Ultrasonic Evaluation of Severely Plastically Deformed Metals

摘要

Disc-shaped specimens of nickel and iron of about 30 mm diameter and a few millimeters thick were prepared by the high pressure torsion (HPT) method [1]. The produced equivalent shear strain s linearly increased from a minimum at the centre to the periphery. The cold working process multiplied the dislocations and led to the grain fragmentation. The saturation of the grain refinement was approached at the circumference of the disk-specimens yielding a narrow distribution of the grain size with a mean value of about few hundred nanometers that depends on the material purity, temperature of the deformation [2]. The refinement of the microstructure changes the elastic properties of the material such as hardness, strength and has an influence on the attenuation and phase velocity of the ultrasound [3]. The paper reports the measurements of the longitudinal wave velocity and the attenuation in metals with polycrystalline (pc) and ultrafine (uf) microstructure.