Distinct Microstructural Features Research Articles

Local anisotropy in mineralized fibrocartilage and subchondral bone beneath the tendon-bone interface

The enthesis allows the insertion of tendon into bone thanks to several remarkable strategies. This complex and clinically relevant location often features a thin layer of fibrocartilage sandwiched between tendon and bone to cope with a highly heterogeneous mechanical environment. The main purpose of this study was to investigate whether mineralized fibrocartilage and bone close to the enthesis show distinctive three-dimensional microstructural features, possibly to enable load transfer from tendon to bone. As a model, the Achilles tendon-calcaneus bone system of adult rats was investigated with histology, backscattered electron imaging and micro-computed tomography. The microstructural porosity of bone and mineralized fibrocartilage in different locations including enthesis fibrocartilage, periosteal fibrocartilage and bone away from the enthesis was characterized. We showed that calcaneus bone presents a dedicated protrusion of low porosity where the tendon inserts. A spatially resolved analysis of the trabecular network suggests that such protrusion may promote force flow from the tendon to the plantar ligament, while partially relieving the trabecular bone from such a task. Focusing on the tuberosity, highly specific microstructural aspects were highlighted. Firstly, the interface between mineralized and unmineralized fibrocartilage showed the highest roughness at the tuberosity, possibly to increase failure resistance of a region carrying large stresses. Secondly, fibrochondrocyte lacunae inside mineralized fibrocartilage, in analogy with osteocyte lacunae in bone, had a predominant alignment at the enthesis and a rather random organization away from it. Finally, the network of subchondral channels inside the tuberosity was highly anisotropic when compared to contiguous regions. This dual anisotropy of subchondral channels and cell lacunae at the insertion may reflect the alignment of the underlying collagen network. Our findings suggest that the microstructure of fibrocartilage may be linked with the loading environment. Future studies should characterize those microstructural aspects in aged and or diseased conditions to elucidate the poorly understood role of bone and fibrocartilage in enthesis-related pathologies.

Understanding the influence of microstructure on hot corrosion and erosion behavior of suspension plasma sprayed thermal barrier coatings

Thermal barrier coatings (TBCs) are bilayer systems comprising a 7–8 wt% yttria partially stabilized zirconia (YSZ) top coat deposited over a metallic bond coat. Suspension plasma spraying (SPS) is an advanced and attractive top coat processing technique due to its capability to yield a variety of microstructures, including the desired columnar microstructure for enhanced strain tolerance and durability. This work attempts to investigate the desirable microstructural features in an SPS processed TBCs to mitigate hot corrosion and minimize erosion related losses that are often responsible for coating degradation. SPS processed TBCs were deposited utilizing three different spray conditions to obtain distinct microstructural features (column density, interpass [IP] porosity bands, column width), porosity content, and mechanical properties. Apart from comprehensive characterization utilizing SEM, XRD and micro-indentation tests, the as-deposited TBCs were subjected to hot-corrosion tests in the presence of vanadium pentoxide and sodium sulfate as corrosive salts. Post-corrosion analysis revealed complete infiltration of the molten salts in all the investigated TBCs. However, the delamination cracks generated due to the infiltrated corrosive species were minimal in case of TBCs with higher fracture toughness. The differences in microstructure and mechanical properties also led to differences in erosion performance, with TBCs possessing minimal total porosity content and high fracture toughness best resisting erosion related damage. Post-erosion analysis revealed that the TBCs with higher fracture toughness and micro-hardness showed superior erosion resistance. Based on the erosion and corrosion results and subsequent post-mortem of failed specimens, plausible damage mechanisms are proposed. Findings from this work provide new insights on developing damage tolerant TBCs microstructures with enhanced durability when exposed to erosion and hot corrosion environments. • SPS TBCs with varying columnar microstructural features and mechanical properties were deposited. • Influence of parameters (suspension feed rate, spray distance, etc.) on microstructural features in SPS TBCs examined. • Desirable microstructural features were identified to minimize erosion and hot corrosion.

