Thermodynamic aspects of anisotropy of grain boundary segregation

Previous thermodynamic data on Si, P and C segregation at different grain b oundaries in alpha-Fe were plotted as a dependence of entropy vs. enthalpy. The linear dependence between these two quantities was proved for each seg regant. Based on the analysis of this principal relationship as well as of the different ability of silicon on one hand and phosphorus and carbon on t he other hand to form ordered alloys, it was possible to explain (i) positi ve values of segregation entropy for P and C but negative ones for Si, (ii) higher values of segregation entropy for special grain boundaries as compa red to general ones, and (iii) inverse anisotropy of grain boundary segrega tion at higher temperatures.