Structure evolution in coarse-grained nickel under ultrasonic treatment

Changes in the structure of coarse-grained nickel due to ultrasonic treatment (UST) are studied. For this purpose, commercially pure nickel was annealed at a temperature of 1300 °C for 1 h to obtain a coarse-grained structure with a low dislocation density. On the electrolytically polished surface of the sample, a 2 × 2 mm2 sized area was marked and investigated by EBSD analysis. Further, the sample was subjected to UST with an oscillating stress amplitude of 20 MPa, and the marked area was polished and scanned again. X-ray diffraction analysis and microhardness measurements were carried out before and after UST as well. It is shown that UST leads to dislocation generation, an increase in the fraction of low-angle boundaries, changes in the shape of twins and grain boundaries. The dependence of structural parameters and microhardness on the UST amplitude is also described.