Microstructural characteristics of as-forged and β-air-cooled Zr-2.5Nb alloy

Multiple characterization and analysis techniques including electron backscatter diffraction (EBSD), electron channeling contrast (ECC) imaging, transmission electron microscopy (TEM) and microhardness test were jointly employed to investigate micro structural characteristics such as local composition, morphology, grain boundary characteristics and interphase orientation relationship of a forged Zr-2.5Nb alloy before and after beta-air-cooling. Results show that the as-forged specimen is composed of equiaxed and lamellar alpha grains and continuous net-like beta-Zr films. After the beta-air-cooling, the micro structure of the specimen is featured by basket-weave Widmanstatten structure, in which the inter-alpha-plate second phases are nanoscale beta-Zr. Analyses for crystallographic orientations reveal that the Burgers relationship has been strictly followed during the beta ->alpha cooling. Compared to the as-forged specimen, the hardness of the beta-air-cooled specimen is higher, which could be attributed to the decreased structural sizes of both alpha and beta phases, and the increased fraction of high angle boundaries as well.