Simulation of the precipitation process of ordered intermetallic compounds in binary and ternary Ni-Al-based alloys by the phase-field model

With the microscopic phase-field model, atomic-scale computer simulation programs for the precipitation mechanism of the ordered intermetallic compound gamma' in binary Ni-15.5 at.%Al alloy, theta and gamma' in ternary Ni(75)Al(x)V(25-x) alloys were worked out based on the microscopic diffusion equation and non-equilibrium free energy. The simulation can be applied to the whole precipitation process and composition range. A prior assumptions on the new phase structure or transformation path was unnecessary, the possible non-equilibrium phases, atomic clustering and ordering could be described automatically, and atomic images, order parameters and volume fractions of precipitates were obtained. Computer simulation was performed systematically on the precipitation mechanism, precipitation sequence of theta and gamma' in complicated system with ordering and clustering simultaneously. Through the simulated atomic images and chemical order parameters of precipitates, we can explain the complex precipitation mechanisms of theta (Ni(3)V) and gamma' (Ni(3)Al) ordered phases. For the binary alloy, the precipitation mechanism of gamma' phase has the characteristic of both non-classical nucleation and growth (NCNG) and congruent ordering and spinodal decomposition (COSD). For the ternary alloys, the precipitation characteristic of gamma' phase transforms from NCNG to COSD gradually, otherwise, the precipitation characteristic of theta phase transforms from COSD to NCNG mechanism gradually. (c) 2008 Elsevier B.V. All rights reserved.