Microstructure and high-temperature mechanical properties of a nuclear Zircaloy-4 alloy fabricated by laser powder bed fusion

Additive manufacturing, particularly laser powder bed fusion (LPBF), offers transformative potential for fabricating complex components in nuclear reactor cores. However, the applicability of LPBF technology to specialized nuclear materials such as zirconium alloys, which are designed to withstand the elevated temperature extreme environments within reactors, remains insufficiently explored. In this work, Zircaloy-4 alloy was successfully fabricated via LPBF technology. The microstructure evolution and deformation behavior of the alloy were systematically investigated under uniaxial tensile loading at both room temperature (RT) and an elevated temperature of 380 °C. Furthermore, the α lath morphology, second phase precipitates (SPPs), and the type and configuration of dislocation were characterized before and after deformation. The results indicate that the microstructure in the LPBF-processed Zircaloy-4 alloy consists of epitaxially columnar grains containing fine α laths. Enrichment of Fe and Cr elements was observed at α lath boundaries, and nanoscale SPPs were distributed within α laths. In addition, the LPBF-processed Zircaloy-4 alloy exhibits outstanding mechanical strength (such as ultimate tensile strength, 700 MPa at RT and 368 MPa at 380 °C), outperforming ASTM standard (415 MPa at RT) and sheet samples (204 MPa at 380 °C), respectively. Meanwhile, fracture elongations reached 10.5 % at RT and 16.4 % at 380 °C. The moderate ductility is attributed to the activation of multiple slip and cross-slip systems, with α lath boundaries acting as sources of prismatic <a> and pyramidal <a + c> dislocations to coordinate plastic deformation. The exceptional strength originates primarily from the high density and entanglement of <a> and <a + c> dislocations, as well as from dislocation pinning by nanoscale SPPs. Additionally, the presence of <a> type dislocation loops further contribute to strength enhancement at 380 °C. This work demonstrates the feasibility of LPBF-processed Zircaloy-4 alloy for potential structural applications in 380 °C high temperature reactor environments, offering insights into the advancement of AM technologies in the nuclear industry.