Regularities of Composite Materials with Micrograded Grain Structure Formation
Composite carbide materials in Ti-C, Ti-Nb-C, Ti-Zr-C systems were produced by combustion synthesis using the force SHS-pressing technology and investigated. Composition and structure of the synthesis products before and after annealing at 850oC, 1 hour were studied using optical and SEM, X-ray diffraction and Auger Electron Spectroscopy. It was established that SHSproducts consist of two main phases: TiC0.6+β-Ti, (Ti,Nb)C1-х + β-(Ti,Nb), (Ti,Zr)C 1-х + β-(Ti,Zr). Structure of these composite materials presented by carbide phase with a grain size varying 4-8 µm, and surrounded intergranular thin layer of β-Ti solid solution with width less than 1.5 µm. Composition and structure of carbide grains and intergranular phase just after combustion process is not equilibrium: supersaturated solid solutions are formed because of high temperature gradient and combustion velocity. Annealing results in an equalization of the solid solution composition. Carbide grains content precipitations sized 20-200 nm based on solid solution (Me-Ti). Two possible schemes of concentration separation of supersaturated solid solution were discussed: (Ti, Nb)x+yC = (Ti, Nb)xC 1-х + y(Nb-Ti) and (Ti, Zr)x+y C = (Ti, Zr)xC1-х + y(Ti-Zr). Lattice parameter of the intraganular phase differs from the matrix ones. Graded distribution of Nb and Zr alloying elements inside the carbide grains was observed. The developed composite materials strengthened by nano- or microsized particles are attractive for high-temperature applications.
Omer Van der Biest, Michael Gasik, Jozef Vleugels
V.V. Kurbatkina and E.A. Levashov, "Regularities of Composite Materials with Micrograded Grain Structure Formation", Materials Science Forum, Vols. 492-493, pp. 615-620, 2005