Influence of interstitial impurities on the Griffith work in Ti-based alloys

The influence of interstitial B and C impurities on grain boundary cohesion in the series of B2-TiMe alloys, where Me = Fe, Co, Ni or Pd, was investigated using the plane-wave pseudopotential method within density functional theory. The most preferential sites for interstitial impurity atoms at the TiMe Σ5(310) symmetrical tilt grain boundary were determined. It was shown that the impurities' sorption energies at the grain boundary depend strongly on their local environment. Analysis of the electronic properties allows us to reveal the microscopic nature of the chemical bonding of B and C at the grain boundary. It was shown that, in contrast with hydrogen, both impurities decrease the grain boundary energy more significantly than the surface one. This results in an increase in the Griffith work which also indicates the strengthening of the grain boundary. Our estimation of the Griffith work for the TiMe alloy containing both B and H atoms shows an increase in comparison with the undoped alloy, but the effect of carbon on grain boundary strengthening in the presence of hydrogen seems to be negligible. The contributions of the chemical and elastic mechanisms to the Griffith work are discussed. (paper)