Formation of γ/γ'-delta eutectic microstructure during directional crystallization and after heat treatment

The electron microscopy study was made of the bivariant eutectic Ni-20.1 Nb-5.7 Cr-2.5 Al alloy microstructure. It is shown that after a directed crystallization the alloy structure presents alternations of γ- and sigma-plates. During the decomposition of supersaturated solid solution inside γ-plates precipitation are formed of the cubic morphology γ'-phase, of sigma-phase in the form of thin plates of Widmanstaetten structure, γ''-phase in the form of cubic orientation thin needles. A polythermal section has been plotted for a constant aluminium content of 2.5 wt.%, to explain the alloy crystallization process and the microstructure formed. The variation in the particle dispersion of γ'-phase after quenching from different temperature has been determined