Pushing the strength limit of nickel-based superalloys (DPhil)

Nickel-based superalloys exhibit excellent resistance to inelastic deformation until close to their incipient melting point, it is hence a suitable material for high temperature applications. Over the past decades of development, the new generations of single crystal superalloys possess higher creep resistance but with some compromise to tensile strength. As a result, these grades of superalloys are more prone to fatigue type failures and becomes very hard for heat treatment to take place. New compositional designs to mitigate this are needed, especially to push the limit of strength whilst maintaining creep resistance via microstructural control.

This project will focus on the development of a mechanistic understanding of deformation for a range of single crystal superalloys with an emphasis on the anomalous yielding regime (~750 °C). The choice of superalloy compositions is selected based on a ‘rule-of-mixture’ routine between the 1^st and 5^th generation superalloys. This will involve characterising various mechanical properties and microstructures to interpret the transition between different active mechanisms at each testing condition, such as anti-phase boundary shearing, micro twinning and dislocation climb. In addition, microstructural sensitive constitutive models will be developed for rationalisation; thermodynamic calculations will be applied to aid the design of heat treatment. The project aims to address the holistic picture of unavoidable property trade-offs and a sweet spot at optimisation.