Abstract
The formation of precipitates with an atomic volume different from their parent phase eventually leads to a loss of the lattice continuity at the matrix–precipitate interface. Here, we show the creation or removal of lattice sites mediated by lattice point defects is an accommodation mechanism of the coherency loss and even a precipitation driving force. We introduce a thermodynamic approach that rationalizes the selection of phases resulting from chemical and crystallographic constraints in relation to point defect properties. The resulting semi-coherent phase diagram and the precipitation kinetic model depend on the equilibrium phase diagram, the eigenstrain of the precipitating phase, and the chemical potential of point defects. From a joint experimental and modeling study, we uncover the prominent role of excess point defects in unforeseen phase transformations of the Fe–Ni metallic system under irradiation. By addressing the fundamental role of lattice point defects in the accommodation mechanisms of precipitation, we provide a step torwards the understanding of semi-coherent phase transformations occurring in solid materials upon synthesis and in use.
Highlights
The formation of precipitates with an atomic volume different from their parent phase eventually leads to a loss of the lattice continuity at the matrix–precipitate interface
Microstructural characterization of one face-centered cubic γ precipitate is presented in Fig. 3 (HRTEM images of four other precipitates are presented in Supplementary Note 1 and Fig. 1)
Building semi-coherent phase diagrams and deducing kinetic laws of precipitation can be intended using the constrained thermodynamic model developed in the present work
Summary
The formation of precipitates with an atomic volume different from their parent phase eventually leads to a loss of the lattice continuity at the matrix–precipitate interface. Whenever the precipitate eigenstrain is not compensated by an elastic strain, precipitates feature a loss of coherency at the interface, i.e., the number of lattice sites across the interface is not conserved It occurs through sequences of kinetic mechanisms involving lattice point and dislocation defects, such as the absorption of point defects condensing in precipitates and forming extra atomic planes (dislocations)[3,4] (Fig. 1c). In these examples, dislocations and point defects act as local sources and sinks of lattice sites. In systems submitted to thermal quenching, severe mechanical solicitation, or irradiation, point defects are in excess The removal of these point defects resulting from semi-coherent precipitation stabilizes the system, increases the precipitation driving force[12,14]. GVa temperature Gibbs free energy atomic fraction of solute of this interplay on the precipitation driving force, has been completely underestimated up to now
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