arXiv subjects

Finn Giuliani

Publications and source records attributed to Finn Giuliani.

At least 19 recordsLinked to original sources

arXiv2026

Fracture energy of 6H-SiC at the microscale: effects of testing geometry and notch preparation

Micromechanical testing enables small-scale fracture energy measurements, but values depend strongly on geometry and specimen preparation. Here, the fracture energy of the single-crystal 6H-SiC {10-10} plane was measured using microscale double cantilever beam (DCB) and single cantilever beam (SCB) geometries. DCBs showed stable crack growth under displacement control and obtained 7.5 +- 0.3 J/m2. In contrast, SCBs notched by a Ga focused ion beam gave fracture energies over twice this value, indicating Ga implantation and near-notch residual stresses. Increasing the final notching current increased the measured fracture energy further. Although near-cryogenic notching limited ion-beam-induced damage, it did not reconcile SCB-derived values with DCB test results. Vacuum annealing substantially lowered the fracture energy and brought SCB results into close agreement with DCB measurements, whereas annealing in argon was less effective. Our findings highlight the importance of careful sample preparation and testing geometry selection for reliable fracture property measurement in ceramic materials.

cond-mat.mtrl-sci↗

arXiv2026

Revealing the Atomic-Scale Structure of the Copper Sulfuric Acid Interface

Corrosion originates from atomistic reactions occurring at dynamic solid liquid interfaces however, direct experimental observation of these reactions has remained elusive due to the inability to preserve transient interfacial states during characterization. To refine corrosion models, advanced techniques capable of analyzing corrosion interfaces at the atomic scale are essential. Recent advancements in cryogenic atom probe tomography (cryoAPT) enabled 3D nanoscale analysis of frozen liquid metal interfaces. However, challenges remain in sample preparation for cryoAPT on metals undergoing corrosion. This study introduces a microcorrosion cell fabricated using localized electrodeposition in liquid (LEL), enabling atomic scale capture of liquid metal reactions by integrating picoliterscale electrolytes encapsulated within sealed metallic microvessels, subsequently analyzed using cryoAPT.This approach enables 3D, nanoscale mapping of corrosion reactions with simultaneous spatial, chemical, and temporal resolution. As a model system, copper exposed to aerated dilute sulphuric acid reveals temperature and time dependent interfacial evolution, including nanoscale clustering of copper sulphate species, enhanced ion pairing at elevated temperature, and the emergence of transient carbon based interfacial complexes inaccessible to conventional characterization methods.Beyond copper corrosion, the presented microcorrosion cell architecture establishes a strategy for interrogating confined electrochemical and degradation processes across a wide range of material liquid systems, using a combination of microfabrication and cryoAPT.

cond-mat.mtrl-sci↗

arXiv2026

Atomic-scale Imaging of Iodide-Gold Interactions in Nanoconfined Liquid-Solid Interfaces

Functionalization of nanoporous metallic materials enables the tailoring of surface chemistry and morphology in nanostructured materials, optimising their performance for electrocatalytic and sensor applications. Liquid phase chemical functionalization is governed by liquid solid interfaces. Yet, these interfaces remain poorly understood due to the challenges of characterising the liquid phase at high spatial and chemical resolutions. To elucidate pathways for functionalizing nanoscale metals, it is crucial to measure the distribution of species, including light elements, across the liquid solid interface, capturing both reactants and products. Here, we employ cryogenic atom probe tomography to directly analyse frozen liquid solid reaction interfaces at near atomic resolution. Focusing on the interaction of iodide and sodium ions with nanoporous gold, we observe the formation of iodine containing complexes on gold nanoligament surfaces and subsurfaces. These findings reveal aspects of the gold iodide system that were previously hidden, including the reaction mechanism between iodide and gold atoms on the surface, and the multiple gold iodide complexes forming. Our work demonstrates that cryogenic atom probe tomography can provide unprecedented visualisation and characterisation of nanoscale interfaces during chemical and electrochemical reactions, with potential implications for modern manufacturing, energy technologies, and sustainable materials development.

cond-mat.mtrl-sci↗

arXiv2024

Observing the crack tip behaviour at the nanoscale during fracture of ceramics

Ultimately, brittle fracture involves breaking atomic bonds. However, we still lack a clear picture of what happens in the highly deformed region around a moving crack tip. Consequently, we still cannot link nano to atomic-scale phenomena with the macroscopic toughness of materials. The unsolved challenge is to observe the movement of the crack front at the nanoscale while extracting quantitative information. Here we address this challenge by monitoring stable crack growth inside a TEM. Our analysis demonstrates how phase transformation toughening, previously thought to be effective at the microscale and above, promotes crack deflection at the nano-level and increases the fracture resistance by ~50%. The work will help to connect the atomistic and continuous view of fracture in a way that can guide the design of the next generation of strong and tough materials demanded by technologies as diverse as healthcare, energy generation or transport.

