Influence of nanostructuration on the sound velocity in copper Cu_99.75

The paper proposes is a multidisciplinary study on the influence of nanostructured material obtained by severe plastic deformation, in this case the copper with a purity of 99.75% (Cu_99.75), on the sound velocity. The study of nanomaterials is a branch of material science on the basis of which nanotechnology can be approached. He studies materials with morphological characteristics at the nanoscale, and especially those with special properties resulting from their nanometric dimensions. The nanometer scale is usually defined as less than one-tenth of a micrometer in at least one dimension, although this term is sometimes used for powders. Severe plastic deformation (SPD) is a generic term describing a group of metal and alloy processing techniques involving very high stresses without including significant changes in the overall dimensions of the model or workpiece. Another defining feature of severe plastic deformation techniques is that shape retention is achieved due to special geometries of the mold, involving the free flow of the material and thus producing significant hydrostatic pressure. Because the workpiece dimensions do not change during severe plastic deformation processing, the process can be repeatedly applied to impose very high stresses. The deformation process is discontinuous and comprises deformation processes defining a severe plastic deformation cycle. Samples were obtained by the cyclic closed die forging process, samples that were subjected to 12 deformation cycles. The sample is of a regular quadrangular prism shape with the side square of a = 10 mm and the height of h = 16 mm, so with a dimensional factor h / a = 1.6. The velocity of ultrasound waves propagation was determined by material based on two calibrated dimensions present on the sample, a and h. For each sample, a number of 7 determinations were performed to establish a mean value for the sound velocity. The variation of the sound velocity was plotted against the number of deformation cycles, a variation describing a convex line having a minimum in the area of the deformation cycle number 4. As a result of the microstructural analysis, it is observed that at the deformation cycle 4 the grains have an average size between 250 and 500 nm. On the basis of the above, it can be deduced that the area of passageways 3, 4 and 5 is, in fact, precisely the transition zone between micrometric granulation and mesoscopic (ultrafine) granulation, which is merely an intermediate zone between micrometric granulation and nanometric granulation. (paper)