Properties of cryo-drawn copper with severely twinned microstructure

We present the work hardening behaviour, mechanical and electrical properties of pure copper subjected to wire drawing at 77 K and 295 K, respectively. The deformation per pass is increased up to true strain of 0.4 by adopting pressure die/drawing die combinations in order to optimize lubricant residuals of MoS2 on the wire surface at 77 K. The onset of deformation twinning for wire drawing at 77 K was found to be 0.3 and 0.4 for a true strain of 0.1 and 0.4 per pass, respectively. Twinning activity, texture strength and homogeneity are enhanced by increasing deformation per pass while the number of processing steps required for a certain deformation are reduced significantly. A considerably altered electrical conductivity, medium strength increase accompanied with a loss of ductility and a limited thermal stability suggest the formation of non-coherent twin boundaries or destructed twin orientation relationship in cryo-drawn wires. Evidence was found for the latter possibility by local investigation of deformation twins in the final stage of deformation.