A Comparative Differential Scanning Calorimetry Study of Precipitation Hardenable Copper-Based Alloys with Optimized Strength and High Conductivity

Abstract

Copper alloys with chromium, hafnium, and scandium combining enhanced strength as well as high electrical and thermal conductivity are analyzed in depth. The aim is to compare the precipitation process during temperature exposure to meet increasing material requirements. This research focuses on alloying elements having a limited, maximum 1 wt.%, and with temperature decreasing solubility in copper. For the simultaneous enhancement of mechanical strength and conductivity, precipitation hardening is the utilized mechanism during the processing of as-casted annealed and quenched specimens and in combination with optional cold-rolling prior to the aging process. Extensive DSC measurements, accompanied by metallographic investigations, and the analysis of hardness and electrical conductivity, lead to a versatile description and comparison of different alloying systems. CuCr0.7 starts to precipitate early and is mainly influenced by the temperature of aging. Provoking the solid solution with cold deformation has a less significant influence on the following precipitation. CuSc0.3 and CuHf0.7 precipitate at higher temperatures and are highly influenced by cold deformation prior to aging. Furthermore, CuHf0.7 and CuSc0.3 show advantages regarding the recrystallization behavior, making them especially applicable for higher operating temperatures. Future research will assess ternary alloy combinations to further scoop the potential.

DSC Analysis of the Effect of Cold Deformation on the Precipitation Kinetics of a Binary Cu-Sc Alloy

“…In addition, the curves show the peak of the second exothermic reaction (indicated by the number 1 with arrows), which can be attributed to recrystallization of the microstructure. This investigation agrees with the findings of Dölling et al [31] obtained with a directly comparable experimental setup and raw materials. The obtained peak temperature values related to Cu4Sc precipitation as a function of heating rates are shown in Table 1.…”

“…The DSC scans at different heating rates (10, 15, 20, and 40 K/min) for the nondeformed CuSc0.4 specimen (Figure 2a) all show an exothermic peak (Exo) between 760 K and 950 K. A closely related study by Dölling et al [31] showed highly comparable curves for a non-deformed CuSc0.3 alloy at a 10 K/min heating rate with a peak temperature of 842.1 K. Furthermore, there was no recrystallization detected for non-formed Cu-Sc specimens, resulting in only a single peak indicating the precipitation reaction.…”

DSC Analysis of the Effect of Cold Deformation on the Precipitation Kinetics of a Binary Cu-SC Alloy

“…The curves also show peaks of the second exothermic reaction (arrows 1), which can be attributed to a recrystallization of the microstructure. This investigation agrees with the findings of Dölling et al [31] with a directly comparable experimental setup and the chosen raw material. The obtained peak temperature values related to Cu4Sc precipitation as a function of heating rates are shown in Table 1.…”

“…The fine lamellar structures (dark grey) are homogeneously distributed within the copper matrix (light grey). The characteristics of the Cu4Sc precipitates are comparable to those of Dölling et al [31], which were analyzed at the same heating rate but slightly lower final temperature (600 °C). Energy Dispersive X-ray spectroscopy (EDX) showed that these structures are directly associated with an increased scandium content.…”

“…The DSC scans at different heating rates (10, 15, 20 and 40 K/min) for the non-deformed CuSc0.4 specimen (Figure 2a) all show an exothermic peak (Exo) between 760 K and 950 K. A closely related study by Dölling et al [31] showed highly comparable curves for a non-deformed CuSc0.3 alloy at 10 K/min heating rate with a peak temperature of 842,05 K. Furthermore, there was no recrystallization detected for non-formed Cu-Sc specimens, resulting in the only peak present indicating the precipitation reaction.…”