Julie Yeomans

Professor Julie Yeomans

Professor Emerita of Ceramic Materials
MA, PhD, CEng, CSci, FIMMM
+44 (0)1483 689613
28 AB 03

Academic and research departments

School of Mechanical Engineering Sciences.



Research interests

Research projects


ITSASO ECHEVERRIA, David T. Fishpool, Virtudes Rubio Diaz, ROBERT ANDREW DOREY, JULIE ANNE YEOMANS (2022)Evaluation of polymer matrix composite manufacturing routes for production of an oxide/oxide ceramic matrix composite, In: Journal of the European Ceramic Society [e-journal].42(5) Elsevier

The use of manufacturing methods commonly used for polymer matrix composites (PMCs) in the production of ceramic matrix composites (CMCs), as opposed to more traditional ceramic manufacturing methods, has the potential to reduce the cost of components. This work focuses on three typical PMC manufacturing methods and assesses their suitability for the production of an oxide-oxide porous matrix ceramic composite, starting from a commercially available pre-impregnated Nextel 610®/aluminium oxide material. While all the techniques can be used to produce CMCs, results showed that compared with vacuum bagging and warm pressing, autoclave processing produced the best outcome. It resulted in the most uniform thickness laminates and the lowest macro-porosity, as well as the highest flexural strength. 

I.M. Low, Julie Anne Yeomans (2006)Ceramic-matrix composites Woodhead

The advent of engineering-designed polymer matrix composites in the late 1940s has provided an impetus for the emergence of sophisticated ceramic matrix composites. The development of CMCs is a promising means of achieving lightweight, structural materials combining high temperature strength with improved fracture toughness, damage tolerance and thermal shock resistance. Considerable research effort is being expended in the optimisation of ceramic matrix composite systems, with particular emphasis being placed on the establishment of reliable and cost-effective fabrication procedures. Ceramic matrix composites consists of a collection of chapters reviewing and describing the latest advances, challenges and future trends in the microstructure and property relationship of five areas of CMCs. Part one focuses on fibre, whisker and particulate-reinforced ceramic matrix composites, part two explores graded and layered ceramics, while the five chapters in part three cover nanostructured CMCs in some detail. Refractory and speciality ceramic composites are looked at in part four, with chapters on magnesia-spinel composite refractory materials, thermal shock of CMCs and superplastic CMCs. Finally, part four is dedicated to non-oxide ceramic composites. Ceramic matrix composites is a comprehensive evaluation of all aspects of the interdependence of processing, microstructure, properties and performance of each of the five categories of CMC, with chapters from experienced and established researchers. It will be essential for researchers and engineers in the field of ceramics and more widely, in the field of inorganic materials. Looks at the latest advances, challenges and future trendsCompiled by experienced and established researchers in the fieldEssential for researchers and engineers.

C Kastritseas, P Smith, J Yeomans (2006)Thermal shock of ceramic matrix compositespp. 400-433
C Kastritseas, PA Smith, JA Yeomans (2006)Damage characterisation of thermally shocked cross-ply ceramic composite laminates, In: JOURNAL OF MATERIALS SCIENCE41(3)pp. 951-962 SPRINGER
AJ Harris, B Vaughan, ST Burnage, JA Yeomans, PA Smith (2013)Surface preparation of alumina for improved adhesive bond strength in armor applications, In: Ceramic Engineering and Science Proceedings33(5)pp. 149-159 Wiley Blackwell

Surface treatments of alumina have been investigated with the aim of increasing the strength of the bond created between the alumina and a toughened epoxy adhesive. Four surface conditions have been assessed: as-fired; grit blasted; and krypton fluoride excimer laser treated under two sets of conditions. Compared with the as-fired surface, the grit blasted surface was rougher with poorer wettability, probably due to surface contamination. It was found that the laser treatments removed some of the sintering additives and caused rounding of the alumina grains, slightly increasing the surface roughness. Further, the laser treatment led to an increased surface energy and wettability, which has been linked tentatively to an observed increase in the hydroxyl groups on the surface. The adhesive bond strength was assessed by testing joints in tension and shear. It was found that the laser treated surfaces demonstrated slight improvements in bond strength, with a cohesive failure of the adhesive in tension for surfaces subjected to one of the two laser treatments, compared with failure at the interface for the as-fired, grit blasted and other laser treated samples in tension and for all samples in shear. Thus, it has been demonstrated that modifications to the surface of alumina can result in mechanical and chemical changes which affect roughness, wettability, bond strength and the locus of failure.

