Kinetics of Discontinuous Precipitation and Coarsening in Ni-In Alloys

摘要

The morphology and growth kinetics of cellular precipitation and discontinuous coarsening of cellular precipitates have been studied in two Ni-In alloys containing 4 and 6 at.% In in the temperature range 740 to 1010 K. The data for 2 and 8 at.% In alloys have been taken from earlier investigations. Growth rate measurements were carried out utilizing optical microscopy. Both optical microscopy and scanning electron microscopy were utilized for interlamellar spacing measurements. All alloys were observed to decompose completely by the cellular precipitation reaction into a lamellar structure consisting of alternate lamellae of the a and Ni_3In phases at all aging temperatures. The fine lamellar structure of the primary cells decomposed into a coarse lamellar structure consisting of the same two phases. The primary and secondary cell growth data were analysed by using model after Petermann and Hornbogen. From the diffusivity values, it has been concluded that the growth of primary and secondary cells occurs by diffusion of In along the grain boundaries. The rate of migration of the reaction front for both cellular precipitation and discontinuous coarsening is increased markedly with increasing In content.