Effect of Sn on stacking fault energies in zirconium and its hydrides

Hydrogen embrittlement in Zr-alloy fuel cladding is a primary safety concern for water-based nuclear reactors. Here we investigated the stabilization of planar defects within the forming hydrides by Sn, the primary alloying element of Zircaloy-4 used in the cladding. In order to explain the formation of hydrides and planar defects observed in our experiments, we performed atomic-scale calculations focusing on the solute interactions with generalized stacking faults in hcp <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>α</a:mi></a:math>-Zr and fcc zirconium hydrides. Our calculations showed that an increase in Sn concentration leads to a stabilization of stacking faults in both the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>α</b:mi></b:math>-Zr and hydride phases. However, the solution enthalpy of Sn is lower in the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>α</c:mi></c:math>-Zr as compared to the other hydride phases, indicative of two competing processes of Sn depletion/enrichment at the Zr hydride/matrix interface. This is corroborated by experimental findings, where Sn is less soluble in hydrides and is mostly found trapped at interfaces and planar defects, indicative of stacking faults inside the hydride phases. Our systematic investigation enables us to understand the presence and distribution of solutes in the hydride phases, which provides a deeper insight into the microstructural evolution of such alloy's properties during its service lifetime.