Macroscopic plastic response and atomic-scale dislocation evolution of Ti-6Al-4V alloy during ultrasonic surface rolling

To address the insufficient understanding of the surface plastic deformation mechanism of Ti-6Al-4V alloy during ultrasonic surface rolling processing (USRP), this study adopts an approach combining finite element (FE) simulation and molecular dynamics (MD) analysis. The effects of static load, ultrasonic vibration frequency, and ultrasonic amplitude on residual stress and surface plastic deformation are investigated, and the dislocation evolution and local deformation response under ultrasonic vibration are analyzed at the atomic scale. A three-dimensional explicit dynamic FE model based on the Johnson-Cook constitutive law is established to examine the variations of surface residual stress, equivalent plastic strain, and plastic displacement under different static loads, ultrasonic vibration frequencies, and ultrasonic amplitudes, and the validity of the FE model is verified against experimentally measured residual stress results. The results show that static load is the dominant factor governing the degree of macroscopic surface plastic deformation. Within the investigated static-load range of 100–400 N, the magnitude of the peak residual compressive stress increases overall from 685.11 MPa to 722.09 MPa, although the variation is not strictly monotonic, while the maximum PEEQ increases from 0.12481 to 0.38641 and the affected depths increase markedly. Increasing the ultrasonic amplitude further enhances near-surface plastic deformation, whereas the influence of ultrasonic vibration frequency on macroscopic plastic deformation is relatively limited within the 20–29 kHz range. On this basis, a simplified Ti-Al atomic model of the α phase of Ti-6Al-4V alloy is established to analyze the effect of ultrasonic vibration on atomic-scale plastic deformation behavior by comparing the dislocation evolution, loading force, and system potential energy under conditions with and without ultrasonic vibration. The MD results indicate that periodic excitation is accompanied by an increase in the number and total line length of detected dislocations, together with lower time-averaged indentation reaction forces and higher reported potential-energy values under the investigated simulation conditions. These observations suggest that periodic excitation modifies local defect evolution and indentation response within the simplified atomic model, providing complementary insights into atomic-scale plastic deformation. This study can provide a reference for process optimization and surface strengthening mechanism research of Ti-6Al-4V alloy during USRP.