The impact of introducing trace transition elements on the thermal stability and conductivity of pure copper was examined through metallographic microscopy (OM), transmission electron microscopy (TEM), and electrical conductivity measurements; the interaction between trace transition element and trace impurity element S in the matrix was analyzed. The results show that the addition of trace Ti and trace Cr, Ni, and Ag elements significantly enhances the thermal stability of the pure copper grain size. After high-temperature treatment at 900 °C/30 min, the grain sizes of Cu, Cu-Ti-S, and Cu-Cr-Ni-Ag-S were measured and found to be 200.24 μm, 83.83 μm, and 31.08 μm, respectively, thus establishing a thermal stability ranking of Cu-Cr-Ni-Ag-S > Cu-Ti-S > Cu. Furthermore, the conductivities of pure copper remain high even after the addition of trace transition elements, with recorded values for Cu, Cu-Ti-S, and Cu-Cr-Ni-Ag-S of 100.7% IACS, 100.2% IACS, and 98.5% IACS, respectively. The enhancement of thermal stability is primarily attributed to the pinning effect of the TiS and CrS phases, as well as the solid solution dragging of Ni and Ag elements. Trace Ti and Cr elements can react with S impurities to form a hexagonal-structure TiS phase and monoclinic-structure CrS phase, which are non-coherent with the matrix. Notably, the CrS phase is smaller than the TiS phase. In addition, the precipitation of these compounds also reduces the scattering of free electrons by solute atoms, thereby minimizing their impact on the alloy’s conductivity.

The effect of trace Bi impurities on the flow stress, microstructure evolution, and dynamic recrystallization (DRX) of the ultrahigh-purity copper was systematically investigated by a hot compression test at 600 °C. The results show that the peak stress of the ultrahigh-purity copper gradually decreases with increasing Bi content. Trace Bi impurities can refine the microstructure of ultrahigh-purity copper. However, the refinement effect of 50 wt ppm Bi is much more significant than that of 140 wt ppm Bi during the hot deformation. This effect is ascribed to the higher concentration of Bi at GBs, which induces severe GB cracks that reduces the driving force for the nucleation of DRX grains. In addition, the introduction of Bi inhibits the DRX of the ultrahigh-purity copper and transforms its DRX process from the discontinuous dynamic recrystallization (DDRX) to the coexistence of DDRX and continuous dynamic recrystallization (CDRX) mechanisms.