Investigation On The Rapid Sintering And Performance Of Ti₃AlC₂-based Ceramic Composites

As a ternary layered ceramic,Ti₃AlC₂ exhibits unique combination properties of both metal and ceramic,including the good thermal conductivity,low hardness,excellent oxidation resistance and thermal shock performance,good machinability and self-lubricant property etc.Usually,Ti₃AlC₂ and related MAX compounds were assumed as high-temperature-structural ceramics?HTSCs?.In this thesis,the pure Ti₃AlC₂ powders were fabricated with a self-propagating reaction route.And the Ti₃AlC₂-contained ceramic composites,including ZrB₂/Ti₃AlC₂,Ti₃AlC₂/BN and Ti₃AlC₂/Si₃N₄,were sintered with the Spark Plasma Sintering?SPS?technology.The phase compositions,microstructures and mechanical properties of these ceramic composites were studied in detail.We also used the first-principle calculations based on density functional theory?DFT?to investigate the crystal structure,stability,electronic structure and elastic properties of the MAX-based solid solutions.With comparasion to the typical HTSCs,the strength of Ti₃AlC₂ is not high enough to satisify the requirements under severe conditions.In the thesis,ZrB₂/Ti₃AlC₂ powder mixtures were designed and sintered with the SPS technology.During the SPS process,two main reactions occurred.First is the decomposition of Ti₃AlC₂,which resulted in Ti₃C₂ and melting Al.The second is the reaction among ZrB₂,Al and Ti₃C₂,which resulted in the depersion distribution of the hard TiC,ZrC,AlB₂,ZrB particles.Hereinto,the as-prepared ceramic composites were dense and exhibited higher bending strength,fracture toughness and Vicker's hardness than those of pure Ti₃AlC₂.The oxidation behaviors of ZrB₂/Ti₃AlC₂ceramic composites were also studied at the temperature range from 900 to 1100?under air condition.The ZrB₂/Ti₃AlC₂ ceramic composites showed inferior resistance to high-temperature oxidation than that of Ti3AlC2.The Ti₃AlC₂ powders were applied as the sintering additives to densitify hBN and Si3N4 ceramics by SPS technique.With the addition of Ti3AlC2,the dense hBN ceramic composites were fabricated at 1250¹500?.The bending strength of the as-prepared hBN-matrix composites was greatly improved with increasing of the content of Ti3AlC2 in the powder mixtures.Furthermore,the oriented microstures of layered hBN were also observed.The bulk Si3N4 ceramics were not abtained with the addition of Ti3AlC2 in this study.Finally,we also carried out the first-principle calculations on the crystal structure,thermodynamic stability,electronic structures and elastic properties of the 22 solid solutions based on Ti₂AlC,Ti₃AlC₂,Ti₄AlC₃.The results showed that the designed compounds are thermodynamically stable.The hardness and elastic modulus of carbon compounds is higher than that doped with Zr and B compounds,and the properties of the later ones decrease with the increase of Zr content.