Preparation and characterization of composite materials obtained by pressure infiltration of aluminum in sintered SiC/kaolin preforms

摘要

The present work involved the preparation and characterization of SiC-Al composites containing kaolin concentrations varying from 10 to 50% in substitution of the major SiC phase. Ceramic preforms were produced, controlling the granulometric fraction of SiC/kaolin. After sintering at 1100 A degrees C, these preforms were highly porous. XRD analyses revealed the existence of quartz and SiC phase. During the infiltration process, the molten aluminum reacted preferentially with the quartz and with other aluminosilicates in the preforms, reducing them and precipitating alumina and silica in the microstructure, which also showed excess aluminum that did not react in the process. The silica and silicates of the preform, by reacting preferentially with the aluminum, preventing the formation of Al4C3 phase. The SiC-kaolin-Al composites developed here can be used in applications that require high flexural strength (240-300 MPa), low density, and surface hardness of 180-380 kgf/mm(2).