Papers by Shirley Northover
CORROSION, 1988
The influence of grain boundary microstructure on the susceptibility of thermally treated (TT) In... more The influence of grain boundary microstructure on the susceptibility of thermally treated (TT) Inconel Alloy 600 to intergranular attack (IGA) and stress corrosion cracking (SCC) in 30%NaOH + 10%Na2SO4 at 350 C was investigated. Both milt-annealed (MA) and laboratory solution-annealed alloys were aged at 700 C to establish the effect of initial processing on the material's response to thermal treatment. Treatments of 1 h or more at 700 C greatly improved the SCC resistance of solution-annealed material but did not improve the performance of MA material containing a high density of intragranular carbides. The poor behavior of this material after thermal treatment was associated with the formation of small M23C6 carbides growing at a high angle to the boundaries and the development of these into cellular colonies. This is attributed to the use of a MA temperature that was too low to take into solution sufficient carbon for the development of semicontinuous grain boundary carbides during the subsequent TT process.
Alongside well-studied intragranular precipitation reactions, age-hardening silver copper alloys ... more Alongside well-studied intragranular precipitation reactions, age-hardening silver copper alloys undergo a range of slower grain boundary initiated transformations including chemically-induced grain boundary migration and cellular precipitation reactions. These are of great interest both for their effect upon mechanical properties and because it has been suggested that the observation of such grain boundary effects offers a means of distinguishing ancient silver objects from modern ones. Optical and scanning electron microscopy have been used to find the temperature dependence of the overall growth rates of cellular colonies in Ag-7.5Cu and Ag-4.16Cu. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) have been used to determine the crystallographic relationships between the different transformation products and the parent grains. The extent of transformation varies greatly from boundary to boundary and EBSD has shown that the extent of transformati...
[About the book] In 1991, sports divers discovered a previously unknown section of wooden shipwre... more [About the book] In 1991, sports divers discovered a previously unknown section of wooden shipwreck, subsequently named Alum Bay 1, lying in the sheltered waters of Alum Bay on the north-west coast of the Isle of Wight. The identity of the vessel was initially unknown but it was strongly linked to the loss of the 38-gun frigate HMS Pomone on the nearby Needles in 1811, an identification formally confirmed by the research detailed in this monograph. Archaeological work on the site since 1993 has comprised a seabed survey of the site, targeted excavation of specific areas and sampling of structural remains for dendrochronological and metallurgical analysis. In 2001, a second shipwreck was discovered a short distance away and the focus of archaeological work shifted to this new set of remains, named Alum Bay 2. This vessel proved to be a much smaller vessel that was upturned on the seabed and covered by a thin layer of sediment. This vessel was also subject to archaeological survey and investigation, including dendrochronological analysis. On the basis of the ship structure surviving on the seabed, Alum Bay 2 has been classified as a relatively small vessel that was likely to have been involved in local transport or coastal trade in the very late 18th century and early decades of the 19th century. The role of public engagement in the management of such archaeological sites was developed further in the mid-2000s when a dive trail was established around the two Alum Bay shipwrecks. The dive trail in Alum Bay provides an interesting case study in this form of archaeological interaction with the diving public. In concert with such outreach work, further archaeological survey was been undertaken across Alum Bay in the light of a number of isolated finds being reported by sports divers including parts of cannon carriages and hull elements. Investigative work in Alum Bay has also encompassed the broken remains of the Victorian Pier that was constructed in 1887 to serve the growing boom in seaside tourism. The two shipwrecks of Alum Bay 1 and 2 provide a snapshot of two different aspects of English shipbuilding, naval and merchant, in the very late 18th and early 19th century. The archaeological work conducted in their investigation forms the core of this monograph, with further chapters that discuss the wider searches of Alum Bay and also the installation and use of the public Alum Bay Dive Trail. Such an account represents the results of twenty years of archaeological investigation within Alum Bay by the Maritime Archaeology Trust (which incorporates the Hampshire and Wight Trust for Maritime Archaeology). This work has been undertaken across a time span in which maritime archaeology in the UK has seen tremendous changes, becoming ever more integrated into the wider heritage discipline and with increasing numbers of professional archaeologists working within the marine zone. Throughout this period, archaeological work in Alum Bay has brought together professional and a-vocational archaeologists, who have worked successfully alongside each other. The various fieldwork seasons have provided extensive opportunities for people to receive archaeological training and develop their experience. This monograph therefore represents the last stage of this work, addressing the processing, analysis, interpretation and finally publication and dissemination.
