Beta Phase Research Articles

Anharmonic Effects on the Thermodynamic Properties of Quartz from First Principles Calculations.

The simple chemistry and structure of quartz together with its abundance in nature and its piezoelectric properties make convenient its employment for several applications, from engineering to Earth sciences. For these purposes, the quartz equations of state, thermoelastic and thermodynamic properties have been studied since decades. Alpha quartz is stable up to 2.5 GPa at room temperature where it converts to coesite, and at ambient pressure up to 847 K where it transforms to the beta phase. In particular, the displacive phase transition at 847 K at ambient pressure is driven by intrinsic anharmonicity effects (soft-mode phase transition) and its precise mechanism is difficult to be investigated experimentally. Therefore, we studied these anharmonic effects by means of ab initio calculations in the framework of the statistical thermodynamics approach. We determined the principal thermodynamic quantities accounting for the intrinsic anharmonicity and compared them against experimental data. Our results up to 700 K show a very good agreement with experiments. The same procedures and algorithms illustrated here can also be applied to determine the thermodynamic properties of other crystalline phases possibly affected by intrinsic anharmonic effects, that could partially invalidate the standard quasi-harmonic approach.

Property Improvement of Additively Manufactured Ti64 by Heat Treatment Characterized by In Situ High Temperature EBSD and Neutron Diffraction

Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free of the preferred orientation of the α-Ti phase as well as a low beta phase fraction of ∼1 wt%. However, when further heat treatment of up to 1050 ∘C was applied to the material in our previous study, a strong texture aligning the hexagonal basal plane of α phase with the build direction and about 6% β phase appeared at room temperature. In this study, to understand the mechanism of this heat treatment, the grain level microstructure of the additively manufactured Ti-6Al-4V was investigated using in situ high temperature EBSD up to 1000 ∘C, which allows the tracking of individual grains during a heat cycle. As a result, we found a random texture originating from the fine grains in the initial material and observed a significant suppression of α phase nucleation in the slow cooling after heating to 950 ∘C within the α and β dual phase regime but close to the the β-transus temperature at ∼980 ∘C, which led to a coarse microstructure. Furthermore, the texture resulting from phase transformation of the additively manufactured Ti-6Al-4V assuming nucleation at the grain boundaries was modeled, using the double Burgers orientation relationship for the first time. The model successfully reproduced the measured texture, suggesting that the texture enhancement of the α phase by the additional heat treatment derives also from the variant selection during the phase transformation and nucleation on grain boundaries.

Chemical solution deposition of epitaxial indium- and aluminum-doped Ga2O3 thin films on sapphire with tunable bandgaps

Compared to the vacuum-required deposition techniques, the chemical solution deposition (CSD) technique is superior in terms of low cost and ease of cation adjustment and upscaling. In this work, highly epitaxial indium- and aluminum-doped Ga2O3 thin films are deposited using a novel CSD technique. The 2θ, rocking curve, and φ-scan modes of x-ray diffraction (XRD) measurements and high-resolution transmission electron microscopy suggest that these thin films have a pure beta phase with good in- and out-of-plane crystallization qualities. The effect of incorporating indium and aluminum into the crystallization process is studied using high-temperature in situ XRD measurements. The results indicate that indium and aluminum doping can shift the crystallization of the thin films to lower and higher temperatures, respectively. Additionally, ultraviolet-visible spectroscopy measurements indicate that the bandgap of the sintered thin films can be tuned from 4.05 to 5.03 eV using a mixed precursor solution of In:Ga = 3:7 and Al:Ga = 3:7. The photodetectors based on the (InGa)2O3, pure Ga2O3, and (AlGa)2O3 samples exhibit the maximum photocurrents at 280, 255, and 230 nm, respectively. The results suggest that the described CSD technique is promising for producing high-quality bandgap tunable deep-ultraviolet photoelectrical and high-power devices.

