Hyun-Seo Yoon

Reaction sintering process of tyranno SA/SiC composites and their characterization

Abstract This paper deals with the efficiency of fiber preform preparation route for the fabrication of reaction sintering (RS) SiC f /SiC composites and their characterization, including density, microstructure and mechanical property. The applicability of carbon interfacial layer has been investigated in the RS process. The fiber preform was prepared by the consecutive slurry infiltration process, which associated with the combination of constant gas impregnation pressure and different magnitudes of cold pressure. The consecutive slurry infiltration process used for the preparation of fiber preform can be regarded as a promising technique for high density RS-SiC f /SiC composites, even if their mechanical properties depend on the magnitudes of cold pressure used. RS-SiC f /SiC composites entirely showed the morphology of near stoichiometric SiC phase in the intra-fiber bundle matrix, compared to that in the inter-fiber bundle matrix. The carbon interfacial layer was insufficient for the pseudo-ductile failure of RS-SiC f /SiC composites, even if some amount of fiber pull-out and interfacial delamination was observed in the tensile surface of bending test sample.

Process, microstructure and flexural properties of reaction sintered Tyranno SA/SiC composites

Abstract The preparation routes of fiber preform for the fabrication of RS-SiC/SiC composites have been investigated, based on the mechanical property–microstructure correlations. Tyranno SA SiC fiber reinforced SiC composites have been fabricated by a reaction sintering process, which is associated with the consecutive slurry infiltration process of low pressure slurry impregnation with various filler particles and with the magnitudes of the cold pressures. The characterization of RS-Tyranno SA/SiC composites was evaluated by means of SEM, EDS and three point bending test. The consecutive slurry infiltration process of low impregnation pressure and cold pressure for the preparation of fiber preform provided the required density for RS-Tyranno SA/SiC composites (>2.9 mg/m3), even if there was a large amount of Si rich SiC phases in the matrix of the intra-fiber bundle. The flexural properties of RS-Tyranno SA/SiC composites depended on the magnitudes of cold pressure used for the preparation of the fiber preform.

Evaluation of fracture toughness of ceramic matrix composites using small specimens

Abstract Ceramic matrix composites (CMC) are being developed for high temperature utilization in aerospace and other industrial application. They offer several attractive features including high strength and modulus, improved fracture toughness, light weight, low thermal expansion coefficient and high thermal conductivity which contribute to good thermal shock resistance and high temperature stability in chemical and oxidative environments. Though the enhancement of fracture toughness is one of key issues for the development of these materials, the standardized evaluation method for the characterization of fracture toughness has not been established yet. Miniaturization of the test specimen for these tests has been also considered to be one of the most necessary issues because of the high cost of materials and the restriction of experimental environments. In this study, the influences of specimen size on the fracture resistance properties of plain-woven (P/W) Carbon/Carbon and Tyranno-LoxM/SiC composite were investigated. The fracture toughness tests with the unloading–reloading sequences were conducted with the compact tension specimens of different thicknesses and widths. The initiation fracture toughness JQ of both materials increased with increasing of specimen thickness. It seems that interlayer frictional sliding between layered fabrics is one of energy dissipating mechanism in these materials. The initiation fracture toughness, JQ, of both materials also increased with increasing of specimen width. The specimen width and the fabric condition affect the size of fracture process zone in 2D woven CMC.