Sol-gel Elaboration of Porous Oxide Coatings as Interphase in SiC/SiC Ceramic Matrix Composites
- PDF / 1,706,385 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 4 Downloads / 216 Views
P3.24.1
Sol-gel elaboration of porous oxide coatings as interphase in SiC/SiC Ceramic Matrix Composites M. Verdenelli, S. Parola*, F. Chassagneux, S. Jacques, H. Vincent, J. Dazord, J.P. Scharff, E. Bourgeat-Lami1 Laboratoire des Multimatériaux et Interfaces UMR CNRS 5615 Université Claude Bernard Lyon 1 – 69622 Villeurbanne cedex, France. E-mail : [email protected] 1 Laboratoire de Chimie et Procédés de Polymérisation UMR 140, ESCPE, Villeurbanne, France. ABSTRACT Combinations of meso-, macro- and microporous coatings with a chemical composition of 90%Al2O3-10%SiO2 were elaborated on SiC Hi-Nicalon fibers using the sol-gel process. They were evaluated as porous interphase for the reinforcement of CMC. The mesoporous oxide, in contact with the fiber, allows cracks deviation whereas the macroporous one, in contact with the matrix, avoids the gaseous infiltration of the mesopores during the SiC CVD matrix process. It also prevents from oxygen diffusion during high temperature under air. The characterization of the composites was performed by SEM (scanning electron microscopy), TEM (transmission electron microscopy), X-ray diffraction, and EDS (energy dispersive spectrometry). TEM evidenced the porosity gradient as expected. A tensile test on the composites revealed brittle behavior (fracture) and no fiber debonding was observed. INTRODUCTION Ceramics are promising materials for high-temperature applications. However, their use is limited because of their low fracture toughness. Extensive work has been developed on ceramic matrix composites (CMC) reinforced with ceramic fibers in order to increase fracture toughness, and has focused on the fiber/matrix interface. In order to improve the mechanical behaviour of such composite, it appeared necessary to elaborate an interphase between the fiber and the matrix [1]. Several concepts were taken in consideration, the most studied one being the lamellar interphase through coatings of C and BN or phyllosiloxide in SiC/SiC composites ; or magnetoplumbite in oxide composites [2-4]. C and BN coatings are susceptible to oxidation, on the contrary of oxide interphases, which are of great interest for high temperature applications. Such interphases were suggested for both oxide and non-oxide composites [5,6]. The interphase must allow fiber debonding and pull-out, and must be chemically compatible with the fiber and the matrix at high temperature. Carpenter et al. introduced the concept of porous interphase [7]. The interphase is inherently weak and may bond strongly to the matrix and the fiber. Previous investigations concerned for example ZrO2 porous interphases in Al2O3/Al2O3 composites or porous Ta2O5 in SiC/SiC composites [8,9]. Both these systems showed fiber debonding but did not allow utilization at high temperature since oxide crystallization occurred with densification and thus loss of porosity. xAl2O3-ySiO2 porous coatings were previously elaborated on SiC HiNicalon fibers [10,11]. It was evidenced that the coatings did not degrade the fiber strength and allow
Data Loading...
