Investigation On The Preparation And Properties Of Ti₃SiC₂/Al₂O₃ Composites By Hot Pressing Sintering

Al₂O₃ has good physicochemical compatibility and complementary mechanical propertie with Ti₃SiC₂,Ti₃SiC₂/Al₂O₃ composites are considered as one kind of ideal structural materials.However,in most studies,Al₂O₃??30.0vol.%?was introduced into Ti₃SiC₂ matrix only as reinforcing phase,resulting in poor high temperature oxidation resistance of composites.At the same time,the preparation process of Ti₃SiC₂ is difficult to control due to the narrow phase region,and the presence of impurity phases such as Ti₅Si₃ further reduces the mechanical properties of Ti₃SiC₂/Al₂O₃ composites.In this study,using Ti₃SiC₂ and Al₂O₃as raw materials,the system design and process optimization of Ti₃SiC₂/Al₂O₃ composites were carried out by orthogonal test in the early stage,and in situ synthesis of Ti₃SiC₂/Al₂O₃composites were investigated in the late stage.The law of phase transformation,mechanical properties and high temperature oxidation behavior of Ti₃SiC₂/Al₂O₃ composites were also explored.Firstiy,four factors and three levels orthogonal experiments were designed by changing temperature,pressure,holding time and raw material ratio of Ti₃SiC₂ and Al₂O₃ via hot pressing sintering method,the basic parameters of preparation and performance optimization of Ti₃SiC₂/Al₂O₃ composite were obtained.After orthogonal analysis,the optimum volume ratio of Ti₃SiC₂ and Al₂O₃ was 4:6,the optimum sintering process was 1500?and holding pressure for 30min at 30MPa.Secordly,in order to research the phase composition and microstructure evolution of Ti-Si-C/Al₂O₃ system,composites were prepared via hot pressing sintering at 1600?under30MPa for 2h using different volume percentages of Ti,SiC and Al₂O₃ powders as raw material.With the increasing of SiC,new phases of TiC,Ti₅Si₃,Ti₃SiC₂ and TiSi₂ were gradually to be detected,which inhibited the abnormal growth of Al₂O₃ grain obviously.Howerer,large amount of molten Si generated at high temperature was not conducive to the in-situ synthesis of Ti₃SiC₂ which illustrated that Ti₃SiC₂/Al₂O₃ composites should be prepared less than 1600?.Thereafter,Ti,SiC,C,Al and Al₂O₃ were optimized as raw material to prepared Ti₃SiC₂/Al₂O₃ composite by in-situ synthesis via hot pressing sintering at1550?under 30MPa for 1.5h.The addition of proper amount of Al could maintain potential balance at weak Ti-Si bond,stabilize the lattice of Ti₃SiC₂ and and reduce the appearance of TiC impurity phase to promote its formation by replacing Si in Ti₃SiC₂.The introduction of Al can promote the sintering densification of Ti₃SiC₂/Al₂O₃composites by melting to produce liquid phase and increasing the content of Ti₃SiC₂ which was beneficial to improving the mechanical properties of Ti₃SiC₂/Al₂O₃ composites.Ti₃SiC₂possess special layered structure which can prolong the crack path and deflect it by means of fracture modes along or through lamellae,thus improving the mechanical properties of Ti₃SiC₂/Al₂O₃ composites.The optimum values of relative density,Vickers hardness,flexural strength and fracture toughness were 99.59%,16.97GPa,553.38MPa and 9.63MPa·m^1/2,respectively.The high temperature oxidation resistance of Ti₃SiC₂/Al₂O₃ composites was studied at different temperatures?1000?,1100?,1200?,1300?and 1400??and holding time?1h,2h,4h,6h and 12h?.The experimental results showed that the change of oxidation weight gain curve of Ti₃SiC₂/Al₂O₃ composites to temperature growth was in accordance with parabolic law.The function equations of reaction rate constant and temperature for blank and Al-doped samples were established,the activation energies of oxidation reaction were218.51kJ/mol and 255.15kJ/mol,respectively.That was to say,the introduction of Al can increase the activation energy of oxidation reaction and inhibit the oxidation reaction.The products and distribution of the oxide layer was analyzed and determined that the high temperature oxidation resistance mechanism of the oxide layer was that the formation of Al₂O₃ and Al₂TiO₅ restricts the exchange of substances between the matrix and external environment.Al doped Ti₃SiC₂/Al₂O₃ composites samples preferentially produce Al₂O₃ and Al₂TiO₅ antioxidant which exhibit higher activation energy and better antioxidant ability at high temperature over a long period of time.