A model for H-gammaFe55Cr25Ni20 interaction

C. LANZ; G. BRIZUELA; A. JUAN; S. SIMONETTI

Conferencia; 21st World Hydrogen Energy Conference 2016; 2016

The interaction of two-hydrogen atoms in a γ-Fe55Cr25Ni20 alloy was studied by tight binding calculations. The theoretical study contributes to interpret the changes in the γ-Fe55Cr25Ni20 electronic structure and the chemical bonding after the H adsorption to better understanding the H embrittlent phenomenon by decohesion mechanism of iron- chromium-nickel alloys. The H atoms are trapped in the zone of a γ-Fe55Cr25Ni20 vacancy. The impurities are located aligned both along [1 -1 0] direction and with the vacancy, in the (111) plane. This behavior can be related with the easiness of hydrogen trapping and forming a lineal hydrogen-vacancy clusterization, as a precursor to crack initiation. An electron transfer to the H atoms from the Fe, Cr and Ni nearest neighbor atoms is observed. The electron transfer process helps to form the new H-metal bonds. The atomic orbital occupations of the metallic bonds close to the H atoms are affected. The mainly changes are presented in Cr 4py and Fe 4px orbitals. The 3dx2-y2, 3dz2 and 3dxz metallic orbitals have also participation in the hydrogen-metal interactions. The strengths of the metallic bonds nearest neighbors to the H atoms decrease. The Cr atoms have an important role in the embrittlent process, the H-Cr overlap population is the highest and the Cr-M (M=Fe, Ni) bond strength is the most affected after H adsorption. We found same H-H interaction that could be associated with the precursor of hydrogen bubble but it is far away to a typical H2 chemical bond. The embrittlement mechanism helps to form the bonds between metals and H atoms and finally break the metal?metal bonds. This process plays a key role in subsequent localized corrosion nucleation such as the initiation of stress corrosion cracking.