Kinetics of discontinuous coarsening of cellular precipitate in a Ni-8 at.% in alloy

Abstract

The morphology and growth kinetics of the cellular precipitate and products of two discontinuous coarsening reactions have been studied in the temperature range 710–1025 K. The NiIn alloy was observed to decompose completely by cellular precipitation reaction into a lamellar structure consisting of alternate lamellae of α and φ phases at all aging temperatures. The fine lamellar structure of the primary cells decomposed into a coarse lamellar structure in two stages. In the first stage, the secondary cells with larger interlamellar spacing decomposed the primary cells. In the second stage, the tertiary cells were also observed to decompose the primary cells. The primary cell growth data were analysed by using theories of Cahn, Hillert, Turnbull, and, Petermann and Hornbogen. The secondary and tertiary cell growth data were analysed by using theories of Livingston and Cahn and Petermann and Hornbogen. The driving force available for the transformation was calculated from the regular solution model. From the diffusivity values, it has been concluded that the growth of primary, secondary and tertiary cells occurs by diffusion of indium along the migrating grain boundaries.