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At least 199 records · Page 11

Lamellae of α phase in a metastable β -Ti alloy studied by small-angle x-ray scattering

The shapes and orientations of lamellae of the hexagonal close-packed α phase in single crystals of the body-centred cubic β phase in a metastable β -Ti alloy (Timetal LCB) were investigated by synchrotron small-angle x-ray scattering. Several steps of thermal treatment with various annealing times and temperatures were employed. The measured scattering data were fitted to a model of ellipsoidal lamellae of random sizes, and the mean lamella shapes and orientations of their axes with respect to the β -Ti matrix were determined from the fit. The number and relative volume of the lamellae were estimated from the integrated scattered intensity. The elastic energy of the lamellae as well as the energy of defects at the α / β interface (misfit dislocations) were calculated from the parameters of the lamellae. In conclusion, the results provide information on the kinetics of the β $ \rightarrow$ α transformation in metastable β -Ti alloys and allow assessing the degree of thermodynamic equilibrium of the final α / β composite.

36 MATERIALS SCIENCE↗

Incorporating dynamic recrystallization into a crystal plasticity model for high-temperature deformation of Ti-6Al-4V

During hot deformation of (α + β) titanium alloys, the simultaneous action of strain and temperature in the (α + β) regime facilitates dynamic recovery, dynamic recrystallization (DRX), and phase transformations via non-equilibrium paths. DRX is manifested in the form of fine recrystallized α or β grains. Here, in the present study, a two-phase crystal plasticity finite element framework (CP-DRX) has been developed which incorporates DRX kinetics into the crystal plasticity (CP) model to predict the flow characteristics of Ti-6Al-4V alloys during thermo-mechanical processing. The CP slip system parameters, as well as elastic properties from both α and β phases of Ti, are calibrated for different strain rate conditions. An EBSD-informed two-phase microstructure representation has been utilized in the CP-DRX framework to explore the time-dependent evolution of DRX microstructure and crystal orientation for different strain rate conditions. The proposed CP-DRX can capture the evolution of crystal orientation and plastic flow stress–strain response of polycrystalline Ti-6Al-4V during the deformation process. Furthermore, the proposed model is able to capture the softening behavior, observed in average stress–strain response from experiments performed using a Gleeble thermomechanical simulator and predict the recrystallization texture.

(α+ β)-Titanium (Ti) Alloys↗

Materials Data on Ti(NO3)4 by Materials Project

Ti(NO3)4 is beta Sn-like structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four Ti(NO3)4 clusters. Ti4+ is bonded in a distorted hexagonal bipyramidal geometry to eight O2- atoms. There are a spread of Ti–O bond distances ranging from 2.09–2.12 Å. There are four inequivalent N5+ sites. In the first N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.20–1.32 Å. In the second N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.20–1.32 Å. In the third N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.20–1.32 Å. In the fourth N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.20–1.31 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the second O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the third O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the fifth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the sixth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the seventh O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the eighth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the ninth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the tenth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom. In the eleventh O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the twelfth O2- site, O2- is bonded in an L-shaped geometry to one Ti4+ and one N5+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ti(AlBr4)2 by Materials Project

Ti(AlBr4)2 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of two Ti(AlBr4)2 ribbons oriented in the (0, 0, 1) direction. Ti2+ is bonded to six Br1- atoms to form TiBr6 octahedra that share corners with two equivalent AlBr4 tetrahedra and edges with two equivalent AlBr4 tetrahedra. There are a spread of Ti–Br bond distances ranging from 2.71–2.73 Å. Al3+ is bonded to four Br1- atoms to form AlBr4 tetrahedra that share a cornercorner with one TiBr6 octahedra and an edgeedge with one TiBr6 octahedra. The corner-sharing octahedral tilt angles are 56°. There are a spread of Al–Br bond distances ranging from 2.27–2.38 Å. There are four inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a single-bond geometry to one Al3+ atom. In the second Br1- site, Br1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom. In the third Br1- site, Br1- is bonded in a bent 120 degrees geometry to one Ti2+ and one Al3+ atom. In the fourth Br1- site, Br1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ti(AlCl4)2 by Materials Project

