Wire electric discharge machining and its effect on the surface finish of HfNbTaTiZr refractory high-entropy alloy

Abstract

Refractory high-entropy alloys (RHEAs) have high strength and hardness but limited plasticity at room temperature, making them challenging to process and shape using conventional techniques. In the current study, HfNbTaTiZr RHEAs were machined using wire electric discharge machining (WEDM), which enables precision shaping of hard and brittle materials without subjecting them to high stresses. The roughness of the surfaces and sections cut using WEDM was compared. Average surface roughness (R-a) increased by approximately 0.75 mu m due to the limited heat transfer capability of the dielectric fluid in removing debris and cooling the interior of the sample. SEM and EDS analyses taken from the machined surfaces revealed microcracks, voids, globules, craters, and debris formed on the surface because of the sudden cooling of the dielectric liquid after melting and evaporation under intense heat. Cross-section analysis showed that the microcracks on the surface were approximately 30 mu m deep in the heat-affected zone and did not go further into the workpiece. Hf, Nb, Ta, Ti, and Zr as well as Cu and Zn were found on all machined surfaces indicating the consumption of the wire electrodes.