Microstructure evolutions in pearlitic steels and Cu/Nb wires resulting from severe plastic deformation during drawing

The aim of this paper is to present recent microstructural investigations c oncerning two kinds of materials produced by industrial processes through h igh level of plastic deformations. To help in further understanding in the strengthening mechanism of such nanocomposite wires, the evolution of the m icrostructure was investigated using field ion microscopy (FIM), Transmissi on Electron Microscopy (TEM) and Three Dimensional Atom Probe (3D-AP). Niob ium fibres and copper channels a few nanometers width with smooth interface s were exhibited in the Cu/Nb wire. A deep interdiffusion of Cu and Nb was pointed out. This mechanical alloying induced by drawing is attributed to t he strong increase of the interfacial energy of the system. Shear bands wer e also observed perpendicular to the wire axis. They were attributed to the tracks of moving dislocations in the (I I I) Cu plane, along the < 110 > d irection. Cold drawn pearlitic steel wires were also studied. Because of th e plastic deformation. cementite lamellae aligned themselves along the wire axis and are thinned down to a few nanometres. 3D-AP data clearly reveal p artly dissolved cementite lamellae. As in the Cu/Nb system, the dissolution of cementite is discussed on the basis of thermodynamical arguments.