Atomic-Scale Mechanisms of Ultrasonic-Assisted Ultra-Precision Cutting of W-Mo70 Alloy: Experimental Benchmarking and Molecular Dynamics Simulation

W-Mo70 alloys feature high hardness, a high melting point and poor machinability, resulting in large cutting loads and complex subsurface plastic deformation during ultra-precision machining. To reveal the atomic-scale mechanism by which ultrasonic elliptical vibration regulates material removal and defect evolution, three-dimensional molecular dynamics (MD) models of conventional cutting (CC) and ultrasonic elliptical vibration cutting (UEVC) were established with previously published ultra-precision turning experiments as the macroscopic benchmark. The material removal behavior, cutting force response, interfacial loading characteristics and dislocation evolution law were systematically analyzed. The results show that UEVC exhibits a reduction trend in the cycle-averaged main cutting force compared with CC, which is qualitatively consistent with the experimental trend. However, the reduction magnitude should not be directly compared with experimental results because of the significant differences in machining scale, cutting velocity, strain rate, and tool geometry between MD simulations and experiments. The average normal force remains nearly unchanged but exhibits a significant vibration-induced transient loading–unloading response. Under UEVC, dislocation evolution transforms from continuous accumulation under CC to transient activation at the high-load stage and defect reorganization during the unloading stage. This study reveals the atomic-scale mechanism of UEVC characterized by a vibration-induced transient loading–unloading response, interfacial unloading, defect reorganization and phase-dependent localized material removal, providing atomic-level theoretical support for subsurface defect regulation in ultra-precision cutting of difficult-to-machine W-Mo alloys.