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  • Journal article
    Poloni E, Bouville F, Schmid AL, Pelissari PIBGB, Pandolfelli VC, Sousa MLC, Tervoort E, Christidis G, Shklover V, Leuthold J, Studart ARet al., 2022,

    Carbon ablators with porosity tailored for aerospace thermal protection during atmospheric re-entry

    , Carbon, Vol: 195, Pages: 80-91, ISSN: 0008-6223

    Porous carbon ablators offer cost-effective thermal protection for aerospace vehicles during re-entry into planetary atmospheres. However, the exploration of more distant planets requires the development of ablators that are able to withstand stronger thermal radiation conditions. Here, we report the development of bio-inspired porous carbon insulators with pore sizes that are deliberately tuned to enhance heat-shielding performance by increasing scattering of high-temperature thermal radiation. Pore size intervals that promote scattering are first estimated using an established model for the radiative contribution to the thermal conductivity of porous insulators. On the basis of this theoretical analysis, we identify a polymer additive that enables the formation of pores in the desired size range through the polymerization-induced phase separation of a mixture of phenolic resin and ethylene glycol. Optical and electron microscopy, porosimetry and mechanical tests are used to characterize the structure and properties of porous insulators prepared with different resin formulations. Insulators with pore sizes in the optimal scattering range reduce laser-induced damage of the porous structures by up to 42%, thus offering a promising and simple route for the fabrication of carbon ablators for enhanced thermal protection at high temperatures.

  • Journal article
    Magrini T, Senol A, Style R, Bouville F, Studart ARet al., 2022,

    Fracture of hierarchical multi-layered bioinspired composites

    , Journal of the Mechanics and Physics of Solids, Vol: 159, ISSN: 0022-5096

    Lightweight composites have revolutionized the sector of aircrafts and will continue to play a major role in future energy-efficient transportation systems. However, the design of composites featuring high strength and high fracture toughness remains challenging due to the usual trade-off between these properties in synthetic materials. Inspired by the strong and tough hierarchical architecture of mollusk shells, we create tough composites by combining soft polymer layers with alternating, nacre-like layers that are infiltrated with the same polymer. Here, we study the fracture behavior and the toughening mechanisms underlying the high crack growth resistance of these hierarchical composites. Polymer layers with different stiffness and yield strength were designed in order to evaluate the effect of plastic deformation and bridging of the polymer phase on the early and late stages of the fracture process. Controlled fracture experiments allowed us to visualize the interactions of a propagating crack with the hierarchical architecture and to quantify the resistance of the polymer layer against early-stage fracture. Our findings provide new insights into the interplay of multiscale toughening mechanisms in hierarchical bioinspired architectures and offer guidelines for the design and manufacturing of strong and tough lightweight composites.

  • Journal article
    Li M, Li W, Guan Q, Dai X, Lv J, Xia Z, Ong W-J, Saiz E, Hou Xet al., 2021,

    A Tough Reversible Biomimetic Transparent Adhesive Tape with Pressure-Sensitive and Wet-Cleaning Properties

    , ACS NANO, Vol: 15, Pages: 19194-19201, ISSN: 1936-0851
  • Journal article
    Collett H, Bouville F, Giuliani F, Schofield Eet al., 2021,

    Structural monitoring of a large archaeological wooden structure in real time, post PEG treatment

    , Forests, Vol: 12, Pages: 1-13, ISSN: 1999-4907

    Large archaeological wooden structures are potentially at risk of structural failure through deformation and cracking over time if they are left untreated and their structural health is not maintained. This could be in part due to, for example, the shrinkage of waterlogged wood as it dries, or time-dependent creep processes. These dimensional changes are accompanied by associated stresses. However, there are few studies analysing the movement of large wooden structures in real time as they dry, particularly after their conservation treatment. This paper follows the structural monitoring of the Mary Rose from after the conservation treatment, where it was sprayed with polyethylene glycol, through to the ship’s air-drying process and beyond to assess the effects that drying has had on the displacement of the timbers. A laser-based target system was used to collect displacement data between 2013 and 2020 and the data showed a significant slowing of displacement as the drying reached an equilibrium.

