Studies On Cluster-Related Composition Design And Properties Of Electrical Conductivity Cu-Ni-Sn-based Alloys

Electrical conductivity Cu alloys have been used to produce electron devices, sucn as relays, switches, and electrical connectors, due to their good electrical conductivity, mechanical properites and corrosion-resistance. Among them, beryllium bronze (Cu-Be alloys), Phosphor bronze (Cu-Sn-P alloys) and Cu-Ni-Sn alloys are porpular in the present Cu alloys. Beryllium bronze has not only superior mechanical properties (high strength, good fatigue-resistant properties), but also possesses high conductivity, which could satisfy the requirments of advanced electrical devices. However, it is costly and poisonous that some kind of substitutional materials need to be seeked urgently. Phosphor bronze has generally poor conductivity and poor mechnical properites so that it is just used to make cheap switches. The properties of Cu-Ni-Sn alloys are between within them and such kind of materials are potentical to substitute for the beryllium bronze. It is noted that the conductivities of most of the conventional Cu-Ni-Sn alloys need to be improved further, which means that the conductivity should be not less than 15.0 %IACS. Therefore, how to improve the conductivities of Cu-Ni-Sn-based alloys is the key step to develop this kind of materials.Since the conductivity reflects the purity of alloy matrix, the main idea of the present work is to control the solute amounts and the ratio between solute elements through composition design to realize the second compounds precipitated from Cu matrix completely. For Cu-Ni-Sn system, the solutes Ni and Sn are solid-solutioned in Cu matrix at high temperature to form supersaturated FCC-α solid solution, then they would be precipitated with the form of (Cu,Ni)3Sn phase with DO22 and L12 structures respectively. Thus the high strength and good conductivity are reaches simultaneously. The previous studies showed that both (Ni+Sn) content and Ni/Sn ratio affect the conductivities and strengths of Cu alloys. However, up to now, the controlment of (Ni+Sn) content and Ni/Sn ratio have been realized through try-and-error experiments, and no suitable composition methods were reported. Thereof, the present work aims to explore the composition rule of the conductive Cu-Ni-Sn-based alloys via our developed’cluster-plus-glue-atom’model. Taking the C72700 industry alloy (Cu-9Ni-6Sn, wt.%) as a research background, two series of cluster formulae, [Cu-Cu12](Sn1/4Ni3/4)xCu6-x (Series 1) and [Cu-Cu12](Sn1/1+yNiy/1+y)2.5Cu3.5 (Series 2, y being Ni/Sn ratio) are first designed to investigate the effects of (Ni+Sn) contents and Ni/Sn ratios on the conductivities and microhardness HV of Cu-Ni-Sn ternary alloys, respectively, where the optimum (Ni+Sn) content and Ni/Sn ratio are expected to be achieved. That Fe, Mn and Nb minor-alloyed of Cu-Ni-Sn would form the cluster formula [Cu-Cu)2](Fem(Niy/(1+y)Sn1/(1+y))nMn0.044Nb0.0i3Cu3.5) (m+n+0.044+0.013=2.5) to investigate how impurity Fe content and Ni/Sn affect the conductivity and HV. Thus it will give a support to control the Fe impuriy in indurstry to optimize the conductive Cu-Ni-Sn-based alloys.The alloy ingots of designed three series were prepared by arc-melting the mixtures of Cu, Ni, Sn, and minor Fe, Mo and Nb with high purities in the Ti-gettered high-purity argon atmosphere. The ingots were flipped and remelted at least three times to ensure the chemical homogeneity. The as-cast ingots were solid-solutioned at 1073 K for 12 h with a vaccum condition of 6*10-3 Pa, followed by a water-quenching, and pre-deformed with a 75% deformation, and then aged at 673 K for 2h. The micro structrual analysis were carried on with OM, XRD, SEM and TEM machines. The microhardess, conductivity and Youn’s modulus were also measured using special machines. The conclusions are as follows.(1) Fixing the Ni/Sn ratio as 3 which is the ratio of (Cu,Ni)3Sn phase composition, the conducivities of aged Cu-Ni-Sn alloys (Series 1) decrease with (Ni+Sn) contents increasing, from 19.1%IACS to 13.1 %IACS, while the microhardness HV values increase with (Ni+Sn), from 226 to 300 HV. The Young’s modulus E of alloys keeps constant almostly. Thus, the solute contents of (Ni+Sn) should be within the range of 10.0 at.%≤(Ni+Sn)≤16.0 at.%(12.0 wt.%<(Ni+Sn)<18.0 wt.%) to ensure the conductivities of alloy not less than 15.0%IACS.(2) Fixing the (Ni+Sn) and changing Ni/Sn ratio, the conducivities of aged Cu-Ni-Sn alloys (Series 2) decrease with Ni/Sn ratios increasing, from 21.3%IACS to 17.2%IACS, while the microhardness HV are not sensentive with Ni/Sn, and are in the range of 206-227 HV. The Cu-Ni-Sn alloys with Ni/Sn ratios of 2.0 and 2.5 have generally higher conductivities.(3) In the Fe, Mn and Nb minor-alloyed Cu-Ni-Sn-based alloys (Series 3), the Fe affects the conductivities of Cu alloys negatively on a large extent. It needs to control of Fe within 0.33 at.%(0.30 wt.%) for reaching the requirement that the conductivity is not less than 15.0%IACS. In addition, the microhardness of alloys are not sensetive to the Fe content. Finially a good Cu-Ni-Sn-based alloy is reached at [Cu-Cu12](Fe0.063(N12/3Sn1/3)2.38Mn0.044Nb0.013Cu3.5)(=Cu84,36Ni7.49Sn2.58Fe0.28Mn0.20Nb0.09 wt.%) with a conductivity of 16.7%IACS and HV=296.Compared with the referred alloy Cu-9Ni-6Sn (Cu85.23Ni8.36Sn5.63Fe0.49Mn0.20Nb0.10wt.%) with a conductivity of 13.5%IACS and HV=303, the conductivity of the good alloy is enhance by 23.7% than that of the reffered alloy.