Additive Manufactured 316L Stainless-Steel Samples: Microstructure, Residual Stress and Corrosion Characteristics after Post-Processing

Additive manufacturing (AM) is a relatively new manufacturing method that can produce complex geometries and optimized shapes with less process steps. In addition to distinct microstructural features, residual stresses and their formation are also inherent to AM components. AM components require several post-processing steps before they are ready for use. To change the traditional manufacturing method to AM, comprehensive characterization is needed to verify the suitability of AM components. On very demanding corrosion atmospheres, the question is does AM lower or eliminate the risk of stress corrosion cracking (SCC) compared to welded 316L components? This work concentrates on post-processing and its influence on the microstructure and surface and subsurface residual stresses. The shot peening (SP) post-processing levelled out the residual stress differences, producing compressive residual stresses of more than −400 MPa in the AM samples and the effect exceeded an over 100 µm layer below the surface. Post-processing caused grain refinement and low-angle boundary formation on the sample surface layer and silicon carbide (SiC) residue adhesion, which should be taken into account when using the components. Immersion tests with four-point-bending in the heated 80 °C magnesium chloride solution for SCC showed no difference between AM and reference samples even after a 674 h immersion.

Microstructural features of the cerebral cortex: Implications for predicting epilepsy relapse after drug withdrawal

A considerable portion of patients with well-controlled seizures and visually normal brain structures experience seizure recurrence after anti-seizure medication is withdrawn. Microstructural abnormalities of the cortex may play an essential role in epilepsy relapse. Patients with idiopathic/cryptogenic epilepsy were registered. At the follow-up endpoint, 18 patients with relapse (PR+ group), 20 patients without relapse (PR− group), and 30 healthy controls were included. High-resolution T1-weighted images were obtained at the time of drug withdrawal. Microstructural features including cortical thickness, surface area, cortical volume and mean curvature in 68 cortical areas were calculated. A general linear model was applied to investigate intergroup differences, and then post hoc analysis was performed. Additionally, factor analysis was conducted to extract components from imaging measures showing a difference between PR− and PR+ groups, and independent associations between components and epilepsy relapse were assessed using a logistic regression model. Cortical thickness of the left paracentral lobule, left temporal pole and right superior frontal gyrus; surface area of the bilateral lingual gyrus and bilateral pericalcarine cortex; and cortical volume of the bilateral pericalcarine cortex had significant intergroup differences (false discovery rate correction, P < 0.05). All measures, except for cortical thickness of the left temporal pole, showed differences between PR− and PR+ groups. Two dominant components were extracted from these measures, and both were independently associated with epilepsy relapse. In conclusion, epilepsy patients with relapse presented distinct microstructural features of cortex at the time of drug withdrawal, which may serve as a potential biomarker for predicting seizure recurrence.

In situ ornamenting poly(ε-caprolactone) electrospun fibers with different fiber diameters using chondrocyte-derived extracellular matrix for chondrogenesis of mesenchymal stem cells

Biomimetic instructive tissue engineering scaffolds are critical for achieving successful tissue regeneration. In the present study, we developed a novel scaffold via ornamenting poly(ε-caprolactone) (PCL) electrospun fibers with a chondrocyte-derived extracellular matrix (ECM)-coating, which was applied for chondrogenesis of mesenchymal stem cells (MSCs). PCL fibrous films with different fiber diameters (1282±121 nm, 549±61 nm and 285±38 nm) were first prepared via electrospinning. Rabbit articular chondrocytes (rACs) were cultured on PCL fibrous scaffolds, followed by a decellularization treatment to generate decellularized ECM (dECM)-coated PCL scaffolds (dECM/PCL). Rabbit bone marrow-derived MSCs (rMSCs) were then seeded onto these scaffolds and adhesion, proliferation and chondrogenic differentiation were evaluated. dECM/PCL scaffolds displayed distinct surface microstructural features with varying fiber diameters and fibrous mesh-like ECM with more developed collagen fibers was observed on nanofibers. On dECM/PCL scaffolds, rMSCs tended to spread more at 24 h post-seeding and proliferated better within 7 d compared to those on uncoated PCL scaffolds. Based on analysis of gene expression, rMSCs underwent the best chondrogenic differentiation on dECM/PCL scaffolds of 549-nm fibers. Collectively, such dECM/PCL composite scaffolds are very promising for cartilage tissue regeneration.

