The hydration process and the associated microstructural evolution of cement paste are complicated and need accurate numerical models to elucidate their complex mechanisms. Most existing models rely on idealised initial microstructures and thus have not been directly and faithfully validated by experiments. Here, time-lapse X-ray computed micro-tomography (mu XCT) was first used to follow the hydration process from 1 to 28 days in two Portland cement paste specimens with water-to-cement ratios of 0.4 and 0.6, respectively. The evolution of microstructure, porosity and hydration degree was tracked at 2.7 mu m voxel resolution and statistically analyzed for each specimen by processing 7 successive 3D mu XCT scans. For each specimen, the day 1 mu XCT image was then segmented and used as the initial image-based microstructure for our recently developed continuous hydration model to simulate the hydration process. The simulated evolution of microstructure, porosity and hydration degree was found in good agreement with the time-lapse mu XCT data. This study represents the first-time direct experimental validation of a hydration model for cement paste, and demonstrates the powerful synergy between mu XCT tests and image-based modelling in elucidating the full hydration process.

Despite its importance when considering jet engine environments, the behavior of ceramic matrix composites following high temperature exposure in steam has received much less attention than in air. The present study investigates the oxidation behavior and the corresponding mechanical properties of a SiC/BN/SiBCN composite after exposure to steam at 950 degrees C, 1050 degrees C, 1200 degrees C and 1350 degrees C for 30 h. The SiBCN matrix shows crack-filling behavior, whereby microcracks are filled with oxide hindering internal oxidation of the composite. The oxide layers formed on both the SiC fiber and the SiBCN matrix exhibit a double layer structure, with the outer layer being more porous. With increasing temperature, the BN interphase is consumed and replaced by borosilicate glass that bonds the fiber and matrix. This alters the debonding location from the fiber/BN interface to the BN/ SiBCN matrix interface. Three-point bending test shows the composite retains good flexural strength and a tough failure response even after exposure to steam at 1350 degrees C. Single fibre push-out test shows a slight increase in interfacial shear strength with increasing thermal exposure.

The microstructural changes in SiCf/BN/SiBCN composite arising from oxidation in air at high temperatures from 1050 to 1350 degrees C are investigated. In particular, the microstructure and elemental composition of the oxide layer on both the SiC fibre and SiBCN matrix are studied and compared. BN recession occurs which can leave hallow matrix/fibre channels at 1050 C. At higher temperatures and for thin BN interphases, a dense oxide can seal this interface. Dense oxide layers are formed on the surface of both SiC fibre and SiBCN matrix, the latter being thicker. When oxidised at 1350 degrees C, the oxide layer on the SiC fibre is composed of an external crystallised layer with developed cristobalite and inner layer with deformed grains. The oxide layer on the surface of the SiBCN matrix exhibits a porous structure, comprising a porous external crystallised layer and an inner amorphous oxide layer. The SiBCN matrix is oxidised in preference to the SiC fibres, suggesting that the fibres can be protected somewhat by oxidation of the SiBCN matrix.

Lithium phosphides are an emerging class of Li+ ion conductors for solid state battery applications. Despite potentially favorable characteristics as a solid electrolyte, stoichiometric crystalline Li3AlP2 has been reported to be an ionic insulator. Using a combined computational and experimental approach, we investigate the underlying reasons for this and show that ion transport can be induced via defects and structural disorder in this material. Lithium vacancies are shown to promote diffusion, and a low barrier to Li+ hopping of 0.2-0.3 eV is revealed by both simulations and experiment. However, polycrystalline pellets exhibit low ionic conductivity (≈10−8 S cm−1) at room temperature, attributed to crystalline anisotropy and the presence of resistive grain boundaries. These aspects can be overcome in nanocrystalline Li3AlP2, where ionic conductivity values approaching 10−6 S cm−1 and low electronic conductivities are achieved. This approach, leveraging both defects and structural disorder, should have relevance to the discovery of new, or previously overlooked, ion conducting materials.

