Processing, characterization and properties of oxide based nanocomposites.

摘要

The synthesis, characterization and mechanical properties of oxide based nanocomposites are reported in this dissertation. Two binary systems are studied: Al{dollar}sb2{dollar}O{dollar}sb3{dollar}-MgO and {dollar}rm Alsb2Osb3{dollar}-ZrO{dollar}sb2{dollar}. Al{dollar}sb2{dollar}O{dollar}sb3{dollar}-MgO was chosen because of its relatively large field of solid solubilities at a moderate temperature. On the other hand, {dollar}rm Alsb2Osb3{dollar}-ZrO{dollar}sb2{dollar} was chosen because it shows minimal solid solubility of the constituents.; A novel "Auto Ignition" process using suitable fuels and oxidizers was utilized in the synthesis of nanocomposites and solid solutions. Thermodynamic calculations were carried out in predicting end point adiabatic temperatures (T{dollar}sb{lcub}rm ad{rcub}{dollar}) for each composition in both systems. Combustion temperatures were experimentally measured by means of a data acquisition system. Characterizations of the powders were carried out by x-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive analysis (EDAX) and differential thermal analysis (DTA). Heat treatment experiments were carried out to study the grain growth behavior.; A hot isostatic pressing (HIP) model was developed for the present nanoceramics. Input parameters were carefully chosen for such nanomaterials. The as-synthesized nanocrystalline powders were consolidated to near theoretical density by hot isostatic pressing (HIPing) while retaining fine grain size. The experimental results were compared with the predictions of the model. Mechanical properties, such as room temperature toughness, low temperatures well as high temperature hardness, were determined for both systems. Room temperature hardness values were (2.89-7.79) GPa and fracture toughness was between 2.7 and 5.82 MPa.m{dollar}sp{lcub}1/2{rcub}{dollar} for various compositions in the {dollar}rm Alsb2Osb3{dollar}-MgO system. Room temperature hardness values were between 5.33 and 8.71 GPa and fracture toughness values ranged from (5.3-9.62) MPa.m{dollar}sp{lcub}1/2{rcub}{dollar} for various compositions in the {dollar}rm Alsb2Osb3{dollar}-ZrO{dollar}sb2{dollar} system.; Nanoindentation experiments were carried out to further explore the room temperature ductility in the materials. The results showed that material is piled up around the indent thereby proving that these materials are softer than their conventional counterpart.; Over the past several years, research on nanocrystalline ceramic materials has been motivated by the prospects of low temperature superplastic deformation for net shaping applications. Hot hardness experiments are particularly important in order to determine the brittle to ductile transition temperature (BDTT) for deformation processing. Hot hardness experiments were carried out for the {dollar}rm Alsb2Osb3{dollar}-MgO and {dollar}rm Alsb2Osb3{dollar}-ZrO{dollar}sb2{dollar} systems. A reduction in hardness was noted at moderate temperatures.