THE EFFECT OF PRECIPITATION CHARACTERISTICS ON HARDENING BEHAVIOR IN Cu–Cr–Sn ALLOY WITH Sn VARIATION

Abstract

The influence of minor solute additions of Sn on hardening behavior and microstructure evolution of the Cu–Cr–Sn alloys has been investigated with help of an optical microscope, scanning electron microscope, transmission electron microscopy, and the Vickers hardness tester. Experimental results show that the Sn solutes, homogeneously distributed within the Cu matrix, provide a weak solid solution strengthening effect in the Cu–Cr–Sn alloy, nevertheless are important in enhancing precipitation hardening. The Cu–0.43Cr–0.36Sn alloy exhibits a significant age-hardening effect with a hardness increase by 62 HV after peak aging at 450 °C, which is stronger than that of the Cu–0.43Cr–0.08Sn and the Cu–0.43Cr–0.17Zr–0.05Mg–0.1RE alloys. A trace amount of Sn is highly effective at suppressing the transformation of the Cr-rich phase from the face-centered cubic (FCC) into the body-centered cubic (BCC) structure in the Cu–Cr alloys during the aging process, and therefore the FCC Cr-rich precipitate is the dominant strengthening phase in the Cu–Cr–Sn alloys. Besides, a higher areal number density of Cr-rich precipitates (~4.2 • 10¹⁵ m^–2) was observed in peak-aging Cu–0.43Cr–0.36Sn alloy as compared to Cu–0.43Cr–0.08Sn alloy, which shows that the adding Sn to Cu–Cr alloy can accelerate the nucleation of the Cr-rich precipitates. The improvement of precipitation hardening and hardening kinetics in the Cu–0.43Cr–0.36Sn alloy is mainly attributed to the acceleration in the nucleation of Cr-rich precipitates through Sn addition.