Ultrasonic vibration-assisted arc machining of Inconel 718: Achieving concurrent processing efficiency enhancement and microstructure regulation.

The arc discharge machining technology achieves efficient material erosion through high-energy discharge, but its intense thermal coupling leads to instability in phase transition control, resulting in an essential conflict between processing efficiency and surface integrity. This fundamental scientific issue hinders the high-integrity manufacturing of advanced materials under extreme conditions. The intermittent contact of ultrasonic vibration-assisted machining technology explains its advantages in processing performance. Based on this, this paper proposes a new paradigm of ultrasonic-arc composite machining (UEAM), which achieves the coordinated regulation of the energy-precision paradox through dynamic modulation of multi-physical fields. Firstly, the full-cycle dynamic evolution of the plasma channel in UEAM and conventional electrical arc machining (EAM) is captured through pulse discharge tests combined with in-situ high-speed photography. On this basis, the processing performance of UEAM is verified through continuous milling discharge tests. The research shows: The ultrasonic vibration induces spatial-temporal reconstruction of the plasma, shortening the breakdown delay by 84.6 % (from 812.5 μs to 125 μs), while increasing the discharge frequency by 150 % (from 16 peaks/s to 40 peaks/s); The 20 kHz lateral vibration excites cavitation microjet and melt pool micro-turbulence, synergistically reducing the C/O enrichment of the recast layer by 31.36 %/70.73 % (to 18.65 %/3.52 %), and restoring the Ni content to 40.89 %; XRD phase analysis confirms that ultrasonic vibration significantly inhibits the formation of brittle phases such as Cr2O3 and NiFe2O4, reducing the recast layer thickness by 74.8 % (from 103 μm to 26 μm). This technology achieves the coordinated enhancement of element distribution homogeneity and surface integrity through a three-level synergistic mechanism of "plasma dispersion-melt pool mass transfer-solidification control" providing a general solution for high-precision and low-damage machining of high-temperature alloys.