Peculiarities of the formation of high-defect states in mechanocomposites and powders of niobium and aluminum under severe deformation in planetary ball mills

Abstract

The microstructural peculiarities of Nb powder and Nb + Al powder mixtures after mechanical activation in a high-energy planetary ball mill were investigated by transmission electron microscopy. The materials revealed two-level structural states: nanograins of size from 50 to 100 nm that contain subgrains of size ∼20 nm and less with low-angle misorientation boundaries, elastic lattice curvature gCij≈100°…200°μm−1, curl or curvature gradient ∂χij/∂r > 100 μm−2 and high (up to 10E μm−1) local stress gradients (couples). An important factor in the formation of the above states is the capability of nano-objects to reach high elastic lattice curvature, high gradients of this curvature, and high local internal stress gradients at rather low absolute values of the internal stress.