Influence of the WEDM process on the fatigue behavior of Inconel® 718

Abstract

The use of alternative processes for the manufacturing of aeronautical components is essential in order to fulfill the requirements that have been set by the aircraft sector. One particular solution that has been used for certain applications is that of Electrical Discharge Machining (EDM). The EDM process can machine any electrically conductive material, irrespective of its hardness or mechanical properties, and is thus a useful solution for difficult-to-machine aerospace alloys. However, due to its thermal nature, the EDM process induces metallurgical changes in the machined material, which in turn may reduce its fatigue service life. For this reason, the aerospace industry has restricted the use of EDM to the manufacturing of selected components. Nevertheless, there have recently been significant advances in the development of EDM generators that minimize thermal input toward the machined component. As a consequence, it is critical to know the extent to which these new EDM processes affect fatigue service life in aerospace alloys, in order to adequately evaluate the feasibility of using this process. Given the limited information in the literature regarding this topic, the present paper describes a study of the fatigue life of WEDM produced nickel-based Inconel® 718. In order to examine the capabilities of WEDM, fatigue specimens were manufactured using both this procedure and the grinding process (used as a reference for comparison). Surface analysis, metallographic studies, residual stresses, fractography and axial fatigue tests are described and discussed. The results showed that conducting the WEDM process with the new generation of machines has a detrimental effect at high fatigue cycles, reducing fatigue strength by approximately 10% in comparison with ground specimens. However, at low fatigue cycles, no significant differences were observed between ground and WEDM samples. These findings have implications for the potential use of the WEDM process in the manufacturing of disk turbine fir-trees.