Piezoelectric Properties of PVDF-Zn2GeO4 Fine Fiber Mats

The current paper presents the development and characterization of polyvinylidene fluoride (PVDF)-Zn2GeO4 (ZGO) fine fiber mats. ZGO nanorods (NRs) were synthesized using a hydrothermal method and incorporated in a PVDF solution to produce fine fiber mats. The fiber mats were prepared by varying the concentration of ZGO NRs (1.25–10 wt %) using the Forcespinning® method. The developed mats showed long, continuous, and homogeneous fibers, with average fiber diameters varying from 0.7 to 1 µm, depending on the ZGO concentration. X-ray diffraction spectra depicted a positive correlation among concentration of ZGO NRs and strengthening of the beta phase within the PVDF fibers. The composite system containing 1.25 wt % of ZGO displayed the highest piezoelectric response of 172 V. This fine fiber composite system has promising potential applications for energy harvesting and the powering of wearable and portable electronics.

Phase and power modulations on the amplitude of TMS-induced motor evoked potentials.

The evaluation of transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) promises valuable information about fundamental brain related mechanisms and may serve as a diagnostic tool for clinical monitoring of therapeutic progress or surgery procedures. However, reports about spontaneous fluctuations of MEP amplitudes causing high intra-individual variability have led to increased concerns about the reliability of this measure. One possible cause for high variability of MEPs could be neuronal oscillatory activity, which reflects fluctuations of membrane potentials that systematically increase and decrease the excitability of neuronal networks. Here, we investigate the dependence of MEP amplitude on oscillation power and phase by combining the application of single pulse TMS over the primary motor cortex with concurrent recordings of electromyography and electroencephalography. Our results show that MEP amplitude is correlated to alpha phase, alpha power as well as beta phase. These findings may help explain corticospinal excitability fluctuations by highlighting the modulatory effect of alpha and beta phase on MEPs. In the future, controlling for such a causal relationship may allow for the development of new protocols, improve this method as a (diagnostic) tool and increase the specificity and efficacy of general TMS applications.

Rapid dynamic transformation in the initial stage of hot deformation of a near alpha titanium alloy

The peak flow stress of a near alpha high temperature titanium alloy exhibits a special rapid drop behavior at low strain during hot compression. The experimental result indicates that this rapid drop of peak flow stress is related to the rapid dynamic transformation from alpha phase into beta phase which is induced by the deformation at elevated temperature. Both peak flow stress and the dynamic transformation change with different hot deformation parameters, and the drop of peak flow stress keeps almost consistent variation with the evolution of dynamic transformation observed from the microstructural morphology. The higher deformation temperature and the lower strain rate with the small increase of strain are beneficial to accelerate the dynamic transformation and the drop of peak flow stress. The dynamic transformation is mainly controlled by the immigration of alpha/beta interface shrinking from edge to center of equiaxed alpha phase or the penetration of beta phase into alpha phase from edge to inside.

Effects of non-electrical parameters on profile accuracies and surface characteristics during wire-EDM of titanium alloy

Wire lag plays a major role in causing inaccuracies in certain geometrical shapes and profiles during machining of complex structures using wire-EDM. While previous studies focused on investigating effects of electrical parameters on machining performance and accuracy during wire EDM, the effects of non-electrical parameters on corner and profile accuracies have not been studied comprehensively. The objective of this study is to investigate effects of non-electrical parameters on the geometric and profile accuracies as well as surface and subsurface characteristics during WEDM of Ti-6Al-4V alloy. A complex part including corners with 45°, 90°, and 112.5° as well as thin wall section for measuring the kerf accuracy was designed. It is found that the profile accuracy improves as the wire tension increases. However, too high wire tension results in curved path in the sharp corners. The effect of wire tension is more pronounced on the workpiece with higher thickness. Too high wire feed rate reduces the accuracy for target angles, especially for lower thickness of workpiece. The kerf width is smaller for thinner workpiece and improves with lower wire feed rate and wire tension. While the wire tension and wire feed rate do not have an impact on surface roughness, higher surface feed rate increases surface roughness. Higher wire tensions lead to higher surface cracking due to more rapid cooling. With increase of surface feed, the percentage of arcing pulses increases due to increased instability, which results in rougher surface and increased percentage of beta phases at the subsurface.

