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The present study focuses on investigating the microstructure, hardness, wear, and corrosion resistance of Al1.2CoCrFeNiScxhigh entropy alloys, where the Sc content (x) varies between 0, 0.1, 0.2, and 0.3. The results indicate that the addition of Sc promotes the formation of the FCC phase and improves the hardness and wear resistance, but reduces the corrosion resistance of the alloy. The alloy's evolution can be observed as a transition from a single BCC phase to a combination of Fe, Cr-rich BCC phase, Al, Co, Ni-rich BCC phase, and Ni, Sc-rich FCC phase. As the Sc content increases from 0 to 0.3, the hardness increases from 438 HV to 581 HV, representing a 32.6 % increment. This increase can be mainly attributed to grain size strengthening and solid solution strengthening. Additionally, the average friction coefficient experiences a notable reduction from 0.999 to 0.574, indicating a 42.5 % decrease. With respect to wear resistance, the Al1.2CoCrFeNiSc0.3alloy exhibits superior performance, demonstrated by its lower friction coefficient, reduced wear rate, and smaller volume, width and depth of wear marks. Furthermore, the addition of Sc to the Al1.2CoCrFeNiScxalloys leads to an overall decrease in corrosion potential, accompanied by an increase in corrosion current density, suggesting that Sc has a detrimental effect on the corrosion resistance of the alloy. Moreover, the Al1.2CoCrFeNi alloy displays pitting corrosion, while the Al1.2CoCrFeNiScxalloys demonstrate intercrystalline corrosion, which preferentially occurs on the Ni, Sc-rich phase due to the high electrochemical activity and low equivalent chemical potential.

Substitution of Nb by W in Nb48Ti27Co25dual phase hydrogen permeable alloy was carried out. The elemental W replacing Nb mainly dissolved into the primary body-centered cubic (bcc)-(Nb) phase to modify its composition and crystal lattice. The W alloying effect on hydrogen transportation was systematically discussed based on hydrogen chemical potentials and first principle calculations. The substitution of Nb by W reduced the hydrogen solubility, and led to an improved intrinsic hydrogen diffusion coefficient, especially at temperature below 573 K, which promoted the hydrogen permeation flux of Nb48Ti27Co25alloy membrane at 523 K. According to the theoretical study based on density function theory of the Nb–W system, the reduced hydrogen solubility can be attributed to the weakened binding strength between hydrogen atoms and the bcc-(Nb) lattice and the reduced charge gained by hydrogen atoms after W substitution for Nb. In addition, the W occupying the Nb sublattice can change the diffusion path of hydrogen atoms in the bcc-(Nb) lattice, thereby reducing the diffusion energy barrier for high hydrogen diffusivity.