cond-mat.mtrl-sci↗

arXiv2023

Accessing slip activity in high purity tin with electron backscatter diffraction and measurement of slip strength

Beta-tin has been used widely as an interconnect in modern electronics. To improve the understanding of the reliability of these components, we directly measure the critical resolved shear stress of individual slip systems in beta-tin using micropillar compression tests at room temperature with crystal orientations near-[100] and [001] in the loading direction within a large grain high purity tin (99.99%) sample. This activates the (110)[1-11]/2, (110)[1-1-1]/2, (010)[001] and (110)[001] slip systems. Analysis of the slip traces and load-displacement curves enables measurement of the critical resolved shear stress for epsilon=10^(-4) of tau_(CRSS)^({110}<1-11>/2)=10.4+/-0.4 and tau_(CRSS)^({010}<001>)=3.9+/-0.3 MPa.

cond-mat.mtrl-sci↗

arXiv2023

Shear and delamination behaviour of basal planes in Zr3AlC2 MAX phase studied by micromechanical testing

The mechanical properties of layered, hexagonal-structured MAX phases often show the combined merits of metals and ceramics, making them promising material candidates for safety critical applications. While their unique mechanical performance largely arises from the crystal structure, the effect of chemistry on the properties of these materials remains unclear. To study this, here we employed two in situ electron microscope small scale testing approaches to examine the micromechanical properties of Zr3AlC2, and compared the results with the properties of Ti3SiC2: we used micropillar compression tests to measure basal slip strength, and double cantilever beam splitting tests to evaluate fracture energy for basal plane delamination. We observed distinct and systematic differences in these measured properties between Zr3AlC2 and Ti3SiC2, where Zr3AlC2 appeared to be stronger but more brittle at the microscale, and discussed the implications of the results in the selection, design, and engineering of MAX phases for targeted engineering applications.

cond-mat.mtrl-sci↗

arXiv2023

Determining the Fundamental Failure Modes in Ni-rich Lithium Ion Battery Cathodes

Challenges associated with in-service mechanical degradation of Li-ion battery cathodes has prompted a transition from polycrystalline to single crystal cathode materials. Whilst for single crystal materials, dislocation-assisted crack formation is assumed to be the dominating failure mechanism throughout battery life, there is little direct information about their mechanical behaviour, and mechanistic understanding remains elusive. Here, we demonstrated, using in situ micromechanical testing, direct measurement of local mechanical properties within LiNi0.8Mn0.1Co0.1O2 single crystalline domains. We elucidated the dislocation slip systems, their critical stresses, and how slip facilitate cracking. We then compared single crystal and polycrystal deformation behaviour. Our findings answer two fundamental questions critical to understanding cathode degradation: What dislocation slip systems operate in Ni-rich cathode materials? And how does slip cause fracture? This knowledge unlocks our ability to develop tools for lifetime prediction and failure risk assessment, as well as in designing novel cathode materials with increased toughness in-service.

cond-mat.mtrl-sci↗

arXiv2023

Characterisation of the strain rate sensitivity of basal, prismatic and pyramidal slip in Zircaloy-4 using micropillar compression

The slip strength of individual slip systems at different strain rates will control the mechanical response and strongly influence the anisotropy of plastic deformation. In this work, the slip activity and strain rate sensitivity of the basal, prismatic, and pyramidal slip systems are explored by testing at variable strain rates (from 10E-4 s^-1 to 125 s^-1) using single crystal micropillar compression tests. These systematic experiments enable the direct fitting of the strain rate sensitivities of the different slips using a simple analytical model and this model reveals that deformation in polycrystals will be accommodated using different slip systems depending on the strain rate of deformation in addition to the stress state (i.e. Schmid's law). It was found that the engineering yield stress increases with strain rate, and this varied by slip systems. Activation of the prismatic slip system results in a high density of parallel, clearly discrete slip planes, while the activation of the pyramidal slip leads to the plastic collapse of the pillar, leading to a 'mushroom' morphology of the deformed pillar. This characterization and model provide insight that helps inform metal forming and understanding of the mechanical performance of these engineering alloys in the extremes of service conditions.

cond-mat.mtrl-sci↗

arXiv2023

Fracture properties of La(Fe,Mn,Si)13 magnetocaloric materials

La(Fe,Mn,Si)13 alloys are a promising material family for magnetic refrigeration. Challenges associated with their structural integrity during device assembly and operation requires deep understanding of the mechanical properties. Here we developed a workflow to quantitatively study the fracture properties of La(Fe,Mn,Si)13 plates used in magnetic cooling devices. We employed microstructural characterisation, optical examination of defects, and four-point bending tests of samples with known defect sizes to evaluate their mechanical performance. We established the residual strength curve which directly links observed defects to mechanical strength. The estimated fracture toughness KC of hydrogenated La(Fe,Mn,Si)13 is approximately 4 MPa m^1/2 for the geometry employed. The established relationship between strength and crack length enables the prediction of mechanical performance through examination of defects via optical microscopy, therefore can be used industrially for directing plate selection to guarantee the mechanical stability of refrigeration devices.

