Silicide based composites

Titanium-based composites discontinuously reinforced with silicides, borides and their mixtures are an attractive candidate to be a material with... 

M.J. Maloney and R.J. Hecht, Development of continuous Fiber-Reinforced MoSi2-base Composites, in High Temperature Silicides, Eds., A.K. Vasudevan and J.J. Petrovic, North Holland, NY, 19-32 (1992). 

Oxidation of niobium silicide-based in-situ composites... 

The effects of alloying additions on the oxidation of Nb silicide-based in-situ composites have also been investigated and could be summarised as follows ... 

Titanium silicides are used in the preparation of abrasion- and heat-resistant refractories. Compositions based on mixtures of T Si, TiC, and diamond have been claimed to make wear-resistant cutting-tool tips (157). Titanium silicide can be used as an electric—resistant material, in electrically conducting ceramics (158), and in pressure-sensitive elastic resistors, the electric resistance of which varies with pressure (159). 

Primer compositions fall into two main categories corrosive mix types based on potassium chlorate/lead thiocyanate and noncorrosive mix types based on lead styphnate/tetracene. Some of these mixes were listed in the previously in Table 23.2. High-temperature-resistant mixes (designated by a G following the mix name or number) are a varient of the corrosive mix types. These are based on potassium chlorate /antimony trisulfide/calcium silicide. 

Hypoeutectic Ti-3Al-4Si and Ti-3Al-6Si alloys have a dendrite-like microstructure with eutectic colonies between dendrites, which is typical for alloys of the Ti-Si-system (Fig. le,k). The introduction of Zr to these alloys results in both refinement of the alloy microstructure and the eutectic silicides, and a changing of phase composition (Table 1). Another type of eutectic based on the ternary (Ti,Zr)2Si silicides is formed in hypoeutectic alloys containing a high content of Zr (Fig. lm). 

In order to take advantage of the superior properties of these refractory silicides in combination with a ductile titanium matrix particle and fiber reinforced composites based on a-Ti-Si-(Al) have been developed. Two different processing routes have been performed ... 

The densities of the stoichiometric compositions were determined to 4.32 g/cm3 for Ti5Si3 and 4.07 g/cm3 for TiSi2. Both compounds possess lower densities than titanium base alloys. A good correlation between binding energies, melting temperatures and microhardness of the investigated silicides is shown in table I. 

The research activity on the oxidation and corrosion in Japan is characterised by the fact that the major effort has been expended on TiAl-base materials. The research on MoSi2 follows that on TiAl-base materials with much small percentage. Other alumi-nides and silicides are being dealt with. There seems to be no research on beryllides. Throughout this paper AI203 means a-alumina and TiOz rutile, and the specimen composition is expressed in mass per cent unless otherwise stated. 

The partial substitution of the transition element M in MjSi by a second transition metal M leads to ternary silicides of approximate composition MM Si corresponding to (M,M )2Si. Such ternaries are primarily the Si-containing E phases and V phases (Jeitschko etal., 1969 Jeitschko, 1970) and the ternary Si-containing Laves phases (Bardos etal., 1961), which were discussed in Sec. 8, as well as many other phases, which all differ by composition and crystal structure (Nowotny, 1972 a). This is exemplified by the Fe-Nb-Si system with the ternary silicides E, V, Xj, Xj, Xj and the Laves phase Nb(Fe,Si)2 with up to 25 at.% Si (Raghavan, 1987), or the Co-Nb-Si system with the ternary silicides E, T, v, Ti, v i, and the ternary Laves phase Nb(Co,Si)2 with Si contents between about 10 and 20 at.% (Argent, 1984). Finally, it is noted that other phases - in particular a phases and A13 Mn-base phases - dissolve large amounts of Si by which these phases are stabilized (Gupta et al., 1960 Bardos et al., 1966). 

Multiphase Hard Materials Based on Carbide-Nitride-Boride-Silicide Composites... 

Although the data presented in Fig. 11.2 are useful for a fundamental understanding of silicon-containing materials, considering the practical applications, the capacity per unit weight is the most important parameter. As can be seen clearly in Table 11.2, most of the silicides can hardly compete with modem carbonaceous anodes. Therefore, a technically interesting choice is to use composite materials based on elemental silicon or SiO. 

The history of ceramics is as old as civilization, and our use of ceramics is a measure of the technological progress of a civilization. Ceramics have important effects on human history and human civilization. Earlier transitional ceramics, several thousand years ago, were made by clay minerals such as kaolinite. Modem ceramics are classified as advanced and fine ceramics. Both include three distinct material categories oxides such as alumina and zirconia, nonoxides such as carbide, boride, nitride, and silicide, as well as composite materials such as particulate reinforced and fiber reinforced combinations of oxides and nonoxides. These advanced ceramics, made by modem chemical compounds, can be used in the fields of mechanics, metallurgy, chemistry, medicine, optical, thermal, magnetic, electrical and electronics industries, because of the suitable chemical and physical properties. In particular, photoelectron and microelectronics devices, which are the basis of the modern information era, are fabricated by diferent kinds of optical and electronic ceramics. In other words, optical and electronic ceramics are the base materials of the modern information era. 

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