Zr-4 alloy tubes, as the primary cladding material in nuclear reactor cores, face the critical challenge of oxidative attack in 1200 °C steam environments. To address this issue, high-temperature oxidation-resistant coatings fabricated via extreme high-speed laser cladding (EHLA) present a promising mitigation strategy. In this study, Y₂O₃-modified (0.0–5.0 wt.%) Cr/FeCrAl composite coatings were designed and fabricated on Zr-4 substrates using the EHLA process, followed by systematic investigation of Y doping effects on coating microstructures and steam oxidation resistance (1200 °C, H₂O atmosphere). Experimental results demonstrate that Y₂O₃ doping remarkably enhanced the oxidation resistance, with optimal performance achieved at 2.0 wt.% Y₂O₃ (31% oxidation mass gain compared to the substrate after 120-min exposure). Microstructural analysis reveals that the dense grain boundary network facilitates rapid surface diffusion of Al, promoting continuous Al₂O₃ protective film formation. Additionally, Y segregation at grain boundaries suppressed outward diffusion of Cr³⁺ cations, effectively inhibiting void formation at the oxide-coating interface and improving interfacial stability. The developed rare-earth-oxide-doped composite coating via extreme high-speed laser cladding process shows promising applications in surface-strengthening engineering for nuclear reactor Zr-4 alloy cladding tubes, providing both theoretical insights and technical references for the design of high-temperature oxidation-resistant coatings in nuclear industry.

Deep-sea polymetallic nodule provinces harbor rich benthic microbial communities that underpin biogeochemical cycles and sustain abyssal ecosystem functions. Recent studies have begun to map their abundance, diversity and community structure, emphasizing the role of environmental gradients and spatial heterogeneity. Yet the spatiotemporal dynamics and assembly mechanisms of these microbes remain largely unresolved. Mining-induced sediment plumes further complicate the picture: they modify microbial biomass, activity and composition, but the trajectories of community succession and the functional consequences of disturbance are still unclear. Thresholds used to gauge plume impacts also differ markedly among studies, hampering consistent risk assessments. In summary, a stark contrast exists between the limited in situ observational data, the widely varying impact thresholds reported across studies, and the pressing need for unified standards in environmental impact assessments for deep-sea mining. It recommends future work that integrates multi-omics, time-series in situ monitoring, cross-regional comparisons and standardized evaluation frameworks to refine microbial indicators and ecological thresholds for deep-sea mining impact assessments.

Dense polymetallic nodule fields are found in different areas of the Pacific and Indian Oceans. However, limited knowledge exists about microbial diversity, processes and functions in deep-sea polymetallic nodule sediments. This study investigated microbial diversity, composition and function in sediments from various locations and depths in a western Pacific polymetallic nodule province. Sediment cores were collected, DNA extracted, and the V3–V4 regions of the 16S rRNA gene were sequenced using Illumina MiSeq. The test results show that the abundance and diversity of microbial communities in sediments from different sites vary significantly. The dominant microbial communities at the family level in the three sediment samples were all mainly Marinobacteraceae and Alcanivoracaceae. Sediment samples from core 1 had similar microbial structures and microbial community functions. Surface sediment had higher species richness, diversity and evenness than the middle layer. The dominant phylum at different depths was consistent. There was significant spatial heterogeneity in the microbial community within sediments from polymetallic nodule regions. This study expands on our knowledge of the spatial and vertical distribution of microbial community diversity beneath polymetallic nodules in deep-sea settings.