Abstract
The effect of heat treatment on the microstructure of dendrites in directionally solidified Ni-22.2Al-8.1Cr-5Ti-0.8Mo-0.58Zr (at.%) alloy was studied. The heat treatment consisted of three-step solution annealing (1323 K/4 h, 1373 K/6 h and 1503 K/6 h) and precipitation hardening in the temperature range from 1223 to 1323 K for 1 up to 25 h in air. It was found that during precipitation hardening the growth of α-Cr precipitates is controlled by volume difusion of Cr in β(NiAl) dendrites according to the relationship d³ ∝ t. The growth of γ'(Ni3Al) precipitates is controlled by the diffusion along γ'/β interfaces according to the relationship d⁴ ∝ t. The parameters of kinetic equations for coarsening of these precipitates were calculated, which allow to predict the precipitate size during the heat treatment.

Key words
nickel aluminides, NiAl, precipitation, kinetics, microstructure, heat treatment

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