cond-mat.mtrl-sci↗

arXiv2022

In-situ sputtering from the micromanipulator to enable cryogenic preparation of specimens for atom probe tomography by focused-ion beam

Workflows have been developed in the past decade to enable atom probe tomography analysis at cryogenic temperatures. The inability to control the local deposition of the metallic precursor from the gas-injection system (GIS) at cryogenic temperature makes the preparation of site-specific specimens by using lift-out extremely challenging in the focused-ion beam. Schreiber et al. exploited redeposition to weld the lifted-out sample to a support. Here we build on their approach to attach the region-of-interest and additionally strengthen the interface with locally sputtered metal from the micromanipulator. Following standard focused-ion beam annular milling, we demonstrate atom probe analysis of Si in both laser pulsing and voltage mode, with comparable analytical performance as a pre-sharpened microtip coupon. Our welding approach is versatile, as various metals could be used for sputtering, and allows similar flexibility as the GIS in principle.

cond-mat.mtrl-sci↗

arXiv2022

Multi-scale plasticity homogenization of Sn-3Ag-0.5Cu: from β-Sn micropillars to polycrystals with intermetallics

The mechanical properties of $β$-Sn single crystals have been systematically investigated using a combined methodology of micropillar tests and rate-dependent crystal plasticity modelling. The slip strength and rate sensitivity of several key slip systems within $β$-Sn single crystals have been determined. Consistency between the numerically predicted and experimentally observed slip traces has been shown for pillars oriented to activate single and double slip. Subsequently, the temperature-dependent, intermetallic-size-governing behaviour of a polycrystal $β$-Sn-rich alloy SAC305 (96.5Sn-3Ag-0.5Cu wt%) is predicted through a multi-scale homogenization approach, and the predicted temperature- and rate-sensitivity reproduce independent experimental results. The integrated experimental and numerical approaches provide mechanistic understanding and fundamental material properties of microstructure-sensitive behaviour of electronic solders subject to thermomechanical loading, including thermal fatigue.

cond-mat.mtrl-sci↗

arXiv2022

Understanding the degradation of a model Si-anode in Li-ion battery at the atomic-scale

Si-anodes have long been candidates thanks to an expected ten-fold increase in capacity compared to graphite. However, details of the mechanisms governing their degradation remain elusive, hindering science-guided development of long-lived Si-based anodes. Here we demonstrate how the latest developments in cryo-atom probe tomography enable the in-depth analysis of the electrode and electrolyte, and their interface at atomic-level.

cond-mat.mtrl-sci↗

arXiv2022

The effect of hydrogen on the multiscale mechanical behaviour of a La(Fe,Mn,Si)13-based magnetocaloric material

Magnetocaloric cooling offers the potential to improve the efficiency of refrigeration devices and hence cut the significant CO2 emissions associated with cooling processes. A critical issue in deployment of this technology is the mechanical degradation of the magnetocaloric material during processing and operation, leading to limited service-life. The mechanical properties of hydrogenated La(Fe,Mn,Si)13-based magnetocaloric material are studied using macroscale bending tests of polycrystalline specimens and in situ micropillar compression tests of single crystal specimens. The impact of hydrogenation on the mechanical properties are quantified. Understanding of the deformation/failure mechanisms is aided by characterization with transmission electron microscopy and atom probe tomography to reveal the arrangement of hydrogen atoms in the crystal lattice. Results indicate that the intrinsic strength of this material is ~3-6 GPa and is dependent on the crystal orientation. Single crystals under compressive load exhibit shearing along specific crystallographic planes. Hydrogen deteriorates the strength of La(Fe,Mn,Si)13 through promotion of transgranular fracture. The weakening effect of hydrogen on single crystals is anisotropic; it is significant upon shearing parallel to the {111} crystallographic planes but is negligible when the shear plane is {001}-oriented. APT analysis suggests that this is associated with the close arrangement of hydrogen atoms on {222} planes.

cond-mat.mtrl-sci↗

arXiv2021

Environment-assisted crack nucleation in La(Fe,Mn,Si)13-based magnetocaloric materials

Cracking in La(Fe,Si)13-based magnetocaloric materials has been observed to predominantly form around La-rich (La2O3) particles and pose a threat to their long-term structural integrity. To understand the formation of these cracks, FIB cross-sectional polishing followed by SEM characterisation was employed to study local microstructural evolution after air exposure. Results suggest that volume expansion and internal degradation associated with a chemical reaction between La2O3 particles and water/moisture can lead to crack nucleation in the 1:13 phase adjacent to La-rich particles. This observation indicates that the formation of La-rich phase should be suppressed, or their size minimised during material processing to ensure the long-term structural integrity of La(Fe,Mn,Si)13 magnetocaloric materials.

