Cross-sectional helium irradiation revealing interface-controlled bubble evolution in Cr/CrAlSiN multilayer coatings on zirconium alloys

• Cross-sectional helium irradiation reveals the interface-controlled evolution of helium bubbles in Cr/CrAlSiN multilayer coatings on zirconium alloys. • The Cr/CrAlSiN multilayers show spatial modulation of bubble size and density, with interfaces acting as sinks that suppress bubble coalescence and swelling. • A nitrogen-enriched ZrN interlayer forms spontaneously at the Cr/AlSiN-Zr interface, preventing large cavity formation and enhancing interfacial stability under irradiation at 750°C. • Compared to monolayer Cr coatings, Cr/CrAlSiN multilayers exhibit superior irradiation resistance due to dynamic helium redistribution and stable coating-substrate interfaces. The irradiation stability of Cr-based protective coatings on zirconium alloys is critical for the development of accident-tolerant fuel claddings. However, conventional surface irradiation often produces shallow, nonuniform damage, obscuring interfacial behavior. In this study, we perform cross-sectional He 2+ irradiation to directly examine the interfacial response and He bubble evolution across Cr monolayer and Cr/CrAlSiN multilayer coatings on Zr substrates. Irradiation was carried out at 500 and 750 °C to doses of 2–3 displacements per atom (dpa), enabling a direct comparison of temperature-dependent microstructural evolution. In the Cr monolayer, He implantation produced a homogeneous distribution of nanoscale bubbles throughout the damaged region and large cavities at the Cr/Zr interface, indicating severe Kirkendall-type voiding and interfacial decohesion at elevated temperature. In contrast, the Cr/CrAlSiN multilayer exhibited a periodically modulated bubble distribution, with bubble fragmentation and transformation into nanoscale platelets at CrAlSiN interfaces. A N-enriched Zr(N) interlayer formed spontaneously at the CrAlSiN/Zr interface, effectively suppressing bubble accumulation and interdiffusion. The nanochannel interfaces acted as He sinks and diffusion barriers, enhancing interfacial bonding and mitigating swelling. This work demonstrates that cross-sectional ion irradiation is a powerful approach for probing interfacial stability in multilayer systems, offering new insights into He-defect interactions and radiation tolerance engineering at buried interfaces. The findings highlight the potential of Cr/CrAlSiN multilayers as advanced coating architectures for high-temperature nuclear environments.