Effect of Tool Material on Metal Removal Efficiency, Surface Integrity, and Electrochemical Corrosion Resistance in EDM of Gamma Titanium Aluminide Alloy

Modern intermetallic compound of gamma titanium aluminide (γ-TiAl) due to its low density, high elastic modulus, high resistance to oxidation, corrosion, and ignition has recently been considered in the aerospace and automotive industries. Traditional machining of this alloy is so difficult. In the current study, electrical discharge machining of γ-TiAl samples is investigated using different tool electrodes of graphite, copper, and aluminum. The results show that when using aluminum electrodes, tool wear rate is averagely 3.2 times more than copper and 5.8 times more than graphite tools. In addition, when using graphite electrodes, the average material removal rate is 4.2 times more than copper and 7.7 times more than aluminum. Machining by aluminum tool leads to formation of Al2O3 and TiO2 oxide compounds on the work surface but in machining by graphite electrode, TiC and Ti8C5 carbide phases are created on the work surface. In machining by graphite due to formation of hard carbide compounds in the recast layer, the microhardness is higher than the machined sample by the aluminum tool, where oxide compounds exist on the surface and the hardness of recast layer in the machined sample by copper electrode is less than the other two electrodes, because of existing phases such as copper oxide with less hardness. The highest electrochemical corrosion resistance belongs to the machined specimen using graphite tool and the lowest corrosion resistance is related to the machined sample by aluminum electrode. Reducing oxide and aluminum compounds and increasing carbide phases enhance the corrosion resistance of γ-TiAl machined samples.