M Tillman, JA Yeomans, RA Dorey (2014)The effect of a constraint on the sintering and stress development in alumina thick films, In: Ceramics International4(7)pp. 9715-9721 Elsevier

The microstructural and stress evolution of thick (25 μm) alumina films on dense alumina substrates sintered at temperatures from 1300 °C to 1600 °C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300 °C-1600 °C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40 MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded. © 2014 The Authors.

Y. Ji, J.A. Yeomans (2002)Processing and mechanical properties of Al 2O 3–5 vol.% Cr nanocomposites, In: Journal of the European Ceramic Society22(12)pp. 1927-1936 Elsevier Ltd

The use of chromium (III) acetylacetonate as a source of nanometre sized chromium particles for the production of Al 2O 3–5 vol.% Cr nanocomposites has been investigated. The details of the processing procedure are crucial in determining the mechanical properties of the composite. The highest strength and fracture toughness, 736±29 MPa and 4.0±0.2 MPa m 1/2, respectively, were obtained for the nanocomposite hot pressed at 1450 °C. It is shown that the strengthening in Al 2O 3–5% Cr nanocomposites mainly results from microstructure refinement in that the mean alumina matrix grain size in the optimum composite was 0.68 μm compared with a grain size of 3.6 μm in the monolithic alumina hot pressed under identical conditions. Crack bridging and crack deflection by the nano-sized Cr particles did not occur to any significant extent. The slight improvement in fracture toughness may result from the observed change in fracture mode from intergranular fracture for monolithic alumina to transgranular failure for the nanocomposites.

S Kiani, J Pan, JA Yeomans, M Barriere, P Blanchart (2007)Finite element analysis of sintering deformation using densification data instead of a constitutive law, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY27(6)pp. 2377-2383 ELSEVIER SCI LTD
D Mahdi, A Riches, M Gester, J Yeomans, P Smith (2015)Rolling and sliding: Separation of adhesion and deformation friction and their relative contribution to total friction, In: TRIBOLOGY INTERNATIONAL89pp. 128-134 ELSEVIER SCI LTD
S Kiani, J Pan, JA Yeomans (2006)A new scheme of finding the master sintering curve, In: J AM CERAM SOC89(11)pp. 3393-3396 BLACKWELL PUBLISHING

The master sintering curve approach represents densification data in terms of a master variable that combines sintering time and temperature. Recently, a finite-element scheme to predict sintering deformation that requires only the master sintering curve instead of a full constitutive law as the input data has been developed. Here, a modification to the original master sintering curve approach, so that it is more suitable for finite-element analysis, is presented. Finite-element shape functions are used to represent the densification data as well as the master sintering curve. This approach confers extra flexibility to the master sintering curve approach, even when it is not used with finite-element analysis. For example, by using shape functions, a varying activation energy can be used to obtain a master sintering curve for a set of densification data that cannot be fitted using a constant activation energy.

GJ Wright, JA Yeomans (2008)The influence of screen-printing parameters on the microstructure and gas permeance of a zirconia electrolyte, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY28(4)pp. 779-785 ELSEVIER SCI LTD
GJ Wright, JA Yeomans (2009)Three-step sintering of constrained yttria stabilised zirconia layers and its effect on microstructure and gas permeance, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY29(10)pp. 1933-1938 ELSEVIER SCI LTD
C Kastritseas, PA Smith, JA Yeomans (2010)Thermal shock fracture in cross-ply fibre-reinforced ceramic-matrix composites, In: PHILOSOPHICAL MAGAZINE90(31-32)PII 923938pp. 4209-4226 TAYLOR & FRANCIS LTD
AJ Harris, B Vaughan, Julie Yeomans, Paul Smith, ST Burnage (2017)Ballistic testing of surface treated alumina and silicon carbide with improved adhesive bond strength, In: International Journal of Applied Ceramic Technology: ceramic product development and commercialization14(3)pp. 323-330 Wiley

