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 s(1) (a = 0.780(4) nm; c = 0.544(7) nm) and s(2) (a = 0.70(1) nm; c = 0.36(8) nm) coexist in the ternary alloy Ti-5Zr-Si; however, only the s(2) silicide exists when the addition of beta stabilizing element is made. In addition, there is no common agreement about the space group of s(2) silicide while the space group of s(1) silicide was found to be P6(3)/mcm (hP16). The (TiZr)(6)Si-3 stoichiometry of s(2) silicide is based on the experimental findings; however, the (TiZr)(5)Si-3 stoichiometry of s(1) silicide is simply deduced. Also the orientation relationships of silicides with a and beta phases of the matrix are discussed.