  Grain boundary (GB) enthalpies in nanocrystalline (NC) $\mathrm
{Pd_{90}Au_{10}}$ are studied after preparation, thermal relaxation and plastic
deformation. By comparing results from atomistic computer simulations and
calorimetry, we show that increasing plastic deformation of equilibrated NC
$\mathrm {Pd_{90}Au_{10}}$ specimen causes an increase of the stored GB
enthalpy $\Delta \gamma$. We interpret this change of $\Delta \gamma$ as
stress-induced complexion transition from a low-energy to a high-energy GB-core
state. In fact, GBs behave not only as mere sinks and sources of zero- and
one-dimensional defects or act as migration barriers to the latter but also
have the capability of storing deformation history through configurational
changes of their core structure and hence GB enthalpy. Such a scenario can be
understood as a continuous complexion transition under non-equilibrium
conditions, which is related to hysteresis effects under loading-unloading
conditions.
