Various engineering alloys display load drops and strain localisation during constant strain rate tensile testing, termed the Portevin-Le Chatelier (PLC) effect. This includes nickel-based superalloys, between approximately 200 °C and 600 °C. The PLC effect is widely attributed to Dynamic Strain Ageing (DSA), referring to dislocation pinning effects caused by the diffusion of solute to dislocations, driven by elastic interactions. DSA is widely adopted to explain the PLC effect in superalloys, but was initially applied to model the effect of interstitial solutes in carbon-containing steel. There is often an implicit, mostly unsubstantiated assumption that substitutional solutes can create a strong pinning effect. Doubts remain over whether substitutional solute atoms are sufficiently mobile in the temperature regime of the PLC effect, and details of the atomistic mechanisms in superalloys have not been experimentally elucidated. The origins of the effect warrant attention, given possible effects of the accompanying strain localisation on the ductility and fatigue life of polycrystalline superalloys at in-service temperatures in the turbine engine.

This thesis presents a wide experimental account of the PLC effect in a nickel-based superalloy, RR1000. A binary alloy, Ni-20Cr (weight %), is also investigated to facilitate understanding. A characterisation of the macroscopic serration and strain localisation characteristics is first presented, through optical Digital Image Correlation (DIC). From this, load drops are unambiguously associated with the presence of bursts of localised strain within so-called Lüders bands. Wide similarities between the behaviour of the superalloy and the binary alloy suggest that the microstructural complexity of the superalloy is not necessary to explain the effect. The presence of history dependent effects upon a change in strain rate or isothermal hold are also characterised, demonstrating that the PLC effect likely originates from a time-dependent strengthening effect.

Scanning electron microscope based DIC techniques are subsequently employed across large (0.2 mm × 6 mm) areas spanning a Lüders band, providing the most detailed image of strain localisation within a Lüders band to date. Results from fast Fourier transform based techniques for slip band detection and quantification demonstrate little variation in the distributions of slip band spacings between tests where the PLC effect is present or absent. The results challenge the view sometimes held, that the PLC effect is directly associated with the accumulation of enhanced strain localisation at the microscale. An investigation of the accompanying defect structures demonstrates that coupled anti phase boundary configurations remain dominant when the PLC effect is present, disputing the view that the PLC effect in superalloys is caused by the growth of stacking faults.

Finally, preliminary experimental results are provided of the compositional profiles around strain localisation features, through a combination of atom probe tomography and electron microscopy techniques. Results do not demonstrate clear solute enrichment around dislocations. Rather, electron microscopy techniques provide preliminary evidence for the formation of short-range ordered domains in both alloys, an alternative theorised cause of the PLC effect. The results suggest a need for closer scrutiny of the wide attribution of the PLC effect in superalloys to DSA, with the ultimate goal of providing an increased physical understanding of how to control the extent of the PLC effect and its influence on the mechanical properties of hot components of the turbine engine, such as the fatigue life.