Hydrogen and carbon interaction in a FeNi alloy with a vacancy

E. GONZÁLEZ; P. JASEN; G. GONZÁLEZ; L. MORO; A. JUAN

PHYSICA STATUS SOLIDI B-BASIC RESEARCH

WILEY-V C H VERLAG GMBH

Año: 2009 vol. 246 p. 1275 - 1285

0370-1972

The bonding of hydrogen and carbon to Fe and Ni in a 50:50 alloy is analyzed using density functional calculations.  The changes in the electronic structure of a L10 alloy upon C and H introduction at a vacancy region are addressed and a comparison with H or C in pure metals is drawn.  H in bulk FeNi alloy with a vacancy locates at a tetrahedral site shifted towards the vacancy.  Instead, C prefers an octahedral site (-Fe based).  The vacancy acts as strong traps of both C and H.  Fe-Ni atoms are initially more strongly bonded to each other due to the vacancy formation. Consequently, the Fe-Fe, Fe-Ni and Ni-Ni bond strength is diminished as new metal-C or metal-H bonds are formed.  The most affected bond is the Fe-Ni, whose overlap population decreases 72%.  An analysis of the orbital interaction reveals the Fe-H bonding involves mainly the Fe 4s,  H 1s orbitals and Ni 4s orbitals.  In the case of the sequential absorption, the C-H interaction is almost zero at a distance of 2.72 Å.  The main interactions of these interstitials are developed with either Fe or Ni.  We also considered the absorption sequence (H first or C first) and its influence on the electronic structure.  Our results could be relevant to understand some steps of the carburization process during thermal cracking opera-tions where hydrogen atoms are present.