Crystal orientation dependence of the instantaneous removal mechanism and subsurface dislocation evolution in ultrasonic elliptical vibration cutting of tungsten alloys

Ultrasonic elliptical vibration cutting (UEVC) is recognized as a pivotal technique for achieving ultra-precision machining of tungsten alloys. However, the mechanisms of material removal and subsurface formation remain inadequately elucidated. Utilizing molecular dynamics (MD) simulations and experimental validation, this study investigates the influence of distinct grain orientations (<100>, <110>, <111>) on the transient removal behavior and subsurface damage characteristics of single-crystal tungsten particles. The transient material removal mechanism in UEVC is identified as an “extrusion-shear” process. The dynamic variation in the cutting direction induces dynamic evolution in the activation state of slip systems, consequently regulating both the transient material removal mechanism and dislocation evolution. Cutting along the <100> crystallographic orientation achieves the “maximum material removal rate”. Cutting along the <110> orientation produces the “highest dislocation density” within the subsurface region, accompanied by a broader distribution of high dislocation density zones, while local phase transformation (BCC→FCC) facilitates the plastic removal of the material. Conversely, cutting along the <111> orientation results in “reduced dislocation density” within the surface layer, with material removal occurring predominantly through “brittle fracture”. This work establishes a crucial theoretical foundation for the precise control of grain orientation in ultra-precision machining of difficult-to-cut body-centered cubic (BCC) metals.