Study On The Synthesis Of Ternary Layered Machinable Carbide Ti₂AlC

Ti2A1C is a new kind of ceramic material that combines the merits of both metals and other ceramics. Its unique property lies on the fact that it has high fracture toughness and can be easily machined like metal. Furthermore, it has high electricity conductivity of metal and high strength and excellent oxidation-resistance of ceramic. So it is a new promising structure & function integrated ceramic material that will be widely used in the future. However, fabrication of single-phase Ti2AlC material is a tough task since TiC and other phases always exist in the final product as impurities. So we focused on the synthesis of single-phase Ti2AlC bulk ceramic in this research. Apparatus used for analysis and detection included X-ray diffraction system (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), and electron probe microanalyzer (EPMA).The emphasis of this research is on the synthesis of single-phase Ti2AlC bulk ceramic by hot pressing. Effects of different process parameters including hot pressing temperature, soaking time, aluminum content of the powder mixture, sorts of the raw materials (elemental powder mixture of Ti, Al and active carbon or powder mixture of TiC, Ti and Al), and Si additive on the synthesis process and the content of Ti2AlC in the final product were investigated.Research on the fabrication of single-phase Ti2AlC bulk ceramic by spark plasma sintering form elemental powder mixture of Ti, Al and active carbon was also conducted. Effects of different process parameters including synthesis temperature, aluminum content of the powder mixture, and Si additive on the content of H2A1C in the final product were investigated.Finally, we characterized the properties of Ti2AlC bulk ceramic synthesized in this research and carried out analysis on its damage-tolerance mechanisms.Results show that dense Ti2AlC bulk material with only a few Ti3AlC2 as secondary phase and without any other impurity such as TiC can be prepared by hot pressing process. Properly increasing Al content of powder mixture composed of Ti, Al, and active carbon eliminated the appearance of TiC in the final product and thus improved the content of Ti2AlC in the product. Proper increase of Al content also boosted the reaction speed and finished the reaction at lowertemperature within given soaking time. Further increasing Al content of powder mixture composed of Ti, Al, and active carbon enhanced the formation of Ti3AlC2 and Ti-Al intermetallic in the final product and thus was not good for the synthesis of Ti2AlC. Best result was achieved when powder mixture of 2.0Ti/1.1A1/1.0C was hot pressed at 1450 for 60 minutes. Replacing elemental powder Ti and active carbon with TiC increased the reaction speed and also finished the synthesis process at lower temperature of 1400 within given soaking time. However, Al content nearly had no effect on the reaction speed when TiC was used as raw materials. In the same way, excessively increasing Al content of powder mixture composed of TiC, Ti and Al resulted in the formation of a large amount of Ti3AlC2 and Ti-Al intermetallic in the final product.It is found in hot pressing process that adding Si in the raw materials resulted in the appearance of Ti3SiC2, and further enhanced the formation ofTi3AlC2 in the final product due to the crystal seed effect (template effect) of Ti3SiC2, no matter elemental powder mixture of Ti, Al, and active carbon or powder mixture of TiC, Ti, and Al was used. So Si additive did harm to the synthesis of single-phase Ti2AlC material in hot pressing. Moreover, such effect was more violent and more obvious when TiC was used to replace elemental powders of Ti and active carbon as raw materials: three phases Ti2AlC, Ti3AlC2 and Ti3SiC2 co-existed in the final product even more Si was added to the powder mixture of Ti, Al and active carbon and Ti2AlC was the main phase; however, the final product was composed of single-phase Ti3 A1C2 even less Si was added to the powder mixture of TiC, Ti, and Al.It is also shown that T...