Synergetic influence of microconstituents on the damage accumulation and consequent effect on the flow behaviour in cast Mg–Ca–Sn alloys

Combined role of microconstituents (particles, eutectic fraction and its morphology) on the damage accumulation of three as-cast Mg–Ca–Sn alloys having distinctive microstructural features is studied. Flow stress normalized with that of a solid solution alloy brought out the sole contribution of microconstituents to the deformation. For identifying the influence of microconstituents on strain hardening rate, Kocks-Mecking analysis is utilized together with intermittent post-deformation microstructures. Comprehensive microstructural characterization as a function of strain facilitated to unravel the distinction in internal damage accumulation among the alloys. Further, the internal damage accumulation variation due to distinct variation in the microconstituents is attributed to the differences in hardening rate trends among the three alloys. The reduction in hardening rate is analyzed to occur due to damage accumulation through eutectic fracture or interphase cracking. Thus, the damage mechanism and its influence on strain hardening in cast magnesium alloys is proposed.

Experimental Investigation of the Blanked Surface of C5191 Phosphor Bronze Sheet over a Wide Range of Blanking Speeds.

The influence of blanking speed on the blanked surface quality of C5191 bronze phosphorus sheets, with a thickness of 0.12 mm, was systematically studied to demonstrate the mechanism under high speed blanking. The morphology and microstructure of the blanked edge were observed by using a variety of techniques, including optical microscopy (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The results revealed that the local temperature and microhardness of the shear zone increased with the increase in blanking speed. Moreover, the quality of blanked edge significantly improved with the increase in blanking speed due to the combined influence of strain rate hardening and thermal softening. In addition, the blanked edge grains were elongated along the blanking direction and formed dislocation cells and sub-grains in some areas. The blanked edge is dominated by {000} <100> cubic texture at higher blanking speeds, and {112} <111> texture at lower blanking speeds. When punched at an ultra-high speed of 3000 strokes per minute (SPM 3000), the local area of the blanked edge exhibited distinct microstructural features, including low dislocation density, nanocrystals with high-angle grain boundaries, and significant differences in grain orientation. Additionally, the selected area electron diffraction (SAED) pattern exhibited a discontinuous ring-like structure, indicating the occurrence of adiabatic shearing with dynamic recrystallization.

Universal Material Constants for MultiStage Fatigue (MSF) Modeling of the Process–Structure–Property (PSP) Relations of A000, 2000, 5000, and 7000 Series Aluminum Alloys

A MultiStage Fatigue (MSF) model that admits different hierarchical microstructural features and their stereological information is used to predict the fatigue behavior of 17 different processed aluminum alloys: A000 series (A319, A356, A357, and A380), 2000 series (2024, 2055, 2099, 2198, 2297), 5000 series (5052, 5456), and 7000 series (7050, 7055, 7065, 7075, 7085, 7175). A single set of MSF model constants was validated for all of the aforementioned aluminum alloys, wherein the variation in fatigue life has been captured according to distinct microstructural features (pore size, pore nearest neighbor distance, porosity, particle size, grain size, crystallographic orientation, and misorientation) that differ arising from their native material processing method (casting, rolling, or extrusion). The MSF model’s total number of cycles distinguishes two different regimes: crack incubation (Inc) and Microstructurally Small Crack (long cracks are not considered herein). The previous MSF model in the literature had been associated with the pore size, pore nearest neighbor distance, porosity, particle size, and grain size, but a new contribution in this work is the contribution of the grain orientation and misorientation angles. We show that the MSF model now has the necessary and sufficient equations to predict the Process–Structure–Property relationships for aluminum alloys, allowing for expansion of fatigue prediction even beyond the alloys studied herein.

