Nonequilibrium relaxations in a multiplicity of tilted grain boundaries (GBs) subjected to ultrafast thermal driving forces are investigated by atomistic modeling. By scrutinizing the intermediate metastable microstates and their assessable activation barriers in the underlying energy landscape

we demonstrate the energetics and atomic diffusions in tilted metastable GBs are disorder-driven rather than free volume-driven. A critical transition temperature is identified

separating the nonequilibrium GBs’ evolution into a fast-varying stage

and a tuning-ineffective stage

respectively. We further discover a universal correlation between such critical temperature and GBs’ inherent structure energy

which enables predicting the tunability of metastable GBs’ kinetic and mechanical properties.