R.C. Buckingham

Bio: R.C. Buckingham is an academic researcher from Swansea University. The author has contributed to research in topics: Superalloy & Metallurgy. The author has an hindex of 2, co-authored 2 publications receiving 60 citations.

The Effect of Strain Distribution on Microstructural Developments during Forging in a Newly Developed Nickel Base Superalloy

Abstract: In the current study, the effect of strain distribution in a simple forging geometry on the propensity for recrystallization, and its impact on mechanical properties has been investigated in a newly developed experimental nickel-based superalloy. The new alloy was produced via a Powder Metallurgy (PM) route and was subsequently Hot Isostatic Processed (HIP), isothermally forged, and heat treated to produce a coarse grain microstructure with average grain size of 23–32 μm. The alloy was examined by means of Electron Back-Scatter Diffraction (EBSD) to characterise the microstructural features such as grain orientation and morphology, grain boundary characteristics and the identification of potential Prior Particle Boundaries (PPBs) throughout each stage of the processing route. Results at the central region of the cross-section plane parallel to the loading direction showed significant microstructural differences across the forging depth. This microstructural variation was found to be highly dependent on the value of local strain imparted during forging such that areas of low effective strain showed partial recrystallisation and a necklace grain structure was observed following heat treatment. Meanwhile, a fully recrystallised microstructure with no PPBs was observed in the areas of high strain values, in the central region of the forging.

Transmission Kikuchi diffraction in a scanning electron microscope: A review

Abstract: Transmission Kikuchi diffraction (TKD), also known as transmission electron backscatter diffraction (t-EBSD), has received significant interest for the characterisation of nanocrystalline materials and nanostructures. In this paper, we will review the development of TKD, including forescatter detector imaging and ongoing parameter optimisation, as well as some of the current applications of the technique. A comparison to other microanalysis techniques is also included, highlighting their relative strengths and weaknesses and their complementarity with TKD. Finally, potential applications of the technique and possible future developments are discussed.

Grain boundary mediated hydriding phase transformations in individual polycrystalline metal nanoparticles

Abstract: Grain boundaries separate crystallites in solids and influence material properties, as widely documented for bulk materials. In nanomaterials, however, investigations of grain boundaries are very challenging and just beginning. Here, we report the systematic mapping of the role of grain boundaries in the hydrogenation phase transformation in individual Pd nanoparticles. Employing multichannel single-particle plasmonic nanospectroscopy, we observe large variation in particle-specific hydride-formation pressure, which is absent in hydride decomposition. Transmission Kikuchi diffraction suggests direct correlation between length and type of grain boundaries and hydride-formation pressure. This correlation is consistent with tensile lattice strain induced by hydrogen localized near grain boundaries as the dominant factor controlling the phase transition during hydrogen absorption. In contrast, such correlation is absent for hydride decomposition, suggesting a different phase-transition pathway. In a wider context, our experimental setup represents a powerful platform to unravel microstructure-function correlations at the individual-nanoparticle level.

Morphology change of retained austenite during austempering of carbide-free bainitic steel

Abstract: A change in the mechanical properties of a carbide-free bainitic steel was observed during prolonged holding at austempering temperature after termination of the bainitic transformation. To determine the origin of the property change, the microstructure was investigated by correlative electron microscopy. Although the retained austenite content remains the same during prolonged holding, its morphology changes from thin films separating the individual bainitic sub-units to a more globular structure. Since films of austenite contain a higher C concentration, the blocky austenite becomes gradually enriched in C during this morphology change. The more homogeneous distribution of the C after prolonged austempering leads to higher deformability as a result of a more pronounced TRIP effect.