Microstructure driven magnetodielectric behavior in ex-situ combustion derived BaTiO3-ferrite multiferroic composites

The present work investigates the magnetodielectric behavior of ex-situ combustion derived 7BaTiO3@3ferrite and 3ferrite@7BaTiO3 multiferroic composites. Three different ferrites, such as CoFe2O4, ZnFe2O4, and Co0.5Zn0.5Fe2O4, have been selected for the preparation of multiferroic composites. Distinct microstructural features were observed in 7BaTiO3@3ferrite and 3ferrite@7BaTiO3 composites. X-ray diffraction study confirmed the presence of hexagonal and tetragonal BaTiO3 in 3ferrite@7BaTiO3 composites. Plate-like and spherical BaTiO3 grains were observed in these composites. However, only spherical or polyhedral BaTiO3 grains were found in 7BaTiO3@3ferrite composites, as confirmed from EDS mapping. Also, plate-like BaFe12O19 and polyhedral ferrite grains were detected in all composites. The presence of BaFe12O19 and its effect on magnetic and dielectric behavior of composites was also analyzed in this work. Maxwell-Wagner polarization phenomenon due to charge depletion at the BaTiO3-ferrite interface was found to be prominent in 7BaTiO3@3ferrite composites because of the maximum connectivity of ferrite phases. The main factors for the magnetocapacitance response in the present systems are due to the combined effects of interface-dominated magnetoresistance, magnetostriction of ferrites and microstructure of composites. The variation in magnetocapacitance response of these multiferroic composites may be suitable for potential applications in the field of sensors and devices.

Manual dexterity of mice during food-handling involves the thumb and a set of fast basic movements.

The small first digit (D1) of the mouse's hand resembles a volar pad, but its thumb-like anatomy suggests ethological importance for manipulating small objects. To explore this possibility, we recorded high-speed close-up video of mice eating seeds and other food items. Analyses of ethograms and automated tracking with DeepLabCut revealed multiple distinct microstructural features of food-handling. First, we found that mice indeed made extensive use of D1 for dexterous manipulations. In particular, mice used D1 to hold food with either of two grip types: a pincer-type grasp, or a "thumb-hold" grip, pressing with D1 from the side. Thumb-holding was preferentially used for handling smaller items, with the smallest items held between the two D1s alone. Second, we observed that mice cycled rapidly between two postural modes while feeding, with the hands positioned either at the mouth (oromanual phase) or resting below (holding phase). Third, we identified two highly stereotyped D1-related movements during feeding, including an extraordinarily fast (~20 ms) "regrip" maneuver, and a fast (~100 ms) "sniff" maneuver. Lastly, in addition to these characteristic simpler movements and postures, we also observed highly complex movements, including rapid D1-assisted rotations of food items and dexterous simultaneous double-gripping of two food fragments. Manipulation behaviors were generally conserved for different food types, and for head-fixed mice. Wild squirrels displayed a similar repertoire of D1-related movements. Our results define, for the mouse, a set of kinematic building-blocks of manual dexterity, and reveal an outsized role for D1 in these actions.

Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718

The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The &lt;100&gt; crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.

