Synthesis of CuCr and CuCrAg alloys with extended solid solubility with nano-Al2O3 dispersion by mechanical alloying and consolidation by high pressure sintering

Abstract

Cu–4.5Cr and Cu–4.5Cr–3Ag (wt%) alloys with nanocrystalline Al2O3 dispersion (5 or 10wt%) were synthesized by mechanical alloying and consolidated by high pressure sintering at two different temperatures. Mechanical alloying/milling leads to formation of nanocrystalline matrix grains of about 40–60nm after 25h of milling with nanometric (<20nm) Al2O3 particles dispersed in it. After consolidation by high pressure sintering (8GPa at 600–800°C), the dispersoids nearly retain their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. Apparent density of the compacts is about 95% of the theoretical density of the corresponding compositions. 10wt% Al2O3 dispersed Cu–4.5Cr–3Ag alloy consolidated at 800°C shows maximum hardness (435 VHN) and wear resistance. High hardness at this material is due to fine grain structure with nano-dispersoids. The fine grained structure is generated due to dynamic recrystallization during high pressure sintering which has been observed through metallography as well as macro-/micro-texture analysis. The electrical conductivity of the pellets without and with nano-Al2O3 dispersion is about 40–45% IACS (International Annealing Copper Standard) and 35% IACS, respectively. Thus, mechanical alloying followed by high pressure sintering seems a potential route for developing nano-Al2O3 dispersed Cu–Cr and Cu–Cr–Ag alloys for heavy duty electrical contacts.