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High-temperature differential scanning calorimetry was used to understand the thermal properties of Si-rich metal–silicon alloys. Insoluble metals (A and B) were found to produce an alloy with discrete ASi2 and BSi2 dispersed phases. In contrast, metals that form a solid solution result in a dispersed phase that has a composition of AxB1−xSi2, where x varies continuously across each inclusion. This complex composition distribution is putatively caused by differences in the solidification temperatures of ASi2 versus BSi2. Though this behavior was observed for several different combinations of metals, we focus here specifically on the Cr/V/Si system. To better understand the range and most probable element concentrations in the dispersed silicide domains, a method was devised to generate histograms of their Cr and V concentrations from energy-dispersive X-ray spectroscopy hyperspectral images. Varying the Cr/V/Si ratio was found to change the shape of the element histograms, indicating that the distribution of silicide compositions that form is controlled by the input composition. Adding aluminum was found to result in dispersed phases that had a single composition rather than a range of Cr and V concentrations. This demonstrates that aluminum can be an effective additive for altering solidification kinetics in silicon alloys.
The mineral composition of eggshells is assumed to be a conserved phylogenetic feature. Avian eggshells are composed of calcite, whereas those of taxa within Chelonia are aragonitic. Yet, the eggshells of a passerine bird were reported to be made of aragonite. Here, we report a new study of the same bird eggshells using a combination of in situ microscopy and chemical techniques. A microstructural analysis finds a similar arrangement to other avian eggshells, despite their very thin and fragile nature. Fourier transform infrared spectrometry (FTIR) and electron backscatter diffraction (EBSD) results also confirm that the eggshells are entirely composed of calcite. Our findings demonstrate that passerine eggshells are not an exception and similar to other birds and reinforce the phylogenetic placement of this bird species.
Softness has a great impact on the properties of colloidal suspensions, especially at high concentrations. Particle deformability due to crowding is responsible for elastic interactions strongly affecting the dynamical properties, which therefore differ from those of hard spheres. The universal aspects of the linear and nonlinear rheological response, based on appropriate scaling, are discussed. Different approaches to determine an effective volume fraction and its role on the low frequency plateau modulus in the glassy and jamming regimes are presented. The flow properties often follow Herschel–Bulkley behavior, with the particle microstructure and interactions affecting the yield stress and causing shear banding or wall slip in some cases. Concentrated suspensions exhibit aging and internal stresses with several common but also distinct features compared to hard sphere glasses. The rich state diagrams of mixtures involving soft colloidal glasses and additives (linear polymers, soft or hard particles) suggest the possibility to tailor their flow properties, often in unprecedented ways, by means of osmotic interactions. This wealth of physical properties in relation to particle interactions can be described by different microstructural, statistical, and phenomenological models which offer a valuable predictive toolbox for understanding the complex and tunable rheology of this class of systems.
The microstructure of colloidal suspensions, both at rest and under flow, is a function of the particle and fluid properties, interparticle potential, and processing or flow history. Indeed, complex, nonlinear rheological phenomena, such as thixotropy and shear thickening, are associated with significant changes in microstructure during flow and processing. A modern understanding of colloidal suspension rheology thus necessitates measurement of colloidal suspension microstructure under flow as well as at rest. Two popular classes of experimental methods for microstructure measurement are introduced and explained, namely confocal microscopy and scattering of light, neutrons, and x-rays.
The chapter begins by defining mixing and then discusses how ocean mixing is studied by a combination of direct observations, process studies, and studies integrated with modeling. The role of mixing in the meridional overturning circulation is examined in detail, including current suggestions termed ‘upside-down’ mixing. The chapter concludes with energy and scalar budgets that determine average mixing levels throughout the ocean.
The stratified ocean mixes episodically in small patches where energy is dissipated and density smoothed over scales of centimeters. The net effect of these countless events effects the shape of the ocean's thermocline, how heat is transported from the sea surface to the interior, and how dense bottom water is lifted into the global overturning circulation. This book explores the primary factors affecting mixing, beginning with the thermodynamics of seawater, how they vary in the ocean and how they depend on the physical properties of seawater. Turbulence and double diffusion are then discussed, which determines how mixing evolves and the different impacts it has on velocity, temperature, and salinity. It reviews insights from both laboratory studies and numerical modelling, emphasising the assumptions and limitations of these methods. This is an excellent reference for researchers and graduate students working to advance our understanding of mixing, including oceanographers, atmospheric scientists and limnologists.