Long-Term Atmospheric Corrosion of 304 Stainless Steel Used in Spent Dry Nuclear Fuel Storage Containers

Long-term Atmospheric Corrosion of 304 Stainless Steel Used in Spent Dry Nuclear Fuel Storage Containers J. Srinivasan1, J. S. Locke1, T. Weirich1, J. Taylor2, C. Bryan2, E. J. Schindelholz2 1: Fontana Corrosion Center, Department of Materials Science and Engineering, The Ohio State University, 105 W Woodruff Ave, Columbus, OH 43210 2: Sandia National Laboratories, Materials Reliability Department and Department of Storage and Transportation Technologies, Albuquerque, NM 87185 Containers made from welded austenitic stainless steels (types 304 and 316) are typically used to store dry spent nuclear fuel at several facilities across the US. Exposure to the ambient environment can lead to salt deposition on the metal that can result in the onset of pitting and possible risk for stress corrosion cracking. In this study, the effect of atmospheric sea salt environments on pitting and SCC in 304H stainless steel coupons was investigated with the aim of replicating near-marine environments. Key experimental variables examined include salt loading density, relative humidity (RH), and exposure time (ranging from 1 week to 2 years). Pit initiation was observed to be particularly dependent on the surface finish of the exposed metal. Pitting was observed only on the ground coupons and within 1 week of exposure, while those with a mirror finish were unaffected even after a year of exposure. Relative humidity played an influential role in determining pit density and morphology, with up to 7.5 times more pits growing at 40% RH than at 76% RH. Further, at 76% RH, pits were confined to specific areas on the surface in comparison to a more uniform distribution at 40% RH. This occurrence can be attributed to the restricted cathodic area available in the latter case, in broad accordance with model predictions outlined in the literature.1 Morphologically, pits grown at 76% RH displayed an ellipsoidal surface geometry with smooth facets at the pit base whereas those grown at 40% showed evidence of attack along distinct microstructural features that appear to be slip bands. Moreover, SCC initiation in the absence of an externally applied load was observed at the edges of the pits grown at 40% RH. This occurrence of SCC appeared to be associated with residual stresses from surface grinding. A possible mechanistic hypothesis for the observed pit morphology and consequent SCC is proposed based on synergistic electrochemical and microstructural causes. At low RH conditions, high [Cl−], mass transport restriction due to precipitated salts2, and preferential dissolution along slip bands3 result in a fissure-like pit geometry which serves as a stress concentrator. In concert, residual stresses from surface grinding may form strain-induced martensite, which could undergo hydrogen environment embrittlement4 due to hydrogen generation from metal ion hydrolysis in pits, resulting in favorable conditions for SCC initiation. Current studies are focused on examining this hypothesis further to understand the effects of RH and mixed salt electrolyte chemistry on pitting and to characterize the susceptible microstructure for evidence of strain-induced martensite. The SCC response of the alloy to externally applied loads to determine the effects of pit morphology, RH, and possibly sensitization on crack propagation will also be investigated. References Z. Y. Chen, F. Cui, and R. G. Kelly, J. Electrochem. Soc., 155, C360–C368 (2008).L. Guo et al., J. Electrochem. Soc., 166, 3010–3014 (2019).P. Sadler, N. C. Pruitt, T. S. Sudarshan, and M. R. Louthan, J. Mater. Eng, 9, 151–156 (1987).Y. Mine, Z. Horita, and Y. Murakami, Acta Mater., 57, 2993–3002 (2009). This work is supported at The Ohio State University by Sandia National Laboratories and The Center for Performance and Design of Nuclear Waste Forms and Containers (WastePD), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584. The work conducted under WastePD is all stress corrosion cracking analysis and corrosion morphology investigations utilizing optical profilometry. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

3D characterization of defects in deep-powder-bed manufactured Ti–6Al–4V and their influence on tensile properties

