Formation of nanocrystalline structures by ultrasonic impact treatment and their effect on mechanical characteristics of steels and alloys

The effect of ultrasonic impact treatment (UIT) on the surface layer structures and the deformation behavior of bulk samples of the Ti-6Al-4V alloy, the Fe-16.5Cr-18.8Mn-0.53N-0.1C high-nitrogen and Fe-15Cr-9Mn-Ni-Cu-N metastable austenitic steels, as well as the TiNi(Fe, Mo) single crystal was studied by transmission electron microscopy, X-ray diffraction analysis, and uniaxial tensile testing. It was that gradient deformed structures had been formed during the UIT process. The main reasons of the surface layer strengthening had been the formation of a nanocrystalline structure and enrichment of the materials with oxygen. This had caused solid solution hardening and the formation of oxide layers. The surface properties significantly affected stages of stress–strain curves and the strain hardening macro-kinetics of the bulk alloy samples.