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Single-component polymeric precursors to SiC/Si 3 N 4 /C/BN and Si 3 N 4 /BN ceramic nanocomposites were synthesized via hydroboration and dehydrocoupling of vinyl-containing cyclotrisilazanes. The polymer-to-ceramic conversion process was investigated by 13 C, 29 Si, and 11 B solid-state magic-angle spinning (MAS) NMR spectroscopy, FTIR spectroscopy, thermal analysis, elemental analysis, X-ray diffraction (XRD), and transmission electron microscopy. The yields, processibility, and resulting microstructure of the ceramics were dependent on the starting Si/B ratio in the polymers and the atmosphere used for pyrolysis. Thermal conversion of the polymers from 200 to 600 °C involved loss of vinyl functionality, an increase in the amount of B-N environments, and possibly some degradation of the silazane ring structure. Conversion of the polymeric environment to that of mixed-phase ceramic was complete between 600 and 1000 °C; XRD, however, showed the products to be amorphous even after heating to 1600 °C. Heating the N 2 pyrolyzed products to 1800 °C resulted in β-Si 3 N 4 , β-SiC, and t-BN peaks in the XRD powder patterns, while R-Si 3 N 4 and β-Si 3 N 4 peaks were observed for the NH 3 pyrolyzed products.

With recent advancements in additive manufacturing (AM) technology, it is possible to deposit copper conductive paths and insulation layers of an electric machine in a selective controlled manner. AM of copper enables higher fill factors that improves the internal thermal conduction in the stator core of the electric machine (induction motor), which will enhance its efficiency and power density. This will reduce the motor size and weight and make it more suitable for aerospace and electric vehicle applications, while reducing/eliminating the rare-earth dependency. The objective of this paper is to present the challenges associated with AM of copper coils having 1 × 1 mm cross section and complex features that are used in producing ultra-high efficiency induction motor for traction applications. The paper also proposes different approaches that were used by the authors in attempts to overcome those challenges. The results of the developed technologies illustrate the important of copper powder treatment to help in flowing the powder easier during deposition. In addition, the treated powder has higher resistance to surface oxidation, which led to a high reduction in porosity formation and improved the quality of the copper deposits. The laser powder direct energy deposition (LPDED) process modeling approach helps in optimizing the powder deposition path, the laser power, and feed rate that allow the production of porosity free thin wall and thin floor components. The laser powder bed fusion (LPBF) models identify the optimum process parameters that are used to produce test specimens with >90% density and minimum porosity.

Three series of SiC/AlN samples were prepared by pyrolysis of “poly(aluminosilazane)”, the product of the reaction between hexamethylcyclotrisilazane and triethylaluminum. The Si/Al ratio was varied for one series (with constant pyrolysis temperature) and the pyrolysis temperature was varied for the other two series, with Si/Al = 1 and 3. 27Al and 29Si magic angle spinning NMR were used to analyze these samples in terms of coordination number, nearest neighbor atoms, and crystallinity. NMR results indicate that higher crystallinity and phase separation into discrete SiC and AlN crystallites accompany an increase in pyrolysis temperature. Disorder and increased heterogeneity in connectivity are observed with increasing Si/Al ratio of the initial reactants.

sible that as lithium is being removed from the structure the anti-site defect concentration is increased, blocking the lithium diffusion paths and making subsequent lithium intercalation/deintercalation more difficult or even impossible.40,41 This may also be a source of irreversibility in the electrochemical reactions. under contract DE-AC02-76CH0001 to D. E. Cox.

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Chemical processing routes to advanced ceramic materials are gaining importance as a convenient approach to control the stoichiometry, purity, microstructure and final form of the ceramic products [1]. The pyrolytic conversion of organometallic molecules and polymers is one such chemical processing route that has been widely applied in ceramic fiber technology [1,2], in coating processes [1,2], and in the sintering of bulk ceramic objects [3]. Despite these advances in practical applications, there is a continuing need in this area for a better fundamental understanding of the chemistry involved during the precursor-to-ceramic conversion process and for the development of new precursors which yield the desired ceramic(s) in high yield and purity.