Micro/nano scale Laves phases enhanced hydrogen trapping in as-cast high entropy alloy for hydrogen storage applications

CoCrFeMnNi high entropy alloy (HEA) is considered ideal hydrogen storage material due to its high resistance to hydrogen embrittlement (HE), but its lower mechanical strength and hydrogen desorption content restricted comprehensive application. Therefore, it was desirable to design the HEA that possessed both excellent hydrogen storage property and superior strength. In this work, the eutectic high entropy alloy (EHEA) reinforced by C14 Laves phases were designed and forecasted combined with the thermodynamic calculations and thermal desorption analysis. The results revealed that the designed CoCrFeMnNiNb0.5 EHEA with hydrogen (H) charging remained the higher hydrogen storage content of 49.2 ppm and UTS of 369.4 MPa because of the enhancement effect induced by C14 Laves phase when compared to CoCrFeMnNi HEA with H charging (20.2 ppm, 191.5 MPa). For the as-cast CoCrFeMnNi HEA with H charging, the hydrogen enrichment at grain boundaries induced stress concentration and significantly decreased strength and ductility. However, in the as-cast CoCrFeMnNiNb0.5 EHEA with H charging, the cracks were extended with random orientation in C14 Laves phases, endowing its higher strength. This work paved the way to develop advanced HEA with excellent hydrogen storage and higher strength, and demonstrates the great potential of EHEA strengthened by C14 Laves phases for hydrogen storage applications in the near future.