  • Journal article
    Li M, Li C, Blackman BRK, Saiz Eet al., 2021,

    Energy conversion based on bio-inspired superwetting interfaces

    , Matter, Vol: 4, Pages: 3400-3414, ISSN: 2590-2385
  • Journal article
    Li M, Li C, Blackman BRK, Eduardo Set al., 2021,

    Mimicking nature to control bio-material surface wetting and adhesion

    , International Materials Reviews, Pages: 1-24, ISSN: 0950-6608

    Nature has developed unique strategies to refine and optimise structural performance. Using surfaces designed at multiple length scales, from micro to nano levels, combined with complex chemistries, different natural organisms can exhibit similar wetting but different adhesion to liquids under specific environments. These biological surfaces have inspired researchers to develop new approaches to control surface wetting and liquid behaviour via surface adhesion. Here we review natural strategies to control the interaction of liquids with solid surfaces and the efforts to implement these strategies in synthetic materials designed to work in either atmospheric or underwater environment. Particular attention is paid to droplet behaviour on the special-adhesion surfaces in nature and artificial smart surfaces. We highlight recent progress, identify the common threads, and discuss the fundamental differences in a way that can help formulate rational approaches towards surface engineering, and identify current challenges as well as future directions for the field.

  • Journal article
    Gavalda-Diaz O, Manno R, Melro A, Allegri G, Hallett SR, Vandeperre L, Saiz E, Giuliani Fet al., 2021,

    Mode I and Mode II interfacial fracture energy of SiC/BN/SiC CMCs

    , Acta Materialia, Vol: 215, Pages: 1-11, ISSN: 1359-6454

    Quantifying the mixed mode fracture toughness of interfaces in ceramic matrix composites (CMCs) is crucial for understanding their failure. In this work we use in situ micromechanical testing in the scanning electron microscope to achieve stable interfacial crack propagation in Mode I (Double Cantilever Beam) and Mode II (Push out) and measure the corresponding fracture resistances. We use this approach to measure the interfacial fracture resistance in SiC/BN/SiC CMCs and compare it to the fracture energy of the fibres. During in-situ testing, fracture paths can be observed while data is acquired simultaneously. We clearly observe debonding at the BN-fibre interface (i.e. inside adhesive debonding). The critical energy release rate of the BN-fibre interface for Mode I and II (GIc ≈ 2.1 ± 1.0 J/m2 and GIIc ≈ 1.2 ± 0.5 J/m2) are equivalent and is lower than that measured for the fibre using microscopic DCB tests (GIc ≈ 6.0 ± 2.0 J/m2). These results explain the generalized fibre debonding and pull out observed in the fracture of these CMCs. By enabling direct observation of crack paths and quantifying the corresponding fracture energies, we highlight possible routes for the optimisation and modelling of the new generation of CMC interphases.

  • Journal article
    Cao C, Lin Z, Liu X, Jia Y, Saiz E, Wolf SE, Wagner HD, Jiang L, Cheng Qet al., 2021,

    Strong Reduced Graphene Oxide Coated Bombyx mori Silk

  • Journal article
    Li C, Li M, Ni Z, Guan Q, Blackman BRK, Saiz Eet al., 2021,

    Stimuli-responsive surfaces for switchable wettability and adhesion

  • Journal article
    De Meyere RMG, Song K, Gale L, Harris S, Edmonds IM, Marrow TJ, Saiz E, Giuliani F, Armstrong DEJ, Gavalda-Diaz Oet al., 2021,

    A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites

    , Journal of Materials Research, Vol: 36, Pages: 2305-2314, ISSN: 0884-2914

    Traditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations—solutions for which are addressed in this work by introducing the novel trench push-out test. The trench push-out makes use of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events. SiCf/BN/SiC composites—candidate material for turbine engines—were used as model materials in this work. Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of 14 ± 7 MPa and 20 ± 2 MPa, respectively, during fibre sliding. The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement.

