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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Hydrogen-enabled microstructure and fatigue strength engineering of titanium alloys

Traditionally, titanium alloys with satisfactory mechanical properties can only be produced via energy-intensive and costly wrought processes, while titanium alloys produced using low-cost powder metallurgy methods consistently result in inferior mechanical properties, especially low fatigue strength. Herein, we demonstrate a new microstructural engineering approach for producing low-cost titanium alloys with exceptional fatigue strength via the hydrogen sintering and phase transformation (HSPT) process. The high fatigue strength presented in this work is achieved by creating wroughtlike microstructures without resorting to wrought processing. This is accomplished by generating an ultrafine-grained as-sintered microstructure through hydrogen-enabled phase transformations, facilitating the subsequent creation of fatigue-resistant microstructures via simple heat treatments. Finally, the exceptional strength, ductility, and fatigue performance reported in this paper are a breakthrough in the field of low-cost titanium processing.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Friction and wear of titanium alloys and copper alloys sliding against titanium 6-percent-aluminum - 4-percent-vanadium alloy in air at 430 C

Experiments were conducted to determine the friction and wear characteristics of aluminum bronzes and copper-tin, titanium-tin, and copper-silver alloys sliding against a titanium-6% aluminum-4% vanadium alloy (Ti-6Al-4V). Hemispherically tipped riders of aluminum bronze and the titanium and copper alloys were run against Ti-6Al-4V disks in air at 430 C. The sliding velocity was 13 cm/sec, and the load was 250 g. Results revealed that high tin content titanium and copper alloys underwent significantly less wear and galling than commonly used aluminum bronzes. Also friction force was less erratic than with the aluminum bronzes.

Wisander, D. W.↗
DOE OSTI2019

Equilibrium of [Si]/(SiO{sub 2}) in Carbothermic Selective Reduction of Titanium Concentrate Ore for the Preparation of Titanium Oxycarbide

Carbothermic selective reduction of titanium concentrate ore for the preparation of titanium oxycarbide was presented and SiO{sub 2} was found to be partly reduced during the process. The equilibrium relationship between Si dissolved in metallic Fe and SiO{sub 2} existed in corresponding slag was analyzed thermodynamically, and then revealed by a series of designed equilibration experiments. The results are in accordance with the calculated values obtained from thermodynamic analysis and have well explained the phenomenon that part of SiO{sub 2} is reduced during selective reduction processing of titanium concentrate ore.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In-situ Experiments to Capture the Evolution of Microstructure During Phase Transformation of Titanium Under Dynamic Loading

Under sufficient stresses, such as during dynamic loading, titanium experiences a phase transformation from hcp alpha phase to hexagonal omega phase. Omega phase is often retained in the microstructure after unloading, and has a strong influence on subsequent mechanical properties. Simulations suggest there are multiple pathways and underlying mechanisms for this transformation. Due to the incredibly short timescales involved, experimental measurements for model validation have been difficult. However, new capabilities at the Advanced Photon Source have enabled diffraction measurements during plate impact experiments to study the evolution of titanium during transformation. These high-rate data allow us to probe the mechanism and kinetics of phase transformations in new ways. Recent results will be presented and compared to post-mortem characterization of soft-recovered shocked specimens. Comparisons are then made with previous tests where material was shock-loaded and soft recovered for microstructural analysis. Together these techniques create a consistent picture of material behavior during the shock-induced α–ω phase transformation in titanium.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Nitriding of titanium and titanium: 8 percent aluminum, 1 percent molybdenum, 1 percent vanadium alloy with an ion-beam source

Titanium and Ti-8Al-1Mo-1V alloy were nitrided with an ion-beam source of nitrogen or argon and nitrogen at a total pressure of 2 x 10 to the minus 4th power to 10 x 10 to the minus 4th power torr. The treated surface was characterized by surface profilometry, X-ray diffractometry, Auger electron spectroscopy and microhardness measurements. The tetragonal Ti2N phase formed in pure titanium and Ti-8Al-1Mo-1V alloy with traces of AlN in the alloy. Two opposite processes competed during the ion-beam-nitriding process: (1) formation of nitrides in the surface layer and (2) sputtering of the nitrided layers by the ion beam. The highest surface hardnesses, about 500 kg/sq mm in titanium and 800 kg/sq mm in Ti-8Al-1Mo-1V, were obtained by ion nitriding with an ion beam of pure nitrogen at 4.2 x 10 to the minus 4th power torr at a beam voltage of 1000 V.

