Deuterium induced defects and embrittlement behavior of a Co-free high entropy alloy

Long-term exposure of structural materials to extreme hydrogen-enriched environments will lead to hydrogen embrittlement, and thus search and design of new alloys with economic and safety benefits against hydrogen embrittlement have become a top priority for the development of many engineering fields. In this work, the hydrogen embrittlement behavior of a new cobalt-free high-entropy alloy (HEA) Fe ₂₇Ni ₂₈Mn ₂₇Cr ₁₈ was systematically studied and compared with a typical quaternary HEA Fe ₂₅Co ₂₅Cr ₂₅Ni ₂₅ . Numerous vacancies are produced in the process of electrochemical deuterium charging and the corresponding concentration is related with the solubility of deuterium atoms. Fe ₂₇Ni ₂₈Mn ₂₇Cr ₁₈ has much higher concentrations of deuterium and vacancies than Fe ₂₅Co ₂₅Cr ₂₅Ni ₂₅ , which is attributed to the Mn induced severe lattice distortion and results in different variations of mechanical properties. The ultimate tensile strength (UTS) of Fe ₂₇Ni ₂₈Mn ₂₇Cr ₁₈ increases from 353.73 MPa to 589.50 MPa after electrochemical hydrogen charging while the elongation still remains at 74.73%, and its deformation mechanism is dominated by dislocation proliferation. In contrast, the UTS of hydrogen charged Fe ₂₅Co ₂₅Cr ₂₅Ni ₂₅ decreases from 552.79 MPa to 501.53 MPa and the corresponding elongation also decreases from 74.65% to 67.24%, and the plastic deformation mechanism is dominated by twinning. This work demonstrates an economic cobalt-free HEA with great resistance to hydrogen embrittlement, which would enhance the applications of HEAs in hydrogen-enriched environments.