Aging of Fe-C martensite II. Spinodal decomposition

This paper deals with the spinodal decomposition of Fe-1.83C martensite during aging at room temperature. Spinodal mechanism is confirmed by using Fourier analysis of diffuse scattering from martensite and direct microstructural analysis. It is found that the modulated structure is composed of dominant wave of about 1 nm and non-dominant wave of longer waves. For the first time it is found that the modulated structure of Fe-1.83C martensite does not grow even after aging for several months, this is due to the strong elastic interactions among carbon enriched and depleted regions prohibiting the further growth of the spinodal products. The coexistence of ordering and spinodal decomposition found in this study appears to be a great challenge to the classical theory of phase transformation, and the failure of classical theory in explaining the coexistence of ordering and spinodal decomposition is due to its over-simplified nearest neighbor atomic interaction hypothesis.