Physical Co-location: an intersection of problem-solving and vicarious learning

ABSTRACT Scholars have examined Revans' problem-solving praxeology in many contexts but have not fully explored the concept in the case of physical co-location. Hence, we focussed on investigating Revans' conceptualisation in a co-located context by paying particular attention to the ‘different forms of learning' that emerged from it. The research setting for this study involved two coworking spaces in Bangalore, India, whose constituents were co-located start-ups and established enterprises. Held from January to March 2020, the study involved conducting exploratory, semi-structured interviews with twelve firms. The findings suggested that in a co-located environment, a) firms learnt ‘vicariously' from a rich, external knowledge base during the enquiry-led Alpha phase b) firms learnt ‘experientially', through learning by doing and reflecting in the implementation-focussed Beta phase c) firms learnt through the process of ‘emergence’ that resulted from personal reflection and team interaction, in the revelatory Gamma phase. This study lends a novel direction in acknowledging that vicarious learning, that is, learning through the experience of others, serves as a starting point for problem-solving in a co-located context. We demonstrate that firms gain familiarity with the problem through vicarious sources, that is, from those experienced co-located firms who had journeyed on a similar path.

Properties Improvement of Spark Plasma Sintered Ti-7Al-1Mo Ternary Alloy by TiN Nanoparticles Addition

Titanium (Ti) alloys are materials of interest in structural and chemical applications due to their low density, outstanding mechanical and chemical resistance properties. However, the mechanical properties still need to be enhanced to make them suitable as a replacement for Ni-based superalloys. There have been significant breakthroughs in the reinforcement of Ti alloy with a small weight percentage (wt.%) of ceramics. This work investigates the effect of TiN nanoparticles’ addition on the densification, phase transformation, microstructure, hardness, and compressive properties of Ti-7Al-1Mo ternary alloy. 3 wt.% of TiN nanoparticles was blended with Ti-7Al-1Mo powder, and the resulting admixed powder was consolidated via spark plasma sintering technique at 50 MPa pressure, 10 min holding time, and 1000 °C temperature. Scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry were used to characterise the microstructure and phase composition respectively. The microstructure of Ti-7Al-1Mo revealed a lamellar structure with alpha (α) phase and minor beta (β) phase with visible grain boundaries, while TiN reinforced Ti-7Al-1Mo composite microstructure shows a bimodal structure with reduction in the lamellar structure. Ti-7Al-1Mo ternary alloy has a hardness value of 352±17 HV0.1 and a compressive yield strength of 985±31 MPa. The composite shows an increment of 74 HV and 323 MPa in its hardness and compressive yield strength respectively in comparison to the ternary alloy.

Study of titanium oxidation kinetics at temperature above polymorphic transformation

The object of research is the analytical description of the phenomena in the near-surface layer, which are caused by the interaction of titanium with oxygen at high temperatures. These are temperatures that exceed the polymorphic transformation of the metal. High-temperature oxidation gives titanium products unique performance properties. Of course, such characteristics are determined, first of all, by the state of the near-surface layer. Therefore, an understanding of oxidation processes will make it possible to predict the state of the near-surface layer after heat treatment. However, to date, no unified approach has been created to describe the mechanism and kinetics of high-temperature oxidation of titanium in the near-surface layer. Indeed, most of the existing approaches make it possible to predict the nature of oxidation in the bulk of the metal. Some scientific papers describe the kinetics of oxidation, taking into account only the formation and growth of oxide layers. However, simultaneously with oxide formation, a diffusion zone is formed, which significantly affects the kinetics. Therefore, today one of the most problematic areas of high-temperature titanium oxidation is the description of the processes that take place in the near-surface layer. In this work, to describe the kinetics of high-temperature oxidation of titanium, in addition to the formation and growth of the oxide layer, the formation and growth of the diffusion zone is taken into account. In the diffusion zone, under the influence of structural phase transformations, solid solutions of oxygen are formed in the alpha and beta phases. This approach made it possible to take into account additional factors and thereby more accurately describe the processes of high-temperature oxidation of titanium. As a result of the calculations, the thickness of the oxide layer of the diffusion zone is given depending on the oxygen concentration and the duration of treatment. And also the dependences of the kinetics of displacement of the boundary of the oxide-diffusion layer are given and a system of equations for calculating the ratio of the formed phase components is developed. Thanks to the proposed analytical approach, it will be possible to calculate the sizes of interphase boundaries on the basis of temperature-time parameters and oxygen concentration and thereby form a hardened near-surface layer with certain functional properties

