Fatigue properties of Cu–Cr in situ composite

Abstract

The new electrical conductive material, Cu–15 mass%Cr in situ composite, has been developed for the application to lead frame, high field magnet and trolley wire. The Cu–Cr composite was fabricated by casting method in vacuum and forged, solution-treated and cold drawn. The value of the cold drawing strains, η, for the composite were 4.66 and 6.94. η is defined by the value of ln( A 0/ A), where A 0 and A are virgin area and final area of material, respectively. The cold drawn Cu–Cr composite was tested using a rotating bending fatigue testing machine and axial loading fatigue testing machine ( R = 0.1, where R is stress ratio of minimum stress to maximum stress) at room temperature in comparison to the data for pure copper. The fatigue stresses decreased with increasing number of cycles to failure. The double-knees, which have been found in other face centered cubic materials, such as aluminum alloys, were not seen on the S– N curves for both alloys. The fatigue strength of Cu–Cr composite was twice higher than that for pure copper. The fatigue strength of Cu–Cr composite cold drawn up to η = 6.94 was higher than that drawn up to η = 4.66 when tested under an axial loading. In the fatigue fracture surface, the fatigue crack initiated from the un-dissolved chromium particle situated beneath the specimen surface and the crack direction was changed along the chromium fiber. It was suggested that, in order to improve the fatigue strength of Cu–Cr composite, it is very important to reduce the size and amount of un-dissolved chromium particles.