Interface Structure and Properties of Alumina/Glass Ceramic Composites

摘要

Tough fiber-reinforced composites depend on fiber pull-out and crack bridging to arrest cracks in the matrix. In order to achieve fiber pull-out, there must be a weak interface between the matrix and the fiber. In this study, the interface formed at elevated temperatures between alumina and a zirconia-bearing glass-ceramic was characterized to determine its chemical and mechanical properties. The interface was analyzed in planar and cross-sectional specimens by SEM, TEM, optical microscopy, and x-ray diffraction. It was found that the diffusion of alumina into the glass-ceramic produces a dense layer of zirconia crystallization in the glass-ceramic within 20 microns of the alumina. The strength of the interface is inversely proportional to the thickness of this layer. Firing at longer times and higher temperatures produces the weakest interface. Activation energies (Q) and diffusion coefficients of aluminum into the glass matrix were calculated using a nonlinear regression analysis and data from ion microprobe profiles. Q was calculated to be 538 kJ/mol and the preexponential diffusion coefficient, D sub 0 , was found to be 4.96 x 10 sup 7 cm sup 2 /s. Some interfaces fractured spontaneously, possibly because of the martensitic transformation of zirconia. Although it is possible to achieve a weak interface, a weak interface demands long firing times (greater than three hours) or high temperatures (greater than 1425 sup 0 C). Under such rigorous conditions, a 20 mu m diameter alumina fiber will totally dissolve. For this reason, the development of an in-situ ZrO sub 2 crystallization layer is not a suitable method to produce tough alumina fiber reinforced/glass ceramic composites. 18 figs., 4 tabs. (ERA citation 13:018707)