Minor-alloyed Cu-Ni-Si alloys with high hardness and electric conductivity designed by a cluster formula approach

Cu-Ni-Si alloys are widely used due to their good electrical conductivities in combination with high strength and hardness. In the present work, minor-alloying with M = (Cr, Fe, Mo, Zr) was conducted for the objective of further improving their hardness while maintaining their conductivity level. A cluster-plus-glue-atom model was introduced to design the compositions of M-alloyed Cu-Ni-Si alloys, in which an ideal composition formula [(Ni,Si,M)-Cu12]Cu3 (molar proportion) was proposed. To guarantee the complete precipitation of solute elements in fine δ-Ni2Si precipitates, the atomic ratio of (Ni,M)/Si was set as 2/1. Thus the designed alloy series of Cu93.75(Ni/Zr)3.75Si2.08(Cr/Fe/Mo)0.42 (at%) were arc-melted into ingots under argon atmosphere, and solid-solutioned at 950 °C for 1 h plus water quenching and then aged at 450 °C for different hours. The experimental results showed that these designed alloys exhibit high hardness (HV > 1.7 GPa) and good electrical conductivities (≥ 35% IACS). Specifically, the quinary Cu93.75Ni3.54Si2.08(Cr/Fe)0.42Zr0.21 alloys (Cu-3.32Ni-0.93Si-0.37(Cr/Fe)−0.30Zr wt%) possess both a high hardness with HV = 2.5-2.7 GPa, comparable to the high-strength KLFA85 alloy (Cu-3.2Ni-0.7Si-1.1Zn wt%, HV = 2.548 GPa), and a good electrical conductivity (35-36% IACS).