Analysis of the metallography parameters and residual stress induced when producing bolt holes in Inconel 718 alloy

Inconel 718 is a structural material used to produce highly stressed rotating aero-engine components. Such components have to meet the most exacting requirements in terms of reliability and component service life. Bolt holes in rotating turbine and compressor discs are among the most highly stressed geometric features of jet engines. In-flight failure of these bolt holes may, in fact, result in the loss of the aircraft and imperilment of human lives. For this reason, the quality and reliability of hole-making are of utmost importance. The integrity and reliability of the machined engine component are the sole factors for which all efforts are taken for system of design, material selection, manufacturing and inspection of these rotating aero-engine components. This paper aims to contribute towards a safer production of bolt holes in highly stressed turbine discs made from nickel based super-alloy, which acts as a linking sequence between microstructural surface integrity and descriptive residual stress parameters. The magnitude of the residual stress was determined by means of combining two various methods, namely surface stress measurement by X-ray diffraction and hole-drilling, to achieve residual stress in the profile depth.