Mechanisms of hydrogen embrittlement resistances in FCC concentrated solid solution alloys

Hydrogen embrittlement (HE) can lead to the unintentional fracture of large engineering materials, resulting in severe economic losses and safety hazards. It is critical to explore economical and scalable solutions to overcome the challenges of HE. In this work, the HE resistances of four face -centered cubic (FCC) concentrated solid solution alloys (CSAs), including NiFe20, NiCoCr, NiCoCrFe, NiCoCrFeMn, and pure Ni were comprehensively investigated and compared by using TDS, EBSD and TEM. It was found that Fe and Cr element can effectively inhibit the solubility of deuterium in the CSAs and alleviate the HE behaviors. In contrast, Mn element significantly increases the solubility of deuterium and caused brittle fractures. Tensile experiments were performed to compare the HE sensitivity of CSAs. The tensile strength of pure Ni and NiFe20 alloys decreased after deuterium charged, whereas the tensile strength of NiCoCr, NiCoCrFe and NiCoCrFeMn alloys increased. Based on the experimental results, it is deduced that deuterium atoms promote dislocation accumulation and twin growth by reducing the stacking fault energy, which eventually leads to an increase in yield strength and a decrease in plasticity. In addition, the accumulation of deuterium atoms near grain boundaries and cracks during deformation leads to dislocation pinning and stress concentration, which ultimately promotes crack nucleation and propagation. The HE resistances of CSAs are strongly influenced by the deuterium concentration, which depends on the effects of constituent elements and deuterium charging time on the deuterium concentration. Collectively, the specific alloying elements play more important role for the HE resistances of CSAs than the number of elements in the current study. These results provide valuable insights for further understanding and design higher HE resistance CSAs in the future.