https://doi.org/10.3390/met13010150
“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.”
”
The precipitation behavior was substantiated by utilizing differential scanning calorimetry (DSC) (STA 449 F3 Jupiter equipped with a platinum oven for usage up to 1500 °C, NETZSCH-Gerätebau GmbH, Selb, Germany). Within the chamber, two Al2O3 crucibles with lids were positioned with high repeatability. One of them was permanently the empty reference. The temperature and enthalpy were calibrated by melting pure In, Sn, Bi, Zn, and Al multiple times. During the whole experiment, the temperature was regulated using the sample temperature controller (STC). A reproducible baseline with empty crucibles was checked initially and regularly during the experiments to ensure repeatability. The heat flow signal of the baseline was subtracted from the alloy measurements to correct the signal. To perform calibration and tests in an atmosphere of argon, the protective (20 mL/min) and purge inlets (50 mL/min) were used during heating with 10 K/min from room temperature (RT) to 600 °C and 800 °C. After holding the final temperature for 1 min, the cooling process followed, as visualized in .
The solution annealed and quenched specimens, with optional cold deformation, were machined to cylinders with 4 mm diameter, followed by a surface grinding (up to P2500). All DSC specimens had a comparable mass of 117 mg, which was adjusted by their height. A reference of pure copper (Cu-OFE) with identical processing was measured for comparison. The onset temperatures were conducted according to DIN EN ISO 11357-1:2016, visualized with a (*) in the corresponding Figures 4, 7 and 11.
”
”
In order to characterize the precise temperature positions of the reactions, the DSC analysis in illustrates onset and peak temperatures up to conditions 1 and 2 (referring to ), emphasizing the experiments’ high reproducibility. Generally, the DSC signals of CuCr0.7 appeared with a large exothermic peak at lower temperatures. Cold rolling, prior to the in-situ aging during the DSC measurement, did not promote solid-state reactions with huge impacts. The average peak temperature of specimens with 75% cross section reduction was 454.7 °C (455.9 °C and 453.5 °C) and only 16 K lower compared to the average 470.8 °C (468.1 °C and 473.5 °C) for specimens without cold rolling prior to the measurements. This investigation correlates well with developments in hardness and electrical conductivity (), confirming that the alloy reacted more sensitively to temperature than to the introduction of crystallographic defects.
“