P 59. Real-time prefrontal beta phase estimation during emotional interference inhibition

Previous studies suggest a common brain network including the right inferior frontal gyrus and pre-supplementary motor area integral to various types of emotional interference inhibition, i.e. suppression of task-irrelevant stimuli to pursue goal-directed behavior in the context of emotional distraction. This network reacts differently to emotional interference in individual subjects and exhibits a specific spectral signature in the beta-band. Here we analyze 64 channel surface EEG data during emotional interference inhibition operationalized by a Flanker task with preceding emotionally salient stimuli to determine “true phase” estimates and perform real-time (predictive) phase estimation of task-related beta-band oscillations. EEG data was spectrally analyzed, signal-to-noise ratios (SNRs) of periodic components of the power spectra calculated, and non-causal phase estimations (i.e. using data extending both directions around the time point of interest) performed to yield “true phase” estimates of task-related beta oscillations after Flanker signal presentation. Causal phase estimation of task-related EEG beta oscillations was achieved using an autoregressive forward prediction algorithm on data preceding the time point of interest only. Results show that real-time (i.e. causal) phase estimation of beta oscillations in the emotional Flanker task is feasible with satisfactory circular deviations of “true phase” estimates, but needs individual optimization of phase estimation parameters (i.e. window size [samples], FIR filter order, number of samples removed at data window edge, order of the autoregressive model). Findings have implications for the design of real-time EEG-triggered brain oscillation-synchronized TMS experiments to causally study the role of task-related beta-band activity for emotional interference inhibition. This study was supported by the Boehringer Ingelheim Foundation.“

Growth of spherical carbon nitride with crystalline alpha and beta phases

Carbon is a versatile element, and its allotropes play a center role in both science and technology. Further, doping of nitrogen into carbon network has been of great interest as it leads to superior properties such as chemical, mechanical and electronic properties. Though the preparation of ultrahard β-carbon nitride remains challenging one, it owes great attention due to its superior properties. This work reports preparation and characterization of crystalline carbon nitride on silicon (100) substrate. The X-Ray diffraction revealed that the deposited film- have α and β carbon nitride crystalline phases. The calculated lattice parameters are found to be a = 6.26 Å, c = 2.38 Å for β-C3N4 and a = 6.8 Å, c = 4.6 Å for α-C3N4. The X-Ray photoelectron spectroscopy study confirms that carbon atom is bonded tetrahedrally (sp3) with nitrogen atoms as expected for the formation of crystalline C3N4, and also the presence of C = N trigonal (sp2) bond. The surface morphology of the film examined by field emission scanning electron microscopy shows the formation of carbon nitride spheres.

Structural Factors Inducing Cracking of Brass Fittings.