Hardened copper bolts were the ¿new technology¿ that saved the Royal Navy when iron bolts no long... more Hardened copper bolts were the ¿new technology¿ that saved the Royal Navy when iron bolts no longer held ships together safely after their wooden hulls had been sheathed in copper in the mid-18th century. It is important both for naval history and for the history of the metal industry during the Industrial Revolution to understand how copper was provided for the Navy. The competing manufacturing processes have been shown to result in different patterns of preferred orientations of the tiny copper crystals that make up a solid bolt. Bolts recovered from shipwrecks of the time are up to 1m long and neutron diffraction is the only non-destructive technique that can reveal these distinctive patterns and how they vary in different parts of the bolt. Five such bolts will be examined to show their manufacturing routes. The better methods of doing this can then be applied to modern materials too
Since the crystallographic orientation of a cellular colony derives from the grain it grows away ... more Since the crystallographic orientation of a cellular colony derives from the grain it grows away from, experimental interest in discontinuous precipitation (DP) has centred on how nucleation and growth rates are affected by the misorientation of the initiating grain boundary. There has been little attention paid to the nature of the interface at the reaction front. Ageing experiments on Ag-7.5Cu at 2500C showed there to be two DP colony populations with distinctly different growth behaviours. EBSD studies have shown that as the colonies grow there is a build-up of misorientation behind the reaction front and eventually the fast growing colonies are surrounded by interfaces close to particular low Σ coincident site lattice (CSL) misorientations with respect to the grain into which they are growing. On the other hand, slow growing colonies are characterised by misorientations close to a different set of low ΣCSLs. The growth mechanisms behind this behaviour will be discussed.
In June 1813, several ships from a combined fleet that unsuccessfully tried to liberate Tarragona... more In June 1813, several ships from a combined fleet that unsuccessfully tried to liberate Tarragona from Napoleonic forces ran aground in the Ebro Delta (Catalonia coast, Spain). One, a British transport is currently the subject of research by the Catalan Centre for Underwater Archeology. In this context, crystallographic texture analyses of the bolts used to fasten different wooden components of the hull's structure can shed light on some aspects of the technology used during the early stage of industrialization in Britain. Specifically, spatially resolved neutron texture analyses offer a great advantage to understanding metal objects' manufacturing routes. The main aim of this project is to perform spatially resolved neutron texture analysis on four copper bolts used to fasten different wooden components of the hull's structure recovered from the Deltebre I site.
Applications of Electron Backscatter Diffraction (EBSD) in Archaeology Book Chapter How to cite: ... more Applications of Electron Backscatter Diffraction (EBSD) in Archaeology Book Chapter How to cite: Northover, S. M. and Northover, J. P. (2012). Applications of Electron Backscatter Diffraction (EBSD) in Archaeology. In: Meeks, Nigel; Cartwright, Caroline; Meek, Andrew and Mongiatti, Aude eds. Historical Technology, Materials and Conservation: SEM and Microanalysis. Archetype Publications, pp. 76–85.
During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The...
Journal of Applied Crystallography
The spatial resolution achievable by a time-of-flight neutron strain scanner has been harnessed u... more The spatial resolution achievable by a time-of-flight neutron strain scanner has been harnessed using a new data analysis methodology (NyRTex) to determine, nondestructively, the spatial variation of crystallographic texture in objects of cultural heritage. Previous studies on the crystallographic texture at the centre of three Napoleonic War era copper bolts, which demonstrated the value of this technique in differentiating between the different production processes of the different types of bolts, were extended to four copper bolts from the wrecks of HMS Impregnable (completed 1786), HMS Amethyst (1799), HMS Pomone (1805) and HMS Maeander (1840) along with a cylindrical `segment' of a further incomplete bolt from HMS Pomone. These included bolts with works stamps, allowing comparison with documentary accounts of the manufacturing processes used, and the results demonstrated unequivocally that bolts with a `Westwood and Collins' patent stamp were made using the Collins rath...
Cast silver-copper alloy objects form a significant part of the archaeological record of silver f... more Cast silver-copper alloy objects form a significant part of the archaeological record of silver from at least the first millennium BC onwards but there has been little study of their microstructures. Wrought silver-copper alloys have been more extensively studied with a particular focus on the evidence for discontinuous precipitation of copper from supersaturated solid solution at ambient temperature over archaeological time and whether this could be used as an indicator or measure of age (see eg [1][2]). Studies of the cast alloys are hindered by the very fine scale of precipitation which forms within the grains over a broad range of cooling rates which challenges the resolving power of optical methods while there are significant experimental difficulties of determining orientation relationships using either X-ray methods or by transmission electron microscopy. The work presented here used a combination of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD...
Procedia Structural Integrity, 2016
Metallurgical and Materials Transactions A, 2014
ABSTRACT Accurate prediction of microstructural stability in an alloy depends not only on a sound... more ABSTRACT Accurate prediction of microstructural stability in an alloy depends not only on a sound knowledge of the thermodynamics of the system but also of the kinetics of the phase changes involved. Conventionally, precipitate growth mechanisms have been inferred from the variation with aging time of various single parameters such as the mean, mode or maximum of the precipitate size distribution, which has then been compared to theoretical models of growth of an individual precipitate. In the present study, the development, with aging time at 1003 K (730 °C), of the size and shape distributions of grain boundary precipitates in Co-20Fe has been examined to determine the rate-controlling processes, and the conclusions compared to those from conventional analysis. The growth of the precipitates was well described by the grain boundary-dependent collector plate mechanism of Brailsford and Aaron. As the precipitates grew, low-energy facets were formed, which could move only by the propagation of ledges, and thickening was inhibited. The precipitates’ diffusion fields in the grain boundary overlapped and the size distributions of the longest aged specimens showed that local coarsening occurred under partial interface control.
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Papers by Shirley Northover