Liquid phase separation of Cu–Cr alloys during the vacuum breakdown

The microstructures of the surfaces and cross sections of Cu–Cr contact alloys were analyzed after the vacuum breakdown was repeated for 100 times. The results reveal that the liquid phase separation was involved in the microstructure evolution of the alloys during the breakdown. The Cr-rich phase from the liquid separation featured the morphology of spherical- and sheeted-shaped particles. The sizes of the Cr spheres ranged from several nanometers to hundreds of nanometers, and were not strongly dependent on the compositions of the alloys. The large Cr-rich droplets could be elongated and swirled due to the liquid flow, resulting in the formation of the Cr phase with sheeted-shaped particles. The fractions of Cr sheets increased with the increasing of the Cr contents; however, their sizes decreased significantly, compared with those of their parent alloys.

► Liquid phase separation is involved in the microstructure evolution of the Cu–Cr alloys during vacuum breakdown.
► The morphology of the Cr-rich phase with spherical and sheeted shapes results from the liquid separation.
► Cr-rich spheres in nanometer size are formed in the melt layer.