaxial creep behavior of HANA-4 alloy was studied through internal pressurization of closed end tubes by applying a range of hoop stresses (27 MPa–156 MPa) at two temperatures: 400 °C and 500 °C. Test specimens included two HANA-4 tubes hydrided using an electrolytic method with 387 ppm and 715 ppm of hydrogen, respectively, and non-hydrided HANA-4 tubes as the control sample. To understand the effect of hydriding on creep, steady state creep rates and stress exponents of the specimens were determined from the creep data. Furthermore, in situ X-ray diffraction (XRD) experiments were conducted on the hydrided HANA-4 specimens during heating to detect the dissolution limit of the hydride phase. On examining the results of the creep tests and the XRD experiments collectively, it is concluded that hydrogen while being fully dissolved into the solid solution enhances the creep rate of HANA-4 tubes. On the other hand, hydrogen present, even partially, as hydride phase at the creep test temperature lowers the creep rate. The rate controlling mechanisms of creep in HANA-4, however, remained unchanged as noted from similar stress exponents of the hydrided and non-hydrided specimens. The rationale behind these observations is explained based up on models predicting the interaction of dislocations with hydrogen and hydride phase.
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