Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure

Abstract

Inconel 718 is a nickel-based superalloy that is extensively used as a disc material in gas turbine engines. The service life of gas turbine discs is normally governed by the modes of material degradation and fatigue failure since they work mostly at high temperatures and are subjected to cyclic mechanical loadings. Fatigue failures often start with the initiation of cracks at the surface and the precise details of the failure process significantly depend on the surface conditions. In turbine disc production, one of the last manufacturing steps is to broach root fixings, commonly of fir-tree design, for blade mounting. It has always been a challenge when machining Inconel 718 due to its high strength retention at elevated temperatures, rapid work hardening, as well as low thermal conductivity. This usually leads to rapid tool wear, and consequently shorter tool life, and at the end to the deterioration of the surface integrity of the machined components.

Surface Integrity and Fatigue Performance of Nickel-based Superalloys

“…The kappa is an introductory text in which the different parts of the thesis are integrated. It was built upon the licentiate thesis Surface Integrity of Broached Inconel 718 and Influence of Thermal Exposure [5], which was presented in October, 2014. Since then new work has been conducted, which is presented in this Ph.D. thesis.…”

“…peak broadening). Residual stresses were calculated based on the "sin Details with respect to the principle of the "sin 2 ψ" method has been addressed both in the previous Licentiate thesis [5] and in [141]. The in-depth profiles of residual stresses were obtained by layer removal using electrolytic polishing with Struers LectroPol-5.…”