Hydrogen embrittlement of a Fe-Cr-Ni alloy: Analysis of the physical and chemical processes in the early stage of stress corrosion cracking initiation

SIMONETTI, S., LANZ, C. , BRIZUELA, G.

SOLID STATE SCIENCES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 15 p. 137 - 141

1293-2558

The interaction of two-hydrogen atoms in a zone of γ-Fe 55Cr25Ni20 alloy having a vacancy (V) was studied by the atom superposition and electron delocalization molecular orbital (ASED-MO) method. The impurities are located aligned both along [1-10] direction and with the vacancy, in the (111) plane. This behavior can be related with a lineal hydrogen-vacancy clusterization, as a precursor to crack initiation. The electronic structure of the Fe, Cr and Ni atoms near the vacancy, changes after hydrogen´s location. The interactions mainly involve Fe 4px and Cr 4py atomic orbitals. The 3dx2-y2, 3dz2 and 3dxz metallic orbitals also have participation in the hydrogen-alloy interactions. An electron transfer to the H atoms from the Fe, Cr and Ni nearest neighbor atoms contributes to form the new H-metal bonds. The metal-metal bonds weakened as the new H-Fe, H-Cr, and H-Ni pairs were formed. The Cr atoms have an important role in the embrittlent process; the strengths of the Cr-Fe, Cr-Cr and Cr-Ni bonds are the most affected while the H-Cr interaction has the highest overlap population. Same H-H interaction is observed and could be associated with the precursor of hydrogen bubble but it is far away to a typical H2 chemical bond. All the cited physical and chemical processes play a key role in subsequent localized corrosion nucleation such as the initiation of stress corrosion cracking.