Fyzikální ústav Akademie věd ČR

Grain boundaries are important structural component of materials. Their structure as well as chemical composition differ from those of the crystal interior and thus, they may limit the applicability of the materials. Based on careful study of segregation at individual grain boundaries in model b.c.c. Fe–base alloys we were able to propose and prove a method of the prediction of the segregation of any solute (i.e. its composition) at any grain boundary at chosen temperature.

Using the grain boundary segregation diagram (Fig. 1a), the standard enthalpy of segregation, ΔH_I⁰, of a chosen solute is determined knowing only its solubility in the matrix element in solid state (cf. Fig. 1b). Knowing ΔH_I⁰, the standard entropy of segregation, ΔS_I⁰, of this element at the same boundary is determined using the compensation effect (i.e. linear relationship between ΔH_I⁰ and ΔS_I⁰, Fig. 2) providing the position (i.e. substitution or interstitial) the element segregates at the boundary. Using this method, thermodynamic parameters of the segregation of 52 solutes in α-iron at 19 selected grain boundaries were determined (e.g. Table 1). The results were compared to all available literature data with high level of the agreement. It was also found that this method is well applicable even to complex systems – ferritic steels and cast irons.

P. Lejček, S. Hofmann: Thermodynamics of Grain Boundary Segregation and Applications to Anisotropy, Compensation Effect and Prediction, Crit. Rev. Sol. State Mater. Sci. 33 (2008) 133–163. doi: 10.1080/10408430801907649;

P. Lejček, R. Konečná, J. Janovec: Solute segregation to ferrite grain boundaries in nodular cast iron: experiment and prediction, Surf. Interface Anal. 40 (2008) 503–506. doi 10.1002/sia.2659;

P. Lejček, S. Hofmann, J. Janovec: Prediction of enthalpy and entropy of solute segregation at individual grain boundaries of α-iron and ferrite steels, Mater. Sci. Eng. A 462 (2007) 76–85. doi:10.1016/j.msea.2006.02.463;

P. Lejček, S. Hofmann: Grain boundary segregation, anisotropy and prediction, In: Encyclopedia of Materials: Science and Technology – Updates, K.H.J. Bunshaw, R.W. Cahn, M.C. Flemings, E.J. Kramer and S. Mahajan, Eds., Pergamon, Amsterdam, 2002, #200115, pp. 1–7.