Kinetics of Cellular Growth and Coarsening in Aged U-Nb Alloys

Abstract

Lamellar decomposition products result when U-Nb alloys are transformed between about 300C and the 647C monotectoid temperature. The kinetics of these cellular precipitation reactions are of interest since the resulting microstructures give undesirable properties. Detailed kinetic studies of these reactions were undertaken in U-Nb alloys isothermally transformed over a wide span of time and temperature. The volume fractions, growth rates, interlamellar spacings, and phase compositions of the discontinuous precipitation as well as the succeeding discontinuous coarsening reactions were measured. These results will be compared with theories of cellular growth. The added effects of non-steady-state growth, diverging lamellae, and the effect of nucleation site (grain boundary vs. carbide inclusions) will be highlighted.