A Fe-4.34Ni alloy was solidified directionally in the Bridgman system. The solid-liquid interface has been frozen and doublet structure revealed. Energy Dispersive Spectroscopy proved that peritectic reaction had occurred during solidification and modified profile of solute redistribution within primary phase existed just before peritectic reaction. Energ Dispersive X-Ray Spectrimetry (EDXS) solute measurements confirmed also the influence of doublet tip splitting on the solute redistribution. The obtained profile of solute redistribution modified by tip splitting has been compared to analogous profile obtained for the Al-3.5Li alloy in which doublet structure has also been formed but peritectic reaction does not exist. However, in the latter some precipitates have been predicted and revealed by use of the Scanning Electron Microscopy. Relevant equations have been formulated in order to fit experimental solute redistribution within frozen morphology of the Fe-4.34Ni alloy. The formulated equations are an analytical description of the peritectic reaction. It employs the merastable solidus line position known from the Fe-Ni phase diagram. An orientation of the doublet topography has also been determined based on electron backscatter diffraction (EBSD) acquired from the Al-3.5Li doublet shaped cells solidified and frozen during microgravity test.