Effects of Ni Addition on the Mechanical and Electrical Properties of Cu-15 mass%Cr In-Situ Composites

Effects of Ni and Al addition on the mechanical and electrical properties in the Cu-15 mass%Cr in-situ composite are examined. The process consists of melting, hot forging, heavy cold rolling and aging. Ni is partitioned into the Cr phase to make an intermetallic precipitates. The Cr phase in the Cu-15 mass%Cr-10 mass%Ni shows 3.6 times harder compared with the Cu matrix resulting in the poor cold drawability and low strength. The addition of 1 mass% Ni and 0.15 mass%Al is recommended to get good cold drawability and high strength, but it is necessary to make a compound such as Ni 3 Al to increase the electrical conductivity

Effect of the addition of Si on the microstructure and mechanical properties of as drawn Cu-15Cr based in situ composites

0.5 mass% Si has been added into the Cu–15Cr based alloy for the purpose of strengthening. The microstructure and properties of Cu–15Cr–0.5Si in situ composites have been investigated. Because of the effective hardening to Cr phase due to the addition of Si, both the thickness of Cr fibres and the interphase spacing are larger than the previous results in Cu–15Cr in situ composites at the same drawing strain, therefore, the drawn structure is coarser due to the addition of Si. In addition to dissolving in Cu and Cr phases, Si also reacts with Cr to form Cr3Si (accounts for 4 vol.%), which is brittle and was broken during the following cold deformation. The hardness of both Cu and Cr phases in the as drawn wire increases with increasing drawing strain by work hardening. The tensile strength of as drawn Cu–15Cr–0.5Si in situ composites is superior to that of Cu–15Cr binary in situ composites only when the drawing strain is lower than 4.5

Effect of alloying elements on the cold deformation behavior of Cr and tensile strength of Cu-15Cr based in situ composites

Deformation behavior of Cr phase in Cu-15Cr based in situ composites during cold deformation has been examined. Deformation strain partitioning between Cu and Cr phases after cold drawing occurs because the Cr phase tends to elongate less than Cu phase due to its higher flow stress and modulus. The deformation process of Cr phase during cold drawing comprises slight, steady and slow deforming stages, and the Cr phase is primarily deformed in the second stage. At a given drawing strain, the deformation strain of Cr phase increases with increasing hardness ratio of Cu phase to Cr phase, therefore, the finer drawing structure (with smaller interphase spacing and Cr thickness) will be obtained with either increasing hardness of Cu phase or reducing hardness of Cr. Hardening of Cr phase by the addition of alloying elements affects the strength of Cu-15Cr based in situ composites in two opposite ways-increasing the second phase strengthening and reducing the structural refinement strengthening, the latter is more prominent at higher drawing strain. The strength improvement of the as cold drawn Cu-15Cr based in situ composites can be achieved by increasing hardness ratio of Cu to Cr through either softening of the Cr phase or hardening of the Cu phase

Effect of alloying elements on the mechanical properties in the Cu-15% Cr in-situ composites

The effects of alloying elements on the mechanical properties as well as electrical conductivity in Cu-15%Cr(mass fraction) in-situ composites were systematically studied and high strength and high electrical conductive Cu base in-situ composites have been developed. The best combination is the addition of 0.1% to 0.2% Zr, Ti, or Sn in Cu-15%Cr in-situ composite, thermomechanical treatment to refine the microstructure and optimizing the precipitation of second phase. The strength is controlled by high density of dislocations in the Cu matrix, the lamellar spacing of the second phase, and the fine Cr precipitates. The aging treatment to reduce solute atoms has a beneficial effect on the increase of electrical conductivity. The addition of Zr, or Ti of about 0.15% to 0.2% promotes the precipitation of Cr particles