c00.52es and manufacturing ELSEVIER Composites: Part A 32(2001)1007-1012 Fabrication of high-temperature resistant oxide ceramic matrix composites I.A. H. Al-Dawery". E. G. Butler Ceramic Matrix Composites Group, Interdisciplinary Research Centre(IRC) in Materials for High Performance Applications. The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Abstract The main objectives of this work are to develop and apply new ceramic matrix materials by which a relatively high level of densification of the final composite may be achieved by pressureless-sintering at temperatures close to 1200.C. A cost-effective processing method for the production of oxide/oxide CMCs materials and components has been achieved. A range of interphase materials is applied to Nextel 720 fibres. These include zirconia, neodymium and lanthanum phosphate. A combination of ZrO2 and the AKP50 alumina powder have been selected as the successful candidates for the interphase and the matrix material, respectively. Work has been conducted on the preparation of slurry systems consisting of these two materials. The prime target was to establish the possibility of achieving good coating around the bulk of the fibres together with a high level of impregnation with the matrix material. Furthermore, the pressure infiltration technique has been applied and as a result composite samples with fibre volume content of 40%0, and remaining porosity of around 20 vol% have been routinely produced. Composite room and high-temperature tensile strengths of around 200 MPa have been accomplished. o 2001 Published by elsevier Science Ltd. Keywords: A Ceramic matrix composities( CMCs); Nextel720 1. Introduction purity ultra fine alumina offers the advantage of being sintered readily at temperature above 800C [5]. Thus Continuous fibre reinforced ceramic matrix composites composite materials can be processed at temperatures that CMCs) with suitable interfaces can exhibit inelastic defor- mation behaviour which enable these materials to retain It is very essential during the fabrication stages that the trength in the presence of holes and notches. This damage intrinsic strength of the fibres is retained as far as possible tolerance, coupled with their inherent refractoriness, has and that the matrix material is able to translate efficiently the enabled CMCs to emerge as successful candidates for fibre properties into composite strength and stiffness many high-temperature thermostructural high performance Normally, the reinforcement material(Nextel720 fibres applications [1]. Careful microstructural design has been 3M, USA)is first coated with a low debond energy inter- defined as a key factor in the development of oxide/oxide phase(typically using ZrO2 sol). This would be followed by CMCs. The majority of these developments have been a second stage of incorporating the matrix material using based upon a selection of a weak interface concept, using pressure infiltration techniques. Eventually green com- stable oxide interphases with suitably low fracture tough- posites are densified by pressureless sintering at 1200.C ness[2,3]. Furthermore, sintering kinetics suggests adequate for 4 h. The method of matrix infiltration using aqueous microstructural stability for applications such as in the sols and slurries is an extremely demanding challenge gas turbine engine, where initial target wall tempera- Here there are two issues. The first one is that when fibre tures are in the range of 1100-1200"C. Here there is mats are coated with the Zro2 interphase a web-type solid a processing challenge. Most matrices require sintering structure, covering most voids within the fibre mats, is temperatures of or above 1200C to achieve sufficient formed. Such formation will act as a barrier towards incom- bonding between matrix particles. However, most ing sols and slurries aiming at filling the much bigger voids commercial oxide fibres are susceptible to micro- within fibre tows. As a result of this, incomplete infiltration structural degradation at these temperatures [4]. High with the matrix slurry cannot be avoided. It was therefore decided to conduct experiments through which the inter Corresponding author. Tel. +44-121-414-3449: fax: +44-121-414- phase sol and the matrix slurry were both applied in one simple and single stage. Composite samples were later made E-mail address: i aldawery ( bham ac uk (I.A.H. Al-Dawery ) using the above approach 9-835X/01/S- see front matter e 2001 Published by Elsevier Science Ltd S1359-835X(00)001676
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