  • Journal article
    Magrini T, Kiebala D, Grimm D, Nelson A, Schrettl S, Bouville F, Weder C, Studart ARet al., 2021,

    Tough Bioinspired Composites That Self-Report Damage

    , ACS APPLIED MATERIALS & INTERFACES, Vol: 13, Pages: 27481-27490, ISSN: 1944-8244
  • Journal article
    Gavalda-Diaz O, Lyons J, Wang S, Emmanuel M, Marquardt K, Saiz E, Giuliani Fet al., 2021,

    Basal plane delamination energy measurement in a Ti3SiC2 MAX phase

    , JOM, Vol: 73, Pages: 1582-1588, ISSN: 1047-4838

    The {0001} basal plane delamination dominating the crack-wake bridging in MAX phases at a bulk scale has been investigated by studying the small-scale fracture of a Ti3SiC2. In situ micro-double cantilever beam (DCB) tests in a scanning electron microscope were used to grow a stable crack along the basal plane, measure the fracture energy, and study the crack propagation mechanism at the nanoscale. The results show that the fracture energy (10–50 J/m2) depends on small misorientations angles (e.g., 5°) of the basal plane to the stress field. This induces permanent deformation which can be observed once the DCB has been unloaded. The nanoscale study of the crack shows that the plasticity at the crack tip is small, but a number of pairs of dislocations are forming at each side of the crack. Hence, this study helps to explain the enhanced fracture energy values and possible sources of energy dissipation in basal plane delamination, which is the one of the main toughening mechanisms in the bulk fracture of MAX phases.

  • Journal article
    Leung CLA, Elizarova I, Isaacs M, Marathe S, Saiz E, Lee PDet al., 2021,

    Enhanced near-infrared absorption for laser powder bed fusion using reduced graphene oxide

    , Applied Materials Today, Vol: 23, Pages: 1-10, ISSN: 2352-9407

    Laser powder bed fusion (LPBF) is a revolutionary manufacturing technology that fabricates parts with unparalleled complexity, layer-by-layer. However, there are limited choices of commercial powders for LPBF, constrained partly by the laser absorbance, an area that is not well investigated. Carbon additives are commonly used to promote near infra-red (NIR) absorbance of the powders but their efficiency is limited. Here, we combine operando synchrotron X-ray imaging with chemical characterisation techniques to elucidate the role of additives on NIR absorption, melt track and defect evolution mechanisms during LPBF. We employ a reduced graphene oxide (rGO) additive to enable LPBF of low NIR absorbance powder, SiO2, under systematic build conditions. This work successfully manufactured glass tracks with a high relative density (99.6%) and overhang features (> 5 mm long) without pre/post heat treatment. Compared to conventional carbon additives, the rGO increases the powder's NIR absorbance by ca. 3 times and decreases the warpage and porosity in LPBF glass tracks. Our approach will dramatically widen the palette of materials for laser processing and enable existing LPBF machines to process low absorbance powder, such as SiO2, using a NIR beam.

  • Journal article
    Azcune I, Huegun A, Ruiz de Luzuriaga A, Saiz E, Rekondo Aet al., 2021,

    The effect of matrix on shape properties of aromatic disulfide based epoxy vitrimers

    , European Polymer Journal, Vol: 148, Pages: 1-10, ISSN: 0014-3057

    Aromatic disulfide based vitrimers show elasticity driven shape-memory and plastic reprocessability via associative rearrangement of dynamic covalent crosslinks. Those processess represent the two sides of a coin: the storage and relaxation of the strain energy caused by a deformation load. The key temperatures that trigger the underlying mechanisms, i.e. phase transition and disulfide exchange reaction, are extremely sensitive to the molecular structure of the polymer and under certain condition overlap. To gain insight on the relationship between the structure, dynamic and shape-changing properties, five aromatic disulfide-based epoxy networks with a range of Tg values (32–142 °C), molecular structure and crosslink densities (2252–462 mol m−3) were synthesized. The epoxy matrices were formulated combining different ratios of rigid bisphenol A diglycidyl ether (DGEBA) and flexible poly(propylene glycol) diglycidic ether (DGEPPG) epoxy monomers crosslinked by 4-aminophenyldisulfide hardener.

