Abstract
Inconel 718 is a nickel based superalloy that is widely used as a turbine disc material in gas turbine industries. This study details the effect of thermal exposure on the residual stresses produced when broaching Inconel 718. The chosen parameters for broaching in this study are similar to those used when manufacturing turbine discs. The broaching operation produced a high level of tensile residual stresses at the broached surface. A layer with tensile residual stresses was formed in the sub-surface region, followed by a layer several times thicker with compressive residual stresses. Thermal exposure was conducted at 550 °C. The depth distributions of residual stresses after thermal exposure are presented and discussed in this paper. Complete relaxation of the surface tensile residual stresses was observed after 30 h thermal exposure, whereas the 3000 h thermal exposure influenced both the surface and sub-surface residual stress states.
Highlights
The main machining process of Inconel 718 in gas turbine industries is to broach fir-tree root fixings for gas turbine blade mounting
Residual stresses generated in the broaching operation of Inconel 718 with similar parameters applied in the gas turbine industry have been measured and the influence of thermal exposure at 550 ̊C on the residual stresses has been investigated in this study
Complete relaxation of the surface tensile residual stresses can be obtained after 30 h thermal exposure due to the occurrence of recrystallization in the surface layer
Summary
The main machining process of Inconel 718 in gas turbine industries is to broach fir-tree root fixings for gas turbine blade mounting. The profile after 3000 h thermal exposure showed larger compressive residual stresses in the sub-surface region in both ∥ and .
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