Effect of Variables on Equilibrium Grain Boundary Segregation

This chapter deals with considering various effects on equilibrium grain boundary segregation. The effects of intensive thermodynamic variables – temperature, concentration, pressure, magnetic field – are discussed in detail and documented by literature data. Special attention is paid to the effect of the grain boundary energy – anisotropy of interfacial segregation. Orientation dependences of both the grain boundary concentration and the standard enthalpy of segregation are documented on data found in literature. It is shown that nature of the grain boundary segregation can be considered as the effect of changed interfacial energy. The data on anisotropy of grain boundary segregation are generalised in constructing the grain boundary segregation diagram. Another important relationship – enthalpy–entropy compensation effect – is introduced and thoroughly discussed. Based on the last two effects, a method of prediction of segregation enthalpy and entropy is presented. Besides the effect of intensive variables to grain boundary segregation, it is shown that another parameter – grain size – can affect the grain boundary segregation mainly in case of nanosized grains. The problems of segregation in nanograined metallic materials as well as the effect of segregation to stabilisation of the nanostructure are briefly displayed.