SKM 2023 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 41: Topical Session: Defect Phases III

MM 41.1: Topical Talk

Donnerstag, 30. März 2023, 15:45–16:15, SCH A 216

Entropy in grain boundary segregation — •Pavel Lejcek — CEITEC, BUT, Brno, Czechia — Institute of Physics, AS CR, Prague Czechia

Experimentally, a linear dependence between the standard entropy and the standard enthalpy of solute segregation at grain boundaries was established which is called *enthalpy-entropy compensation effect*. In this dependence, there exists a region in which the product of temperature and segregation entropy ('entropy term') is larger than the absolute value of the segregation enthalpy, so that the controlling parameter, the Gibbs energy of segregation, is negative. Under this condition the grain boundary segregation is dominated by the entropy, i.e., the phenomenon of the entropy-dominated grain boundary segregation occurs. We show numerous examples of the grain boundaries and solutes in bcc-iron-based alloys exhibiting this phenomenon. In addition, we formulate the idea that a solute can also segregate at the grain boundary (site) that exhibits positive segregation energy/enthalpy (so called *anti-segregation site*) if the entropy term is larger than the segregation enthalpy, so that the Gibbs energy o segregation is negative. In this way, the solute segregation is completely controlled by the entropy term and an entropy-driven grain boundary segregation will exist. We suggest the entropy-driven grain boundary segregation for several model examples in iron-based systems thus serving as indirect evidence of the phenomenon. Finally, the grain boundary configurational entropy is discussed in relation to its volume counterpart and to the segregation variables.