The laser treatment of ceramics can lead to increased concentrations of hydroxyl ions on the surface, resulting in improved adhesive bond strength in quasi-static tests. Whether the improvement can be translated to armor applications is investigated here. The ballistic testing of composite-backed, surface treated and non-treated ‘control’ alumina and silicon carbide panels was undertaken. The failure locus of the ceramic to adhesive/composite joint and the qualitative degree of damage were assessed. Laser surface treated samples performed better than control samples, with silicon carbide moving from single shot to multi-shot capability, thus giving significant advantages for the deployment of these materials.

Adam Healey, J Cotton, S Maclachlan, Paul Smith, Julie Yeomans (2016)Understanding the Ballistic Event: Methodology and Initial Observations, In: Journal of Materials Science52(6)pp. 3074-3085 Springer

The purpose of the study is to accelerate the development of ceramic materials for armour applications, by substantially increasing the information obtained from a high-energy projectile impact event. This has been achieved by modifying an existing test configuration to incorporate a block of ballistic gel, attached to the strike face of a ceramic armour system, to capture fragments generated during the ballistic event such that their final positions are maintained. Three different materials, representative of the major classes of ceramics for armour applications, alumina, silicon carbide and boron carbide, have been tested using this system. Ring-on-ring biaxial disc testing has also been carried out on the same materials. Qualitative analysis of the fracture surfaces using scanning electron microscopy and surface roughness quantification, via stereoimaging, has shown that the fracture surfaces of biaxial fragments and ballistic fragments recovered from the edges of the tile are indistinguishable. Although the alumina and boron carbide fragments generated from areas closer to the point of impact were also similar, the silicon carbide fragments showed an increase in porosity with respect to the fragments from further away and from biaxial testing. This porosity was found to result from the loss of a boron-rich second phase, which was widespread elsewhere in the material, although the relevance of this to ballistic performance needs further investigation. The technique developed in this work will help facilitate such studies.

P Yates, Christopher Mallinson, P Mallinson, Mark Whiting, Julie Yeomans (2017)An Investigation into the Nature of the Oxide Layer Formed on Kovar (Fe-29Ni-17Co) Wires Following Oxidation in Air at 700 °C and 800 °C, In: Oxidation of Metals: an international journal of the science of gas-solid reactions88(5-6)pp. 733-747 Springer

This work provides new insight and evidence that challenges and extends the accepted view of the oxidation of Kovar (ASTM-15). Specimens of 2 mm diameter Kovar wire were oxidised in air at 700 °C or 800 °C for 10 minutes. The resulting oxide layers were analysed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, scanning transmission electron microscopy and Raman spectroscopy. Oxide layers of approximately 2 μm and 4 μm thick were formed at 700 °C and 800 °C, respectively. These were found to contain iron, cobalt and traces of nickel. The combination of analysis techniques revealed that the oxide contains Fe2O3 in addition to (Fe,Co,Ni)3O4, a spinel oxide, in contrast to the combinations of Fe3O4, Fe2O3 and FeO that are typically reported. The oxide layer was found to be complex, consisting of multiple layers with different compositions which is overlooked in the existing literature.

C Kastritseas, PA Smith, JA Yeomans (2008)Thermal shock behaviour of angle-ply and woven dense ceramic-matrix composites, In: JOURNAL OF MATERIALS SCIENCE43(12)pp. 4112-4118 SPRINGER
RA Dorey, JA Yeomans, PA Smith, J Pan (2001)In situ optical dilatometric measurements of the initial stages of sintering of alumina, In: ACTA MATERIALIA49(3)pp. 519-527 PERGAMON-ELSEVIER SCIENCE LTD
Edward H. Williamson, Mark Gee, Daniel Robertson, John F. Watts, Mark J. Whiting, Julie A. Yeomans (2019)Wear performance and characterisation of coatings for nuclear applications: WC-(W,Cr)2C-Ni and hard chromium plate, In: Wear430pp. 169-182 Elsevier