Ti(AlCl4)2 crystallizes in the monoclinic P2_1/c space group. The structure is one-dimensional and consists of two Ti(AlCl4)2 ribbons oriented in the (1, 0, 0) direction. Ti2+ is bonded to six Cl1- atoms to form TiCl6 octahedra that share corners with two equivalent AlCl4 tetrahedra and edges with two equivalent AlCl4 tetrahedra. There are a spread of Ti–Cl bond distances ranging from 2.55–2.58 Å. Al3+ is bonded to four Cl1- atoms to form AlCl4 tetrahedra that share a cornercorner with one TiCl6 octahedra and an edgeedge with one TiCl6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Al–Cl bond distances ranging from 2.10–2.20 Å. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the second Cl1- site, Cl1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom. In the third Cl1- site, Cl1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom. In the fourth Cl1- site, Cl1- is bonded in a distorted bent 120 degrees geometry to one Ti2+ and one Al3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ti(AlCl4)2 by Materials Project

Ti(AlCl4)2 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of two Ti(AlCl4)2 ribbons oriented in the (0, 0, 1) direction. Ti2+ is bonded to six Cl1- atoms to form TiCl6 octahedra that share corners with two equivalent AlCl4 tetrahedra and edges with two equivalent AlCl4 tetrahedra. There are a spread of Ti–Cl bond distances ranging from 2.55–2.57 Å. Al3+ is bonded to four Cl1- atoms to form AlCl4 tetrahedra that share a cornercorner with one TiCl6 octahedra and an edgeedge with one TiCl6 octahedra. The corner-sharing octahedral tilt angles are 54°. There are a spread of Al–Cl bond distances ranging from 2.10–2.20 Å. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the second Cl1- site, Cl1- is bonded in a bent 120 degrees geometry to one Ti2+ and one Al3+ atom. In the third Cl1- site, Cl1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom. In the fourth Cl1- site, Cl1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ti(AlBr4)2 by Materials Project

Ti(AlBr4)2 crystallizes in the orthorhombic Pnn2 space group. The structure is one-dimensional and consists of two Ti(AlBr4)2 ribbons oriented in the (1, 0, 0) direction. Ti2+ is bonded to six Br1- atoms to form TiBr6 octahedra that share corners with two equivalent AlBr4 tetrahedra and edges with two equivalent AlBr4 tetrahedra. There are four shorter (2.70 Å) and two longer (2.73 Å) Ti–Br bond lengths. Al3+ is bonded to four Br1- atoms to form AlBr4 tetrahedra that share a cornercorner with one TiBr6 octahedra and an edgeedge with one TiBr6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Al–Br bond distances ranging from 2.27–2.37 Å. There are four inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a bent 120 degrees geometry to one Ti2+ and one Al3+ atom. In the second Br1- site, Br1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom. In the third Br1- site, Br1- is bonded in a single-bond geometry to one Al3+ atom. In the fourth Br1- site, Br1- is bonded in an L-shaped geometry to one Ti2+ and one Al3+ atom.

36 MATERIALS SCIENCE↗

Materials Data on Ti(FeSe2)2 by Materials Project

Ti(FeSe2)2 crystallizes in the triclinic P-1 space group. The structure is two-dimensional and consists of one Ti(FeSe2)2 sheet oriented in the (0, 0, 1) direction. Ti4+ is bonded to six Se2- atoms to form distorted TiSe6 octahedra that share corners with two equivalent FeSe5 trigonal bipyramids, edges with two equivalent TiSe6 octahedra, and faces with four equivalent FeSe5 trigonal bipyramids. There are a spread of Ti–Se bond distances ranging from 2.57–2.84 Å. Fe2+ is bonded to five Se2- atoms to form FeSe5 trigonal bipyramids that share a cornercorner with one TiSe6 octahedra, corners with two equivalent FeSe5 trigonal bipyramids, edges with three equivalent FeSe5 trigonal bipyramids, and faces with two equivalent TiSe6 octahedra. The corner-sharing octahedral tilt angles are 73°. There are a spread of Fe–Se bond distances ranging from 2.32–2.54 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to one Ti4+ and three equivalent Fe2+ atoms. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent Ti4+ and two equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗

