Equal channel angular extrusion of niobium single crystals

Niobium single crystals were deformed by equal channel angular extrusion (ECAE) with one, four, and eight passes at room temperature. Microstructural characterization was performed using scanning electron microscopy (SEM) and electron-backscattered diffraction (EBSD). The microstructure of the sample deformed after one ECAE pass displays uniformly spaced coarse parallel sets of shear bands. After four passes, the shear bands intersect each other throughout the sample giving rise to the development of finegrained crystallites at their intersections. In the most deformed specimen (eight ECAE passes), the microstructure becomes more uniform and consists of fine grains with sizes of about 1 (mu)m and elongated subgrains lying nearly parallel to the extrusion direction. The fraction of high angle boundaries is about 48%.