Effect of alloying elements on the hydrogen diffusion and trapping in high entropy alloys

The effect of the concentration of alloy elements on hydrogen diffusivity and trapping for two high-entropy alloys: Fe20Mn20Ni20Co20Cr20 and Fe22Mn40Ni30Co6Cr2, were investigated. Hydrogen diffusivity as a function of temperature (300-550°C) was obtained from gas permeation tests for both alloys. A sigmoidal behavior was observed for both face-centered cubic alloys, following the solution of Fick's Second Law. The variation in diffusivity as a function of temperature is given by the following equations: D=4.3x10−7exp(−51.7kJ/molRT) and D=2.8x10−8exp(−30.5kJ/molRT) for the equiatomic and non-equiatomic alloys, respectively. The results from first-principles simulations show that the difference in diffusivity can be mainly attributed to the decrease in Cr, which has a strong interaction with hydrogen when in solid solution. A comparison of HEA with traditional steels as a function of Cr % reinforces this analysis.