  • Journal article
    Aldegaither N, Sernicola G, Mesgarnejad A, Karma A, Balint D, Wang J, Saiz E, Shefelbine SJ, Porter AE, Giuliani Fet al., 2021,

    Fracture toughness of bone at the microscale

    , Acta Biomaterialia, Vol: 121, Pages: 475-483, ISSN: 1742-7061

    Bone's hierarchical arrangement of collagen and mineral generates a confluence of toughening mechanisms acting at every length scale from the molecular to the macroscopic level. Molecular defects, disease, and age alter bone structure at different levels and diminish its fracture resistance. However, the inability to isolate and quantify the influence of specific features hampers our understanding and the development of new therapies. Here, we combine in situ micromechanical testing, transmission electron microscopy and phase-field modelling to quantify intrinsic deformation and toughening at the fibrillar level and unveil the critical role of fibril orientation on crack deflection. At this level dry bone is highly anisotropic, with fracture energies ranging between 5 and 30 J/m2 depending on the direction of crack propagation. These values are lower than previously calculated for dehydrated samples from large-scale tests. However, they still suggest a significant amount of energy dissipation. This approach provides a new tool to uncouple and quantify, from the bottom up, the roles played by the structural features and constituents of bone on fracture and how can they be affected by different pathologies. The methodology can be extended to support the rational development of new structural composites.

  • Journal article
    Poloni E, Bouville F, Dreimol CH, Niebel TP, Weber T, Biedermann AR, Hirt AM, Studart ARet al., 2021,

    Tough metal-ceramic composites with multifunctional nacre-like architecture

    , SCIENTIFIC REPORTS, Vol: 11, ISSN: 2045-2322
  • Journal article
    Cao C, Peng J, Liang X, Saiz E, Wolf SE, Wagner HD, Jiang L, Cheng Qet al., 2021,

    Strong, conductive aramid fiber functionalized by graphene

  • Conference paper
    Petrova NL, Cai Q, Petrov PK, Saiz E, Shanahan CM, Edmonds MEet al., 2020,

    Can novel bone substitutes withstand the enhanced resorbing activity of Charcot osteoclasts?

    , Publisher: WILEY, Pages: 48-48, ISSN: 0742-3071
  • Journal article
    Diaz OG, Marquardt K, Harris S, Gale L, Vandeperre L, Saiz E, Giuliani Fet al., 2020,

    Degradation mechanisms of SiC/BN/SiC after low temperature humidity exposure

    , Journal of the European Ceramic Society, Vol: 40, Pages: 3863-3874, ISSN: 0955-2219

    The environmental degradation of SiC/BN/SiC CMCs under low temperature water exposure is still an unexplored field. This work shows how the effect of low temperature humid environments can be detrimental for turbostratic BN interphases, leading to a drop in mechanical properties. Furthermore, initial low-temperature humid environments can induce a faster degradation during subsequent thermal exposure. In order to understand how low temperature water exposure affects the CMC and how these changes affect the material response to subsequent exposures, intermediate temperature (800 °C) exposures have been studied before and after the low temperature humidity tests. The main challenge of this work consists of understanding how different constituents of the CMC structure (e.g. fibres and interphases) are degrading and consequently affecting the overall bulk mechanical performance and failure modes of the material. For this, linking the change in morphology and chemistry of the interphases with the micromechanical properties each constituent has been crucial.