The nuclear industry has used hard chromium plate for many years but is seeking alternatives, due to the adverse health effects of Cr(VI) employed in electroplating. In this study, testing and analysis regimes for the comparison of the sliding wear performance of candidate materials have been established and the performance of WC-(W,Cr)2C-Ni has been compared with that of hard chromium plate. WC-(W,Cr)2C-Ni was applied to Inconel 625 substrates using a detonation gun thermal spray technique. Sliding wear testing was performed using a ball-on-flat configuration reciprocating tribometer at 20 °C in three environments: dry, deionised water and simulated nuclear reactor water chemistry. Wear rates have been evaluated, using both mass and volume loss, and the worn samples were analysed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The WC-(W,Cr)2C-Ni coating had a broadly comparable wear performance to hard chromium plate in all three environments. There were differences between deionised and borated water, such that the latter needs to be used in further evaluation. SEM and XPS analyses enabled the wear mechanisms for WC-(W,Cr)2C-Ni and HCP to be elucidated, including pull-out and tribolayer formation. XPS has shown that the tribolayer on WC-(W,Cr)2C-Ni is stratified and undergoes chemical changes as a result of wear.

JA Yeomans (2008)Ductile particle ceramic matrix composites - Scientific curiosities or engineering materials?, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY28(7)pp. 1543-1550 ELSEVIER SCI LTD

This review is concerned with ductile particle ceramic matrix composites, which are a group of materials comprising micro- or nano-scale metallic particles in a ceramic matrix. The most studied materials have an alumina matrix; nickel, iron, molybdenum, copper, and silver are some of the more frequently used metals. In contrast to conventional cermets and composites containing an interconnected metallic phase, the particles are discrete. The larger particles provide a toughening increment by deforming plastically and bridging an advancing crack. For the nanoscale composites significant improvements in strength have been reported. Improvements in strength and toughness, coupled with changes to elastic properties and thermal conductivity, have led to improved thermal shock resistance and a consideration of these materials for wear applications.

RA Dorey, JA Yeomans, PA Smith (2002)Effect of pore clustering on the mechanical properties of ceramics, In: JOURNAL OF THE EUROPEAN CERAMIC SOCIETY22(4)pp. 403-409 ELSEVIER SCI LTD
PM Delaforce, JA Yeomans, NC Filkin, GJ Wright, RC Thomson (2007)Effect of NiO on the phase stability and microstructure of yttria-stabilized zirconia, In: JOURNAL OF THE AMERICAN CERAMIC SOCIETY90(3)pp. 918-924 BLACKWELL PUBLISHING
MJ Blissett, PA Smith, JA Yeomans (1997)Thermal shock behaviour of unidirectional silicon carbide fibre reinforced calcium aluminosilicate, In: JOURNAL OF MATERIALS SCIENCE32(2)pp. 317-325 CHAPMAN HALL LTD
MJ Whiting, MT Staff, JA Fernie, PM Mallinson, JA Yeomans (2016)Fabrication of a Glass-Ceramic-to-Metal Seal between Ti-6Al-4V and a Strontium Boroaluminate Glass, In: International Journal of Applied Ceramic Technology: ceramic product development and commercialization13(5)pp. 956-965 Wiley

Glass-ceramics are widely utilized in the electronics industry to provide electrical insulation and to form leak tight joints with a range of metals. The coefficient of thermal expansion (CTE) of the glass-ceramic can be controlled by the extent of crystallization to reduce detrimental tensile stresses in the joint. In recent years there has been interest in using titanium alloys, in place of stainless steels, due to their lower density and superior specific strength. In this study, the heat treatment of a strontium boroaluminate glass has been tailored to create glass-ceramics with mean CTEs ranging from 5.7 ± 0.1 × 10-6 K-1 to 9.7 ± 0.1 × 10-6 K-1 over the temperature range 303 K to 693 K. The resultant glass-ceramic consists of three crystalline phases and residual glass. A glass-ceramic with a mean CTE of 6.9 ± 0.1 × 10-6 K-1 was subsequently fabricated to form a compression seal with a Ti-6Al-4V housing and a pre-oxidized Kovar pin. Single pin assemblies were shown to be reproducible in terms of microstructure and all passed a standard helium leak test, indicating that a successful seal had been produced.

