Daudi R. Waryoba

Restoration mechanisms in highly deformed Cu-based conductor wires

Conductor wires used in pulsed magnets are traditionally fabricated by wire drawing. The strength of the conductors is influenced by the microstructure, which is partly dependent on the restoration mechanisms occurring during processing. This study provides an insight into the types of restoration mechanisms occurring during wire drawing of OFHC copper. The effects of the restoration mechanisms on the mechanical and electrical properties of the material were determined. Tensile tests revealed the existence of steady state stress followed by strength softening at large processing strain. Optical and orientation imaging microscopy (OIM) showed that the strength softening coincided with the onset of recrystallization in the material. Although restoration mechanisms of recovery and recrystallization played some role in the strengthening they had little or no effect on the resistivity of the material.

Texture and Microstructure Variation in Severe Plastic Deformed OFHC Cu Wires

The texture and microstructure resulting from heavily drawn and annealed oxygen-free high conducting (OFHC) copper wires have been investigated using several microscopical techniques including orientation imaging microscopy and nano-indentation. In the as-drawn condition, the microstructure and texture were heterogeneous across the wires, and consisted of three distinct concentric regimes: the inner core, the mid section, and the outer region. Whilst the microtexture of the inner core was dominated by a strong <111>+weak<100> duplex fiber texture, the mid section and the outer region had a comparatively weak fiber texture. Analysis using a Taylor-type viscoplasticity model revealed that the weak texture observed in this material was a direct consequence of shear deformation during drawing. The recrystallization kinetics of the wires upon isothermal annealing at various temperature was influenced by the deformation heterogeneity, and can be accurately described by a modified JMAK-Microhardness model. In this approach, the JMAK model is expressed in terms of microhardness data, from which the parameters of the different restoration kinetics were determined.

Textural and Microstructural Inhomogeneities in Drawn and Annealed OFHC Copper Wire

This work presents the results of a study on textural and microstructural inhomogeneities that develop during annealing of heavily drawn Oxygen free high conducting (OFHC) copper wire. The wire was drawn at room temperature to a true strain of 2.31 and isothermally annealed at 750°C for annealing times ranging from 10s to 1hr. The inhomogeneity of microstructure across the wire was clearly visible as three distinct concentric regions, which were classified as: the inner core, the mid section, and the outer surface. Two texture transitions were observed. At shorter annealing time, recrystallization which originated from the mid section, resulted into a strong<100>+weak<111> duplex fiber texture. However, prolonged annealing gave rise to abnormal grain-growth that proceed from the mid section to the outer surfaces with a dominant <111> fiber component at the mid and inner region, and mixed components of <111>, <100>, and <112> at the outer surfaces.

Deformation and Recrystallization Texture of Heavily Drawn OFHC Copper

Deformation and recrystallization texture has been investigated in Oxygen free high conducting (OFHC) copper wires drawn at room temperature to true strain of 2.31, and isothermally annealed at various temperatures between 150°C and 750°C. Local orientations of the microstructures were measured by means of electron backscattered diffraction (EBSD) technique. While the drawn wire was characterized by a major<111> + minor<100> duplex fiber texture, recrystallization occurred at annealing temperatures between 250°C and 400°C and resulted into a major<100>+minor<111> recrystallization texture. At temperatures above 500°C, the <100> dominated recrystallization texture changed to the <111> dominated growth texture due to secondary recrystallization, which favored the <111> orientation at the expense of the <100> component.