Fish-scale-like melt pool structures and internal defects are characteristic features in additively manufactured (AM) metals. These play a critical role in the damage and fracture processes under different service loading conditions. However, the relationship between these damage features and loading conditions, as well as the spatial interactions between melt pool structures and internal defects remains poorly understood. Using in situ time-lapse synchrotron X-ray tomography and diffraction, we identify the initiation and growth events of lifelimiting damage under tensile, low cycle fatigue (LCF), and high cycle fatigue (HCF) loading. A novel transition from meso-structure insensitive, defect-dominated short fatigue crack propagation to a meso-structure sensitive mechanism occurs as the plastic zone expands ahead of a growing crack from HCF to LCF to tensile loading. Under tension and LCF, the damage accumulation gradually increases and micro-voids nucleate at the melt pool boundaries (MPBs) after which the crack path follows the MPBs. In contrast, under HCF, surface defects initiate fatigue cracking and the MPBs have a very limited effect on the crack propagation path. Finally, a physics-informed machine learning method is introduced to develop a novel methodology for predicting fatigue life by including three-dimensional features of defects in AM parts.

Silicon carbide fiber (SiCf) reinforced/silicon carbide (SiC) matrix composites (SiCf/SiC) produced by polymer impregnation and pyrolysis (PIP) typically exhibit low density and crystallinity due to the formation of a SiCxOy amorphous matrix. This compromises the mechanical and thermal properties of the composites. Here, a particle enhanced PIP (PE-PIP) method is proposed whereby fine silicon carbide particles (SiCp) containing amorphous silica (SiO2) layer are incorporated into the liquid poly (carbosilane) (PCS)-based precursor. The addition of SiCp improved the bulk density and decreased the open porosity of the composites compared to conventional PIP processing. After heat treatment at 1400 degrees C for 8 h, the true density of the composites was enhanced further with a reduced carbon content via the carbothermal reactions between SiO2 and the excess carbon present in the PIP matrix. However, the bulk density reduced due to increased open porosity which could be sealed by subsequent processing. This novel processing approach has the potential to deliver high density, high crystallinity SiCf/SiC with low carbon content by PIP at low temperature (1400 degrees C).

The toughness of SiC fiber reinforced ceramic matrix composites (CMCs) can be significantly improved by the adoption of a pyrolytic carbon (PyC) interphase but this cannot be exposed to oxidizing environments at high temperatures. Here we considered a BN interphase as an alternative and investigated the flexural properties of SiCf/BN/SiBCN CMCs before and after high temperature exposure (1050 degrees C, 1200 degrees C and 1350 degrees C) in air. The flexural and interfacial shear strengths were determined by three-point bending and single fiber push-out tests, respectively. The flexural strength of the composites decreased from 325 f 23 MPa to 165 f 15 MPa, while the interfacial shear strength increased from 32 f 9 MPa to 88 f 18 MPa after oxidation at 1350 C for 30 h. Digital image correlation (DIC) was used to visualize crack initiation and growth during the bending tests. This revealed that cracks formed on the tensile side of the specimens before being deflected and eventually passed through the fiber tow. The oxidation of the SiCf/BN/SiBCN composite at high-temperature resulted in the formation of borosilicate glass along the interphase area, and a porous structure was observed after oxidation at high temperatures due to its evaporation. The interfacial shear strength between the fiber and matrix increased after oxidation at high temperatures, which resulted in brittle failure of the composite.