This article presents a review on recent advances in the fatigue behavior of Ti alloys, especially the main commercial compositions for orthopedic applications. In the case of well-known Ti–6Al–4V alloy, the major concern is related to the effect of the surface modification necessary to improve the osseointegration. The introduction of surface discontinuities due to the growth of a porous oxide layer, or the roughness development, may severely affect the fatigue performance depending on the level of alteration. In the case of additive manufactured Ti–6Al–4V, the fatigue response is also influenced by inherent defects of as-built parts. Regarding the recently developed metastable β alloys, information about the fatigue properties is still scarce and mainly related to the effect of second phase precipitates, which are introduced to optimize the mechanical properties. The fatigue behavior of the Ti alloys is complex, as is their microstructure, and should not be neglected when the alloys are being developed or improved to be applied in medical devices.
Fe–Al–O ODS alloy prepared via mechanical alloying was subjected to three different heat treatments. Material basic state exhibited a fine-grained (300–500 nm) microstructure with fine dispersion of aluminum oxide particles (60% up to 20 nm). Heat treatment at 1100 °C for 3 h resulted in local grain and particles coarsening. Prolongation of the heat treatment to 24 h resulted in further grain (50 % up to 5 μm) and particle (25 % with size 25–40 nm) coarsening. Annealing at 1200 °C for 24 h led to a bimodal microstructure (35 % of grains with size 100–250 μm and 45 % of particles with size 30–60 nm) and substantial oxide particle coarsening. Microstructural changes resulted in tensile strength decrease and ductility increase. Tensile tests at 800 °C revealed a 90% decrease of tensile strength while ductility increased 4–6 times when compared to the room temperature tests. The hardening ratio was below 10 % for all the alloys and both test temperatures.
Hot deformation and softening response for the titanium aluminide Ti–48Al–2V–0.2B has been investigated. The deformation response to softening mechanisms has been examined. Deformation experiments were carried out in the strain rate range 0.01–10 s−1 keeping the temperature constant at 1200 °C and in the temperature range 1000–1200 °C at the strain rate 1 s−1. With an increase in strain rate, the microstructural changes associated with the softening mechanism include breaking of the lamellae, spheroidization of the broken laths and dynamic recrystallization. For the strain rate 1 s−1, deformation in the (α2 +γ) phase field leads to fine recrystallized grains, remnant lamellae and cavitation along the grain boundaries (for temperatures 1000 and 1100 °C). Deformation in the (α +γ) phase field leads to dynamic recrystallization at the shear bands, within the lamellae, breaking and rotation of the α phase during the continuous increase in the deformation strain.
Soyarslan et al. [J. Mater. Res. 33(20), 3371 (2018)] proposed a beam-finite element model for the computation of effective elastic properties of nanoporous materials, where the ligament diameter along the skeleton is determined with the biggest sphere algorithm. Although this algorithm is often used in the literature, it is known that it systematically overestimates the diameter in network structures. Thus, the need for further stiffening of the junction zones as proposed by the authors is in contradiction to the literature. Furthermore, the factor 40 appears to be one order of magnitude too high. We show that the 3D microstructures generated from random Gaussian fields contain features that are violating the assumption of circular cross-sections and, therefore, cannot be captured by the biggest sphere algorithm. Consequently, the authors required an unphysically high value of 40 to compensate this hidden effect.
In modern lexicography, a core distinction has been made between diachronic and synchronic dictionaries, and English dictionaries are no exception. In fact, English dictionaries are at the centre of this debate, since the Oxford English Dictionary, a landmark scholarly undertaking of the nineteenth century, is arguably the most successful exposition of the diachronic approach to dictionary making. While many other historical language dictionaries have modelled themselves on the OED, the development of a more theoretical basis for synchronic dictionaries was largely led by English language learner dictionaries in the late twentieth century. This chapter seeks to explain the distinctions between diachronic, or historical, dictionaries and their synchronic counterparts; how the distinction arose in English lexicography; what it means for those using or writing dictionaries; and, perhaps, why it’s important. While there is some underlying theoretical basis, the story of dictionaries is overwhelmingly one of practice, the findings are based on illustrative examples from English dictionaries throughout. In conclusion, there is an assessment of how meaningful the distinction continues to be today, and what changes we might expect to see in the future.
