Microanalytical study of discontinuous precipitation and dissolution in Ni–4 at.% Sn: local and global characterization of the reactions

Abstract

The morphology and kinetics of the discontinuous precipitation (DP) and discontinuous dissolution (DD) reactions have been studied in a Ni–4 at.% Sn alloy. High spatial resolution energy-dispersive X-ray microanalysis has been used to determine the Sn concentration profiles left behind the moving reaction front for the individual cells of the Sn-depleted α lamellae and Ni 3Sn compound. These data, combined with the local values of the reaction front velocity and the thickness of the α lamellae, have been used to evaluate the local sδD b values ( D b is the grain-boundary chemical diffusion coefficient, δ is the grain-boundary thickness and s is the segregation factor). The obtained results have been compared with those calculated by the global approach to the DP and DD reactions, which is relevant for the whole population of the cells. It has been shown that the application of the local characterization of the DP and DD reactions removes essentially the differences between the sδD b values calculated by the Petermann–Hornbogen equation and the equations of Cahn and Zięba–Pawłowski. Moreover, both sets of data do not show any substantial differences from the sδD b values obtained from measurements of the tracer diffusion of tin along stationary grain boundaries in nickel.