cond-mat.mtrl-sci↗

arXiv2020

Slip-hydride interactions in Zircaloy-4: Multiscale mechanical testing and characterisation

The interactions between δ-hydrides and plastic slip in a commercial zirconium alloy, Zircaloy-4, under stress were studied using in situ secondary electron microscope (SEM) micropillar compression tests of single crystal samples and ex situ digital image correlation (DIC) macroscale tensile tests of polycrystalline samples. The hydrides decorate near basal planes in orientation, and for micropillars orientated for basal slip localised shear at the hydride-matrix interface is favoured over slip in α-Zr matrix due to a lower shear stress required. In contrast, for pillars oriented for prismatic slip the shear stress needed to trigger plastic slip within the hydride is slightly higher than the critical resolved shear stress (CRSS) for the prismatic slip system. In this case, slip in the hydride is likely achieved through <110>-type shear which is parallel to the activated -type shear in the parent matrix. At a longer lengthscale, these results are used to inform polycrystalline samples analysed using high spatial resolution DIC. Here localised interface shear remains to be a significant deformation path which can both cause and be caused by matrix slip on planes closely-oriented to the phase boundaries. Matrix slip on planes nearly perpendicular to the adjacent hydride-matrix interfaces can either result in plastic slip within the hydrides or get arrested at the interfaces, generating local stress concentration. Through these mechanisms, the presence of δ-hydrides leads to enhanced strain localisation in Zircaloy-4 early in the plastic regime.

cond-mat.mtrl-sci↗

arXiv2019

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

Zircaloy-4 is used extensively as nuclear fuel cladding materials and hydride embrittlement is a major failure mechanism. To explore the effect of δ-hydride on plastic deformation and performance of Zircaloy-4, in situ high angular resolution electron backscatter diffraction (HR-EBSD) was used to quantify stress and geometrically necessary dislocation (GND) density during bending tests of hydride-free and hydride-containing single crystal Zircaloy-4 microcantilevers. Results suggest that while the stress applied was accommodated by plastic slip in the hydride-free cantilever, the hydride-containing cantilever showed precipitation induced GND pile-up at hydride-matrix interface pre-deformation, and considerable locally increasing GND density under tensile stress upon plastic deformation.

cond-mat.mtrl-sci↗

arXiv2019

The role of β-titanium ligaments in the deformation of dual phase titanium alloys

Multiphase titanium alloys are critical materials in high value engineering components, for instance in aero engines. Microstructural complexity is exploited through interface engineering during mechanical processing to realise significant improvements in fatigue and fracture resistance and strength. In this work, we explore the role of select interfaces using in-situ micromechanical testing with concurrent observations from high angular resolution electron backscatter diffraction (HR-EBSD). Our results are supported with post mortem transmission electron microscopy (TEM). Using micro-pillar compression, we performed in-depth analysis of the role of select β-titanium (body centred cubic) ligaments which separate neighbouring α-titanium (hexagonal close packed) regions and inhibit the dislocation motion and impact strength during mechanical deformation. These results shed light on the strengthening mechanisms and those that can lead to strain localisation during fatigue and failure.

cond-mat.mtrl-sci↗

arXiv2018

Microstructure and formation mechanisms of δ-hydrides in variable grain size Zircaloy-4 studied by electron backscatter diffraction

Microstructure and crystallography of δ phase hydrides in as-received fine grain and 'blocky' alpha large grain Zircaloy-4 (average grain size ~11 μm and >200 μm, respectively) were examined using electron backscatter diffraction. Results suggest that the the matrix-hydride orientation relationship is {0001}α||{111}δ;<11-20>α||<110>δ for all the cases studied. The habit plane of intragranular hydrides and some intergranular hydrides has been found to be {10-17} of the surrounding matrix. The morphology of intergranular hydrides can vary depending upon the angle between the grain boundary and the hydride habit plane. The misfit strain between α-Zr and δ-hydride is accommodated by high density of dislocations and twin structures in the hydrides, and a mechanism of twin formation in the hydrides has been proposed. The growth of hydrides across grain boundaries is achieved through an auto-catalytic manner similar to the growth pattern of intragranular hydrides. Easy collective shear along <1-100> makes it possible for hydride nucleation at any grain boundaries, while the process seems to favour grain boundaries with low (<40°) and high (>80°) c-axis misorientation angles. Moreover, the angle between the grain boundary and the adjacent basal planes does not influence the propensity for hydride nucleation.

cond-mat.mtrl-sci↗