Papers by Author: Natalia I. Baklanova

Abstract: Adhesion force measurements by atomic force microscopy (AFM) have been carried out to investigate the adhesion between the Si3N4 cantilever tip and the surface of the initial SiC-based Hi-Nicalon, Hi-Nicalon S, and Tyranno-SA fibers, as well as the ZrO2-coated and oxidized coated fibers. It was shown that the application of coating resulted in a change of the roughness parameters and a decrease of the adhesive forces between the Si3N4 cantilever tip and the fiber surface. Surface heterogeneity at the nanoscale could be responsible for the dispersion of adhesive forces. The results open the possibility of transferring nano mechanical information to meso or macro mechanical properties of ceramic matrix composites.

Abstract: Ceramic matrix composites reinforced by carbon or SiC-based fibers achieve high toughness and damage tolerance through the disposal of weak fiber coating which can deflect cracks and promote debonding at the fiber/matrix region. The methods for fabrication, as well as different techniques including SEM/EDS, XPS, XRD, AFM, micro Raman for evaluation of properties of the interphase zone are considered. The morphology, composition, topography, roughness, tensile properties of coated carbon and SiC fibers are discussed in details. The behavior of coated fibers is governed by the chemistry, procedure for coating fabrication, nanostructural factors.

Abstract: CMC's reinforced by SiC-based fibers achieve high toughness and damage tolerance through the disposal of weak fiber coating which can deflect cracks and promote debonding at the fiber/matrix region. Refractory oxide-based systems are considered as the most promising ones for this purpose. Sols of zirconia, including stabilized zirconia were used as simple and readily processable precursors for obtaining interfacial coatings on SiC tow and cloth. The morphology, composition, topography, roughness, tensile properties of as-prepared and exposed to air at 1000°C coated fibers were evaluated by SEM/EDS, XPS, XRD, AFM, micro Raman analysis. The peculiarities of the behavior of oxide-coated fibers are governed by the properties of initial sols, procedure for coating fabrication, chemical and nanostructural factors. The peculiarities of the behavior of the stabilized zirconia interphase with accurate phase control will be discussed. A monitoring of the t→ m phase transformation within ZrO2 interfacial coating on SiC fiber using micro Raman makes it possible quantitatively to evaluate an ability of ZrO2 as oxidation resistance and readily deformable weak interfacial coating for the next-generation CMC's.