Two equalisation or reheating temperatures (1050°C and 1150°C) and three equalisation or reheating times (53 min, 318 min, and 1333 min) were applied to three V- and V-Ti- microalloyed steels, which contain a low carbon content (0.067 ~ 0.073 wt%) and high nitrogen content (0.017 ~ 0.021 wt%), by the simulated direct charging or conventional cold charging processes. The experimental results show that in directly charged V-microalloyed steels, MnS provides the main pinning effect but does not have a sufficient ability to prevent the austenite grains from growing during the equalisation. Because of the slow precipitation, AIN only precipitates at the longest equalisation time and is the main compound which has an obvious pinning effect on the austenite grain growth in V-microalloyed steels. Austenite grain growth appears more likely to be abnormal as a result of the direct charging than of the cold charging due to the precipitation of fine AIN particles during the phase transformations. The experimental results also show that the longer equalisation or reheating time in the furnace does not result in a significant change in the microstructures and in the austenite grain size, because of the precipitation of AIN during equalisation or reheating. However, in V-Ti-microalloyed steels, the existence of titanium can promote the precipitation of complex (Ti×V₁₋×)N particles during equalisation or reheating. In the cold charged V-Ti-N microalloyed steel, the fine austenite grains produced (<10μm) can be observed after the reheating and water-quenching due to the significant pinning effect of (Ti×V₁₋×)N. When the reheating time of V-Ti-N microalloyed steels at 1150°C is longer than 318 min, the coarsening of (Ti×V₁₋×)N precipitates occurs and leads to abnormal austenite grain growth. The TEM results also show that cruciform (Ti×V₁₋×)N particles can only be found indirectly charged steels but not in cold charged steels.

Thesis (PhD)--University of South Australia, 2002.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [158]-168).

Polycrystalline AlN thin films were reactively deposited onto Al layers on negatively biased glass and Si substrates at temperatures < 80 oC by coherent magnetron sputtering. The target-to-substrate distance is 17 cm. The microstructures and morphology of the films grown at different bias voltages on the substrates were investigated. Typical thickness of the deposited film is 600 nm. The films were amorphous when no bias was applied to the substrates. Diffraction peak of AlN (002) direction was observed at bias voltages of -180 and -210 V. At a bias voltage of -210 V, the (002) granular crystal with the maximum diameter of 80 nm was obtained. In addition to the AlN (002) direction, AlN (100) direction was observed when the bias voltage was increased to -240 and -270 V. The peak of (002) plane vanished at a bias voltage of -320 V. Moreover, the deposited AlN films have specular reflectance owning to the large target-to-substrate distance. The maximum roughness of the films was 47.2¡Ó5.0 nm at a bias voltage of -210 V. The hardness and microstructure of aluminum nitride (AlN) thin films prepared by long-distance magnetron sputtering at room temperature has been investigated. The hardness and microstructure of the films were found to vary greatly with different substrate biases. At a bias voltage of ¡V210 V, the (002) polycrystalline AlN with the maximum hardness of 17.5 GPa was observed. The water droplet contact angle under this bias condition is larger than 90¢X indicating that hydrophobicity can be obtained at the film surface. In addition, hardness of (002) AlN films prepared by sputtering of AlN target at room temperature and by reactive sputtering of Al target at 400¢XC were discussed and compared with that of AlN films prepared by long-distance reactive sputtering.

Aluminum nitride (AlN) thin films were deposited on Z-cut LiNbO3 substrates using the reactive RF magnetron sputtering in this thesis. By means of the analyses of XRD, SEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power of 165W and substrate temperature of 400¢J. The piezoelectric bi-layers structure of SAW devices was then fabricated. The interdigital transducers (IDTs) were fabricated on bi-layers structure. The AlN thin film thickness of piezoelectric bi-layers structure was varied in order to discuss its effects on SAW devices. From the experimental results, it reveals that the center frequency of SAW filters increases with the increased AlN thin films thickness. It means that the SAW velocity increases as the AlN thin films thickness increases. The effects of bi-layers structure on SAW devices can be discussed in detail by measuring the parameters of SAW devices like insertion loss (IL), electromechanical coupling coefficient (K2) and the temperature coefficient of delay (TCD).

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

Thesis (Ph. D.)--Lehigh University, 1997. / Includes vita. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains ix, 56 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 46-48).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves [103]-112).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 167-187).