Effects of Nb Addition and Different Cooling Methods on Microstructures and Properties of Cu-Cr Alloys

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 Cu-Cr-Nb alloys consist of primary alpha 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.