Abstract
Microstructures of CuCr25 and CuCr50 alloys treated by high current pulsed electron beam (HCPEB) were investigated in this work. The microstructure and solidification behavior of the Cr-rich phases were characterized by scanning electron microscopy (SEM). Results show that a remelting layer of 3~5 μm is formed on the surface of Cu-Cr alloys. The microstructure of the remelting layer reveals that both the fine dispersion of Cr-rich spheroids and the craters appear after HCPEB treatment. This means that metastable liquid phase separation occurs during rapid solidification under HCPEB treatment. In addition, the appearance of relatively large craters in the subsurface of Cr-rich particles with the distance about 5-10 μm provides direct evidences supporting results reported by other researchers in terms of numerical simulation temperature field of HCPEB treatments.
Highlights
Due to very limited mutual solubility between Cu and Cr at room temperature, Cu-Cr alloys have been developed to meet increasing industrial requirements for its outstanding combination of high mechanical strength and good electrical conductivities[1,2,3,4,5]
Surface morphologies of the CuCr25 alloy after high current pulsed electron beam (HCPEB) treatment is shown in Figure 2a and Figure 2b
Various microstructure features are observed in Figure 2a: the large craters as denoted by the arrow A; the cracks near the crater as indicated by the arrow B; the splashed layer as indicated by the arrow C
Summary
Due to very limited mutual solubility between Cu and Cr at room temperature, Cu-Cr alloys have been developed to meet increasing industrial requirements for its outstanding combination of high mechanical strength and good electrical conductivities[1,2,3,4,5]. Because of high withstand voltage and exceptional current breaking capacity, Cu-Cr alloys have been considered as the best contact material for medium voltage vacuum interrupter[4]. The finer the Cr-rich phase was, the better the electric contact materials properties could be achieved. In order to further improve electrical and mechanical properties, many efforts have been focused on refining and homogenizing the Cr-rich phase. Rapid solidification is believed to be able to refine microstructure and induce supersaturated solid solution, and was used by many researchers to prepare Cu-Cr alloys. Fine Cr-rich spheroids were detected in Cu matrix and attributed to occurrence of the liquid phase separation during rapid solidification
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