Absolute atomic-scale measurements of the Gibbsian interfacial excess of solute at internal interfaces

A method consistent with the Gibbs' formalism is presented for measuring the Gibbsian interfacial excess of solute (Γ) at an internal interface using atom-probe field-ion microscopy (APFIM). The values of Γ are measured directly, that is, without deconvolution procedures. The relationships between Γ and the thermodynamic-state variables of an internal interface are studied using the techniques of APFIM and transmission electron microscopy (TEM). Examples are given of the application of APFIM-TEM to the measurement of Γ at grain boundaries in an Fe(Si) alloy.