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28 results on '"Flewitt, Peter E. J."'

18. Physical Methods for Materials Characterisation

Author

Flewitt, Peter E. J., Wild, R. K., Flewitt, Peter E. J., and Wild, R. K.

Subjects
Materials--Testing, Microstructure
Abstract

In the second edition of this popular text, the authors provide a comprehensive description of the range of techniques currently used for characterizing the microstructure of materials. Introductory chapters cover the basic physics required to describe the microstructure of materials and their interaction with various types of radiation. Much of the hardware involved in these techniques is dependent on a vacuum environment, so a full chapter is devoted to this topic. Characterization techniques are then divided on the basis of the interrogating radiation, with separate chapters dealing with optical and x-ray techniques, electron microscopy and spectroscopy, and ion and particle microscopy and spectroscopy. Within each chapter, material is given covering the radiation sources, the construction and layout of instrumentation and the analysis of data. Comprehensively revised throughout, this edition reflects the rapid changes that have taken place recently. It contains additional material on a range of methods, including scanning probe techniques that reflect the need for analysis of materials at the nanoscale, and a detailed review of recent developments in data analysis and computing techniques.Physical Methods for Materials Characterisation, Second Edition will be of interest to advanced undergraduates, postgraduates, and researchers in physics, materials science, and engineering.

Published
2015

19. The role of ferrite in Type 316H austenitic stainless steels on the susceptibility to creep cavitation

Author

Warren, A D, Griffiths, Ian J, Harniman, Robert L, Flewitt, Peter E J, and Scott, Thomas Bligh

Subjects
Magnetic force microscopy, R-phase, Type 316 austenitic stainless steel, Ferrite, Creep life, Creep cavitation, Electron back-scatter diffraction
Abstract

An ex-service Type 316H stainless steel which was subsequently aged at 500°C for ~22×103h was found to contain approximately 2% mixed (δ and α) ferrite distributed in localised regions of the microstructure. Preferred creep cavitation at boundaries was associated with these ferrite regions. Creep cavities associated with the austenite-austenite-ferrite boundary junctions, showed a lenticular morphology while austenite-austenite grain boundary creep cavities had a more spherical morphology. Details of the microstructure of these localised regions are described together with the creep cavity distribution. It has been established the extended heat treatment post-service did not result in any significant sintering of creep induced cavities. The results are discussed with respect to the contribution of the ferrite on the nucleation and growth of the creep cavities and the influence on the overall creep behaviour. An evaluation of the impact of low volume fractions of widely dispersed ferrite on the creep life-time of Type 316H stainless steel is discussed.

Published
2015

24. A Microstructural Sensitivity Study of 316H Austenitic Stainless Steel to Inter-Granular Creep Fracture

Author

Chen, B., Flewitt, Peter E. J., Smith, David John, and Younes, C.M.

Abstract

A preliminary sensitivity examination of the ductility exhaustion based creep damage prediction model, currently used in the R5 high temperature assessment procedure, showed that material property inputs had significant effects on damage prediction. In the present work, the link between the microstructural factors and the susceptibility to inter-granular high temperature creep failure is considered. The latter was judged to be associated with the low creep ductility. Here, the longitudinal section of a creep specimen and the fracture surface were examined. Auger electron spectroscopy was used to investigate the grain boundary composition in this specimen, which failed after a creep test of 1038h at 550ºC under a triaxial stress state. The present results demonstrate that there is a possibility to correlate the susceptibility to high temperature inter-granular fracture from the low temperature fracture investigations. Finally, the susceptibility of the pre-treated 316H stainless steel to inter-granular high temperature failure and the contribution to the creep damage model are briefly discussed.

Published
2011
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25. The Measurement of Residual Stresses in Thermal Barrier Coated Model Aerofoils

Author

Liu, Dong, Flewitt, Peter E. J., and Hallam, Keith R.

