Surface segregation of Si and its effect on oxygen adsorption on a γ-TiAl(111) surface from first principles

We perform first-principles calculations based on the density-functional theory to study the surface segregation of Si and its effect on the oxygen adsorption on a γ-TiAl(111) surface for a range of oxygen coverage 0<Θ≤1.0 monolayer (ML). The calculated results show that the alloying Si atoms prefer occupying surface Ti sites to the sites in the bulk of γ-TiAl, which suggests the occurrence of Si surface segregation. When oxygen atoms adsorb on a pure γ-TiAl(111) surface, the most favorable sites are the adsorption sites with more Ti atoms as their nearest neighbors in the surface layer at all the calculated coverages and the interactions between adsorbed oxygen atoms are repulsive. However, when oxygen atoms adsorb on an Si-alloyed γ-TiAl(111) surface, the interactions between the adsorbed oxygen atoms are attractive at oxygen coverage 0<Θ≤1.0 ML. Meanwhile, the interactions between O and Al atoms become stronger whereas those between O and Ti atoms become weaker relative to oxygen adsorbed on a pure γ-TiAl(111) surface. The atomic geometry and density of state are analyzed. The results show that the surface ripple of the top metal layer for oxygen on a pure γ-TiAl(111) surface is Ti upwards, while that for oxygen on an Si-alloyed γ-TiAl(111) surface is Al upwards at high oxygen coverage (Θ≥0.50 ML). This effect of Si is of benefit to the nucleation of alumina, which is attributed to Si surface segregation and an increase of the surface Al:Ti ratio. This can help to explain why alloying the γ-TiAl(111) surface with Si could favor the formation of the Al2O3 scale at the first stage and result in good oxidation resistance in experiments.

[1]  Jinlong Yang,et al.  Oxygen adsorption on Zr(0001) surfaces : Density functional calculations and a multiple-layer adsorption model , 2008 .

[2]  J. Shang,et al.  Ab initio study of oxygen adsorption on the Ti(0001) surface , 2007 .

[3]  B. Gleeson,et al.  Surface segregation of Pt in γ′-Ni3Al: A first-principles study , 2007 .

[4]  L. Limin,et al.  FIRST-PRINCIPLES STUDY OF OXYGEN ATOM ADSORPTION ON γ-TiAl(111) SURFACE , 2006 .

[5]  D. Seidman,et al.  Partitioning of solutes in multiphase Ti-Al alloys , 2005 .

[6]  Helmut Clemens,et al.  Processing and applications of intermetallic γ-TiAl-based alloys , 2000 .

[7]  Edward A. Loria,et al.  Gamma titanium aluminides as prospective structural materials , 2000 .

[8]  T. Shibata,et al.  Influence of silicon ion implantation and post-implantation annealing on the oxidation behaviour of TiAl under thermal cycle conditions , 2000 .

[9]  M. Schmitz-niederau,et al.  The Oxidation Behavior of Several Ti-Al Alloys at 900°C in Air , 1999 .

[10]  T. Shibata,et al.  Influence of implantation of Al, Si, Cr or Mo ions on the oxidation behaviour of TiAl under thermal cycle conditions , 1999 .

[11]  L. Bengtsson,et al.  Dipole correction for surface supercell calculations , 1999 .

[12]  G. Kresse,et al.  From ultrasoft pseudopotentials to the projector augmented-wave method , 1999 .

[13]  C. Woodward,et al.  SITE PREFERENCES AND FORMATION ENERGIES OF SUBSTITUTIONAL SI, NB, MO, TA, AND W SOLID SOLUTIONS IN L10 TI-AL , 1998 .

[14]  M. Schütze,et al.  The Initial Stages in the Oxidation of TiAl , 1997 .

[15]  Kresse,et al.  Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. , 1996, Physical review. B, Condensed matter.

[16]  M. Schütze,et al.  TEM investigations of the early stages of TiAl oxidation , 1996 .

[17]  G. Kresse,et al.  Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set , 1996 .

[18]  B. Kim,et al.  Oxidation behavior of TiAl-X (X = Cr, V, Si, Mo or Nb) intermetallics at elevated temperature , 1995 .

[19]  W. J. Quadakkers,et al.  Fundamentals of TiAl oxidation: a critical review , 1995 .

[20]  Blöchl,et al.  Projector augmented-wave method. , 1994, Physical review. B, Condensed matter.

[21]  Hafner,et al.  Ab initio molecular dynamics for open-shell transition metals. , 1993, Physical review. B, Condensed matter.

[22]  Scheffler,et al.  Adsorbate-substrate and adsorbate-adsorbate interactions of Na and K adlayers on Al(111). , 1992, Physical review. B, Condensed matter.

[23]  A. Rahmel,et al.  Mechanism of isothermal oxidation of the intel-metallic TiAl and of TiAl alloys , 1992 .

[24]  D. Eliezer,et al.  Synthesis, properties and applications of titanium aluminides , 1992 .

[25]  Jackson,et al.  Atoms, molecules, solids, and surfaces: Applications of the generalized gradient approximation for exchange and correlation. , 1992, Physical review. B, Condensed matter.

[26]  S. Isobe,et al.  Effect of silicon and niobium on oxidation resistance of TiAl intermetallics , 1992 .

[27]  H. Monkhorst,et al.  SPECIAL POINTS FOR BRILLOUIN-ZONE INTEGRATIONS , 1976 .

[28]  H. Anada,et al.  Role of W, Mo, Nb and Si on Oxidation of TiAl in Air at High Temperatures , 1994 .