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The precipitation hardening of a Cu-11Ni-19Zn-1Sn alloy has been studied by means of Differential Scanning Calorimetry (DSC), High-Resolution Transmission Electron Microscopy (HRTEM), and hardness measurements. The calorimetric curves, in the range of temperatures analyzed, show the presence of one exothermic reaction followed by an endothermic one. The exothermic DSC peak is due to the segregation of CuNiZn precipitates and it is associated to a noticeable improvement of the mechanical properties of the alloy. The endothermic effect is associated to the dissolution of the CuNiZn precipitates into the copper matrix for restoring the starting Cu-11Ni-19Zn-1Sn homogeneous solid solution. The reaction mechanisms of these processes have been proposed from the kinetic analysis of the exothermic and endothermic DSC signals. The results obtained point out that tin plays a decisive role on the precipitation hardening of the alloy, because age hardening is not observed in the case of a Cu-Ni-Zn ternary alloy of similar composition. [ABSTRACT FROM AUTHOR]

Abstract: The hot mechanical behaviour and microstructure of Cu–5vol.% TiC, Cu–5vol.% ZrO2 and Cu–2.5vol.% TiC–2.5vol.% ZrO2 alloys prepared by reaction milling were studied. After a test of 1h annealing at 1173K, the Cu–5vol.% ZrO2 alloy presented the lower softening resistance to annealing, while the other two ones kept their initial room-temperature hardness (about 2GPa). Hot-compression tests at 773 and 1123K, at initial true strain rates of 0.85 × 10-3 and 0.85 × 10-4s-1 were performed. The Cu–2.5vol.% TiC–2.5vol.% ZrO2 and the Cu–5vol.% ZrO2 alloys were the strongest and softest materials, respectively. Moreover, by electron microscopy, nanometric TiC and micrometric particles were detected in the Cu–5vol.% TiC and Cu–5vol.% ZrO2 alloys, respectively. A possible explanation for the observed behaviour of these materials is proposed. In the compression tests, it was also found that strain rate has a low effect on flow stress, as it has been previously observed by various authors in dispersion-strengthened alloys deformed at high temperatures. [Copyright &y& Elsevier]

The mechanical behaviour of Cu–5vol.% Al2O3, Cu–5vol.% TiC and Cu–2.5vol.% TiC–2.5vol.% Al2O3 alloys (nominal compositions) prepared by reaction milling and extrusion at 1023K was studied between 673 and 1123K. The annealing-softening resistance and the compression resistance at elevated temperatures of these alloys increased according to the following trend: Cu–5vol.% Al2O3; Cu–5vol.% TiC; Cu–2.5vol.% TiC–2.5vol.% Al2O3. An explanation for this behaviour is given. [Copyright &y& Elsevier]