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Lu, Ping

Publications and source records attributed to Lu, Ping.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Strain Enhanced Functionality in a Bottom-Up Approach Enabled 3D Super-Nanocomposites

The ability to control nanoparticle size, concentration, and distribution in epitaxial nanocomposite films has been a formidable challenge in the synthesis of nanostructured composite materials. In this paper, a novel 3D super-nanocomposite (3D-sNC) architecture is successfully demonstrated by integrating superlattice and vertically aligned nanocomposite structures. In the 3D-sNC architecture, the feature size and distribution of the nanocylinders such as the height/lateral dimension and the vertical/lateral spacing of nanocylinders can be precisely controlled. The microstructure parameters such as nanocylinder height and spacing modulated interfacial area control the lattice strain, which further tunes the magnetotransport property. These results demonstrate that 3D-sNC is a simple and yet effective architecture to achieve controlled functionalities via the precise control of nanocylinder size, spacing, concentration, and distribution. Lastly, such a 3D-sNC structure can be used to design advanced nanostructures with desired physical properties for a variety of material systems.

36 MATERIALS SCIENCE↗
DOE OSTI2019

On the thermal stability and grain boundary segregation in nanocrystalline PtAu alloys

Grain boundary (GB) solute segregation has been proposed as a new mechanism to stabilize nanocrystalline (NC) metals. In this study, we investigate the thermal stability and GB solute segregation in a noble metal alloy system (Pt–Au). Thermal stability of the Pt .90 Au .10 alloy system was evaluated by annealing a thin film (~20 nm in thickness) at 500°C and 700°C as well as a thick film (~2 µm in thickness) at a temperature range from 200°C to 700°C. The remarkable stability of the Pt .90 Au .10 alloy system was demonstrated by comparing its thermal stability to that of pure Pt films processed under identical conditions. Although presence of voids in the GBs may contribute to thermal stability, the enhanced thermal stability of the Pt .90 Au .10 alloy is mainly attributed to preferential Au segregation to GBs in the alloy film, which is revealed by aberration-corrected scanning transmission electron microscopy. Our results show that Au segregation to GBs is heterogeneous, with variation in solute content between different GBs as well as non-uniformity along individual GBs. The heterogeneity is dependent on the annealing temperature and is less pronounced at a higher processing temperatures (e.g., 700°C). Furthermore, by using the noble Pt–Au system, which avoids oxidation and impurities, this study validates the mechanism of GB solute segregation and provides further understanding of the thermodynamics and kinetics underlying NC stabilization.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Mid-Lift-to-Drag Ratio Rigid Vehicle 6-DOF EDL Performance Using Tunable Apollo Powered Guidance

The Mid-Lift-to-Drag ratio Rigid Vehicle (MRV) is a candidate in the NASA multi-center effort to determine the most cost effective vehicle to deliver a large-mass payload to the surface of Mars for a human mission. Products of this effort include six-degree-of-freedom (6DoF) entry-to-descent trajectory performance studies for each candidate vehicle. These high fidelity analyses help determine the best guidance and control (G&C) strategies for a feasible, robust trajectory. This paper presents an analysis of the MRV's G&C design by applying common entry and descent associated uncertainties using a Fully Numerical Predictor-corrector Entry Guidance (FNPEG) and tunable Apollo powered descent guidance.

human↗
DOE OSTI2018

Microstructure and coercivity in alnico 9

Magnetic property enhancement of alnico, a rare-earth free permanent magnet, is highly dependent on both the initial microstructure and the evolution of the spinodal decomposition (SD) inside each grain during the heat treatment process. The size, shape and distribution of the magnetic FeCo-rich (α 1 ) phase embedded in continuous non-magnetic AlNi-rich (α 2 ) phase as well as a minor Cu-enriched phase residing in between are shown to be crucial in controlling coercivity. Phase and magnetic domain morphology in a commercial alnico 9 alloy was studied using a combination of structural characterization techniques, including scanning electron microscopy, electron backscatter diffraction, aberration-corrected scanning transmission electron microscopy and Lorentz microscopy. Our results showed that casting created structural nonuniformity and defects, such as porosity, TiS 2 precipitates and grain misorientation, are heterogeneously distributed, with the center section having the best crystallographic orientation and minimal defects. The optimal spinodal is a “mosaic structure”, composed of rod-shape α1 phase with {110} or {100} planar faceting and diameter of ~30–45nm. There is also a Cu-enriched phase residing at the corners of two < 110 > facets of the α1 phase. Furthermore, it was observed that grain boundary phase reverse magnetization direction at lower external magnetic field compared to the SD region inside the grain. Improving grain orientation uniformity, reducing detrimental grain boundary phase volume fraction, and the branching of the α 1 rods, as well as their diameter, are promising routes to improve energy product of alnico.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Quantum Nanofabrication: Mechanisms and Fundamental Limits

Quantum-size-controlled photoelectrochemical (QSC-PEC) etching, which uses quantum confinement effects to control size, can potentially enable the fabrication of epitaxial quantum nanostructures with unprecedented accuracy and precision across a wide range of materials systems. However, many open questions remain about this new technique, including its limitations and broader applicability. In this project, using an integrated experimental and theoretical modeling approach, we pursue a greater understanding of the time-dependent QSC-PEC etch process and to uncover the underlying mechanisms that determine its ultimate accuracy and precision. We also seek to broaden our understanding of the scope of its ultimate applicability in emerging nanostructures and nanodevices.

36 MATERIALS SCIENCE↗