Investigation On The Phase Composition,Microstructure And Properties Of Ti₃SiC₂ Matrix Composite

Ternary layered Ti₃SiC₂ as one of the typical 312-phases combines both metallic and ceramic properties.It possesses high melting point,strength,electrical and thermal conductivity,low friction coefficient,good microwave absorbing and thermal stability.Currently,the Ti₃SiC₂ has aroused significant interests in machinery,metallurgy,chemical,electromechanical and aerospace fields.The good electrical conductivity and mechanical properties are demanded while improving its oxidation resistance to facilitate the application of Ti₃SiC₂ extensively.In this study,Ti₃SiC₂-based composites are prepared by hot pressing sintering with the main raw materials of Ti,Si and TiC powders.The types?Al₂O₃,SiC,MgAl₂O₄,TaC?,particle sizes and addition amounts of additives and the reaction temperatures are studied systematically.Above effects on phase composition,microstructure,mechanical properties,oxidation resistance and electrical conductivity of the composites are summarized as follows:?1?Al₂O₃ and MgAl₂O₄ are chemically compatible with Ti₃SiC₂ under hot pressing.The dense Ti₃SiC₂-based composite can be obtained with a suitable amount of micro oxide?20wt%Al₂O₃,30wt%MgAl₂O₄?which is more favorable for the densification than the nano oxide.?2?The compactness of SiC/Ti₃SiC₂ composite decreases with the increase of SiC content at 1450? due to the low diffusion coefficient of covalently bonded SiC which is not favorable to the sintering densification at high temperature.Besides,the excessive SiC affects the sintering and densification of Ti₃SiC₂.The resultant main phases of Ti₃SiC₂ and TaTiC₂ refer to the introduction of TaC.The main phase of Ti₃SiC₂ is substituted by TaTiC₂ and TiC gradually when the amount of additive TaC increase from30wt%to 50%.?3?The mechanical properties of the Ti₃SiC₂-based composites are increased first and then decreased with the increasing second additive.The flexural strength and fracture toughness of Al₂O₃/Ti₃SiC₂ composite reach a maximum of 512 MPa and 7.09MPa·m^1/2 when the Al₂O₃ content is 30wt%and 20%,respectively.In addition,the flexural strength and fracture toughness of MgAl₂O₄/Ti₃SiC₂ composite reaches a maximum of 528MPa and 7.10 MPa·m^1/2 when the content of MgAl₂O₄ is 20wt%at1450?.?4?The 20wt%SiC/Ti₃SiC₂ composite has a flexural strength of 496 MPa and a fracture toughness of 7.70MPa·m^1/2 at 1450?.The mechanical properties of Ti₃SiC₂-based composites reach the highest by adding 30wt%TaC,and then deteriorated with the increasing of TaC corresponding to the greatly changes of phase composition and microstructure.?5?There is a close relationship between the mechanical properties and phase content,particle size of Ti₃SiC₂ for the Ti₃SiC₂-based composites.During the fracture process,the Ti₃SiC₂ wafer is bent and pulled out,resulting in crack deflection.Besides,the second phase causes the grain refinement and dispersion strengthening.?6?Introducing second phase such as Al₂O₃,MgAl₂O₄,SiC and TaC into Ti₃SiC₂,can elevate the high temperature oxidation resistance.The enhanced oxidation resistance of Ti₃SiC₂-based composites can be realized by the increasing amount of the additive.The Ti₃SiC₂-based composite with additive SiC exhibits the best oxidation resistance owing to the compact oxidation layer of SiO₂.?7?The TiO₂-SiO₂,TiO₂-SiO₂-Al₂O₃ and TiO₂-SiO₂-Al₂O₃-MgO phase diagram are calculated by Factsage software to explain the resultant compositions at high temperature and X-ray diffractions of SiC/Ti₃SiC₂,Al₂O₃/Ti₃SiC₂,and MgAl₂O₄/Ti₃SiC₂ composites.?8?The introduction of the second phase will reduce the electrical conductivity of the Ti₃SiC₂-based composite.Both of the smaller particle size and larger amount of additive can lead to the lower electrical conductivity at room temperature.