Cu–Zn–Pb brasses are popular materials, from which numerous industrially and commercially used components are fabricated. These alloys are typically subjected to multiple-step processing—involving casting, extrusion, hot forming, and machining—which can introduce various defects to the final product. The present study focuses on the detailed characterization of the structure of a brass fitting—i.e., a pre-shaped medical gas valve, produced by hot die forging—and attempts to assess the factors beyond local cracking occurring during processing. The analyses involved characterization of plastic flow via optical microscopy, and investigations of the phenomena in the vicinity of the crack, for which we used scanning and transmission electron microscopy. Numerical simulation was implemented not only to characterize the plastic flow more in detail, but primarily to investigate the probability of the occurrence of cracking based on the presence of stress. Last, but not least, microhardness in specific locations of the fitting were examined. The results reveal that the cracking occurring in the location with the highest probability of the occurrence of defects was most likely induced by differences in the chemical composition; the location the crack in which developed exhibited local changes not only in chemical composition—which manifested as the presence of brittle precipitates—but also in beta phase depletion. Moreover, as a result of the presence of oxidic precipitates and the hard and brittle alpha phase, the vicinity of the crack exhibited an increase in microhardness, which contributed to local brittleness.

Microstructural and high-temperature cyclic oxidation response of NiCoCrAlY coatings with and without SiC + ZrB2 reactive-element dispenser

In this study, the microstructural and cyclic-oxidation evolution behavior of bond coats (BC) containing SiC + ZrB2 dispersed particles were evaluated. The SiC + ZrB2 dispersed particles at the oxidation temperature of 1130 °C, dissolved at early stages, stabilizing the beta phase, diminishing the aluminum outward diffusion. The silicon at the BC/TC interface, or very close to it, behaved as a reactive element promoting the rapid formation and stabilization of α-Al2O3 (TGO), and a second scale layer of mixed oxides and silicon-rich compounds, jointly limiting inward oxygen diffusion and resulting in thinner TGO layers, whose kinetic oxidation follows a sub-parabolic behavior, increasing oxidation life-span.

Structural analysis of a Nb-based alloy for biomedical application

The purpose of research in the biomaterials field is to produce new materials with physical and chemical properties close to the tissue to be replaced with minimal toxic response to the foreign body. Among the various metallic materials, titanium and its alloys have this great combination of properties. The most promising alloys are those with niobium, molybdenum, tantalum, and zirconium as alloying elements added to titanium. Thus, this kind of alloys integrate a new class of alloys without aluminum and vanadium (which cause cytotoxicity) and have a low modulus of elasticity (below 100 GPa). The objective of this work is to analyze the structure and microstructure of a niobium-based alloy, Ti-50wt%Nb. This alloy was produced in an arc-melting furnace with an inert atmosphere of argon gas. After melting, the samples were characterized by density, X-ray diffraction, scanning electron microscopy, and hardness. The X-ray diffraction data shows the peaks corresponding to the beta phase (with body-centered cubic crystalline structure), corroborated by scanning electron microscopy images. The value of the lattice parameter of the body-centered cubic crystalline structure was 3.2868 Å.

Implementation Dijkstra’s Algorithm for Non-Players Characters in the Game Dark Lumber

Forest is a unitary ecosystem in the form of a stretch of land containing biological natural resources dominated by trees in their natural environment, which cannot be separated from one another. The importance of forest preservation is based on law, namely ensuring the existence of forests in a sustainable manner while maintaining sustainability and not destroying the environment and the surrounding ecosystem. However, public awareness in preserving the forest is still lacking. Therefore, technology is needed that can provide information about forests and the impact of illegal logging in an attractive manner. Games are multimedia entertainment that is made as attractive as possible. Action games require players to concentrate and think quickly in order to avoid obstacles. Dijkstra’s algorithm looks for the shortest path in a number of steps from which each step selects the minimum weighted value and enters it into the set of solutions. Dijkstra’s algorithm implemented on non-player characters in a game to determine the shortest path to the target player. Games built using unity and developed using the Game Development Life Cycle (GDLC) method. GDLC is a game development process that applies an iterative approach consisting of 6 development phases, starting from the initialization or concept creation, preproduction, production, testing, beta and release phases.

