Effects of Cr content and electromagnetic stirring on the phase separation of Cu-Cr alloy

Abstract

The Cu-Cr immiscible alloys were prepared by arc melting. The effects of Cr addition and electromagnetic stirring on the phase separation, microstructure were examined. The results show that serious phase segregation occurs at the center of the sample with increasing Cr contents, forming a sandwich like structure. The shape of the primary Cr transforms from fine dendrite to more developed dendrite. Thermodynamic analysis indicates that Cr addition increases the driving force for the liquid phase separation. The electromagnetic stirring can facilitate the relative motion between the Cr droplets and the melts, and thus intensify the segregation phenomenon. With Cr additions, the hardness in non-segregated area shows only slight increase, and in Cr segregated area shows a significant increase. While the electrical conductivity shows only slight decrease with increasing Cr content.

Effect of Liquid Miscibility Gap on Defects in Inconel 625–GRCop42 Joints through Analysis of Gradient Composition Microstructure

“…The presence of Cu-deprived and Cu-rich regions in the 30-95 wt.% GRCop42 samples is explained for the first time in this study by the existence of a liquid miscibility gap (i.e., unmixable liquids) in the Inconel 625-GRCop42 system. In contrast to the reported literature, which considers miscibility gaps in Cu-Cr and Cu-Nb binary supercooled systems [28,29], in this work, CALPHAD modeling (which is able to account for the quinary elemental system) shows a lack of liquid state miscibility above the liquidus (Figure 7a-d). The liquidus phase volume fraction plotted as a function of GRCop42 composition in Figure 7a indicates that the miscibility gap is predicted to start at 20 wt.% GRCop42 and end at 80 wt.%.…”

“…A liquid miscibility gap occurs when the Gibbs free energy of mixing (∆G mixing ) is positive because of a highly endothermic enthalpy of mixing (∆H mixing ), which overrides the entropy of mixing term (−T∆S mixing ) [27]. Despite Cu and Ni (the main constituent elements of GRCop42 and Inconel 625, respectively) being able to form a solid solution, lack of miscibility has been reported in supercooled Cu-Cr [28] and Cu-Nb [29] liquids (Cr and Nb are constituent elements of Inconel 625). While evidence of a liquid miscibility gap in the form of distinct Cu-rich and Cu-deprived structures is observed, no failures are reported in these alloys.…”