Abstract
The interphase spacings σ in the microstructures of most binary and pseudobinary “normal” metallic eutectics can roughly be quan‐ tified with regard to their respective solidification rates v according to a general relationship
constant the constant being commonly between 10^−10^ and 10^−11^ cm^3^ ^−1^ The designation “normal” relates to similar degrees of undercooling of either phase on a plain‐front solidification process at variance with anomaleous eutectics which solidify at different degrees of under‐ cooling in an uncoupled or weakly‐coupled manner. The “constant”, however, is an individual value for each eutectic system. It is lowest for “simple” eutectics forming no intermetallic com‐ pounds and having low terminal solid solutions. The constant is raised for systems by 3 orders of magnitude or more if extensive terminal solid solutions are present. A closer fit for deliberate normal eutectics is presented in this pragmatic approach if the concentration differences between the terminal phases in eutectics ΔC~E~ [at%] are attributed to them as a square term according to λ^2^ + · v · ΔC~E~^2^ = constant. The data based on this relation still show some scatter but they are grouping to distinct material families e. g. to Pb‐, Ag‐ or Al‐based eutectics. The remanent differences are estimated to disappear as soon as the relation is extended by the interdiffusion coefficient D according to
as is confirmed in cases where reliable D values are available. These findings are in contrast to the current published theories on eutectic solidification. Suggestions are given where the bound‐ ary conditions have to be altered in order to attain full accord be‐ tween experiment and theory.