Comparison of material specific rim zone effects of Ti6Al4V machined by wire EDM in water- and CH- based dielectrics

Abstract

Because of their lightweight, high-temperature corrosion resistance and fatigue property, titanium alloys are ideal for use in turbomachinery, medical and chemical areas with corrosive environments and precision mechanics as used in aeronautical applications. Wire electro discharge machining (WEDM) is a nearly force free process and hence beneficial compared to classical production technologies when it comes to the production of filigree parts with high aspect ratios. Beside the well-known fact of the heat affected rim zone at WEDM machined parts, titanium alloys have another material specific drawback, called ‘alpha case’, which is developed by diffusion driven interstitials, such as carbon, nitrogen and especially oxygen. The alpha-case is a hard to remove superficial defect, which leads to crack initiation and propagation. The influence of water- and CH-based dielectrics as a source of diffusitives on the formation of alpha-case have to be investigated to predict the part’s fatigue strength.