Comparative Analysis of Surface Degradation Morphology and Microstructural Characterization of Ni–Cu Alloy and 301 Stainless Steel Pipelines After Service in High-Temperature Hydrogen Environment

This study aims to compare the microstructure, post-service degradation morphology and microstructural evolution, and crystallographic characteristics of Ni–Cu alloys and 301 stainless steel under high-temperature, hydrogen-rich conditions (1100–1200 °C, primarily H₂ with HCl, silanes, and silicon powder deposition) inside semiconductor reaction furnaces. The objective of this study is to provide a microstructural basis for material selection and structural reliability assessment, while also supporting the design of corrosion-resistant alloys and extending their service life. Using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) analysis, it was found that 301 stainless steel exhibits a typical austenitic microstructure with distinct grain boundaries, surface oxide particles, and localized deposits, showing significant near-surface plastic deformation, grain fragmentation, and hardness non-uniformity (207–236 HV). Similarly, the nickel-copper alloy exhibited distinct precipitates at the edges, with stable surface hardness (176–182 HV) that decreased gradually with depth; its crystallographic features were dominated by columnar grains and low-angle grain boundaries. Energy-dispersive spectroscopy (EDS) analysis indicates that the edges of the Ni–Cu alloy are enriched with Ti, Cr, Mn, O, and Cl, which aids in the formation of a protective layer; in contrast, 301 stainless steel is dominated by Fe–Si–Ni, making it more susceptible to localized corrosion. XRD analysis confirms that the Ni–Cu alloy possesses a Ni–Cu solid solution matrix containing various compounds, which stands in sharp contrast to the single austenitic phase of 301 stainless steel. Under high-temperature hydrogen chloride corrosion conditions, the Ni–Cu alloy exhibits excellent surface reaction stability due to its matrix properties, elemental segregation, and the formation of a potential protective film. In contrast, 301 stainless steel experiences a significant increase in the risk of “stress-microstructural evolution-localized corrosion sensitivity” due to near-surface deformation and inhomogeneities, indicating that the Ni–Cu alloy is more suitable for such harsh environments.