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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

B2 Grain Growth Behavior of a Ti-22Al-25Nb Alloy Fabricated by Hot Pressing Sintering

Grain growth behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy was investigated by applying a series of isothermal treatment tests over a wide range of temperatures and holding times. An isothermal treatment scheme was conducted in the B2 phase region (1070-1110 °C) and α{sub 2} + B2 phase region (1010-1050 °C) at holding times of 10, 30 min, 1, 2, and 3 h, respectively. The effects of temperature and holding time on the microstructure evolution and microhardness of the P/M Ti-22Al-25Nb alloy at elevated temperatures were evaluated using optical microscope, scanning electron microscope, x-ray diffraction, and Vickers hardness test techniques. The results revealed that the alloy’s treated microstructure was closely linked to temperature and holding time, respectively. The change law of B2 grain growth with holding time and temperature can be well interpreted by the Beck equation and Hillert equation, respectively. The B2 grain growth exponent n and activation energy Q were acquired based on experimental data in the α{sub 2} + B2 and B2 phase regions. In addition, the grain growth contour map for the P/M Ti-22Al-25Nb alloy was constructed to depict variations in B2 grain size based on holding time and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of Triplet Paramagnetic Centers in Diamonds Obtained by Sintering of Detonation Nanodiamonds at High Pressure and Temperature

The electron paramagnetic resonance (EPR) spectra of triplet centers in detonation nanodiamonds (DNDs) and diamond single crystals of submicrometer size, synthesized from those DNDs at high pressures and temperatures, are studied. In the EPR spectra of DNDs, signals from negatively charged nitrogen- vacancy centers (NV)/sup(-) with a g factor of g{sub 1} = 4.24 and multivacancies with g{sub 2} = 4.00 are observed. The signals from (NV)/sup(-) centers disappear in the spectra of diamond single crystals, and a quintet signal with g = 4.00 is detected at the position of the signal from multivacancies. Analysis of the shape and position of the quintet’ lines showed that this ESR signal is due to the pairs of nitrogen substitution centers in diamond, separated from each other by distances not exceeding 0.7 nm, between which a strong exchange interaction takes place. A comparison of the experimental data and the simulation results allows determining the spin-Hamiltonian parameters of the exchange-coupled pairs of paramagnetic impurity nitrogen atoms.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Literature Review of Recycling Polypropylene and Polyamide 12 Powders for Selective Laser Sintering

Additive manufacturing (AM) is the creation of three-dimensional parts by adding material layer-by-layer based on two dimensional “slices” of a CAD file, without molds or tooling. AM has broken the relationship between part complexity and manufacturing cost. As a general rule, for conventional manufacturing, the more complex the part produced, the more costly its manufacturing. For example, in the production of a bracket for a satellite, moving from conventional manufacturing to AM allowed the part to be consolidated from 4 parts to just one, as well as reducing the weight of the part by 35%. A further benefit, AM can be more cost effective for small lot sizes. To illustrate, consider a case study of white board marker caps presented by Klahn et al. The cost to produce 1,000 units of a new design using SLS was about an order of magnitude lower than conventional manufacturing, as shown in Figure 1.

36 MATERIALS SCIENCE↗