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Teslich, N. E.

Publications and source records attributed to Teslich, N. E..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Additive Manufacturing of a y0-Tetragonal Uranium-Niobium Alloy

The ability to process near-net shape structures is of particular interest in applications using rare or expensive materials. Laser powder bed fusion additive manufacturing can meet this challenge, yet also introduces significant processing and materials challenges toward achieving structural integrity. Broadly addressed aspects affecting powder bed fusion structures include surface roughness, residual stresses, and porosity. Here, we focus on materials-specific challenges—namely, the influence of multiple pass reheating during processing and post-processing homogenization on phase transformations and the role of impurities and oxides on grain morphology and mechanical behavior—with a view of adopting laser powder bed fusion processing for the shape memory alloy, uranium-6 wt.% niobium. Our observations to date on the factors influencing material behavior and post-processing requirements and recommendations for process improvement are discussed herein.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Mechanical Behavior of Additively Manufactured Uranium-6 wt. pct. Niobium

This report describes an effort to process uranium-6 weight% niobium using laser powder bed fusion. The chemistry, crystallography, microstructure and mechanical response resulting from this process are discussed with particular emphasis on the effect of the laser powder bed fusion process on impurities. In an effort to achieve homogenization and uniform mechanical behavior from different builds, as well as to induce a more conventional loading response, we explore post-processing heat treatments on this complex alloy. Elevated temperature heat treatment for recrystallization is evaluated and the effect of recrystallization on mechanical behavior in laser powder bed fusion processed U-6Nb is discussed. Wrought-like mechanical behavior and grain sizes are achieved through post-processing and are reported herein.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Corrosion Experiments Using Spherical Uranium Powders

Corrosion experiments using spherical U powders are continuing with scanning electron microscopy (SEM) showing that the particles are highly textured, 5 m to 25 m diameters with 4% larger particles that are fused smaller particles. This U has a high specific surface area with no corners or back-sides, is well annealed with no machining work, and coated with a coherent oxide film, 30 nm to 300 nm thick. Exposure of this powder to low vapor pressure H 2 O in the absence of O 2 , i.e., a vacuum desiccator, resulted in a coherent oxide film growth of ~1 m/y, ~ 10X the growth rate in ambient air, displaying fracture along the growth plane at ~300 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A combined theoretical and experimental investigation of uranium dioxide under high static pressure

In this work, we have investigated the behavior of uranium dioxide (UO2) under high static pressure using a combination of experimental and theoretical techniques. We have made Raman spectroscopic measurements up to 87 GPa, electrical transport measurements up to 50 GPa from 10 K to room temperature, and optical transmission measurements up to 28 GPa. We have also carried out theoretical calculations within the GGA + U framework. We find that Raman frequencies match to a large extent, theoretical predictions for the cotunnite (Pnma) structure above 30 GPa, but at higher pressures some behavior is not captured theoretically. The Raman measurements also imply that the low-pressure fluorite phase coexists with the cotunnite phase up to high pressures, consistent with earlier reports. Electrical transport measurements show that the resistivity decreases by more than six orders of magnitude with increasing pressure up to 50 GPa but that the material never adopts archetypal metallic behavior. Optical transmission spectra show that while UO2 becomes increasingly opaque with increasing pressure, a likely direct optical band gap of more than 1 eV exists up to at least 28 GPa. Together with the electrical transport measurements, we conclude that the high pressure electrical conductivity of UO2 is mediated by variable-range hopping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Steady State Sputtering Yields and Surface Compositions of Depleted Uranium and Uranium Carbide bombarded by 30 keV Gallium or 16 keV Cesium Ions.

Depleted uranium that included carbide inclusions was sputtered with 30-keV gallium ions or 16-kev cesium ions to depths much greater than the ions’ range, i.e. using steady-state sputtering. The recession of both the uranium’s and uranium carbide’s surfaces and the ion corresponding fluences were used to determine the steady-state target sputtering yields of both uranium and uranium carbide, i.e. 6.3 atoms of uranium and 2.4 units of uranium carbide eroded per gallium ion, and 9.9 uranium atoms and 3.65 units of uranium carbide eroded by cesium ions. The steady state surface composition resulting from the simultaneous gallium or cesium implantation and sputter-erosion of uranium and uranium carbide were calculated to be U₈₆Ga₁₄, (UC)₇₀Ga₃₀ and U₈₁Cs₉, (UC)₇₉Cs₂₁, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Steady State Sputtering Yield and Surface Compositions of Depleted Uranium and Uranium Carbide bombarded by 16 and 30 keV Gallium or 16 keV Cesium Ions.

Depleted uranium that included carbide precipitates was sputtered with 30keV gallium ions or 16kev cesium ions to depths much greater than the ions’ range, i.e. using steady state sputtering. The recession of both the uranium’s and uranium carbide’s surfaces and the corresponding ion fluences were used to determine the steady state target sputtering yields of both uranium and uranium carbide. 6.3 and 6.02 atoms of uranium versus 2.4 and 1.45 units of uranium carbide were sputtered per gallium ion at 30 kV and 16 kV, respectively. 9.9 uranium atoms and 3.65 units of uranium carbide sputtered per cesium ion at 16 kV. The measured steady state sputtering coefficients for Ga at 30 keV and Cs at 16 keV are close to, but smaller than calculated sputtering coefficients for pure uranium. The steady state surface composition resulting from the simultaneous gallium or cesium implantation and sputter-erosion of uranium and uranium carbide were calculated to be U86Ga14, (UC) 70 Ga 30 and U 86 Ga 14 , (UC) 59 Ga 41 for Ga at 30keV and 16keV, respectively, and U 81 Cs 9 , (UC) 78 Cs 22 for Cesium at 16 keV,

36 MATERIALS SCIENCE↗