First-principles Study Of Hydrogen Behavior In B2-FeAl Intermetallics

Fe-Al intermetallics?Fe-Al?own many advantages,like enough specific strength,high melting point,creep resistance at high temperature and outstanding corrosion resistance to oxygen and sulfur.As a consequence,it has relatively high application potential.However,its room temperature hydrogen embrittlement?HE?effect cause a seriously low plasticity and dangerous brittleness,and this disadvantage limits its application.As a typical intermetallic,B2 phase Fe-Al has highly symmetrical body centered cubic?bcc?crystal structure and wide existence range on temperature&Al content.It is the most suitable object to deeply investigate the HE of Fe-Al.Despite so many experimental and computational studies of the hydrogen behavior of Fe-Al intermetallics,it still doesn't reach a consensus on hydrogen embrittlement mechanisms,particularly on the mechanisms of hydrogen's permeation,diffusion and interaction with defects in Fe-Al.This paper explored the surface and bulk hydrogen behavior in Fe-Al by density founctional theory?DFT?,and deepened the cognition of HE mechanism from surface area to bulk phase.In the surface study part,FeAl?100?Al-surf is the most stable lattice plane among five low Miller indices lattice planes of B2-FeAl,followed by?110?and?111?Al-surf lattice plane.And the Fe-topsite is the prior site to absorb H2O on FeAl?110?lattice plane,followed Al-topsite.With comparing the DFT study results about the dissociation of H2O on the surface of bcc-FeAl?110?and fcc-Al?111?,it is clarified that the iron atom on the surface of FeAl has catalytic action on the dissociation reaction of H₂O with Al atom.And the H2O dissociation on FeAl?110?-Al-topsite can happen at room temperature,according to the calculation results.Besides,the H2O absorption and dissociation process and H embedding process can happen more easily on FeAl?100?Al-surf with a Fe atom than ideal FeAl?110?.In the bulk phase study part,the interation of hydrogen with the interstitial sites and vacancies of B2-FeAl was studied.Hydrogen prefer to occupy tetrahedral interstitial site,and Fe vacancy is more stable than A1 vacancy.Fe vacancy can spontaneously trap 6 H atoms,while A1 vacancy can spontaneously trap over 8 H atoms.Besides,the bader charge analysis reveals that the hydrogen does weaken the atomic bonding force by occupying interstitial sites and defects.And further more,the clusterization of hydrogen-vacancy complexes in FeAl promote hydrogen blister nucleation.