MJ Blissett, PA Smith, JA Yeomans (1998)Flexural mechanical properties of thermally treated unidirectional and cross-ply Nicalon-reinforced calcium aluminosilicate composites, In: JOURNAL OF MATERIALS SCIENCE33(16)pp. 4181-4190 KLUWER ACADEMIC PUBL
C Kastritseas, PA Smith, JA Yeomans (2005)Thermal shock fracture in unidirectional fibre-reinforced ceramic-matrix composites, In: COMPOSITES SCIENCE AND TECHNOLOGY65(11-12)pp. 1880-1890 ELSEVIER SCI LTD
Simon Parker, Mark Whiting, Julie Yeomans (2017)Control of carbon content in WC-Co hardmetal by heat treatment in reducing atmospheres containing methane., In: International Journal of Refractory Metals and Hard Materials66pp. 204-210 Elsevier

Pressed WC-Co hardmetal compacts of two different compositions, 6 and 10 wt.% Co, were heat treated under flowing atmospheres of nitrogen, hydrogen and methane at temperatures from 500 to 900 °C prior to sintering under argon. Microstructural examination showed excessive carburisation up to 2.5 mm into the compacts with regions most exposed to heat treatment atmospheres showing greatest carburisation. η-phase was present in the 6 wt.% Co samples heat treated at low temperatures without methane but was not present with heat treatment temperatures of 700 °C or above with methane present. The hardness of both materials was significantly lower in highly carburised regions, highlighting the need for careful control of heat treatment parameters.

AJ Harris, B Vaughan, ST Burnage, JA Yeomans, PA Smith (2013)Surface preparation of silicon carbide for improved adhesive bond strength in armour applications, In: Journal of the European Ceramic Society33(15-16)pp. 2925-2934

Surface treatments of silicon carbide have been investigated with the aim of improving the strength of the bond between the ceramic and an epoxy adhesive. Three surface conditions have been characterised; as-fired, air re-fired and KrF laser processed. A number of characterisation techniques have been used to determine the morphological and chemical changes that have occurred to the surface. Scanning electron microscopy of the re-fired and laser processed samples showed surfaces that appeared glassy, with the laser processed surface showing a different morphology. X-ray photoelectron spectroscopy indicated both treatments had oxidised the surface and the laser processed surface also had a greater concentration of hydroxyl groups. The wettability of both surfaces had improved and the laser processed surface was found to be highly hydrophilic. Mechanical testing of joints prepared with this technique showed them to have the highest strength in tension, with the locus of failure being cohesive. © 2013 The Authors.

M Aldridge, J. A Yeomans (1999)The thermal shock behaviour of ductile particle toughened alumina composites, In: Journal of the European Ceramic Society19(9)pp. 1769-1775 Elsevier
A. J. Winn, J. A. Yeomans (1996)A study of microhardness indentation fracture in alumina using confocal scanning laser microscopy, In: Philosophical magazine. A, Physics of condensed matter. Defects and mechanical properties74(5)pp. 1253-1263 Taylor & Francis Group

Quasistatic indentation has been used to study the hardness and fracture toughness of advanced ceramic materials and has been used as the starting point for the modelling of many wear situations. A lack of data on the nature of subsurface cracks in ceramics has resulted in limited evidence to indicate that crack systems generated by indentation bear any relationship to complex wear situations. In the current study, the technique of confocal scanning laser microscopy (CSLM) has been used to obtain subsurface information on a fine-grained alumina ceramic. The alumina has been indented and CSLM has been used to obtain a substantial amount of data on both surface and subsurface cracking. The data have been compared with predictions from existing theories and it has been shown that the subsurface lateral cracking can be predicted by measuring the more easily observable radial cracks. Radial cracking and subsurface damage due to indentation have proved to be similar to that produced by single particle ballistic impact; hence it may be possible to predict erosive wear rates by conducting simple indentation studies.

