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Microstructure and properties of bilayer-graded Al-matrix composites by one-step pressureless infiltration of B4C/rice-husk ash preforms Amin Bahrami1a, Martin I. Pech-Canul1b, Carlos A. Gutiérrez1, Niloofar Soltani1 1

Centro de Investigación y de Estudios Avanzados del IPN Unidad Saltillo, Ave. Industria Metalúrgica No. 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, México, 25900. 1a [email protected], [email protected]

ABSTRACT The quantitative effect of the following parameters on the one single step pressureless infiltration characteristics of bilayer B4Cp/rice-husk ash (RHA) porous preforms by aluminum alloys was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, B4C particle size, RHA percentage, percentage porosity in the preforms, and magnesium content in the alloy. The contributions of each of the parameters to the retained porosity, hardness and modulus of elasticity of the resulting bilayer composites were determined. The parameters that most significantly impact the modulus of elasticity (E) of the resulting composites are chemical composition of Al alloy followed by porosity of preforms and B4C particle size. Their relative contributions to the variance in the values of modulus of elasticity are 25.7, 22.48 and 18.44 %, respectively. Verification tests conducted using the established optimum parameters show a good agreement with those of projected values. INTRODUCTION Despite outstanding physical and mechanical properties of boron carbide, the extreme sensitivity of B4C to brittle fracture and the difficulties associated with fabricating fully dense microstructures are serious limitations. The experiments have demonstrated that these issues can be significantly reduced by introducing a metal phase (i.e., by developing B4C cermet) [1]. There are several methods for fabrication of metal matrix composites, including but not limited to: casting, powder metallurgy, melt infiltration, etc. [2-7]. In this investigation, it is suggested that graded metal matrix composite materials may be produced by one-step infiltration process. Nonetheless, a number 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 spite of various efforts devoted to the optimization of wettability and pressureless infiltration parameters [8], it is expected that in pressureless infiltration-based processing, changes of key parameters (reinforcement composition, size, percentage porosity in the preform) from one section to another within the ceramic preform (layer-by-layer) will increase the inherent barriers and challenges. It was reported that some of the problems associated with the infiltration process can be solved by adding special elements or phases [9]