Microstructure design strategies to mitigate hydrogen embrittlement in metallic materials

Hydrogen embrittlement (HE) is characterized by the sudden loss of a material's mechanical property due to the premature failure induced by the ingress of H atoms and various H-materials interactions. This phenomenon threatens almost all the metallic materials that brings an abrupt halt to some of the pending infrastructures needed for a H economy. The development of microstructure design strategies to mitigate HE is challenging, as the fundamental mechanisms for HE process are still not well understood. Nevertheless, some progresses in this field have been made in recent years. Here, we provide an overview on established microstructural approaches to mitigate HE in metallic materials. These methods include second-phase trapping, grain refinement, grain boundary engineering, solute segregation and heterogeneity, and surface treatment. Their effectiveness and materials applicability are compared. The operating mechanisms, advantages, and limitations of these approaches are also discussed to guide their future development and successful industrial application.