Characterization of silicides in high-temperature titanium alloys

Different types of silicides precipitate in high-temperature titanium alloys depending upon the composition and heat treatment of the alloys. However, there are inconsistencies and lacunae with respect to the chemical and crystallographic characteristics of the silicides and these are pointed out here. Hexagonal silicides s1 (a=0.7804 nm; c=0.5447 nm) and s2 (a=0.701 nm; c=0.368 nm) coexist in the ternary alloy Ti–5Zr–Si; however, only the s2 silicide exists when the addition of stabilizing element is made. In addition, there is no common agreement about the space group of s2 silicide while the space group of s1 silicide was found to be P63/mcm (hP16). The (TiZr)6Si3 stoichiometry of s2 silicide is based on the experimental findings; however, the (TiZr)5Si3 stoichiometry of s1 silicide is simply deduced. Also the orientation relationships of silicides with and phases of the matrix are discussed.