  • Journal article
    McGilvery C, Jiang J, Rounthwaite N, Williams R, Giuliani F, Britton Tet al., 2020,

    Characterisation of carbonaceous deposits on diesel injector nozzles

    , Fuel: the science and technology of fuel and energy, Vol: 274, Pages: 1-9, ISSN: 0016-2361

    Diesel injector nozzles are highly engineered components designed to optimise delivery of fuel into the combustion chamber of modern engines. These components contain narrow channels to enhance spray formation and penetration, hence mixing and combustion. Over time, these injectors can become clogged due to fouling by carbonaceous deposits which may affect the long-term performance of a diesel engine. In this paper we explore the chemical composition and structure of deposits formed within the nozzle at the nanometre scale using electron microscopy. We focus on comparing deposits generated using a chassis dynamometer-based test with Zn fouled fuel with a DW10B dirty up test. We have developed and applied a method to precisely section the deposits for ‘top view’ scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis of the morphology and relative accumulation of deposits formed during chassis dynamometer and engine based dirty-up tests. We extend this analysis to finer length scales through lift-out of ~70 nm thick electron transparent cross section foils, including both the metal substrate and deposit, using focussed ion beam (FIB) machining. These foils are analysed using scanning transmission electron microscopy (STEM) and STEM-EDS. These thin foils reveal thin-film growth and chemical stratification of Zn, C, O and other elements in the organic deposit layers developed during growth on the steel substrate during industry standard fouling tests.

  • Journal article
    Rocha VG, Saiz E, Tirichenko IS, García-Tuñón Eet al., 2020,

    Direct ink writing advances in multi-material structures for a sustainable future

    , Journal of Materials Chemistry A, Vol: 8, Pages: 15646-15657, ISSN: 2050-7488

    Novel manufacturing techniques such as additive manufacturing (AM, also referred to as 3D printing) will play a critical role in building a sustainable future. AM will reduce waste, energy consumption and production time by eliminating the need to assemble components. It will also enable the mass customization of complex devices. To reach their full potential, additive manufacturing technologies should be able to combine different materials in a single processing step. Although the development of multi-material printing is in its infancy, it could have a massive impact in fields as diverse as energy storage and generation, electronic devices, healthcare or structural composites to name a few. Here we provide a critical perspective on the advances and potential of multi-material printing using direct extrusion-based printing, also known as direct ink writing (DIW) or robocasting. We will show examples of devices and structures combining a wide range of materials from ceramics to metals, polymers and carbon with particular focus on three promising applications: energy storage, lightweight composites and sensors. The goals are to assess the progress made so far, to point out specific challenges and areas for further development and to provide guidelines to those interested in multi-material DIW.

  • Journal article
    Jones LD, Vandeperre LJ, Haynes TA, Wenman MRet al., 2020,

    Theory and application of Weibull distributions to 1D peridynamics for brittle solids

    , Computer Methods in Applied Mechanics and Engineering, Vol: 363, Pages: 1-11, ISSN: 0045-7825

    Peridynamics is a continuum mechanics modelling method, which is emerging as a solution for – in particular – the modelling of brittle fracture. The inherent variability of brittle fracture is captured well by the Weibull distribution, which describes the probability of fracture of a given material at a given stress. Recreating a Weibull distribution in peridynamics involves adjusting for the fact that the body is made up of a large number of bonds, and the distribution of strengths associated with these bonds must be different to the distribution of strengths associated with the peridynamic body. In the local case, where the horizon ratio, m=1 is used, Weibull’s original simple size scaling gives exact results, but the overlapping nature of non-local bonds that occurs in higher m cases, typically used in the peridynamics literature (such as m=3), causes a significant distortion of Weibull distributions. The cause of these distortions is spurious toughening and partial component failures as a result of the reduced localisation associated with larger horizon ratios. In order to remove these distortions, appropriate size scaling is used for the bonds, and a methodology that is capable of reflecting the heterogeneity of the material in the model, is proposed. The methodology described means Weibull parameters measured at specimen or component level can be reproduced for higher values of m.

