Synthesis of Cu–Cr Composite Alloys with a Layered Structure Featuring High Arc Resistance

Abstract

Cu–(20 wt %)Cr alloys with a layered structure are synthesized by liquid phase impregnation of chromium powder with copper melt. In synthesizing the alloys, the corresponding composites are subjected to pre-crystallization vibrational treatment. The layers of composites are enriched in chromium to different extents (from ~2 to 90 vol %). The layer composition and structure are shown to depend on the temperature and duration of vibrational treatment, as well as on the degree of pre-synthesis compaction of chromium powder. We study the phase composition of prepared alloys, the element composition of phases, and their microhardness. Our experiments show for the first time the formation of Cr core–(Cr + Cu) shell structures on the basis of chromium particles. These structures have a gradient distribution of the elements in the shell and form at the initial stages of interaction between Cu and Cr. At advanced stages of interaction, chromium particles are permeated with copper completely. In electron microscopy images in backscattered electrons, these formations appear as being greatly blurred and shapeless. In this way, precursors to crystallization of chromium dendrites are formed. The dendrite crystallization takes place in upper layers of the melt provided copper is present at the necessary and sufficient concentration (or at considerable superheating). The morphology of dendrites in which crystallization from precursors was incomplete is studied. The contact area of α-Cu is anticipated to be greatly reduced by the precursors that spread in the copper matrix during arcing. At the same time, contact welding will be considerably reduced, compared to similar composites with purely copper matrices (e.g., Cu–W).