Creep, Fatigue, and Oxidation Interactions During High and Very High Cycle Fatigue at Elevated Temperature of Nickel-Based Single Crystal Superalloys

Very high cycle fatigue durability of an additively manufactured single-crystal Ni-based superalloy

“…The samples were extracted by electric discharge machining and subsequent turning to reach the final shape. Strain-controlled VHCF tests were performed at 1,000 °C (± 2 °C), f = 20 ± 0.5 kHz, Rε = -1 with an ultrasonic fatigue machine used in previous studies [16][17][18][19]21,23,32]. The fatigue tests were performed with a sinusoidal waveform.…”

“…The fatigue tests were performed with a sinusoidal waveform. These tests were performed using alternating stresses allowing i) a direct comparison with conventionally processed Ni-based single crystalline specimens previously tested at Institut Pprime [16][17][18][19]21,23,32], ii) a good control of specimen's temperature and iii) failure of specimens in a reasonable time. An induction coil was used as a heating source, the power of which was controlled by a closed loop with a dualwavelength pyrometer measuring the specimen's central temperature.…”

“…It is also recalled that HCF/VHCF durability is a certifying criteria of airfoils according to airworthiness authorities (e.g. EASA and FAA) [15][16][17], as the loading by vibratory stresses turns out to be a matter of safety requirement of aero-engines.…”

“…In contrast, the present paper focuses on the durability of the same PBF-E SX alloy in the VHCF domain at high temperature/ Rε = -1. In such conditions, the VHCF life of conventionally processed Ni-based SX superalloys is known to be highly dependent on the solidification parameters [14][15][16][17][18][19][20]. In fact, VHCF crack initiation occurs at the largest casting pores in nearly 95 % of the cases at Rε = -1/1000 °C [15,17,19,20] and only occasionally at the Paper Accepted in Additive Manufacturing 9 March 2022. https://doi.org/10.1016/j.addma.2022.102759 surface due to oxidation [15,19,21,22] or due to a prior plastic deformation, inducing surface recrystallization [23].…”