Some aspects of the anisotropy of grain boundary segregation and wetting

A recently developed model of grain boundary (GB) segregation, in terms of the five macroscopic parameters of GB orientation, has been exercised to explore the anisotropy of GB segregation. The five macroscopic GB orientation parameters are defined by means of the orientations of the two crystallographic planes that terminate the crystals on either side of the GB, and a twist angle. Some important conclusions include the following: (a) the composition of a boundary depends on all five parameters of GB orientation, (b) the segregation profile across a GB depends on the two planes which terminate the adjacent crystals, (c) the composition profile across GB’s terminated by identical crystallographic planes is symmetric, but is asymmetric when GB’s are terminated by different planes, and (d) the strength of the segregation on one side of a GB influences the extent of segregation on the other. Some experimental results on Nb-doped TiO2 are presented in order to verify above predicted trends. In addition, it is shown that the model predicts the possibility of anisotropic GB wetting transitions as two-phase coexistence is approached.