K Powell, Ja Yeomans, P Smith, Julie Anne Yeomans (1993)Characterization of subsurface damage in ceramic-matrix composites by confocal scanning laser microscopy, In: Journal of microscopy (Oxford)169(2)pp. 189-195

The techniques of confocal scanning laser microscopy (CSLM) and reflected-light microscopy (RLM) have been combined in a study of the subsurface damage in continuous-fibre reinforced ceramic-matrix composites (CMCs). The damage was induced by subjecting a composite to Vickers hardness indentation tests and single-particle impacts. The subsurface damage was viewed conventionally by RLM at specific depths, following material removal by standard metallographic techniques. Mechanical sectioning, however, is time-consuming and may introduce artefacts in the crack patterns. Consequently CSLM was employed to provide a rapid, non-destructive analysis of the subsurface damage. In the classic description of elastic-plastic indentation of monolithic ceramics, there are two major types of crack: radial cracks, which grow out from the elastic-plastic boundary perpendicular to the surface, and lateral cracks, which are on planes approximately parallel to the surface. In CMCs radial cracks were found to be restricted to the near-surface region. Lateral cracks, however, were located a few micrometres from the free surface. Preliminary analysis of damage about impact sites by mechanical sectioning and CSLM has shown that the crack patterns are similar to those observed in indentation fracture. The topographical-mapping facility of the CSLM has been used to detail the radius of damage about an impact site, which has been found to increase with increasing impact velocity.

J Yeomans, Trevor Page (1989)Chemical stability of ceramic cutting tool materials exposed to liquid metals, In: Wear131(1)pp. 163-175

Authors test an Al#72O#73-based and two Si#73N#74-based ceramics in three common workpieces. The molten metals consist of Fe-Ni alloys and two Ni-based superalloys. Results show Al#72O#73 is resistant to all three metals, but the other two are attacked. The suggested mechanism is diffusion into the metal via the grain boundary phase with subsequent dissolution of Si#73N#74 grains.

R Brydson, H MUeLLEJANS, J Bruley, P Trusty, X Sun, Ja Yeomans, M RUeHLE, Julie Anne Yeomans (1995)Spatially resolved electron energy-loss studies of metal-ceramic interfaces in transition metal/alumina cermets, In: Journal of microscopy (Oxford)177(3)pp. 369-386

Composites consisting of an alumina matrix and 20 vol.% transition metal (Ni or Fe) particles, prepared by hot pressing powder blends, have been studied using spatially resolved transmission electron energy-loss spectroscopy (EELS), and, to a lesser extent, by high-resolution electron microscopy (HREM). Particular attention was paid to the elucidation of the chemical bonding mechanisms at the metal-ceramic interface; EELS spectra from interfacial regions being obtained via a spatial difference technique. From both qualitative and quantitative interpretation of EELS near-edge structures, as well as observed HREM images, the data appear to be consistent with the presence of an Al-terminated alumina at the interface and the formation of direct transition metal - aluminium bonds in Al(O3M) (M = Ni or Fe) tetrahedral units, possibly as a result of the dissolution and interfacial reprecipitation of Al during processing. These results correlate well with similar model studies on diffusion-bonded Nb/Al2O3 interfaces and may, in the light of recent theoretical electronic structure calculations, have implications for the resultant interfacial bond strength in such materials.

Matthew Aldridge, Julie A. Yeomans (2001)Thermal Shock Behavior of Iron-Particle-Toughened Alumina, In: Journal of the American Ceramic Society84(3)pp. 603-607 American Ceramics Society
Xudong Sun, Julie A. Yeomans (1996)Influence of Particle Size Distribution on Ductile-Phase Toughening in Brittle Materials, In: Journal of the American Ceramic Society79(2)pp. 562-564 Blackwell Publishing Ltd
J Pan, H LE, S Kucherenko, J. A Yeomans (1998)A model for the sintering of spherical particles of different sizes by solid state diffusion, In: Acta materialia46(13)pp. 4671-4690 Elsevier Science
J. A Yeomans, T. F Page (1990)Studies of ceramic-liquid metal reaction interfaces, In: Journal of materials science25(5)pp. 2312-2320 Springer
MARK JOHN WHITING, E Williamson, Mark Gee, Daniel Robertson, JOHN FARNHAM WATTS, Mark W. Whiting, JULIE ANNE YEOMANS (2022)A comparative study of the wear performance of hard coatings for nuclear applications, In: Wear488-489204124 Elsevier B.V