Deep-powder-bed additive manufacturing (AM) can lead to distinctive microstructural features. In this study, 300-mm long cylindrical rods (12-mm diameter) of Ti–6Al–4V were vertically built to the limit height of a commercial selective electron beam melting (SEBM) system for quantitative three-dimensional (3D) characterization of the defects by X-ray micro-computed tomography (μ-CT). Detailed μ-CT data from 18,337 consecutive slices revealed a strong dependence of defect characteristics on build height, including defect volume, population, sphericity, major axis length, depth and orientation angle. The first 100-mm build exhibited the worst presence of defects by each measurement, while the middle and last 100-mm builds contained much fewer defects, especially the last 100-mm build, which was free of lack-of-fusion defects (sphericity < 0.5). As a result, the first 100-mm build displayed 50% lower reduction of area and 20% lower strain-to-fracture than the last 100-mm build, while the tensile strengths varied within just ±3%. An outer 3-mm thick ring and a central 1.5-mm diameter region were found to contain substantially less defects along the 300-mm build height. The dependence of defect features on build height was attributed to the existence of an upward temperature gradient during SEBM. The 3D defect features revealed by μ-CT along the build height provide important implications for deep-powder-bed AM by SEBM.

A combined SPM/NI/EDS method to quantify properties of inner and outer C-S-H in OPC and slag-blended cement pastes

To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the coupled techniques of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images, nanoindentation (NI), and energy-dispersive X-ray spectroscopy (EDS) for comprehensive investigation on the chemical-mechanical-morphological properties of C-S-H gel in both ordinary Portland cement (OPC) and slag-blended cement pastes. The thickness of the inner C-S-H (IP) layer is precisely measured for the first time by modulus mapping, it varies with the types of unreacted cores as well as the addition of the supplementary cementitious materials. An interface transition zone (ITZ) is found between the unreacted C3S grain and the surrounding inner C-S-H layer. The mechanical properties of the five types of C-S-H in OPC and the slag-blended pastes are not significantly affected by their chemical compositions. A good correlation between the storage modulus and the indentation modulus of the individual phases is found. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool to characterize the phase in cementitious materials with more attractive features of higher spatial resolution.

Microstructure Representation and Reconstruction of Heterogeneous Materials Via Deep Belief Network for Computational Material Design

Integrated Computational Materials Engineering (ICME) aims to accelerate optimal design of complex material systems by integrating material science and design automation. For tractable ICME, it is required that (1) a structural feature space be identified to allow reconstruction of new designs, and (2) the reconstruction process be property-preserving. The majority of existing structural presentation schemes relies on the designer's understanding of specific material systems to identify geometric and statistical features, which could be biased and insufficient for reconstructing physically meaningful microstructures of complex material systems. In this paper, we develop a feature learning mechanism based on convolutional deep belief network (CDBN) to automate a two-way conversion between microstructures and their lower-dimensional feature representations, and to achieve a 1000-fold dimension reduction from the microstructure space. The proposed model is applied to a wide spectrum of heterogeneous material systems with distinct microstructural features including Ti–6Al–4V alloy, Pb63–Sn37 alloy, Fontainebleau sandstone, and spherical colloids, to produce material reconstructions that are close to the original samples with respect to two-point correlation functions and mean critical fracture strength. This capability is not achieved by existing synthesis methods that rely on the Markovian assumption of material microstructures.

New Nomenclatures for Heat Treatments of Additively Manufactured Titanium Alloys

The heat-treatment designations and microstructure nomenclatures for many structural metallic alloys were established for traditional metals processing, such as casting, hot rolling or forging. These terms do not necessarily apply for additively manufactured (i.e., three-dimensionally printed or “3D printed”) metallic structures. The heat-treatment terminology for titanium alloys generally implies the heat-treatment temperatures and their sequence relative to a thermomechanical processing step (e.g., forging, rolling). These designations include: β-processing, α + β-processing, β-annealing, duplex annealing and mill annealing. Owing to the absence of a thermomechanical processing step, these traditional designations can pose a problem when titanium alloys are first produced via additive manufacturing, and then heat-treated. This communication proposes new nomenclatures for heat treatments of additively manufactured titanium alloys, and uses the distinct microstructural features to provide a correlation between traditional nomenclature and the proposed nomenclature.

