Grain boundary segregation diagrams of α-iron

✍ Scribed by Pavel Lejček; Siegfied Hofmann

• Publisher: Springer
• Year: 1993
• Tongue: English
• Weight: 871 KB
• Volume: 1
• Category: Article
• ISSN: 0927-7056
• DOI: 10.1007/bf00203606

✦ Synopsis

Based on thermodynamic analysis of interracial segregation, the segregation enthalpy AH ~ of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface 9 and the solid solubility limit X~ at temperature T and can be written as

AH~ X;) = AH*(~) + vR[Tln(X;)]

In this equation, the structural dependence of interfacial segregation is contained in AH*(~) which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix.

The product [T ln(X~)] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [T In(X~)]mas. The parameter v > 0 represents the relationship between the activity a} of a solute at the bulk solid solubility limit in a given matrix and X~, a} -(X~) ", and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of a-iron, the averaged value = 0.77 was determined. Values of AH*(4~) range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of oL-iron.