Full Utilization of Lithium Trivandate (Li1.1V3O8) in Thick Porous Electrodes with High Rate Capacity upon Extended Cycling Elucidated Via Operando Energy Dispersive X-Ray Diffraction

Newer, more demanding energy storage systems require high energy density along with high power and fast charge rates. Conventional battery electrode fabrication techniques are often limited by how much active material they can hold in the case of slurry-cast electrodes and how much of the electrode can be utilized in the case of dense pelletized electrodes. Thick porous electrode fabrication techniques have been developed as a way to obtain a higher active mass loading and an architecture which enables ionic and electronic transport. The homogeneity of the phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a fast rate of 1C revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated homogenous lithiation across the electrode upon discharge at 1C consistent with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. The absence of the beta phase peaks in the EDXRD over extended cycling are consistent with electrochemical accessibility of only part of the active material. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

Fatigue crack growth behavior and fracture model of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded joints

Fatigue crack growth behavior of the hydrogenated Ti-0.3Mo-0.8Ni alloy gas tungsten arc welded (GTAW) joints was investigated. Fracture model of hydrogen-induced GTAW joint was revealed in details. The results show that as hydrogen level increased, crack growth rate in Paris and instability growth zones increased, the more the hydride, the more crack growth channels, the faster crack growth rate, and brittle fracture was intensified. There was the mutation of dislocation density on both sides of the hydride, and dislocation tangles and dislocation lines were concentrated in the vicinity of the hydride. Dislocation weakening caused by solute hydrogen and internal stress generated by hydrogen-rich clusters respectively promoted crack initiation. Evolution of hydride morphology and distribution caused by the interaction between the hydride and persistent slip bands (PSB) significantly reduced crack initiation resistance. Hydride inside the PSB as a hardening phase accelerated to separate from the matrix or itself fracture, which further promoted crack initiation. Cracks in Paris zone rapidly propagated along grain boundary of coarse size “cluster”, alpha / beta phase boundary and the hydride, or cut through alternating lamellar alpha and fine needle beta grains and the hydride.

Movement-related changes in pallidocortical synchrony differentiate action execution and observation in humans

ObjectiveSuppression of local and network alpha and beta oscillations in the human basal ganglia-thalamocortical (BGTC) circuit is a prominent feature of movement, including suppression of local alpha/beta power, cross-region beta phase coupling, and cortical and subcortical phase-amplitude coupling (PAC). We hypothesized that network-level coupling is more directly related to movement execution than local power changes, given the role of pathological network hypersynchrony in movement disorders such as Parkinson disease (PD). Understanding the specificity of these movement-related signals is important for designing novel therapeutics. MethodsWe recorded globus pallidus internus (GPi) and motor cortical local field potentials during movement execution, passive movement observation and rest in 12 patients with PD undergoing deep brain stimulator implantation. ResultsLocal alpha/beta power is suppressed in the globus pallidus and motor cortex during both action execution and action observation, although less so during action observation. In contrast, pallidocortical phase synchrony and GPi and motor cortical alpha/beta-gamma PAC are suppressed only during action execution. ConclusionsThe functional dissociation across tasks in pallidocortical network activity suggests a particularly important role of network coupling in motor execution. SignificanceNetwork level recordings provide important specificity in differentiating motor behavior and may provide significant value for future closed loop therapies.

Effect of microstructure, texture and deformation behavior on tensile properties of electrically assisted friction stir welded Ti-6Al-4 V joints

The effect of electric current on microstructure, texture, deformation behavior and tensile properties were investigated for the electrically assisted friction stir welding process of Ti-6Al-4 V alloy. The base material has strong prismatic texture {101¯0} < 112¯0 > linked to strong prismatic <a > slip system {101¯0} < 112¯0>. Texture of the stir zone is randomly distributed with the weak basal {0001} < 112¯0 > texture owing to {101¯2} < 101¯1 > twinning. The introduction of current into the welding process has resulted in the alleviation of the abrupt change of microstructure between the surface, center and bottom of the stir zone, the decrease in texture strength and more uniformly distributed strain. The improvement of tensile properties without loss of ductility for the electrically assisted joints was mainly attributed to microstructure and strain homogeneity, beta phase dissolution and random orientations.