Research On Interfacial Reaction Mechanism And Diffusion Dynamics Of Ti/Al₂O₃ Composites Based On Hot Press Sintering

Ti has good wettability and similar coefficient of thermal expansion with Al₂O₃, so Ti/Al₂O₃ cermets keep the both advantages of the base materials. But Al₂O₃ strongly reacts with Ti at high temperature and leads to the formation of Ti3 Al and Ti Al phases, which decreases the mechanical properties of the Ti/Al₂O₃ composites. In this paper, microstructures, phase compositions and element diffusions at the interfaces were studied in details by vacuum hot-press sintering. Furthermore, the kinetics equation of interfacial reaction was deduced, which provided theoretical basis for the interfacical modifying.The effects of sintering temperature?1150-1450 ?? and holding time?1.5-2.5 h? on the interfacial reactions were studied by hot-press sintering technique and powder-wrapping method. The results showed that the thicknesses of the reaction layers increased in a manner of exponential growth with the increasing of the sintering temperature, and the interfacial microstructures became much denser. At the same time, the thicknesses of the reaction layers increased in a manner of linear growth with the extending of the holding time, and the interfacial microstructures changed very little. Additionally, diffusion coefficients were calculated based on the second Fike's law. At 1450 ?, the thickness of the reaction layer was 112.5 ?m, the diffusion coefficients of Al, O and Ti were 2.71 × 10-8 cm2s-1, 5.22 × 10-10 cm2s-1 and 4.62 × 10-11 cm2s-1, respectively. Among them, Al element had the most powerful diffusivity. So it could be concluded that the formation of the reaction layer was caused by the diffusion of Al into the Ti phase, which was the typical diffusion-controlling growth mode. The growth process was divided into three parts, physical contact, the activation of contact surface and interfacial reaction. The results of XRD indicated that the reaction layer was composed of TiAl and Ti3 Al. Moreover, diffusion mechanism was discussed, which demonstrated that Al element diffused by vacancy mechanism, Ti and O diffused by interstitial mechanism.Rare earth oxide Y₂O₃ and CeO₂ were used as additives to control interfacial reaction and their effecting mechanisms were analyzed. The results showed that the diffusion coefficients were reduced in different degrees due to the additives. Also, the phase compositions of the reaction layers were changed by the generation of CeAlO3, CeAl11O18, YAl and YAl2. As a whole, CeO₂ performed more effective in controlling the interfacial reaction than Y₂O₃, and its superior effect could be explained by its smaller ionic radius, lower bond energy and more powerful ability of combining with Al₂O₃.The growth relationship of the reaction layer with sintering temperature and holding time were presented. The reaction activation energy was calculated to be 153.1 kJ/mol and the dynamic index was 0.96. Meanwhile, reaction activation energy after adding 3 vol.% Y₂O₃ and CeO₂ were calculated to be 159.0 kJ/mol and 172.2 kJ/mol, respectively. Compared with the blank sample, the reaction activation energy could be improved by 3.85 % and 12.48 %, respectively. Thus, the inhibiting effects of Y₂O₃ and CeO₂ could be caused by the improved energy barrier during the elemental diffusion from a dynamic perspective.