Study On Synthesis And Properties Of Ti₃AlC₂/Al₂O₃ Composites By In-situ Reaction

The laminated ternary carbide Ti₃AlC₂, which is a new kind of structural ceramics material, becomes the focus of material researchers attributing to its perfect combination of both merits of metals and ceramics. Like metals, it is a good thermal and electrical conductor, relatively soft. Like ceramics, it is resistant to thermal shock and unusually damage tolerant, and exhibit excellent corrosion resistance. Above all, unlike conventional carbides, they can be machined by using conventional tools without lubricant, which is of great technological importance for their application. Additionally, Ti₃AlC₂ is an exceptional solid lubricant with an ultra-friction. These excellent properties mentioned above make them another family of technically important materials. Unfortunately, there are relatively soft and low creep strength, limit the potential application of as a high-temperature structural material.Incorporation of second phase is an effective way to overcome these weaknesses. Owing to the high hardness, high modulus, excellent chemical stability, and approximate thermal expansion coefficient, Al₂O₃ herein is chosen to produce Ti₃AlC₂/Al₂O₃ composites in order to increase the hardness and strength of Ti₃AlC₂. Also, the microstructures, the physical properties as well as reaction mechanism of the obtained materials were investigated, respectively.In this study, fully dense Ti₃AlC₂/Al₂O₃ composites were synthesized the in-situ SPS sintered at 1250℃and hot pressings sintered at 1400℃with different volume content of Al₂O₃ from 5 to 25vol.%, and Si was chosen as the synthesis additive. Investigated by X-ray diffraction (XRD) of samples sintered by different technics, there were more impurity phases sintered by SPS, the more purity Ti₃AlC₂/Al₂O₃ was synthesized by hot pressing. The hot pressing was chosen as the sinter technics. The results indicated that:(1) The bulk Ti₃AlC₂/Al₂O₃ with a relative density of 99% was fabricated by HP under 30 MPa and at 1400℃for 2h. The main phases were Ti₃AlC₂ and Al₂O₃, including a few of TiC.(2) The results of SEM indicated that: The grains of Ti₃AlC₂/Al₂O₃ composites were structured in a layered form. The grains of Al₂O₃ distributed in Ti₃AlC₂ matrix phases, it was well developed and distributed symmetrically. With the volume content of Al₂O₃ increased, the reaction of layered grains was restrained, the plate-shape diminished obviously and the agglomeration of Al₂O₃ particles could be found.The physical properties, room corrosion and the cyclic oxidation of the Ti₃AlC₂/Al₂O₃ composites with the different content of Al₂O₃ were studied in the paper. Its properties are greatly enhanced with the addition of Al₂O₃. Results revealed that the Vickers hardness is 8.7GPa when the Al₂O₃ content is 25vol.%, the flexural strength and fracture toughness of Ti₃AlC₂/10vol.%Al₂O₃ composites are 461.10MPa and 6.20MPa·m^1/2 , respectively. The electric conductivity of the composites decreased from 3.05×l0⁶S·m^-1 to 2.68×10⁶S·m^-1 with the volume contents of Al₂O₃ ranging from 5 to 25vol%.The corrosion behavior of composites indicated that the sample immersion in HNO₃ had the largest corrosion rate.The cyclic oxidation of resistance of Ti₃AlC₂/10vol.%Al₂O₃ composites at 800℃-1000℃was studied, its cyclic oxidation behavior generally obeys a parabolic law, and the parabolic rate constants are 1.10×10^-11kg²Â·m^-4·s^-1, 3.70×10^-10 kg^·m^-4·s^-1, 6.69×10^-10 kg²Â·m^-4·s^-1, respectively. The oxide scale of oxidized samples consisted of a mass ofα-Al₂O₃ and TiO₂ as a dense and adhesive protect scale. The oxide scale is grown by the inward diffusion of O^2- and the outward diffusion of Al³⁺ and Ti⁴⁺.