In the present work the influence of process parameters on freckle formation in
superalloy CMSX-4 is demonstrated. A series of experiments were carried out using a laboratory
furnace of Bridgman-type in which the temperature gradient G and solidification velocity V can be
precisely controlled and individually varied over a wide range. On the etched surface and
longitudinal sections of the quenched samples the formation and evolution of freckles were
investigated. The initiation position of the freckles within the mushy zone was then determined.
Based on the experimental observations a complete diagram was plotted to indicate the probability
of freckle occurrence which is related to solidification parameters G and V. In this freckling map
the freckle region is delimited by different criteria. Freckles arise only within a certain G/V-range
for columnar dendrite growth; otherwise the solidification structure changes into cellular or
equiaxed structure, depending on whether G/V-value increases or decreases. In comparison with the
well-known freckling map of Copley et al., some new freckle-free regions are proposed. It is
interesting to note that the freckle formation is also suppressed at very low cooling rates. In
addition, the initiation position of the freckle formation in the mushy region was determined to be
less than 2 mm below the dendrite tip of the solidification front.