Phase Formation in the SHS of a Ti-B Mixture with the Addition of Si3N4
D. Yu. Kovalev, A. S. Konstantinov, S. V. Konovalikhin, A. V. Bolotskaya
Merzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, 142432 Russia
Keywords: self-propagating high-temperature synthesis, combustion synthesis, cubic TiB, ceramic material, composite
Abstract
The structure and phase composition of a material obtained via SHS in the combustion of a 87 % Ti + 13 % B powder mixture with the addition of Si3N4 is under study. The phase formation mechanism in this system is discussed. It is established that the material contains 64 % of the TiB phase with an orthorhombic structure and 36 % of the solid boron solution in titanium (α -Ti[T]). The boron content in α -Ti significantly exceeds its equilibrium content according to a state diagram. In the case of combustion of an 87 % Ti + 13 % B mixture with the addition of 5 % Si3N4, the finite product contains TiB, α -Ti[B], TiB2, and Ti5Si3 phase. The TiB phase is present in the form of two modifications: orthorhombic and cubic. The completeness of a structural transition of the cubic modification of TiB into an orthorhombic one is determined by the cooling rate of a sample. It is assumed that the combustion of the mixture with the addition of Si3N4 forms the dispersed discharges of TiN, which are the crystallization centers of cubic TiB.
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