H2-induced environmental embrittlement in ordered and disordered Ni3Fe: An electronic structure approach

The different behaviors in H2-induced environmental embrittlement in ordered and disordered Ni3Fe are associated with differences in their electronic structures. The experimental study on electronic structures of ordered and disordered Ni3Fe has been carried out by electron energy-loss spectroscopy (EELS). The onset energy of Ni L2,3 edges from ordered phase is 0.3 eV lower than that from disordered phase, while the 3d occupancy of Ni atoms in ordered phase is 0.07 electrons/atom less than that in disordered phase. Severe H2-induced environmental embrittlement in ordered phase is attributed to rather negative dissociative adsorption energy of hydrogen at surfaces, which arises from upward shifting of the valence band center of Ni.