Discontinuous coarsening of lamellar cellular precipitate in an austenitic Fe-30 wt%Ni-6wt.%Ti alloy—I. Morphology

Abstract

The morphology of discontinuous coarsening of lamellar cellular precipitate in an austenitic Fe-30 wt.%Ni-6 wt.%Ti alloy aged at temperatures ranging from 400 to 900°C has been studied by light microscopy, electron microscopy and X-ray diffraction. Aging at all temperatures resulted in decomposition of the austenite by a cellular precipitation into alternate lamellae of depleted austenite and Ni 3Ti. This reaction was followed by a second cellular or discontinuous coarsening reaction which decomposed the first lamellar product into a coarse lamellar structure of the same two phases. At all aging temperatures, the lamellar spacings and growth rates of the second cellular reaction were larger and slower, respectively, than those of the first. The second cells also always contained more Ni 3Ti than the first cells.