This review sets out to investigate the detrimental impacts of hydrogen gas (H₂) on critical boiler components and provide appropriate state-of-the-art mitigation measures and future research directions to advance its use in industrial boiler operations. Specifically, the study focused on hydrogen embrittlement (HE) and high-temperature hydrogen attack (HTHA) and their effects on boiler components. The study provided a fundamental understanding of the evolution of these damage mechanisms in materials and their potential impact on critical boiler components in different operational contexts. Subsequently, the review highlighted general and specific mitigation measures, hydrogen-compatible materials (such as single-crystal PWA 1480E, Inconel 625, and Hastelloy X), and hydrogen barrier coatings (such as TiAlN) for mitigating potential hydrogen-induced damages in critical boiler components. This study also identified strategic material selection approaches and advanced approaches based on computational modeling (such as phase-field modeling) and data-driven machine learning models that could be leveraged to mitigate potential equipment failures due to HE and HTHA under elevated H₂ conditions. Finally, future research directions were outlined to facilitate future implementation of mitigation measures, material selection studies, and advanced approaches to promote the extensive and sustainable use of H₂ in industrial boiler operations.

This study investigated the impact of low-temperature heat treatments on the mechanical and thermophysical properties of Cu-10Sn alloys fabricated by a laser powder bed fusion (LPBF) additive manufacturing (AM) process. The microstructure, phase structure, and mechanical and thermal properties of the LPBF Cu-10Sn samples were comparatively investigated under both the as-fabricated (AF) condition and after low-temperature heat treatments at 140, 180, 220, 260, and 300 °C. The results showed that the low-temperature heat treatments did not significantly affect the phase and grain structures of the Cu-10Sn alloys. Both pre- and post-treatment samples displayed consistent grain sizes, with no obvious X-ray diffraction angle shift for the α phase, indicating that atom diffusion of the Sn element is beyond the detection resolution of X-ray diffractometers (XRD). However, the 180 °C heat-treated sample exhibited the highest hardness, while the AF samples had the lowest hardness, which was most likely due to the generation of precipitates according to thermodynamics modeling. Heat-treated samples also displayed higher thermal diffusivity values than their AF counterpart. The AF sample had the longest lifetime of ~0.19 nanoseconds (ns) in the positron annihilation lifetime spectroscopy (PALS) test, indicating the presence of the most atomic-level defects.

This study investigates the coefficient of thermal expansion (CTE) behavior of LPBF-fabricated AlSi10Mg, 316L stainless steel, and Ti-6Al-4V alloys, focusing on the influence of laser power, scanning speed, and annealing. AlSi10Mg exhibits the highest CTE, but its thermal expansion is highly sensitive to porosity and balling defects. 316L stainless steel shows moderate and stable CTE values, with minimal changes after annealing due to its dense microstructure. Ti-6Al-4V has the lowest CTE, with annealing improving expansion. Higher laser power (100 W) improves fusion, reduces porosity, and stabilizes CTE, while lower power (50 W) increases defects, particularly in AlSi10Mg and Ti-6Al-4V. Scanning speed significantly influences porosity, with 0.4 m/s providing an optimal balance between melt efficiency and defect minimization. Annealing enhances CTE uniformity by reducing the lack of fusion defects and refining grain structures, with the greatest improvements seen in low-laser-energy conditions. These findings provide valuable insights for optimizing LPBF parameters to enhance thermal stability and reliability in aerospace, biomedical, and structural applications.

Hydrogen embrittlement severely degrades mechanical properties of austenitic stainless steels (γ-SS), yet the bulk deformation microstructures responsible for this phenomenon have not been directly observed. While the internal microstructure is essential to define metal plasticity, deformation, and fracture, no technique has been able to image the deep subsurface structure. In this work, we use dark-field X-ray microscopy (DFXM) to compare the structure of an annealed single crystal γ-SS sample to one with the same annealing conditions and subsequently hydrogen pre-charged in a high pressure and temperature environment. While the non-charged sample exhibited features characteristic of dislocations packed into boundaries, the pre-charged sample showed diffuse features with a distinctly broader rocking curve characteristic of a higher geometrically necessary dislocation (GND) density. Our results demonstrate the utility of DFXM to characterize the unique subsurface microstructures, offering opportunities for future studies to resolve how these features cause fracture or embrittlement.