A Perspective on MoSi 2 Based Composites
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A PERSPECTIVE ON MoSi2 BASED COMPOSITES J.J. PETROVIC* AND A.K. VASUDEVAN** *Materials Science and Technology Division, Group MST-4, Los Alamos National Laboratory, Los Alamos, NM 87545 "**Office of Naval Research, Code 1222, 800 North Quincy Street, Arlington, VA 222175000 ABSTRACT
MoSi 2 based composites represent an important new class of "high temperature structural silicides", with significant potential for elevated temperature structural applications in the range of 1200-1600 oC in oxidizing and aggressive environments. The properties of MoSi 2 which make it an attractive matrix for high temperature composites are described and the developmental history of these materials traced. Latest results on elevated temperature creep resistance, low temperature fracture toughness, and composite oxidation behavior are summarized. Important avenues for future MoSi2 based composite development are suggested. INTRODUCTION
MoSi2 based composites are attracting increasing attention as high temperature structural materials [1]. The purpose of the present discourse is to provide a perspective on these silicide-based materials, describing their characteristics, highlighting key recent research results, and suggesting important avenues for further development. The intermetallic compound MoSi 2 was first investigated by Hoenigschmid in 1907 [2]. Due to its excellent high temperature oxidation resistance and brittle characteristics at low temperatures, it was initially used as an oxidation resistant coating material for metals. Later, based on its electrical conductivity, it was employed as a heating element material for electrical resistance furnaces [3]. This heating element application continues to the present. In the early 1950's, Maxwell first suggested the use of MoSi 2 as an elevated temperature structural material [4], and determined some of its high temperature mechanical properties. However, due to the low temperature brittle nature of MoSi 2 , Maxwell's work was not continued, since the materials community at that time did not possess the tools to deal with brittle structural materials. In the 1970's, Fitzer began examining MoSi2 composites reinforced with A1203, SiC, and Nb wire as a means to improve the mechanical properties of MoSi2 [5]. Encouraging results obtained by Fitzer lead to a review article by Schlichting [6], suggesting the use of MoSi 2 as a matrix material for high temperature structural composites. Two key articles were published in 1985. The first was an article by Fitzer and Remmele [7], describing in detail their investigations of Nb wire-MoSi2 matrix composites. In particular, they showed that Nb wire reinforcements significantly improved the room temperature mechanical properties of such composites. The second article was by Gac and Petrovic [8], in which they established the feasibility of SiC whisker-MoSi2 Mat. Res. Soc. Symp. Proc. Vol. 273. @1992 Materials Research Society
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matrix composites, demonstrating improvements in room temperature strength and fracture toughness. In 1988, Carter
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