Large room-temperature elastocaloric effect in a bulk polycrystalline Ni-Ti-Cu-Co alloy with low isothermal stress hysteresis

Creation of high-performance advanced elastocaloric materials is essential for the execution of elastocaloric refrigeration that can be an environment-friendly and high-efficiency substitute for the widely used traditional vapor-compression cooling technology. Here we have developed a bulk polycrystalline Ni-Ti-Cu-Co shape memory alloy exhibiting large elastocaloric effect, low stress hysteresis and room temperature working temperature, all of which are of great importance to and urgently demanded for high-efficiency room-temperature elastocaloric refrigeration. This newly developed (Ni 42.5 Ti 50 Cu 7.5 ) 99 Co 1 alloy shows a large room-temperature elastocaloric effect with directly measured adiabatic temperature change up to -14.4 K during unloading. The stress hysteresis of the isothermal superelastic stress-strain curve is as low as 60 MPa when the maximum tensile strain is 2.7%. Owing to the large elastocaloric effect and low stress hysteresis, a very high coefficient of performance up to 19 is achieved on the material level. This newly developed (Ni 42.5 Ti 50 Cu 7.5 ) 99 Co 1 alloy is a robust candidate for efficient elastocaloric refrigeration. Advanced in-situ synchrotron high-energy X-ray diffraction technique was employed to reveal the phase transformation sequence and to accurately determine the crystal structure of different phases, based on which the lattice compatibility between the transforming phases was evaluated and the phase transformation strain was predicted, providing in-depth fundamental understanding of the martensitic transformation in this newly developed alloy. This work could be useful for designing high-performance elastocaloric materials for solid-state cooling applications.

36 MATERIALS SCIENCE↗

Acoustic and electrical properties of Fe-Ti oxides with application to the deep lunar mantle

The overturn of titanium-rich mantle cumulates has been invoked to explain the structure and dynamics of the Moon. These dense cumulates are stable at the core-mantle boundary (CMB) and could explain field observations inferred from geophysical studies. Here, we report acoustic and electrical experiments on natural ilmenite-rutile aggregates up to 4.5 GPa and 1920 K. Seismic velocities show a weak pressure and temperature dependence, with Vs ~ 4.2 (+/-0.2) km/s and Vp ~8.0 (+/-0.2) km/s at the CMB conditions. Conductivity increases by a factor of 10 4 from 373 to 1920 K and is >10(3) S/m above 1573 K. Seismic and electrical models for the lunar mantle based on our results, considering mixtures of Fe-Ti oxides and olivine, indicate that field velocity and conductivity estimates are reproduced satisfactorily with 3-16 vol.% Fe-Ti oxides and 20 vol.% melt. Interactions between a Ti-rich, melt-bearing layer and the adjacent core likely affect the cooling and magnetic history of the Moon.

58 GEOSCIENCES↗

Microstructural effects on the rotating bending fatigue behavior of Ti–6Al–4V produced via laser powder bed fusion with novel heat treatments

The rotating bending fatigue (RBF) behavior (fully reversed, R = -1) of additively manufactured (AM) Ti–6Al–4V alloy produced via laser powder bed fusion (PBF-L) was investigated with respect to different microstructures achieved through novel heat treatments. The investigation herein seeks to elucidate the effect of microstructure by controlling variables that can affect fatigue behavior in Ti–6Al–4V, such as chemistry, porosity, and surface roughness. In order to control these variables, different hot isostatic pressing (HIP) treatments at 800 °C, 920 °C, and 1050 °C with a 920 °C temper were applied to three sets of Ti–6Al–4V cylinders that originated from the same PBF-L build, such that there were 30 tests per condition. After HIP treatment, the specimens were machined and tested. The highest runout stress was achieved after sub-β transus HIP at 800 °C for 2 h at 200 MPa of pressure. A significant drop in fatigue strength was attributed to large prior-β grains and grain boundary α resulting from super-β transus HIP treated specimens. In conclusion, for the sub-β transus HIP specimens, differences in fatigue strength were attributed to α lath thickness, relative dislocation density, and dislocation boundary strengthening.

