First-principles study on segregation of ternary additions for MoSi2/Mo5Si3 interface

We investigate segregation behavior of additional elements M (=Ni, Co, Ta) at the C11b/D8m interface for MoSi2-Mo5Si3 alloys, based on first-principles calculation. We first find energetically stable interface structure with interface energy of 0.08 eV/Å2 (1.3 J/m2). Based on the stable interface, segregation energy for additional elements is calculated for individual atomic layer, which is applied to Monte Carlo statistical simulation under grand-canonical ensemble to quantitatively predict interface segregation profile. We find that our simulation successfully captures the characteristics in measured segregation tendency of (i) similarity in strong segregation at interface both for Ni and Co compared with bulk composition while Ta does not exhibit interface segregation and (ii) stronger segregation for Ni than for Co. The present results indicate that measured segregated interface for MoSi2-Mo5Si3 alloys can be thermodynamically stable.