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MoSi2-based composites reinforced with particles, whiskers, and continuous fibers were fabricated using hot pressing and hot isostatic pressing techniques. The microstructure, interface compatability, and interfacial properties between the reinforcements and matrix are discussed. The microstructural parameters which control the mechanical behavior of the MoSi2 composites were characterized. The need for developing a satisfactory reinforced MoSi2 composite for high-temperature structural applications is also addressed.

I. INTRODUCTION

Molybdenum disilicide (MoSi2) is a promising intermetallic compound for high temperature structural applications in oxidizing atmospheres.1"3 It has a higher melting point (2020 ± 20 °C) than aluminides of iron, nickel, and titanium; furthermore, it has excellent oxidation and hot corrosion resistance approaching that of SiC. Its outstanding oxidation resistance is due to the formation of a glassy silica (SiO2) layer which acts as a protective film at high temperatures. It also possesses good electrical conductivity which is similar to that of steel. However, like most of the intermetallics, the major problems impeding the use of MoSi2 are its extreme brittleness and poor impact strength at lower temperatures. It exhibits a brittle-to-ductile transition at approximately 900-1000 °C. Above this temperature, MoSi2 behaves more like a metal, showing yielding and stress-relieving characteristics. The strength of MoSi2 at elevated temperatures is relatively low since it undergoes creep and plastic deformation at temperatures above the transition temperature. Therefore, to make MoSi2 a viable structural material, it is necessary to improve the room-temperature fracture toughness, elevated-temperature strength, and creep resistance.4 One obvious strengthening/toughness approach is through the incorporation of second phase reinforcements. Previous studies indicate that the addition of SiC whiskers improved the fracture toughness and flexural strength of the MoSi2.5"8 However, the size, geometry, and distribution of the reinforcement will significantly affect the properties of the resulting composites. It has been shown that the addition of 30 vol. % Nb filaments into MoSi2 resulted in improvement of the flexural strength at room temperature.9 Alloying MoSi2 with other silicides such as WSi2 has also been demonstrated as a promising approach to increase the elevated-temperature mechanical properties.7 A significant effort is still needed to understand better the processing, microstructure, and property relationships so J. Mater. Res., Vol. 6, No. 3, Mar 1991 http://journals.cambridge.org

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as to develop a satisfactory reinforced MoSi2 for applications in extreme environments. The purpose of this work is to study the behavior of MoSi2 composites reinforced with particulates, whiskers, and continuous fibers. The microstructural parameters which control the mechanical properties and failure behavior of the MoSi2 are also characterized. II. EXPERIMENTAL A. Processing of Mo