Effect of processing parameters on the production of bilayer-graded Al/SiC p composites by pressureless infiltration E. Parras-Mede ´cigo, M.I. Pech-Canul * , M. Rodrı ´guez-Reyes, A. Gorokhovsky Centro de Investigacio ´n y de Estudios Avanzados del IPN-Unidad Saltillo Carr. Saltillo-Mty Km 13, Apdo. Postal No. 663, Saltillo, Coahuila, Mexico, 25000 Received 11 December 2001; accepted 21 December 2001 Abstract The effect of the following parameters on the infiltration characteristics of bilayer SiC p preforms by the alloy Al – 10.77 wt.% Si – 9.7 wt.% Mg was investigated and quantified: process temperature, infiltration time, SiC particle size, percentage porosity in the preform and preform layer height. The contribution of each of these parameters and their interactions to the height of infiltration are determined. In addition, an optimized process for enhanced infiltration is suggested and validated. The parameter that most significantly affects the height of infiltration is the interaction between porosity and the preform layer height. This interaction has a contribution of 42% on the variability of the infiltration height. It is followed by the infiltration temperature and the interaction between particle size and percentage porosity, which contributions are 25% and 23%, respectively. A verification test with the optimum parameters shows good agreement with the projected value of height of infiltration. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Pressureless infiltration; Graded materials; Al/SiC p composites 1. Introduction A great number of composites applications require a variation of properties with position within the component. Localized regions of stress concentration resulting from abrupt transitions in composition and properties are greatly reduced by a gradual transition in composition and/or microstructure [1,2]. To diminish the effect of stress concentration, functionally graded materials (FGM) have been developed and applied for a long time in structural and non-structural applica- tions. The effect of interface stresses in FGM has been investigated both theoretically and experimentally [2,4,5]. Within the variety of constructive and trans- port-based processes available for the production of functionally graded materials, infiltration of ceramic preforms by liquid metals is a route that offers the potential for the processing of metal matrix composites [2,3]. Near-net shape composites may be produced by pressure or vacuum assisted infiltration and by pres- sureless infiltration of ceramic preforms. The develop- ment of ‘‘pressureless infiltration’’ or ‘‘spontaneous infiltration’’ methods is desirable in order to reduce process costs. The term ‘‘spontaneous infiltration’’ 0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-577X(02)00528-1 * Corresponding author. Tel.: +52-844-4-38-96-00x9678; fax: +52-844-38-96-10. E-mail address: martpech@saltillo.cinvestav.mx (M.I. Pech-Canul). www.elsevier.com/locate/matlet October 2002 Materials Letters 56 (2002) 460 – 464