Effect of rice-husk ash on properties of laminated and functionally graded Al/SiC composites by one-step pressureless infiltration A. Bahrami, M.I. Pech-Canul ⇑ , C.A. Gutierrez, N. Soltani Centro de Investigación y de Estudios Avanzados del IPN Unidad Saltillo, Ave. Industria Metalúrgica No. 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila 25900, Mexico article info Article history: Received 2 February 2015 Received in revised form 25 April 2015 Accepted 27 April 2015 Available online 1 May 2015 Keywords: Pressureless infiltration Graded materials Rice husk ash Metal matrix composites abstract The quantitative effect of the following parameters on the one single step pressureless infiltration char- acteristics of bilayer SiC p /rice-husk ash (RHA) porous preforms by aluminum alloys was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, SiC par- ticle size, RHA percentage, percentage porosity in the preforms, and magnesium content in the alloy. The contributions of each of the parameters and their interactions to the retained porosity, hardness and modulus of elasticity of the resulting bilayer composites were determined. The parameters that most sig- nificantly impact the modulus of elasticity (E) of the resulting composites are infiltration time and SiO 2 phase type (from RHA), with contribution of 27% and 21%, respectively. They are followed by preform porosity, Mg concentration and process temperature, with contributions of 13%, 12% and 11%, corre- spondingly. Verification tests conducted using the established optimum parameters show a good agree- ment with the projected values of modulus of elasticity (169 ± 9 GPa) and retained porosity (1.9 ± 0.8). The in-situ formation of MgAl 2 O 4 and MgO phases with the unique morphology of RHA in the microstruc- ture, was manifested as exothermic peaks in the heat flow curves and identified by XRD and SEM analyses of the composites. A reaction pathway for MgAl 2 O 4 and MgO formation was outlined. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Functionally graded composite materials (FGCMs) have been the subject of intense research efforts in recent years. Several stud- ies have examined the spatial variation of mechanical properties to optimize structural response. Others have considered processing techniques which produce structures with variable reinforcement and thus variable mechanical properties [1–3]. The manufacturing process of a FGM can usually be divided into building the spatially inhomogeneous structure ‘‘gradation’’ and transformation of this structure into a bulk material ‘‘consolidation’’. Gradation processes can be classified into constitutive, homogenizing and segregating processes. Constitutive processes are based on a stepwise build-up of the graded structure from precursor materials or pow- ders. In homogenizing process a sharp interface between two materials is converted into a gradient by material transport. Segregating processes start with a macroscopically homogeneous material which is converted into a graded material by material transport caused by an external filed. Homogenizing and segregating processes produce continuous gradients, but have lim- itations concerning the types of gradients which can be produced [3]. Although the infiltration of ceramic preforms by liquid metals has been typically applied for the processing of composite materi- als with homogeneous reinforcement shape, size and composition [4,5], as a constitutive route, it offers the potential for the produc- tion of graded materials by variation of shape, size, and volume fraction of the reinforcement in superimposed ceramic perform layers over a metallic layer. In this investigation, it is suggested that such graded materials may be produced by one-step infiltration process. Thus, compo- nents such as cylinder liners, brake components and ballistic armor plates may be produced by adequately packing two or more cera- mic preform layers of distinct characteristics. Nonetheless, a num- ber of difficulties related to the processing parameters (infiltration time and temperature, process atmosphere, alloy composition, shape and size of the reinforcement, and percentage porosity in the preform, etc.) are encountered in the production of MMCs via the infiltration of ceramic preforms, particularly when using the capillary effect. In the Al/SiC system, for instance, typical problems are the presence of aluminum carbides and residual porosity in the composites [6]. In spite of various efforts devoted to the http://dx.doi.org/10.1016/j.jallcom.2015.04.194 0925-8388/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +52 (844) 4 38 96 00x8678. E-mail address: martin.pech@cinvestav.edu.mx (M.I. Pech-Canul). Journal of Alloys and Compounds 644 (2015) 256–266 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom