Physical Properties and Precipitate Microstructures of Cu-Hf Alloys at Different Processing Stages

Abstract

The microstructural evolution and hardness and physical properties of a Cu-Hf alloy at the different processing stages were investigated using hardness, conductivity and tensile measurements, metallographic microscopy, scanning electron microscopy, and transmission electron microscopy. The results reveal that the electrical conductivity of these alloys was above 80% IACS after aging at 450°C, and the hardness and conductivity of the Cu-0.9Hf alloy were 180 HV0.5 and 80% IACS, respectively. The softening temperature of the Cu-0.15Hf alloy is 525°C, and the softening temperature of Cu-0.4Hf and Cu-0.9Hf alloys is 550°C. The precipitated Hf-containing phase exhibited a short rod-like structure, the size of which increased with aging time at a slow rate and resulted in the size of ~20 nm after aging at 450°C for 300 min.

Effect of process parameters on the phase transformation kinetics in copper-based alloys and composites

“…Firstly, in the as-cast alloy state, an increase in hardness is noted with the addition of Hf [27]. As can be found in the literature, Cu-0.9Hf has twice the hardness the Cu-0.15Hf alloy has [27][28][29]. On the other hand, this is not a trend that can be applied to the conductivity, as it decreases with the addition of Hf.…”

“…For the first two alloys, Cu-0.15Hf and Cu-0.4Hf, an aging temperature of 450 °C is the optimal temperature where the peak aging occurs after 30 minutes, and for the third Cu-0.9Hf, after 60 minutes. After aging, both the values for conductivity and hardness for these alloys are higher than in other possible states, and so it is preferred [27].…”

“…Due to hafnium's promising characteristics and properties, including tremendous resistance to corrosion, it is viewed as a genuinely desirable material in different superalloys as well as nuclear reactor rods [27]. In the case of copper alloys, the influence of Hf is similar to that of Zr in the sense that it increases the recrystallization temperature and heat resistance of copper.…”

“…A group of authors studied and compared copper alloys [27], with three different Hf contents (Cu-0.15Hf, Cu-0.4Hf, and Cu-0.9Hf). Firstly, in the as-cast alloy state, an increase in hardness is noted with the addition of Hf [27]. As can be found in the literature, Cu-0.9Hf has twice the hardness the Cu-0.15Hf alloy has [27][28][29].…”

“…Showing this through an example, the conductivity of Cu-0.4Hf is higher than that of Cu-0.9Hf alloy. Seen through IACS (International annealed copper standard), the conductivity of Cu-0.9Hf is 44.9% IACS, while the conductivity of Cu-0.9Hf is 36.3% IACS [27]. When the alloys are cold rolled, they all exhibit an increase in hardness, however, in this state conductivity does not change much either.…”