Preparation and forming mechanism of ultrathin-walled Ni-Cu alloy tubes with submicrometer structures by ball spinning

Ball spinning at room temperature produced the ultrathin-walled Ni-Cu alloy tubes with submicrometer structures. The microstructure evolution and strengthening mechanism of tubes with different thickness reduction ratios were investigated. Transmission electron microscopy (TEM) shows that the dislocation slip dominates the formation of ultra-fine laminated (UFL) structures and ultra-fine grains (UFGs) during ball spinning. The high strain rate and strain gradient promote the slip of dislocation, the refinement of grains, the supplement of deformation twins, and eventually form the Ni-Cu alloy tubes with ultra-thin thickness. X-ray diffraction (XRD) and electron back-scattering diffraction (EBSD) analysis suggests that there are more low-angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs) in the tubes when the value of thickness reduction ratio reaches 80%. At this time, the inner texture is primarily < 110 > //RD and cubic. The increase of the thickness reduction ratio to 90% decreases the percentage of LAGBs, the density of GNDs, and the intensity of < 1 1 0 > //RD. A microhardness measurement system was utilised to detect the Vickers hardness of each tube. After ball spinning, the uniformity of structure and hardness of tubes are significantly improved. When the value of thickness reduction ratio is 80%, the average Vickers hardness value of the tube is increased by 74.5%. When the value of thickness reduction ratio attains 90%, the average Vickers hardness is increased by 122.9% compared with the tube blank.