36 MATERIALS SCIENCE↗

Modeling Ti–6Al–4V using crystal plasticity, calibrated with multi-scale experiments, to understand the effect of the orientation and morphology of the α and β phases on time dependent cyclic loading

Classically, crystal plasticity modeling has used a range of constitutive equations, in which the incorporation of additional physics-based relationships typically results in additional model parameters. These additional parameters need to be reliably calibrated, which often necessitates the use of a range of experimental data acquired at multiple length scales. In this work, a crystal plasticity based finite element (CPFE) model for a dual-phase Titanium alloy, Ti–6Al–4V, is developed. The α and β phases of the microstructure are explicitly modeled. The model is calibrated using a systematic optimization routine and experimental data that consist of macroscopic stress-strain curves coupled with lattice strains on different crystallographic planes for the two phases. These experimental data were obtained from in situ high energy X-ray diffraction experiments for multiple material pedigrees, with varying crystallographic orientation distribution and β volume fractions. Depending on the thermomechanical-processing route and the heat treatment used to manufacture the alloy, Ti–6Al–4V can exist in a wide number of microstructural forms, which often results in the α and β phases either having well aligned slip systems (following the Burgers orientation relationship (BOR)) or possessing no alignment of the slip systems across the interphase boundary (not following the BOR). In this study, the fully-calibrated CPFE model is used to gain a comprehensive understanding of the deformation behavior of Ti–6Al–4V, specifically, the effect of microstructures that follow the BOR (or not) on time-dependent cyclic loading (including the effects of dwell hold times).

36 MATERIALS SCIENCE↗

Boosting electrosynthesis of ammonia on surface-engineered MXene Ti 3 C 2

Seeking a breakthrough in the development of efficient nitrogen fixation catalysts has become the frontier of energy and chemical conversion schemes. In this work, we report that the MXene Ti 3 C 2 can serve as a promising catalyst for the electrochemical N 2 reduction reaction (NRR) under ambient conditions. The electrocatalytic performance of Ti 3 C 2 can be further optimized through surface engineering. Specifically, Ti 3 C 2 with the increased surface hydroxyl moieties demonstrates enhanced production of NH 3 with a yield rate of 1.71 μg h -1 cm -2 , a Faradaic efficiency of 7.01% at -0.2 V vs. RHE at 20 °C and an even higher yield rate of 12.46 μg h -1 cm -2 together with a Faradaic efficiency of 9.03% at -0.2 V vs. RHE at 60 °C. The detailed electrochemical analysis suggests that the surface hydroxyl modification can effectively facilitate the electron transfer, surface adsorption and activation of dinitrogen. Our work sheds light on the development of efficient NRR catalysts based on earth-abundant elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Presence of Delocalized Ti 3d Electrons in Ultrathin Single-Crystal SrTiO 3

Strontium titanate (STO), with a wide spectrum of emergent properties such as ferroelectricity and superconductivity, has received significant attention in the community of strongly correlated materials. In the strain-free STO film grown on the SrRuO 3 buffer layer, the existing polar nanoregions can facilitate room-temperature ferroelectricity when the STO film thickness approaches 10 nm. Here we show that around this thickness scale, the freestanding STO films without the influence of a substrate show the tetragonal structure at room temperature, contrasting with the cubic structure seen in bulk form. Further, the spectroscopic measurements reveal the modified Ti-O orbital hybridization that causes the Ti ion to deviate from its nominal 4+ valency (3d o configuration) with excess delocalized 3d electrons. Additionally, the Ti ion in TiO 6 octahedron exhibits an off-center displacement. The inherent symmetry lowering in ultrathin freestanding films offers an alternative way to achieve tunable electronic structures that are of paramount importance for future technological applications.

