Bimodal plate structures induced by pulsed laser in duplex-phase Zr alloy

A duplex-phase Zr-2.5Nb alloy was treated by pulsed laser, followed by careful microstructural characterization using field emission gun scanning electron microscope and attached electron backscatter diffraction. Beneath the modification zones with common uniform α-plate structures（UPS）, a layer of unreported bimodal α-plate structures（BPS） featured by coarse（submicron）plates forming multiple cores surrounded by dense fine（nanoscale） plates was found. Presence of such BPS is attributed to non-equilibrium thermodynamic conditions induced by the pulsed laser treatments. Limited diffusion of Nb due to the short pulse during laser heating allows β phases with distinctly different Nb contents to be presented： Nb-enriched prior β films and Nb-depleted β phases, transforming into the fine and the coarse plates during cooling, respectively. Orientation analyses show that both types of plates in the BPS are aroused essentially from a single β orientation, suggesting epitaxial growth of the Nb-depletedβ phases from the preexisting β films.