  • Journal article
    Zhou T, Wu C, Wang Y, Tomsia AP, Li M, Saiz E, Fang S, Baughman RH, Jiang L, Cheng Qet al., 2020,

    Super-tough MXene-functionalized graphene sheets

    , Nature Communications, Vol: 11, ISSN: 2041-1723

    Flexible reduced graphene oxide (rGO) sheets are being considered for applications in portable electrical devices and flexible energy storage systems. However, the poor mechanical properties and electrical conductivities of rGO sheets are limiting factors for the development of such devices. Here we use MXene (M) nanosheets to functionalize graphene oxide platelets through Ti-O-C covalent bonding to obtain MrGO sheets. A MrGO sheet was crosslinked by a conjugated molecule (1-aminopyrene-disuccinimidyl suberate, AD). The incorporation of MXene nanosheets and AD molecules reduces the voids within the graphene sheet and improves the alignment of graphene platelets, resulting in much higher compactness and high toughness. In situ Raman spectroscopy and molecular dynamics simulations reveal the synergistic interfacial interaction mechanisms of Ti-O-C covalent bonding, sliding of MXene nanosheets, and π-π bridging. Furthermore, a supercapacitor based on our super-tough MXene-functionalized graphene sheets provides a combination of energy and power densities that are high for flexible supercapacitors.

  • Journal article
    Bhowmik A, Lee J, Adande S, Wang-Koh M, Jun T-S, Sernicola G, Ben Britton T, Rae CMF, Balint D, Giuliani Fet al., 2020,

    Investigating spatio-temporal deformation in single crystal Ni-based superalloys using in-situ diffraction experiments and modelling

    , Materialia, Vol: 9, Pages: 1-14, ISSN: 2589-1529

    In this study, we perform a detailed analysis of room temperature deformation of a [100]–orientated singlecrystal Ni-based superalloy, CMSX-4 micropillar, using a combinatorial and complimentary characterisation approach of micro-Laue diffraction coupled with post-deformation microscopy and crystal plasticity modelling.Time-resolved micro-Laue data indicated that deformation was initiated by activation of multiple slip (after 5%engineering strain) which led to the generation of a plastic strain accumulation accompanied by a two-foldincrease in the dislocation density within the micropillar. Subsequent to that, slip occurred primarily on two systems (11̄1)[101] and (111)[1̄01] with the highest Schmid factor in the single crystal micropillar thereby resultingin little accumulation of unpaired GNDs during a major part of the loading cycle, upto 20% strain in this case.Finite element crystal plasticity modelling also showed good agreement with the experimental analyses, wherebysignificant strains were found to develop in the above slip systems with a localisation near the centre of themicropillar. Post-deformation transmission electron microscopy study confirmed that deformation was mediatedthrough a/2<110> dislocations on {111} planes in the 𝛾-phase, while high stress levels led to shearing of the 𝛾′precipitates by a/2<110> partials bounding an anti-phase boundary free to glide on the {111} planes. Duringthe deformation of the single crystal micropillar, independent rotations of the 𝛾 and 𝛾′ phases were quantified byspatially resolved post-deformation micro-Laue patterns. The degree of lattice rotation in the 𝛾-phase was higherthan that in the 𝛾′-phase.

  • Journal article
    Haug M, Bouville F, Ruiz-Agudo C, Avaro J, Gebauer D, Studart ARet al., 2020,

    Cold densification and sintering of nanovaterite by pressing with water

    , JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 40, Pages: 893-900, ISSN: 0955-2219
  • Journal article
    Elizarova I, Vandeperre L, Saiz Gutierrez E, 2020,

    Conformable green bodies: plastic forming of robocasted advanced ceramics

    , Journal of the European Ceramic Society, Vol: 40, Pages: 552-557, ISSN: 0955-2219

    Robocasting, or the additive manufacturing of ceramics by continuous extrusion of a ceramic paste, has limited capabilities when printing complex unsupported structures such as overhangs or free standing thin artefacts. In this paper we address this limitation using a new type of paste, which allows for shaping of the green bodies after printing. To illustrate the flexibility of the paste, it was used to produce both alumina and silicon carbide parts. The paste consists of a solution of phenolic resin in methyl ethyl ketone and ceramic powders. Fabricated parts can be cut, bent, folded and draped over various objects. Once dry and fully solid, the parts become rigid and can be processed further by slow pyrolysis and sintering. Sintered samples exhibit flexural strength comparable to both conventionally produced and robocasted ceramics and shaping of the green bodies after printing does not affect the mechanical strength of the sintered parts.