36 MATERIALS SCIENCE↗

Investigation of Bone Growth in Additive-Manufactured Pedicle Screw Implant by Using Ti-6Al-4V and Bioactive Glass Powder Composite

In this study, we optimized the geometry and composition of additive-manufactured pedicle screws. Metal powders of titanium-aluminum-vanadium (Ti-6Al-4V) were mixed with reactive glass-ceramic biomaterials of bioactive glass (BG) powders. To optimize the geometry of pedicle screws, we applied a novel numerical approach to proposing the optimal shape of the healing chamber to promote biological healing. We examined the geometry and composition effects of pedicle screw implants on the interfacial autologous bone attachment and bone graft incorporation through in vivo studies. The addition of an optimal amount of BG to Ti-6Al-4V leads to a lower elastic modulus of the ceramic-metal composite material, effectively reducing the stress-shielding effects. Pedicle screw implants with optimal shape design and made of the composite material of Ti-6Al-4V doped with BG fabricated through additive manufacturing exhibit greater osseointegration and a more rapid bone volume fraction during the fracture healing process 120 days after implantation, per in vivo studies.

stress-shielding effect↗

Influence of Ti‐incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous H 2 O 2

Abstract Vapor‐phase propylene (C 3 H 6 ) epoxidation kinetics with hydrogen peroxide (H 2 O 2 ) strongly reflects the physical properties of Ti‐incorporated zeolite catalysts and the presence of spectating molecules (“solvent”) near active sites even without a bulk liquid phase. Steady‐state turnover rates of C 3 H 6 epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH) x ) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CH 3 CN) molecules nearby active sites, under identical reaction mechanisms sharing activated H 2 O 2 intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring‐opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following C 3 H 6 epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CH 3 CN. Thus, higher PO selectivities achieved in hydrophilic Ti‐MFI at steady‐state reflect the preferential stabilization of transition states for C 3 H 6 epoxidation (a primary reaction) relative to PO ring‐opening and oxidative cleavage (secondary reactions) that solvation effects that reflect interactions among condensed CH 3 CN within pores and the extended pore structure.

Kwon, Ohsung↗

Influence of Ti‐incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous H 2 O 2

Vapor-phase propylene (C 3 H 6 ) epoxidation kinetics with hydrogen peroxide (H 2 O 2 ) strongly reflects the physical properties of Ti-incorporated zeolite catalysts and the presence of spectating molecules (“solvent”) near active sites even without a bulk liquid phase. Steady-state turnover rates of C 3 H 6 epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH) x ) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CH 3 CN) molecules nearby active sites, under identical reaction mechanisms sharing activated H 2 O 2 intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring-opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following C 3 H 6 epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CH 3 CN. Thus, higher PO selectivities achieved in hydrophilic Ti-MFI at steady-state reflect the preferential stabilization of transition states for C 3 H 6 epoxidation (a primary reaction) relative to PO ring-opening and oxidative cleavage (secondary reactions) that solvation effects that reflect interactions among condensed CH 3 CN within pores and the extended pore structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Free‐Standing α‐MoO 3 / Ti 3 C 2 MXene Hybrid Electrode in Water‐in‐Salt Electrolytes

While transition‐metal oxides such as α‐MoO 3 provide high capacity, their use is limited by modest electronic conductivity and electrochemical instability in aqueous electrolytes. Two‐dimensional (2D) MXenes, offer metallic conductivity, but their capacitance is limited in aqueous electrolytes. Insertion of partially solvated cations into Ti 3 C 2 MXene from lithium‐based water‐in‐salt (WIS) electrolytes enables charge storage at positive potentials, allowing a wider potential window and higher capacitance. Herein, we demonstrate that α‐MoO 3 /Ti 3 C 2 hybrids combine the high capacity of α‐MoO 3 and conductivity of Ti 3 C 2 in WIS (19.8 m LiCl) electrolyte in a wide 1.8 V voltage window. Cyclic voltammograms reveal multiple redox peaks from α‐MoO 3 in addition to the well‐separated peaks of Ti 3 C 2 in the hybrid electrode. This leads to a higher specific charge and a higher rate capability compared to a carbon and binder containing α‐MoO 3 electrode. These results demonstrate that the addition of MXene to less conductive oxides eliminates the need for conductive carbon additives and binders, leads to a larger amount of charge stored, and increases redox capacity at higher rates. In addition, MXene encapsulated α‐MoO 3 showed improved electrochemical stability, which was attributed to the suppressed dissolution of α‐MoO 3 . The work suggests that oxide/MXene hybrids are promising for energy storage.

36 MATERIALS SCIENCE↗