The machining of complex shapes in difficult-to-cut materials is hardly achieved by traditional metal cutting. Particularly small deep holes are often a cause for premature tool failure or even a technological frontier. Yet, the use of Nickel-based alloys is common in high-temperature and aerospace applications, where thin shapes and deep holes are often required. In these cases non-contact processes, such as electrodischarge (ED) drilling, may be the only viable manufacturing solution. Morphology of ED machined surfaces is significantly different than obtained by metal-cutting operation and is known to jeopardize fatigue strength, but the extent needs to be gauged and related to the process parameters. The paper addresses the effect of ED drilled holes (0.8 mm diameter, aspect ratio 10) on the fatigue life of Inconel 718. Rotating bending fatigue tests are executed on specimens drilled under two ED setups, as well as with a traditional cutting tool. Specimens free from holes are fatigued under the same conditions for comparison. Extremal ED parameters are selected based on previous studies: conditions for best surface finish are contrasted with those for highest productivity. S-N curves show that the ED process causes a decrease of the fatigue resistance with respect to traditional drilling, whereas the effect of different ED setups is negligible. Maximum productivity can thus be pursued with no threat to fatigue performance. The fatigue limit variation is quantified by using the superposition effect principle: ED drilling causes an increase of the stress concentration factor around 25% if compared to traditional drilling. The macroscopic fatigue behavior is integrated with a study of the effects of the different drilling processes in the micro-scale, by means of a microstructural and fractographic analysis.
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|Data di pubblicazione:||2017|
|Titolo:||Fatigue life of electrodischarge drilled Inconel 718|
|Appare nelle tipologie:||Articolo su rivista|
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