Ultrasonic–electrical current synergistic milling of Ti/TiC composites: Microscopic lattice evolution and surface damage

Titanium-based titanium carbide (Ti/TiC) composites exhibit immense potential in high-end equipment manufacturing; however, their inherent heterogeneity readily induces particle fracture and pull-out during cutting, restricting high-efficiency machining. Existing pure ultrasonic assistance fails to effectively stimulate the thermal softening of the matrix, whereas pure electrical pulses are prone to triggering interfacial thermal adhesion, failing to balance both machining efficiency and surface integrity. To address this, this paper introduces ultrasonic–electrical current synergistic milling, revealing its macro-microscopic mechanisms by integrating cutting experiments and molecular dynamics simulations. The research confirms that the response of surface integrity to pulsed current density exhibits a non-monotonic characteristic, and the machining core lies in achieving a dynamic balance between electroplastic softening and Joule heating. The comprehensive performance is significantly improved at a current density of 5.293 A/mm2 and a pulse frequency of 400 Hz. Under these parameters, multi-field synergy sufficiently induces the electroplastic softening of the titanium matrix and effectively suppresses Joule heat accumulation and thermal adhesion via the ultrasonic intermittent contact effect, yielding a maximum reduction of 39.81% in the resultant cutting force. Microscopic analysis demonstrates that the electro-thermo-mechanical coupling impels the material rheology to transition from deep rigid extrusion to continuous upward plastic shearing, drastically reducing lattice damage such as subsurface defects and dislocation density. This synergistic mechanism effectively suppresses the brittle fracture of TiC particles and the tearing of the matrix, significantly reducing the surface roughness to 0.146 μm, thereby successfully achieving the high-efficiency and low-damage precision machining of Ti/TiC composites.