Nanoforming behaviour and microstructural evolution during nanoimprinting of ultrafine-grained and nanocrystalline metals

SX-Ni showed the smallest extrusion height together with a sinking-in of the formed region. This is accompanied by strong orientation gradients up to 18° below the cavities. The UFG samples exhibited the best formability, with a subgrain formation inside and around the cavities. The plastic flow is confined to the surface and a pile-up formation occurs. For the nanocrystalline material only a slight elongation of the grains inside the cavity was found, yielding moreover a smooth and homogeneous extruded geometry. These findings can be explained by the grain size to cavity width ratio as well as the yield strength and the work hardening behaviour of the materials.