Synthesis of copper alloys with extended solid solubility and nano Al₂O₃ dispersion by mechanical alloying and equal channel angular pressing

Abstract

Cu–4.5 wt % Cr and Cu–4.5 wt % Cr–3 wt % Ag alloys, with and without nanocrystalline Al₂O₃ dispersions (particle size <10 nm), were synthesized by mechanical alloying/milling and consolidated by equal-channel angular pressing (ECAP) at ambient temperature. Microstructural characterization and phase analysis by X-ray diffraction, as well as scanning and transmission electron microscopy, provided evidence for the formation of a Cu-rich extended solid solution with nanometric (<30 nm) crystallite size after 25 h of milling, with uniformly dispersed alumina nanoparticles embedded in it. Consolidation of Cu–4.5 wt % Cr–3 wt % Ag alloy with 10 wt % nanocrystalline Al₂O₃ by eight ECAP passes was shown to result in a composite with an exceptionally large hardness of 390 VHN and enhanced wear resistance. The electrical conductivity of the pellets of the latter alloy without Al₂O₃ is about 30% IACS (international annealing copper standard), whereas pellets with 5 or 10 wt % Al₂O₃ dispersion exhibit a conductivity of about 20–25% IACS. Thus, the present room temperature synthesis and consolidation route appear to offer a promising avenue for developing high-strength, wear/erosion-resistant Cu-based electrical contacts with nano-ceramic dispersion.

Keywords:

• copper alloys
• mechanical alloying
• ECAP
• nanoparticle dispersion
• wear
• electrical conductivity

Acknowledgement

Partial financial support from the International Copper Association (USA) and Department of Science and Technology, New Delhi (NSTI Grant No. SR/S5/NM-04/2005) is gratefully acknowledged. Technical support from Mr. Peter König, Dr. Gabriele Vidrich and Dr. Markus Krieger is gratefully acknowledged.