The present study investigates the microstructure evolution and subsequent mechanical properties of SiCfiber/ BN/SiBCNmatrix composites after high temperature exposure. These composites display a tough failure response under three-point bending retaining 80 % of the as-processed strength, even after elevated temperature exposure up to 1350 degrees C for 10 h. This is due to crack deflection accompanied by extensive fiber pull-out. In addition, both thermodynamic modelling and phase analysis by XRD show higher matrix degradation in vacuum than in N2 atmosphere due to the lower N2 partial pressure. After thermally exposure at 1500 degrees C, carbothermal reaction in the matrix leads to the formation of a porous composite, and the composites retains a tough failure response. Meanwhile, SiBCN matrix degradation and SiC fiber strength degradation occurs, which results in a significant decrement in composite strength. Modest increases in the fiber/matrix interfacial shear strength occur upon exposure at temperatures up to 1350 degrees C, and then significantly reduce upon exposure to 1500 degrees C in N2.

The migration and deposition of fine particles in porous materials is critical in industries such as energy, pharmaceuticals, and environmental engineering. Using 3D time-lapse synchrotron X-ray imaging, we observe fine particles invading porous media, analyzing the effects of pore size and heterogeneity at both pore and macro scales. Glass beads model homogeneous and heterogeneous conditions, revealing a sequence of deposition processes: surface attachment, throat bridging, blocking, pore filling, compaction, and migration. A critical throat-to-particle size ratio of 1.7 governs deposition behavior. At the macro-scale, heterogeneities like beddings and flow pathways influence fines migration and deposition. Based on dynamic 3D imaging, we propose a mechanism for fines behavior in heterogeneous porous media. These findings enhance understanding of fines migration, offering a predictive framework for managing formation damage and optimizing filter cake design in drilling and clean energy applications.

Liquefied natural gas storage and transportation as well as space propulsion systems have sparked interest in the martensitic transformation and behaviours of 316 L stainless steels (SS) under ultra-cryogenic deformation. In this study, high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations were used to investigate the atomic arrangements and crystalline defects of deformation-induced gamma-austenite -> epsilon-martensite -> alpha ' -martensite and gamma -> alpha ' martensitic transformations in 316 L SS at 15 and 173 K. The gamma -> epsilon transformation involves the glide of Shockley partial dislocations on (111)(gamma) planes without a change in atomic spacing. The formation of an alpha ' inclusion in a single epsilon-band is achieved by a continuous lattice distortion, accompanied by the formation of a transition zone of alpha ' and the expansion of the average atomic spacings due to dislocation shuffling. As alpha ' grows further into gamma, the orientation relationship (OR) of the alpha ' changes by lattice bending. This process follows the Bogers-Burgers-Olson-Cohen model despite it not occurring on intersecting shear bands. Stacking faults and twins can also serve as nucleation sites for alpha ' at 173 K. We also found that direct transformation of gamma -> alpha ' occurs by the glide of root 6a(gamma) [11 (2) over bar]/12 dislocations on every (111)(gamma) plane with misfit dislocations. Overall, this study provides, for the first time, insights into the atomic-scale mechanisms of various two-step and one-step martensitic transformations induced by cryogenic deformation and corresponding local strain, enhancing our understanding of the role of martensitic transformation under ultra-cryogenic-temperature deformation in controlling the properties. (c) 2024 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

This study evaluates the sensitivity of non-destructive imaging methods to characterise in-plane (delaminations) and out-of-plane (matrix cracking/splitting) damage in open-hole carbon fibre reinforced polymer (CFRP) angle-ply specimens as a function of tensile loading to 86% and 97% of the ultimate tensile stress (UTS). Ultrasound, X-ray radiography (with and without contrast agent), and X-ray phase contrast imaging (XPCi) are compared against X-ray computed tomography (XCT). XPCi shows good sensitivity to out-of-plane (transverse) matrix cracks without the need for a contrast agent but has limited ability to assess in-plane delaminations. Conversely, ultrasonic C-scan demonstrated good accuracy for the quantification and depth estimation of in-plane delaminations, being comparable to segmented XCT data. A combination of ultrasound and XPCi could potentially allow planar NDE of delamination and matrix cracking without the access, throughput, and size limitations inherent in computed tomography or the need for invasive and expensive contrast agents required for radiographic imaging.

