Surface alloying of D2 steel using EDM with WC/Co P/M electrodes made of Nano and Micron sized particles

Abstract

The present study is an experimental work carried for surface alloying/modification of D2 alloy steel using WC/Co powder metallurgy (P/M) electrode made of nano, micron and mixture of nano and micron sized particles. Both, machine tool and electrode parameters were selected for study and experiments were planned as per Taguchi’s L18 mixed orthogonal array. Optimal combination of parameters was obtained using Taguchi’s method and analysis of variance (ANOVA) was performed to evaluate influence of parameters on surface roughness (SR) and micro-hardness (MH). The parameters Peak current (IP), pulse on time (TON) and particle size (PS) were found to be most influential on both SR and MH. In EDM, surface modification is performed by deliberate transfer of tool elements onto the work surface. In the present investigation, EDS analysis reveals the migration of tungsten (W) and cobalt (Co) electrode particles, deposition of carbon particles and diffusion of oxygen particles onto the work surface. High reactive surface area of nano particles made greater surface alloying than other tool electrodes and has shown its influence positively on both SR and MH. Low thermal conductivity of nano particle electrodes (NP) makes improved surface alloying than other tool electrodes. Because of the particle size is reduced to nano level its dimension is smaller than the spark gap dimension hence, reduced arcing and improved process stability was obtained, which eventually improved the surface roughness of the component. At optimum MH, higher values of TON and IP gives the sufficient time and temperature for formation of following carbides and oxides viz., Fe3C, Cr23C6 , Cr2Fe14C, Fe2W2C, W3O and Cr3O were responsible for increased hardness of the work surface. The range of roughness values obtained in the present investigation is 1.65-5.82 μm. The highest hardness of 981 HV was obtained without much sacrificing the surface finish.