Effects of Nb Addition and Different Cooling Methods on Microstructures and Properties of Cu-Cr Alloys
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JMEPEG https://doi.org/10.1007/s11665-020-05017-z
Effects of Nb Addition and Different Cooling Methods on Microstructures and Properties of Cu-Cr Alloys X.H. Yang, C.D. Wang, L. Yang, J.T. Zou, P. Xiao, and S.H. Liang (Submitted October 10, 2019; in revised form June 1, 2020) The Cu-Cr-Nb alloys were prepared by vacuum induction melting with different cooling methods. The effects of niobium contents and different cooling methods on the microstructures and properties of these alloys were investigated. The microstructures were characterized by optical microscope, scanning electron microscope and transmission electron microscope. The electrical conductivity, hardness and the tensile strength of Cu-Cr-Nb alloys were tested as well. The results showed that the as-cast microstructures of CuCr-Nb alloys consist of primary a phase dendritic and eutectic phase. With the addition of element Nb, the microstructures were refined and the secondary dendritic arm spacing obviously decreased. Compared with the furnace cooling, the homogeneous and refined microstructures were obtained by the graphite mold, and the hardness of the alloys is enhanced greatly. After the heat treatment, two reinforcing phases of Cr and Cr2Nb are precipitated from the copper matrix. The comprehensive properties were obtained when the Nb content is 0.4%. The Cu-1.2Cr-0.4Nb alloy performed by direct aging treatment without solution treatment exhibits the higher performance, the hardness and electrical conductivity are 143HB and 84%IACS, respectively. In addition, the tensile strength and the elastic limit of the Cu-1.2Cr-0.4Nb alloy can reach up to 413.0 and 238 MPa. Keywords
Cu-Cr-Nb alloy, heat treatment, microstructure, property, secondary dendritic arm spacing
1. Introduction Owing to their high mechanical strength, excellent electrical and thermal conductivities, Cu-Cr alloys have been applied in resistance welding electrodes, integrated circuit lead frame and the railway contact wires (Ref 1-5). The high electrical conductivity is due to the very low solubility of Cr in Cu at room temperature, and the excellent mechanical properties are attributed to the nanoscale Cr precipitates from Cu matrix in the aging process. In order to achieve the better combinations of high strength and high conductivity, many investigations on Cu-Cr system alloys have been conducted, some efforts have been made in the alloy composition design, and the other attempts have focused on the improvement of the preparation methods. Alloying elements addition is an effective method to improve the mechanical properties Cu-Cr system alloys (Ref 2, 5-9). Pangetal (Ref 5) added Zr and (Ni, Si) elements in CuCr alloy and found the cast solute-rich particles and aged precipitates were refined by alloying elements addition. And good balance of hardness and electrical conductivity were achieved after 80% cold rolling and 450 C aging for 6 h,
X.H. Yang, C.D. Wang, L. Yang, J.T. Zou, P. Xiao, and S.H. Liang, Shaanxi Key Laboratory of Electrical Materials and Infiltration Technology, Schoo
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