Metallic crystalline/amorphous core–shell nanoparticles consisting of a crystalline Pd core (c-Pd) surrounded by an amorphous Fe25Sc75 shell (a-FeSc) are prepared by inert-gas condensation. A phase transformation of the c-Pd by a solid-state diffusion process resulting in an amorphous core (a-PdSc) surrounded by an amorphous FeSc shell is observed if the core–shell structure is irradiated at ambient temperature with 300 keV electrons. The amorphization process seems to involve the diffusion of irradiation-induced defects and is presumably driven by the large negative heat of mixing of Pd and Sc, as well as by the excess enthalpy of the interfaces between the c-Pd regions and the surrounding a-FeSc. The structural transformation reported here opens a new way to producing metallic amorphous core–shell nanoparticles of different chemical compositions and probably novel properties.