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Information × Registration Number 0221U107131, 0121U114393 , R & D reports Title Cryogenic Ultrasonic Impact Treatment for Surface Nanotwinning of Metal Alloys popup.stage_title Head Mordiuk Bohdan M., Доктор фізико-математичних наук Registration Date 27-12-2021 Organization Institute of Metal Physics. G.V. Kurdyumov of the National Academy of Sciences of Ukraine popup.description2 The structural-phase state and mechanical properties of 12Х18Н10Т austenitic steel and Cu37Zn brass after high-frequency mechanical impact treatment using ultrasound (ultrasonic impact treatment - UIT) in the air and liquid nitrogen environments were studied. As shown, the same process intensity applied to the steel samples during cryo-UIT results in the structure formation involving twinning and martensitic alpha-epsilon-alpha prime transformations, as well as nanoscale grain structure with smaller grain size than that after the argon-UIT treatment. The brass samples processed by cryo-UIT at the same applied intensity undergo four times higher strain extent than that occurred after air-UIT. It is shown that the change in mechanical properties, namely the increase in hardness measured by nanoindentation, yield strength and tensile strength while maintaining significant tensile plasticity, is due to the formed structural state in the surface layer. The main factors of the cryo-UIT induced hardening are the accumulation of dislocations in pile-ups, the formation of microtwins and shear bands with a high density of dislocations in them, which provide subdivision of the grain structure. A special role is played by the presence of increased number of twin boundaries, recorded both by direct observation by transmission electron microscopy of thin foils and scanning electron microscopy of fracture surfaces, and by analysis of stored energy in grain / twin boundaries by scanning differential calorimetry measurements. Coherent twin boundaries further contribute to the dislocation of dislocations and thus preserve a tolerable plasticity after cryo-UIT, and they play a role of additional hardening factors. This mechanism is consistent with the literature.  Product Description popup.authors Vasyliev Mykhailo O Piskun Nataliya O. Khripta Nataliia I. popup.nrat_date 2022-03-09 Close