The CoCrNiMox (x = 0, 0.1, and 0.2 in molar ratio) medium entropy alloys (MEAs) were fabricated by vacuum arc melting, followed by cold rolling and annealing treatments. The X-ray diffraction (XRD), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) were employed to characterize the microstructures. It has been shown that the CoCrNi MEA has a single FCC phase and the Mo-containing MEAs contain (Cr, Mo)-rich σ precipitates. In addition, the Mo addition caused significant grain refinement, due to the fact that the presence of σ phase exerts a strong pinning effect on the grain boundary migration. The hardness testing results indicate an increment in Vickers hardness from 187.5 ± 4.5 Hv of CoCrNi alloy to 309.5 ± 10.3 Hv of CoCrNiMo0.2 alloy. The yield strength and ultimate tensile strength also increase from 339 ± 2 to 644 ± 5 MPa and from 810 ± 5 to 1071 ± 17 MPa, respectively, but the elongation drops from 88.4 ± 4.0% to 29.5 ± 7.6%. The grain refinement and the precipitation of σ phase make synergistic contribution to the reinforcement of Mo-containing CoCrNi-based MEAs. The details and explanations in this study may guide the future design and research of the CoCrNi-based quaternary alloys with enhanced properties.
Piezoelectric Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) has been found to be a competitive lead-free piezoceramic candidate and was prepared by a sol–gel technique due to its small particle size and homogeneous particle size distribution, but the sintering temperature is still quite high in the previous reports. In the present paper, lithium carbonate (Li2CO3) was used as a sintering aid and dopant for the sol–gel-derived piezoceramic powder, to facilitate the sintering process and adjust the densification, the microstructures and functional properties. With the addition of 0.5 wt% Li2CO3 sintered at 1300 °C, a high relative density 96% with piezoelectric coefficient d33 ~447 pC/N, planar coupling coefficient kp ~0.51, and Curie point TC ~98.7 °C was obtained. The way to properly define the critical changing points on temperature-dependent dielectric curves were further discussed. By altering sintering temperature and the amount of dopant, the mutual influence between the microstructures and the functional properties was explained, to further guide shaping BCZT in more complexed connectivities.
Meteorites have one of the most unique and beautiful microstructures, the Widmanstätten structure. This consists of large, elongated bands which form an intricate octahedral lace of crystalline metal. This structure makes meteorites an ideal case to demonstrate the capabilities of mechanical phase mapping using high-speed nanoindentation. In this work, the mechanical properties and composition of the Taza meteorite were mapped using ~100,000 indentations to statistically determine the properties of the individual phases. Five microstructural phases were characterized in this meteorite: Kamacite, Plessite, Tetrataenite, Cloudy Zone, and Schreibersite. Mechanical phase identification was confirmed using EDX measurements, and the first direct, point-to-point correlation of EDX and large-scale indentation maps was achieved. Mechanical phase maps showed superior phase contrast to EDX in two phases. An indentation property map or a mechanical phase map using a 2D histogram was used to visualize and statistically characterize the phases and identify trends in their relationships.
In this paper, CuCr–Zr alloys prepared by vacuum melting with adding La and Ni elementswere heat-treated and aged, followed by plastic deformation using low-energy cyclic impact tests, to simultaneously improve their mechanical and electrical properties. Results showed that the grain size of the casted Cu–Cr–Zr alloys was significantly reduced after the solid-solution aging and plastic deformation process. There were a lot of dispersed Cr and Cu5Zr precipitates formed in the alloys, and the numbers of dislocations were significantly increased. Accordingly, the hardness was increased from 78 to 232 HV, and the tensile strength was increased from 225 to 691 MPa. Electrical conductivity has not been significantly affected after these processes. The enhancement of overall performance is mainly attributed to the combined effects of solid-solution hardening, fine grain hardening, and precipitation/dislocation strengthening.
