Temperature-controlled ultrasonic vibration assisted machining response and improvement mechanism for Ti2AlNb alloy manufactured by directed energy deposition

Material removal mechanism under the coupling of ultrasonic vibration and heating Machinability of Ti 2 AlNb alloy fabricated by additive manufacturing is investigated via temperature-controlled ultrasonic vibration assisted milling experiments. This study explores the mechanisms of surface defect suppression, material removal behavior, and near-surface grain refinement during the process. Results indicate that the tool path formed by ultrasonic vibration can promote the lifting and detachment of hard particles within workpiece microstructure, avoiding scratches on the workpiece surface and significantly improving surface quality. With the O phase and grain boundary α 2 phase precipitated by heating, micro-voids are generated between the thermally precipitated O phase and B2 phase matrix, while microcracks form inside the α 2 phase under ultrasonic vibration. As the micro-voids and microcracks propagate, a weakened zone is progressively developed within the cutting zone, leading to an 85% reduction in cutting force under optimal parameters. Based on the one-dimensional fluctuation equation, ultrasonic vibration enhances energy input during machining, promoting the healing of near-surface pores and the formation of a pore-free layer with a specific thickness. The thickness of the pore-free layer increases with escalation of ultrasonic vibration energy input, a phenomenon that is crucial for improving the material properties. Under the synergistic effect of thermal softening and ultrasonic vibration energy impact, the high-density dislocations in the microstructure of additive manufacturing material continuously accumulate, annihilate, and rearrange, ultimately achieving grain refinement. Experimental data demonstrate that, in comparison with conventional machining, the grain size of the near-surface layer is reduced by 56.1% when the amplitude is set to 3 μm.