Tübingen, Univ., Diss., 2007.

Titanium-based nitride films are deposited on steels by magnetron reactive sputtering for cutting, forming and decorative applications. The nitride films about 2 m thick with interlayer for better adhesion are grown at a working pressure of 0.8 Pa, discharge power of 220 watt, Ar/N2 gas ratio of 0.93, substrate temperature of 300 ¢J and deposition time of 40 minutes. Four different targets (Ti, Ti-6Al, hot-pressed Ti-6Al-4V, commercial Ti-6Al-4V, where Al and V are in wt.%) and two different steels ( stainless steel (SS) and high speed steel (HSS)) as substrate materials are tested. The indentation technique is used to evaluate the adhesion properties of the nitride films to the substrate and elasticity analysis of indentation to analyze the distribution of the stresses at the interface. The differences in indentation properties between nitride/ SS and nitride/ HSS are examined and correlated with the elastic/plastic analysis. It appears the cracks and spallings observed inside the indentation cavity in nitride/SS system are due to the higher poisson¡¦s ratio of stainless steel but those around the indentation cavity observed in nitride/HSS system are due to the edge (binding) effect. Continuous load ¡Vpenetration depth curve of indentation test shows that TiAlVN/HSS is more fracture¡Vresistant than the pure TiN/HSS. The addition of aluminium into TiN film decreases the lattice constant while further addition of vanadium into TiAlN films causes the lattice constant to increase. This is discussed in terms of bonding characteristics and atomic size of the elements. SEM analysis shows that columnar structure of TiN films is coarser than that of TiAlN and TiAlVN. TEM studies of microstructure and AFM studies of surface roughness show that the TiAlVN film formed by hot¡Vpressed Ti-6Al-4V on HSS has the densest fibrous structure and smoothest surface, and therefore the best mechanical properties such as hardness and indentation fracture resistance. (111) and (200) orientations of TiN, TiAlN, and TiAlVN are observed by XRD analysis. The ) phase is found due to small amount of Fe in the films. The oxynitride phase in the nitride films as indicated by the binding energy shifts of the elements may be due to the trace oxygen during deposition. The interlayers of TiAlN/HSS and TiAlVN/HSS have the preferred orientations of and . The texture (columnar) structure of (111) and (200) orientations are observed in TiAlN and TiAlVN films. An orientation relationship of is found between interlayer and tempered martensite in TiAlVN/HSS. Oxidation test was carried out in oxygen atmosphere at 620-800¢Jfor 3 hours. The TiAlVN film by hot-pressed Ti-6Al-4V on HSS follows the parabolic growth law. It also has the slowest oxidation rate while the TiN/ HSS the fastest one. The activation energy of oxidation of this system is about 184.5 kJ/mole. The oxidation of TiN/ HSS reveals larger area of spallings, while TiAlN/HSS and TiAlVN/ HSS generally show uniform oxidation with small areas of non-uniform growth. There is a dramatic effect of aluminium in facilitating the uniform oxidation for TiAlN and TiAlVN on HSS. The oxidation products of TiAlN/HSS and TiAlVN/ HSS are oxynitride, amorphous Al2O3, Fe2TiO5 and small amount of TiO2 and Fe2O3.

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Haegel, Nancy M. Second Reader: Luscombe, James. "December 2009." Description based on title screen as viewed on January 27, 2010. Author(s) subject terms: Transport imaging, minority carrier, GaN nanowires, diffusion length, near-field scanning optical microscopy, NSOM. Includes bibliographical references (p. 63-64). Also available in print.

Zinc nitride is currently attracting research interest because of its potential for novel electronic and photonic properties. In this thesis the optical properties of Zn3N2 powders have been investigated by photoluminescence (PL) and diffuse reflectance spectroscopy (DR) measurements. The micro structure and composition of zinc nitride were assessed by scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). Measurements of PL, PXRD and DR were carried out on zinc nitride powder samples with different oxygen-nitrogen (O/N) ratios. Photoluminescence spectroscopy of the zinc nitride powder samples allows us to find the optical bandgap of the samples. To the best of our knowledge, this is the first report on the low temperature photoluminescence of zinc nitride powder. This showed us how the band gap energy depends on temperature. The diffuse reflectance measurement let us determine a direct bandgap of 1.12eV for Zn3N2 powders and the PL measurements also demonstrated emission at the same photon energy. In this work, the effect of oxidation on the optical properties has been investigated. The surface oxidation of Zn3N2 powders and the oxygen-nitrogen (O/N) ratio were detected through PXRD scans. Our measurement show that the optical bandgap energy shifts to lower energy due to the oxygen incorporation. The reduction of the Zn3N2 bandgap by oxygen incorporation can be explained by a resonant interaction between the extended states of the conduction band of Zn3N2 and localized oxygen states near the conduction band edge. Additionally, the thermal nitriding process was carried out on the oxidized Zn3N2 powders to vary the O/N ratio which increased the bandgap energy. From our result, the optical bandgap of the Zn3N2 powders is estimated to be ~1.2 eV which decreases by small amount of oxygen contamination due to exposure to air. Powder XRD measurements of thermal oxidation of Zn3N2 indicated that the oxidation of these powders is slow at room temperature. / Graduate

An absorption complex or compound between boron nitride and chromyl chloride was discovered and studied in some detail. The method used to prepare the boron nitride had some effect on the composition of the complex but for a given sample of boron nitride the equilibrium composition for temperatures from 0°C to 160°C was constant. The kinetics of formation were studied at 24.1°C, 67.1°C, and 117.0°C. The reaction was interpreted as diffusion controlled with two diffusion coefficients--each for a certain concentration range. The corresponding two energies of activation were 5.0 and 6.1 kcal. These are of the same order of magnitude as for similar processes. X-ray studies of the complex showed a strong reflection line at the same place as for the main layer separation in boron nitride itself. There could have been a small amount of reflection due to a greater layer spacing, but it was not detected. Water hydrolyses the chromyl chloride in the complex, leaving the original boron nitride and a solution of dichromate and HCl. Carbon tetrachloride would not dissolve out the chromyl chloride from the complex. Similar complexes of chromyl chloride with disulfides of molybdenum, tungsten and uranium and of cupric and aluminum chlorides with boron nitride were discovered but the kinetics of their formation were not studied. The theory of formation of lamellar compounds is discussed. / Science, Faculty of / Chemistry, Department of / Graduate

Because of its attractive material properties like high hardness, high toughness, and excellent high temperature strength, materials like silicon nitride are becoming more common for use in high performance applications. However, there have been limited studies of the fatigue behavior of small cracks in silicon nitride and other materials toughened by grain bridging mechanisms. This study explores using micro Raman spectroscopy, fatigue crack growth data and results from static fracture experiments to determine a bridging stress profile for silicon nitride doped with MgO and Y₂O₃ as sintering additives. These bridging stress profiles allow for the creation of a geometry specific fatigue threshold R-curve which can be used to develop a fatigue endurance strength prediction tool to aid in the design of products using the material. Cyclical fatigue experiments conducted on bend beams with induced semi-elliptical surface cracks were conducted to verify the prediction tool. The results show that no bend beams with this crack geometry failed below the predicted endurance level. It is expected that this method can be extended to create fatigue endurance strength predictions for other materials similarly toughened by grain bridging and other mechanisms. / Graduation date: 2013

No description available.

by Poon Ming-Cheong. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1988. / Bibliography: leaves [163-175]

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 121-127). Also available in print.

Zugl.: Braunschweig, Techn. Univ., Diss., 2008