Gill, A.↗
DOE OSTI2020

Tensile behavior of dual-phase titanium alloys under high-intensity proton beam exposure: radiation-induced omega phase transformation in Ti-6Al-4V

A high-intensity proton beam exposure with 181 MeV energy has been conducted at Brookhaven Linac Isotope Producer facility on various material specimens for accelerator targetry applications, including titanium alloys as a beam window material. The radiation damage level of the analyzed capsule was 0.25 dpa at the beam center region with an irradiation temperature around 120 oC. Tensile tests showed increased hardness and a large decrease in ductility for the dual a+ß-phase Ti-6Al-4V Grade-5 and Grade-23 extra low interstitial alloys, with the near a-phase Ti-3Al-2.5V Grade-9 alloy still exhibiting uniform elongation of a few % after irradiation. Transmission Electron Microscope analyses on Ti-6Al-4V indicated clear evidence of a high-density of defect clusters with size less than 2 nm in each a-phase grain. The ß-phase grains did not contain any visible defects such as loops or black dots, while the diffraction patterns clearly indicated ?-phase precipitation in an advanced formation stage. The radiation-induced ?-phase transformation in the ß-phase could lead to greater loss of ductility in Ti-6Al-4V alloys in comparison with Ti-3Al-2.5V alloy with less ß-phase.google scho

Tensile Test, titanium, acclerator, proton beam↗
DOE OSTI2019

Effects of Synthesis and Processing on Optoelectronic Properties of Titanium Carbonitride MXene

MXenes, a relatively new class of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides, exhibit unique properties such as high electronic conductivity, a wide range of optical characteristics, hydrophilicity, and mechanical stability. Because of the high electronic conductivity, MXenes have shown promise in many applications, such as energy storage, electromagnetic interference shielding, antennas, and transparent coatings. 2D titanium carbide (Ti 3 C 2 T x , where T x represents surface terminations), the first discovered and most studied MXene, has the highest electronic conductivity exceeding 10 000 S cm –1 . There have been several efforts to alter the conductivity of MXenes, such as manipulation of the transition-metal layer and control of surface terminations. However, the impact of the C and N site composition on electronic transport has not been explored. In this study, the effects of synthesis methods on optoelectronic properties of 2D titanium carbonitride, Ti 3 CNT x , were systematically investigated. We show that Ti 3 CNT x , which hosts a mix of carbon and nitrogen atoms in the X layer, has lower electronic conductivity and a blue shift of the main absorption feature within the UV–visible spectrum, compared to Ti 3 C 2 T x . Moreover, intercalants such as water and tetraalkylammonium hydroxides decrease the electronic conductivity of MXene due to increased interflake resistance, leading to an increase in resistivity with decreasing temperature as observed in ensemble transport measurements. When the intercalants are removed, Ti 3 CNT x exhibits its intrinsic metallic behavior in good agreement with Hall measurements and transport properties measured on single-flake field-effect transistor devices. Finally, the dependence of conductivity of Ti 3 CNT x on the presence of intercalants opens wide opportunities for creating MXene-based materials with tunable electronic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature

Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: $\langle$0001$\rangle$ hcp|| $\langle$001$\rangle$ fcc and {$10\bar{1}0$} hcp|| {110} fcc , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pureshuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Structural elucidation of a mononuclear titanium methylidene

The first example of a structurally characterized titanium methylidene, (PN) 2 Ti=CH 2 , has been prepared via one-electron oxidation of (PN) 2 Ti(CH 3 ) followed by deprotonation or by H-atom abstraction using an aryloxyl radical. The Ti=C distance was found to be 1.939(3) Å, and variable temperature, multinuclear, and multidimensional NMR spectroscopic experiments revealed the methylidene to engage in long range interactions with protons on the ligand framework. Here, computational studies showed that the Ti=C bond, which until now has eluded structural studies, displays all the hallmarks of a prototypical Schrock-carbene.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Insulating titanium oxynitride for visible light photocatalysis

We propose insulating titanium oxynitrides Ti n N 2 O 2 n -3 as promising water-splitting photocatalytic materials in the visible light range. Using first-principles many-body perturbation theory based on the GW approximation, we show that corundum-type Ti 2 N 2 O (an example Ti n N 2 O 2 n -3 compound with n =2) has a smaller band gap of about 2.5 eV, which is more suitable to absorb visible light, compared to other Ti-based oxides such as TiO 2 and SrTiO 3 with a band gap of more than 3 eV. Band-gap reduction in Ti 2 N 2 O is caused by an upward shift of the valence band (negative shift to the oxidation potential of H 2 O to O 2 ) due to the presence of nitrogen 2 p states. The conduction band is dominated by Ti 3 d states and the conduction-band minimum is nearly unchanged. As a result, the band-edge potentials of Ti 2 N 2 O are better aligned to the water reduction and oxidation levels. Our theoretical predictions provide useful insights for the discovery of efficient visible-light-driven photocatalysts for water splitting.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Semiconducting cubic titanium nitride in the Th 3 P 4 structure

We report the discovery of a long-sought-after phase of titanium nitride with stoichiometry Ti3N4 using diamond anvil cell experiments combined with in situ high-resolution x-ray diffraction and Raman spectroscopy techniques, supported by ab initio calculations.

14 SOLAR ENERGY↗