Microstructural Evolution in Zr-1Nb and Zr-1Nb-1Sn-0.1Fe Alloys

This article summarizes the evolution of microstructure in binary Zr-1Nb and quaternary Zr-1Nb-1Sn-0.1Fe alloys after (1) β quenching and tempering and (2) cold working and annealing. The morphologies of constituent phases and precipitates, their shape, size, and nature have been studied in detail using transmission electron microscopy (TEM). The β-quenched alloys, in general, exhibited a lath martensitic microstructure. On tempering, the martensitic microstructure underwent considerable changes with respect to the lath dimensions and precipitation behavior, ultimately leading to an equiaxed recrystallized microstructure. Annealing studies of cold-worked binary alloy showed precipitation of the β phase with varying Nb content depending on the heat-treatment temperature and time. In the quaternary alloy, precipitation of the Zr-Nb-Fe type phase along with the β phase took place on annealing the cold-worked samples. High-resolution electron microscopy (HREM) of the recrystallized microstructures was carried out to study the internal structure and the interface structure of the precipitating phases. In the annealing study, mechanical properties of the annealed samples were also determined. Microstructural observations together with mechanical property data concluded that in both alloys, complete recrystallization of the cold-worked microstructures took place on annealing the samples at 853 K for 1 hour.