Characterisation of IN718 fasteners for aero-engine applications

Ma, Yuean (2024). Characterisation of IN718 fasteners for aero-engine applications. University of Birmingham. Ph.D.

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Abstract

Standard IN718 fasteners are widely employed in aeroengine applications owing to their exceptional mechanical properties, including tensile, fatigue and creep strength at temperatures up to 650°C. Notably, IN718 is a cost-effective choice compared with other alloys [1]. However, the flexibility allowed by the industrial manufacturing specification in the choice of raw material and determining the solution treatment temperature range introduces variations in microstructure of bolt and consequently mechanical performance of the bolts [2].

This project focused on examining the microstructure and mechanical properties in the threaded section of IN718 bolts. Bending tests were carried out on the split bolts at 650°C to evaluate the influence of possible microstructural variation and associated failure mechanism. Further investigations into fatigue and creep behaviours were accomplished using the ½” IN718 large bolts through the axial-tension dwell fatigue and stress relaxation tests. These tests also verified the microstructural evolution at the threads under the long-term thermal exposure. As a result, cold rolling in the threaded section demonstrated a clear enhancement in fatigue mechanism at the investigated temperature. In addition to the shank properties, the IN718 test pieces with simulated microstructures were tested, revealing a profound influence of annealing temperature on dwell fatigue life and a noticeable change in failure mechanism. Microstructural characterisation and fractographic examination were conducted
throughout to aid understanding. A manufacturing route of IN718 aero-engine bolts was proposed in the end to better control the microstructure, subsequently the performance of the final products.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):