Study On TiC-Al₂O₃/Fe-Al Composites From Ilmenite By In-Situ Aluminothermic And Carbothermic Reduction

TiC–Al₂O₃/Fe–Al composites have shown excellent properties as a kind of engineering materials. So far, the most common powder metallurgy method has the deficiency of contamination between the hard phase and the metal alloy binder phase, which is bad to the mechanical performances, and this method can caused a high cost. Those are all bottle necks of its applications. The job of exploring a new approach to fabricate composites with a relative lower cost and higher performances becomes very important for its application.TiC–Al₂O₃/Fe–Al composites were fabricated by aluminothermic and carbothermic reduction through self–propagating high–temperature synthesis (SHS) or reaction sintering from abundance natural ilmenite. And then thermodynamic analysis was studied in detail through theoretical analysis and experimental investigated. Meanwhile, the reaction process mechanism of FeTiO₃–Al–C system was elementary discussed. This work contributes to a lot to research and industrialized application of in–situ process for natural mineral fabricating cermets.Through various analytical methods, it is shown that the formation process of TiC–Al₂O₃/Fe–Al composites was multistage: First, ilmenite was reduced to different valent titanium oxides and iron by melting aluminum, including TiO₂, Ti₃O₅, Ti₂O₃ and other unknown Ti_xO_y phases when aluminum and carbon were coexisted. This process can be explained with a dissolution–precipitation mechanism. Then, low valent titanium oxides are directly reverted to TiC by carbon, not through the high active [Ti], when aluminum has not enough reducibility. Following the reactive process, TiC with near stoichiometric ratio is formed step by step from TiC_x with less C content, and thenα–Fe solid solution with aluminum reverted to ordered intermetallics. This research has demonstrated the feasibility of producing TiC–Al₂O₃/Fe–Al composites by SHS from natural ilmenite. It is conduced to the formation of ordered intermetallics through prolonging the preheating time or heat treatment, but the disordered alloys are difficult to eliminate with the preheating time prolonged. The compound powders mainly containing ordered Fe3Al intermetallic can be prepared through heat treatment at 750oC.It is indicated that composites had good properties at 1550oC/30MPa in an inert argon atmosphere when the binder phase is Fe–28at%Al. The beneficial effect additives are due to improve the wettability of the metal alloy binder on the ceramic phases and restrain the reaction between TiC and Al₂O₃. Improved wettability resulted in a decrease in detrimental microstructure defects and an increase in the interphase bond strength and phase uniformity. The bending strength of the cermets reached 613.5MPa and the relatively density was 98.47% with additives of 5wt%Mo, 5wt%Ni, 5wt%Cr2O₃, 0.2wt%Y₂O₃ together.