Nanoscale studies of segregation at coherent heterophase interfaces in α-Fe based systems

Heterophase interfaces are characterized with respect to atomic-scale local compositions in two a-Fe-based alloy systems by three-dimensional atom probe microscopy. The proximity histogram method is utilized for determining the compositions of the precipitates, the matrix phase and the Gibbsian interfacial excess of solute. Suitable methods to measure segregation in multicomponent systems at heterophase interfaces independent of the position of the dividing interface are discussed. Very little Sb segregates to the heterophase interface between coherent plate-shaped moybdenum nitride precipitates, which are <1 nm thick, and the alpha-Fe matrix: the relative interfacial excess of Sb is only 0.12 +/- 0.1 nm(-2). This is in sharp contrast to the interfacial excess of 7 +/- 3 nm(-2) for molybdenum nitride plates that have grown to 2-10 nm thick (or 20-30 nm in diameter for spheroidal precipitates) with a semicoherent interface with misfit dislocations, as reported earlier. Small coherent Cu-rich precipitates with a metastable bcc structure in an a-Fe matrix exhibit interfacial segregation of Ni and Mn at their interfaces with excesses of 1.47 +/- 0.43 and 0.95 +/- 0.31 nm(-2), respectively. Copyright (C) 2004 John Wiley Sons, Ltd.