Hard chromium plate (HCP) has been the wear resistant coating of choice in the nuclear industry for decades, but new protective coatings are required as a result of the hazardous nature of Cr(VI) compounds used in electroplating. This study compares the wear performance of candidate replacements materials, Cr2O3 and Cr3C2–NiCr. These two coatings are also compared with HCP and a WC-(W,Cr)2C–Ni coating assessed in an earlier publication. The Cr2O3 and Cr3C2–NiCr coatings were supplied having been applied to Inconel 625 substrates using high velocity oxy fuel (HVOF) and thermal detonation gun spray techniques, respectively. A ball-on-flat sliding wear configuration was used with three environments: dry, deionised water, and borated water to partially simulate nuclear reactor water chemistry. Wear rates were measured using both volume and mass standard metrics. The wear surface samples were characterised using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in order to establish the operative wear mechanisms. All three candidate coating materials exhibited similar wear performance to HCP in the three test environments. There was, however, enough of a difference between performance in deionised and borated water, to merit the use of borated water in future testing. The data gathered using SEM and XPS provided insight into the wear mechanisms. These include both particle pull-out and tribolayer formation. The XPS data revealed that Cr3C2 is preferentially removed from the Cr3C2–NiCr coating during wear testing in a borated water environment. •Three ceramic and cermet coatings wear tested in reactor coolant water.•Cr2O3 is the best hard chromium plate alternative in the wear system investigated.•Deionised water is not a suitable analogue for borated water during wear testing.•Wear mechanisms include tribolayer formation and particle/material pull-out.•XPS can elucidate further information on tribolayer formation and wear mechanisms.

D Hallam, A Heaton, B James, PA Smith, JA Yeomans (2015)The correlation of indentation behaviour with ballistic performance for spark plasma sintered armour ceramics, In: Journal of the European Ceramics Societypp. 2243-2252 Elsevier

The Knoop and Vickers indentation behaviour of spark plasma sintered SiC–5 wt.% B4 C, B4 C and SiC–2.5 wt.% AlN–3 wt.% C armour ceramics have been investigated and observations correlated with ballistic performance. Surface and sub-surface indentation-induced damage has been characterised via cross-sectioning and serial ceramographic polishing techniques. The nature of the damage appears to be less influential than hardness in relation to ballistic performance, but variability in indentation behaviour appears to correlate with variability in ballistic performance. Examination of the indentation size effect curves shows that both Knoop hardness and predicted transition velocities correlate with V50 ballistic performance against an armour-piercing threat, further supporting the importance of hardness and the potential for indentation to be used as a screening method for armour materials.

KL Powell, JA Yeomans, PA Smith (1993)Localised damage in continuous fibre reinforced ceramic matrix composites, In: Ceramic Engineering and Science Proceedings14(9 -10)pp. 890-895

As a precursor to a study of erosive near behaviour of ceramic matrix composites fracture by indentation and single particle impact has been studied in two glass-ceramic/silicon carbide fibre composite systems. The damage has been characterised and quantified using a combination of confocal scanning laser microscopy and scanning electron microscopy. Lateral cracks which form approximately parallel to the surface, have been found to be the predominant damage event. In the calcium alumino-silicate (CAS)/Nicalon system, lateral cracks tend, to form in regions of the matrix which have a high local fibre volume fraction, whilst in the barium magnesium alumino silicate (BMAS)/Tyranno system they tend to avoid fibre-rich regions. These results are consistent with an analysis of residual thermal stresses in the two systems. In CAS/Nicalon the coefficient of thermal expansion of the matrix is greater than that of the fibre. This puts the matrix into axial tension at room temperature with the stress increasing with local fibre volume fraction. In BMAS/Tyranno the reverse in the case. Thus in both systems, the observed damage is a consequence of the residual stress as well as the stress due to the contact event.

C Kastritseas, PA Smith, JA Yeomans (2005)The onset of thermal shock damage in unidirectional-fibre-reinforced ceramic matrix composites, In: M Singh, RJ Kerans, E LaraCurzio, R Naslain (eds.), HIGH TEMPERATURE CERAMIC MATRIX COMPOSITES 5pp. 235-240