  Through millennia humans exploited the natural property of metals to get
stronger or hardened when mechanically deformed. Ultimately rooted in the
motion of dislocations, mechanisms of metal hardening remained in the
crosshairs of physical metallurgists for over a century. Here, we performed
atomistic simulations at the limits of supercomputing, which are sufficiently
large to be statistically representative of macroscopic crystal plasticity yet
fully resolved to examine the origins of metal hardening at its most
fundamental level of atomic motion. We demonstrate that the notorious staged
(inflection) hardening of metals is a direct consequence of crystal rotation
under uniaxial straining. At variance with widely divergent and contradictory
views in the literature, we observe that basic mechanisms of dislocation
behavior are the same across all stages of metal hardening.
