In this brief review we discuss the transient processes in solids under
irradiation with femtosecond X-ray free-electron-laser (FEL) pulses and
swift-heavy ions (SHI). Both kinds of irradiation produce highly excited
electrons in a target on extremely short timescales. Transfer of the excess
electronic energy into the lattice may lead to observable target modifications
such as phase transitions and damage formation. Transient kinetics of material
excitation and relaxation under FEL or SHI irradiation are comparatively
discussed. The same origin for the electronic and atomic relaxation in both
cases is demonstrated. Differences in these kinetics introduced by the
geometrical effects ({\mu}m-size of a laser spot vs nm-size of an ion track)
and initial irradiation (photoabsorption vs an ion impact) are analyzed. The
basic mechanisms of electron transport and electron-lattice coupling are
addressed. Appropriate models and their limitations are presented.
Possibilities of thermal and nonthermal melting of materials under FEL and SHI
irradiation are discussed