Short-fibre thermoplastic composites offer a balance between cost, processability, and performance, as well as providing a use for recycled fibres making them attractive in various industrial applications. However, the fibres tend to be misaligned due to their low aspect ratio, which can impact mechanical performance. This work examines the as-manufactured microstructure of a chopped carbon fibre-reinforced nylon composite made by material extrusion additive manufacturing in terms of fibre misalignment, void content, shape and distribution before going onto determine its effect on damage evolution under tensile straining by in-situ time-lapse synchrotron computed tomography (CT). To this end, CT scans have been acquired at various stages throughout straining. A high degree of fibre alignment is observed with approximate to 86% within 14 degrees of the extrusion axis, giving a Krenchel orientation factor of 0.75. The time-lapse CT image sequence reveals that because the mean fibre length ( approximate to 98 mu m.) is below the critical fibre length, fibre fracture does not take place during plastic straining. Instead, failure occurs during straining, from pre-existing voids and newly nucleated ones mainly located at fibre ends, their growth and coalescence. The experimental elastic modulus and strength are compared against the Cox-Krenchel and Kelly-Tyson analytical models that take into account fibre misalignment and length, which demonstrate that the fibre orientation is sufficient and future improvements in properties could be achieved by reducing the initial void content (approximate to 2.3%) and increasing the length and volume fraction of the reinforcing fibres.

The effects of CO2 exposure on sodium sulfate-activated blast furnace slag cement paste have been characterised by X-ray (attenuation) computed tomography revealing changes in micron-scale pore structure, and X-ray diffraction computed tomography (XRD-CT) elucidating changes in the spatial distribution of crystalline and semi-crystalline phases. Accelerated carbonation reduced ettringite volumes and induced formation of hydrotalcite, demonstrating the critical role of Mg-Al-SO4-layered double hydroxide phases in the CO2 uptake of these cements. These changes yield a refinement of small pores and increase the overall porosity, reaching values comparable to those of blended Portland cements. Formation factor values were determined considering the pore solution electrical resistivity, calculated from thermodynamic modelling, and the porosity. A correlation between simulated tortuosity and porosity is proposed to estimate the diffusion tortuosity and formation factor of sodium sulfate-activated slag pastes. This approach represents a significant step forward for assessing carbonation resistance and CO2 uptake capacity of cementitious pastes.

Pterosaurs were the largest animals to have achieved powered flight in the history of life on Earth, possessing wingspans akin to some modern light aircraft. Vertebrate fossils have shown their potential to retain information on the chemical, physical, and mechanical properties of precursor bone. However, the fossil record is not a traditional source of inspiration for engineers to create palaeo-bioinspired designs. To explore its potential, this study has imaged the three-dimensional porosity of pterosaur bone intending to inspire and improve the mechanical properties of aerospace materials. Historically, two-dimensional histological analysis has resolved fine-scale structures in fossilised bone, which damages the sample. By applying advanced X-ray imaging techniques in this study (using Image Quality Indicators) we show it is possible to non-destructively resolve/verify the microarchitecture of pterosaur bone not previously seen in three dimensions. Pterosaur bone porosity has helped map the macroscopic stresses of this biomaterial but ultimately presents an opportunity to inspire advanced manufactured materials. This microarchitecture of bone offers a unique geometry where self-healing materials with internal monitoring systems can be developed. The iterative process of Darwinian natural selection has evolved multiple engineering solutions that can be reverse engineered to solve challenges facing industry in the 21st Century.

