Composition complexity enhances the He-retaining ability of Zr-based MPEAs

A thorough investigation of the helium (He) bubble growth mechanism in metals is of crucial importance in proposing alloy design criteria to improve the radiation resistance of nuclear structure materials and the He-retaining ability of tritium storage alloys. In this study, He-containing alloy thin films of ZrCo, as well as TiZrHfMo2 and TiZrHfNb2 multi-principal element alloys (MPEAs) were prepared by magnetron sputtering under a working gas mixture of He and Ar. The He-retaining ability of Zr-based alloys with different composition complexities was investigated by the advanced techniques of electron-energy loss spectrum (EELS) and in-situ heating in a transmission electron microscopy (TEM). The effects of composition complexity, He/Ar flow ratio and in-situ heating temperature on the He bubble size, He volume density and average pressure were systematically analysed. The results show that the increase of the composition complexity inhibits the He atom diffusivity and induces a decrease in the average size of the He bubbles in the alloy, which is beneficial to enhancing the He-retaining ability of the alloy. The potentially higher mechanical strength of MPEAs might also contribute to a stronger strain force resisting He bubble growth in the severely distorted lattice and accommodating the He bubble with higher bubble pressure. Increase of the composition complexity would inhibit the He atom diffusivity and induce the decrease of the average size of the He bubbles in the alloy, which is beneficial to enhancing the He retaining ability of the alloy. [Display omitted] •The method to rapid evaluation He retaining ability of He containing film is improved.•A strategy for Tritium storage candidate material in MEPs is summarized.•The He retention properties/mechanism on MEPs were studied by EELS.•The He bubbles size in ZrCo/MPEAs at different He flow rates and temperature was compared.•Increase the composition complexity of alloy can improve the alloy's He retention ability.