Nickel-based alloys have wide applications in many industries due to their outstanding properties. However, it is very difficult to machine using cutting and grinding methods because of their low thermal conductivity, strong strain hardening, and high strength at elevated temperatures. Electrical discharge machining is an alternative competitive process to machine Nickel-based alloys by electrical erosion. This study focuses on the evolution process of surface integrity and machining efficiency of W-EDM in machining IN 718 by one rough cut (RC) mode followed by three trim cut (TC) modes. Material removal efficiency, surface roughness, surface topography, surface alloying, and microhardness have been characterized. Results show that high material removal efficiency can be achieved in W-EDM. Six-sigma distribution of Ra in RC mode is different from that of TC modes. The high toughness of IN 718 would be the major contributing factor to the absence of microcracks in the TC modes. Microcracks just exist in the white layer. Thick white layers (6-8 mu m) with microcracks in RC mode and very thin white layers (0-2 mu m) free of those defects in TC2 mode can be observed, while white layer is nearly invisible in TC3 mode. The microhardness of white layer in TC mode is higher than that in MC mode. (C) 2014 Elsevier B.V. All rights reserved.