University ’ s repository of research publications and other research outputs The effects of electropulsing on metallic materials Book Chapter
The influence of electropulsing on metallic materials is reviewed, with a focus on phase transformations and grain refinement. While a large and growing body of literature exists on the topic of electropulsing, the mechanisms governing the process are not currently fully understood. Furthermore, the effects of electropulsing on microstructure and mechanical properties are not yet clearly defined. This review seeks to summarise the existing literature in order to highlight and understand research trends across a variety of metals and alloys, and to clarify the state of the art. Research has shown that the electropulsing process is capable of inducing low temperature recrystallisation in metallic materials at an accelerated rate compared to more traditional heat treatment methods. These microstructural changes often alter the mechanical properties of the materials such as ductility, tensile strength and hardness. Crack healing as a result of electropulsing treatment has also been observed in damaged or work hardened materials and pre-deformation of the sample has been shown to enhance the effects of electropulsing.
Electroplastic effect in metals
Abstract : The influence of electric current on the mechanical properties of metals is reviewed. Included are the effects of both low density approx. 1A/sq mm continuous current and high density approx. (1000A/sq mm) current pulses, with special attention given to the latter. The influence of the parameters involved in the thermally-activated overcoming of short-range obstacles to dislocation motion. Considered are: (a) the force drift electrons exert on dislocations held up at obstacles and (b) the influence of drift electrons on the obstacle strength and on the pre-exponential factor. (Author)
Overview no. 49: On the mechanisms for the electroplastic effect in metals
Abstract The effects of high density d.c. current pulses (10 3 A/mm 2 for 60 μs) on the flow stress of a number of polycrystalline metals (Al, Cu, Ni, Fe, Nb, W and Ti) tested in uniaxial tension at 300 K were investigated with the objective of determining the mechanisms responsible for the concurrent load drops. Both reversible and irreversible (plastic) strains contributed to the load drops. The major component of the reversible strain was the thermal expansion due to Joule heating; skin, pinch, and magnetostrictive effects were of less importance. An analysis of the plastic strain contribution to the load drops suggested that it resulted from the enhancement of dislocation mobility due to the action of drift electrons. Employing the thermally activated plastic flow concept, the electron wind “push” coefficient B ew could be determined for Al and Cu and was found to be of the order of 10 4 dyn-s/cm 2 , in accord with Roschupkin et al .'s theory. This value is in accord with the dislocation damping constant B determined by other techniques at ~300 K; it is however about an order of magnitude larger than is normally expected for the electron drag coefficient B e . In addition to the force exerted on dislocations by an electron wind, the analysis indicated that drift electrons also have a significant effect on one or more of the other parameters of the thermally-activated rate equation. Because of test machine inertia effects, oscillations in the load occurred as it dropped in response to a current pulse. A clear resolution of the influence of the oscillations on the results could not however be made, because of the small plastic strains involved ( Δϵ p ≈ 10 −4 ) and the limited accuracy of the thermal activation parameters employed in the analysis.