Effect of Alloying Elements on the Hydrogen Diffusion and Trapping in High Entropy Alloys

Abstract 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 = 4.3 x 10 − 7 exp ( − 51.7 k J / m o l R T ) and D = 2.8 x 10 − 8 exp ( − 30.5 k J / m o l R T ) 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.