The interfacial properties have been measured for a novel AA6061/SiC-C coated silicon carbide SM3256 monofilamentary fibre (Al/SiCf) MMC using a variant of the single fibre fragmentation test. In this test, fibre fragmentation is followed in situ using synchrotron X-ray diffraction to probe the axial fibre elastic strains as a function of applied loading, while X-ray radiography is used to follow the fracture sequence. In this way, the variation in axial fibre stress along the fibre is tracked and hence the variation in interfacial shear stress along the fibre inferred at various stages of fibre fragmentation. Prior to loading, the fibre was in a state of axial compression (approximate to 280 MPa) due to thermal residual stresses representative of cooling from 200 degrees C. During the fragmentation process, the variations in axial strain and interfacial stress show characteristic "stick-slip" behaviour, where the fibre interface must exceed a threshold stress (tau deb = 94 +/- 10 MPa), close to the shear strength of the matrix before debonding. Once debonded, the fibre slides at a frictional shear stress, tau fr, initially of around 40 MPa, but falling with increased sliding distance to around tau fr = 15 +/- 5 MPa. Radiography taken during loading, and post-mortem, indicates that interfacial failure occurs at the fibre-coating interface, leaving coating material lining the pull-out within the matrix. The accumulation of coating damage may be responsible for the progressive decrease in sliding stress with increased sliding. These sliding stresses, are much lower than observed for comparable Ti/SiC composites, and would facilitate significant fibre-pull-out and fibre bridging under fatigue conditions.

Additive manufacturing (AM) of parts is typically associated with the generation of high residual stresses because of repeated exposure to high thermal gradients. Non-destructive means of mapping the residual stresses are required for optimising these processes and/or mitigating such stresses by thermal treatments. However, the reliable determination of residual stress in AM parts remains challenging. Here, neutron diffraction, as well as energy- and angle-dispersive synchrotron X-ray diffraction have been used to map the residual stress within a laser powder bed fusion (LPBF) additively manufactured stainless steel 316L arch. The arch was designed by the EASI-STRESS project as a residual stress benchmarking exercise in order to compare different residual stress analysis techniques. Residual stresses were determined along two scan lines deep within the bulk of the component. The results for the different neutron and synchrotron instruments are found to broadly agree with a standard deviation of 50 MPa or better, as well as with those predicted by an inherent strain finite element model. The results show near-yield level residual stresses and suggest that both synchrotron X-ray diffraction and neutron diffraction can be used to reliably determine the residual stress in LBPF parts.

Focused ion beam (FIB) systems have revolutionized sample preparation for transmission electron microscopy (TEM), enabling precise and site-specific material analysis. However, the conventional ion beam-induced deposition (IBID) approach to preparing FIB samples can lead to contamination effects that can compromise the quality of TEM data acquisition. This study introduces an innovative FIB method for connecting TEM lamellae to support grids via redeposition, avoiding the contamination issue. We demonstrate the effectiveness of this technique through observations of a SiC phase within tristructural-isotropic particles during in situ high-temperature and irradiation TEM experiments, establishing an improved process for characterizing material behaviors during exposure to their industrially relevant environmental conditions.

Background Residual stress development in precipitation strengthened aluminium foundry alloys has seen little attention, despite the prevalence of their use over a wide array of applications. Objective This study aims at the evaluation of the residual stress in a cast aluminium benchmark that develops during precipitation heat treatment and determines the preferable stress relaxing techniques for such applications. Methods The stress states in the as-cast, T4 and T6 tempers of the same AlSi7Cu0.5Mg (A356 with 0.5 wt% Cu) sample were determined through a novel application of the contour method, standard hole drilling, deep hole drilling and incremental deep hole drilling. Results The results of all measurement techniques lie within approximately 40 MPa for all regions available for comparison, with the greatest differences occurring between the contour method and deep hole drilling for the T6 component. It is shown that the peak tensile residual stresses are almost identical between the heat-treated components (75 MPa), but the distribution and magnitude of compressive residual stress are found to be significantly different. Conclusions Among the measurement techniques evaluated, the contour method and incremental hole drilling are found to be more suitable for T6 temper, while all techniques perform equally well for T4 temper due to its relatively low strength. It is hypothesised that the difference between the as-cast and heat-treated samples is due to solution heat treatment and quenching, while the difference in T4 and T6 tempers is attributed to the response to ageing.