Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. Rough diamond anvils are introduced to reach maximum friction equal to yield strength in shear and the first in-situ study of the evolution of the pressure-dependent yield strength and radial distribution of nanostructural parameters are performed for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic

isotropic

and strain-path-independent and reaches steady values of the crystallite size and dislocation density

which are pressure-

strain- and strain-path-independent. However

steady states for α-Zr obtained with smooth and rough anvils are different

causing major challenge in plasticity theory.