  • Journal article
    Peng J, Huang C, Cao C, Saiz E, Du Y, Dou S, Tomsia AP, Wagner HD, Jiang L, Cheng Qet al., 2020,

    Inverse Nacre-like Epoxy-Graphene Layered Nanocomposites with Integration of High Toughness and Self-Monitoring

    , MATTER, Vol: 2, Pages: 220-232, ISSN: 2590-2393
  • Journal article
    Pelissari PIBGB, Pandolfelli VC, Carnelli D, Bouville Fet al., 2020,

    Refractory interphase and its role on the mechanical properties of boron containing nacre-like ceramic

    , JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 40, Pages: 165-172, ISSN: 0955-2219
  • Journal article
    Wang S, Kalácska S, Maeder X, Michler J, Giuliani F, Britton Tet al., 2019,

    The effect of δ-hydride on the micromechanical deformation of Zircaloy-4 studied by in situ high angular resolution electron backscatter diffraction

    , Scripta Materialia, Vol: 173, Pages: 101-105, ISSN: 1359-6462

    Zircaloy-4(Zr-1.5%Sn-0.2%Fe-0.1%Cr wt%)is usedas nuclear fuel cladding materials and hydride embrittlementis amajor failure mechanism. To explore the effect of δ-hydrideon plastic deformation and performance of Zircaloy-4, in situhigh angular resolution electron backscatter diffraction(HR-EBSD)was used to quantify stress andgeometrically necessarydislocation(GND)density during bending tests of hydride-free and hydride-containingsingle crystalZircaloy-4 microcantilevers. Results suggest that while the stress applied was accommodated by plastic slip in the hydride-free cantilever,the hydride-containing cantilever showedprecipitation-induced GND pile-up at hydride-matrix interfacepre-deformation, andconsiderable locally-increasing GNDdensity under tensile stressupon plastic deformation.

  • Journal article
    Giuliani F, Ciurea C, Bhakhri V, Werchota M, Vandeperre LJ, Mayrhofer PHet al., 2019,

    Deformation behaviour of TiN and Ti–Al–N coatings at 295 to 573 K

    , Thin Solid Films, Vol: 688, ISSN: 0040-6090

    Temperature-dependent nanoindentation testing was employed to investigate the deformation behaviour of magnetron sputtered (100) TiN and Ti1-xAlxN (x = 0.34, 0.52, 0.62) coatings in the temperature range from 295 to 573 K. The maximum temperature is sufficiently below the deposition temperature of 773 K to guarantee for stable microstructure and stress state during testing. The TiN coating displayed the same hardness as bulk single crystal (SC) TiNbulk. The addition of aluminium to TiN (to form single-phase face centred cubic structured Ti1-xAlxN coatings) increased the room temperature hardness due to increased bond strength, lattice strain and higher activation energy for the dislocation slip. For coatings with a low aluminium content, Ti0.66Al0.34N, the decrease in hardness with temperature was similar to the TiN coating and SC-TiNbulk. In contrast, the hardness of coatings with moderate, Ti0.48Al0.52N, and high, Ti0.38Al0.62N, aluminium contents varied little up to 573 K. Thus, the Ti1-xAlxN matrix is mechanically more stable at elevated temperatures than its TiN relative, by providing a lower decrease in lattice resistance to the dislocation flow with increasing temperature. The findings suggest that the addition of Al to TiN (to form Ti1-xAlxN solid solutions) not only improves the hardness but also leads to stable hardness with temperature, and emphasizes the importance of bonding states and chemical fluctuations, next to structure and morphology of the coatings that develop with changing the chemistry.

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