α→β Transformation characteristics revealed by pulsed laser-induced non-equilibrium microstructures in duplex-phase Zr alloy

Microstructures of a duplex-phase Zr-2.5Nb alloy treated by pulsed laser were characterized by electron backscatter diffraction (EBSD) and electron channeling contrast (ECC) imaging techniques. Major attention has been paid to non-equilibrium hybrid microstructure consisting of both prior alpha and beta phases, and alpha plates transformed from new beta phases to probe alpha ->beta transformation characteristics in the alloy. The origin of the hybrid microstructure is attributed to the specific thermodynamic conditions induced by the pulsed laser treatment. ECC observation shows that newly formed beta phases during laser heating prefer to nucleate and grow at the expense of edges of prior alpha grains rather than their interiors. EBSD analyses further reveal that orientations of the new beta phases are not determined by the prior alpha grains according to the Burgers relationship but maintain those of the prior beta phases in an epitaxial growth way.