Military operations occurring in particle-laden environments have resulted in aircraft incidents and loss of life due to sand ingestion into the engine. Sand melts in the hot combustion environment and deposits as glassy calcia–magnesia–alumino–silicates (CMAS) which leads to rapid performance degradation due to clogged air pathways in the engine. A novel, composite thermal barrier coating (TBC) consisting of yttria-stabilized zirconia (YSZ) blended with gadolinia is proposed that combines the excellent thermo-mechanical properties of YSZ together with the CMAS resistance of rare-earth oxides. YSZ was blended with 2, 8, 17, and 32 vol% gadolinia and tested under simulated engine-relevant conditions. The presence of gadolinia in the composite coating reduced the adhesion of the CMAS, and at 32 vol% gadolinia addition, the CMAS was completely delaminated. A possible CMAS adhesion mitigating mechanism is discussed. This work demonstrated the capability of a new composite TBC to significantly reduce CMAS adhesion.
TiAl alloys are potential structural high-temperature structural materials at a service temperature of ~900 °C, while poor ductility at room temperature and high creep rate at the elevated temperature limits the applications. To improve the room-temperature and high-temperature mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr, Mo and B were introduced into this system and Ti–44Al–5Nb–3Cr–1.5Zr–xMo–yB alloys were proposed. And then, we, respectively, studied the microstructures and mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr–xMo–0B and Ti–44Al–5Nb–3Cr–1.5Zr–1Mo–yB to elucidate the role for the addition of Mo and B. It is found that Mo can increase the fraction of B2 phase in the alloys and the microstructures of the alloys are greatly refined by the addition of B. The compression test results indicate that Mo has a positive influence on the high-temperature compressive properties of TiAl-based alloys, whereas B addition can improve their room-temperature compressive properties of Ti–44Al–5Nb–3Cr–1.5Zr–1Mo–yB alloys; the morphology of borides in each sample should be the structural origin for these phenomena.
In this investigation, the superalloy IN718 has been prepared by additive manufacturing (AM) following a selective laser melting technique, and the post-AM heat treatments have been optimized. The microstructure of additively manufactured (AM) IN718 is characterized by the presence of dendritic and cellular features with large spatial heterogeneity along and across the build plane. Along the build direction, the 〈100〉 fiber texture dominates. Heat treatment involving two-step solution treatment, and subsequently, two-step aging treatment was specifically designed to facilitate the precipitation of δ phase at the grain boundaries to make the material resistant to grain boundary sliding (GBS). The AM IN718 showed dynamic strain aging (DSA) at three different temperatures, while the critical strain for the onset of serration was extended to a higher value after the heat treatment.
Metal additive manufacturing (AM) provides a platform for microstructure optimization via process control, but establishing a quantitative processing-microstructure linkage necessitates an efficient scheme for microstructure representation and regeneration. Here, we present a deep learning framework to quantitatively analyze the microstructural variations of metals fabricated by AM under different processing conditions. The principal microstructural descriptors are extracted directly from the electron backscatter diffraction patterns, enabling a quantitative measure of the microstructure differences in a reduced representation domain. We also demonstrate the capability of predicting new microstructures within the representation domain using a regeneration neural network, from which we are able to explore the physical insights into the implicitly expressed microstructure descriptors by mapping the regenerated microstructures as a function of principal component values. We validate the effectiveness of the framework using samples fabricated by a solid-state AM technology, additive friction stir deposition, which typically results in equiaxed microstructures.
The microstructure evolution, dynamic recrystallization (DRX) and precipitation of the ZM61 alloy sheets prepared with different rolling conditions were studied. The DRX grain sizes (dDRX) at four high strain rate rolling (HSRR) temperatures (275–350 °C) are 1.9, 2.3, 2.6 and 3.1 μm, respectively, while the DRX volume fractions (fVDRX) are 69, 73, 76 and 82%, respectively. 300 °C is selected as the optimal HSRR temperature. The dDRX and fVDRX of the alloys prepared by pre-rolling (PR) at 300 °C + HSRR are 1.0 μm and 91%, respectively. The PR treatment does not change the types of the precipitates but promotes the precipitation. The tensile strength (UTS) of 369 MPa and yield strength (YS) of 261 MPa can be achieved by HSRR at 300 °C, while a further increase in both UTS and YS can be obtained by PR treatment.