Abstract

In this paper, we explored the relationship between thermal aging and the residual stresses developed within a thermal barrier coating (TBC) and the underlying thermally grown oxide (TGO). Superalloy model specimens (CMSX4) with a curved geometry designed to simulate key features of turbine blades coated with air plasma sprayed (APS) 7 wt.% Y2O3-stabilised ZrO2 applied to an Amdry 995 bond coat were oxidised in the temperature range 900°C to 975°C for various lengths of time. Stress measurements on both the TBC and the underlying TGO were made at positions of known curvature using Raman and photo-stimulated piezo-luminescence spectroscopy (PLPS). The residual stress values reflect the interaction between TGO and TBC, which has the potential to be used as an indicator of service lifetime. The results are discussed with respect to the origin of the stress changes and the long term integrity of the coating.

Published
2011
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26. Comparing Techniques for Quantification of Creep Cavities

Author

Siqi He, Flewitt, Peter E. J., Knowles, David M., Tomas Martin, Tomkins, Brian, Tu, Shan-Tung, Flewitt, Peter EJ, and Sharples, John K

Subjects
Materials Characterisation, Creep cavitation, Microstructure
Abstract

Creep cavitation is a key limitation for the life of a component acting under load at elevated temperatures. This paper compares several modern techniques available to characterize and understand the formation of creep cavities. Conventional 2D imaging techniques such as Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) imaging characterize morphology and distribution over a large area, while scanning transmission electron microscopy (STEM) has higher resolution but limited sampling area. 3D imaging techniques such as X-ray Tomography (XRT) enable the characterization of creep cavities in three dimensions, however XRT can be limited in cavity identification due to resolution. To bridge the length-scale gap, FIB serial sectioning can reconstruct the creep cavities at a single grain boundary with a much higher resolution, whilst advancements in Plasma FIB enable this high resolution characterization over a larger reconstruction volume. For optimum creep cavitation characterization, multiple techniques should be used in complement with each other.

27. Nanometre to micrometre length-scale techniques for characterising environmentally-assisted cracking: An appraisal.

Author

Clark RN, Burrows R, Patel R, Moore S, Hallam KR, and Flewitt PEJ

Abstract

The appraisal is strongly focussed on challenges associated with the nuclear sector, however these are representative of what is generally encountered by a range of engineering applications. Ensuring structural integrity of key nuclear plant components is essential for both safe and economic operation. Structural integrity assessments require knowledge of the mechanical and physical properties of materials, together with an understanding of mechanisms that can limit the overall operating life. With improved mechanistic understanding comes the ability to develop predictive models of the service life of components. Such models often require parameters which can be provided only by characterisation of processes occurring in situ over a range of scales, with the sub-micrometre-scale being particularly important, but also challenging. This appraisal reviews the techniques currently available to characterise microstructural features at the nanometre to micrometre length-scale that can be used to elucidate mechanisms that lead to the early stages of environmentally-assisted crack formation and subsequent growth. Following an appraisal of the techniques and their application, there is a short discussion and consideration for future opportunities., (© 2020 The Author(s).)

Published
2020
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28. Calibration of Raman spectroscopy in the stress measurement of air-plasma-sprayed yttria-stabilized zirconia.

Author

Liu D, Lord O, and Flewitt PE

Abstract

Thermal barrier coatings (TBC) are used widely on a range of components that operate at high temperatures. We report measurement of the factor that is required to convert the Raman shift to stress for air plasma sprayed yttria (7 wt %) stabilized tetragonal zirconia (ZrO(2)) (YSZ) thermal barrier coatings. The factor is evaluated for the as-coated condition and also following a heat treatment at 1000 °C for 1050 h. Two Raman bands at 608 cm(-1) and 640 cm(-1) have been investigated in a diamond anvil cell under hydrostatic pressure up to ~24 GPa. In the range of zero to ~1.6 GPa, a linear behavior was observed in terms of the shifts of these two Raman bands with a gradient similar to dense bulk tetragonal ZrO(2). From these measurements the factors to convert wavenumber shift to stress have been derived. The application of these conversion factors to stress measurement in TBC coated test specimens and components is discussed.

Published
2012
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