Phase quantification in cementitious materials by dynamic modulus mapping

Understanding mechanism at the microscale level is essential for tailoring cementitious material to achieve better concrete and structure performance. To identify the distinct microstructural features and to provide insight into the mechanism by which the phases in hardened paste possess, this study adopts the technique of quantitative modulus mapping in the form of Scanning Probe Microscopy (SPM) images to characterize non-destructively the hardened ordinary Portland cement (OPC) paste and slag-blended cement paste at the microscale level. It is found that SPM modulus mapping is capable of identifying individual phase based on the local variation of nanomechanical properties. A method is proposed to quantify the size of the identified phase, especially the thickness of the inner C-S-H layer. With the facilitation of SPM mapping image, the indent location can be located to recognize in which phase the nanoindentation has been made. The results indicate the significance of SPM-based modulus mapping technique as a powerful tool for fundamental study of the cementitious materials with more attractive features of higher spatial resolution to quantify the phase size in nanometer scale level under a nondestructive testing condition.

Parcellation of Human Amygdala Subfields Using Orientation Distribution Function and Spectral K-means Clustering.

Amygdala plays an important role in fear and emotional learning, which are critical for human survival. Despite the functional relevance and unique circuitry of each human amygdaloid subnuclei, there has yet to be an efficient imaging method for identifying these regions in vivo. A data-driven approach without prior knowledge provides advantages of efficient and objective assessments. The present study uses high angular and high spatial resolution diffusion magnetic resonance imaging to generate orientation distribution function, which bears distinctive microstructural features. The features were extracted using spherical harmonic decomposition to assess microstructural similarity within amygdala subfields are identified via similarity matrices using spectral k-mean clustering. The approach was tested on 32 healthy volunteers and three distinct amygdala subfields were identified including medial, posterior-superior lateral, and anterior-inferior lateral.

A study on microhardness and microstructural evolution of titanium/zirconium diboride cermet coatings with varying scan speeds during laser cladding on Ti6Al4V substrate

Titanium/zirconium diboride cermet coatings were deposited at different laser scan speeds on Ti-6Al-4V alloy using laser cladding technique. Microhardness of the coatings was compared with the microhardness of the substrate, while the microstructural morphologies of coatings were evaluated via scanning electron microscope with energy dispersive spectroscopy. In addition, resultant grain sizes of the coatings were observed and phases formed within the coatings were also examined. The microhardness of the coatings was seen to be four times harder than the substrate. Scanning electron microscopic images exhibited a refinement in grain size and the development of distinct microstructural features. X-ray diffraction patterns showed significant hard phases such as Al2Zr and Ti3B4 which may be responsible for the sky-rocketed microhardness values of the coatings. This study proffers profound insight on the influence of laser scan speed, during deposition, on the microhardness and microstructural morphology of titanium/zirconium diboride cermet coatings.

Fracture in multi-phase materials: Why some microstructures are more critical than others

Our goal is to unravel the mechanisms that lead to failure of a ductile two-phase material – that consists of a ductile soft phase and a relatively brittle hard phase. An idealized microstructural model is used to study damage propagation systematically and transparently. The analysis uncovers distinct microstructural features around early voids, whereby regions of the hard phase are aligned with the tensile axis and regions of the soft phase are aligned with the shear directions. These features are consistently found in regions exhibiting damage propagation, whereby the damage remains initiation driven, i.e. voids nucleate independently of each other. Upon localization, damage is controlled on a longer length-scale relying on a critical relative position of ‘initiation hot-spots’. The damage rapidly increases in bands of the soft phase wherein several voids are aligned with the shear directions. The relative arrangement of the voids determines whether the microstructure fails early, or at a substantially higher strain. Although much research is needed to refine these findings for real or more realistic microstructures, in particular in three-dimensions, this paper opens a route to a deeper understanding of the ultimate failure of multi-phase materials.