Research on the influence of ultrasonic vibration assistance on the plastic deformation behavior of FeCoNiCr thin sheet

Ultrasonic vibration (UV) enhances the dimensional accuracy and forming quality of miniature parts in plastic micro-forming by reducing flow stress and refining microstructure. Therefore, this paper studies the influence of UV assistance on the plastic deformation behavior of FeCoNiCr alloy thin sheets, analyzing the regularity of the impact of UV on deformation microstructure and the influence on size effects. The results show that after applying UV, the flow stress under the same strain decreases more rapidly with increasing grain size than without UV, and the inflection point where the trend of flow stress decrease changes shifts to the right, from t/d≈ 10.6 to around 12.3. After UV-assisted deformation, the twins and geometrically necessary dislocation (GND) density of FeCoNiCr alloy thin sheets have increased. The observed increase in work hardening rate and elongation following UV can be attributed to the improved deformation uniformity, resulting from the increase of twins and the interaction between twins and dislocations. Finally, a model fitting the change in flow stress based on the evolution of GND density was established, which fits well with the stress changes of the material under different grain sizes and with or without UV.