Growth Mechanism And Oxidation Behavior Of Self-propagating High Temperature Synthesis Ti₂Al?C,N?

Ti₂Al?C,N?is the X-site solid solution of MAX phase ceramics,which,like MAX phase ceramics,has the dual properties of metal and ceramics,and has attracted the attention of researchers in recent years.In this paper,a fast and energy-saving self-propagating high-temperature synthesis?SHS?method was used to prepare Ti₂Al?C,N?solid solution from Ti,Al and g-C₃N₄ powders.The effect of Al content on the purity of the product and the morphology of the product were analyzed.The reaction mechanism of Ti₂Al?C,N?and the layered growth mechanism of its grains were studied.The isothermal oxidation behavior of Ti₂Al?C,N?powder in air environment was studied,and the composition and oxidation mechanism of oxidation products were analyzed.Graphite-like layered g-C₃N₄ was prepared by pyrocondensation polymerization with melamine as precursor,and then used as a single source of C and N.Ti₂Al?C,N?solid solution was prepared by self-propagating combustion synthesis using Ti powder,Al powder and g-C₃N₄ powder as raw materials in a stoichiometric ratio of 2:x?x=0.9,0.95,1,1.05,1.1?:1.Appropriate increase in the amount of Al contributes to the improvement of the purity of Ti₂Al?C,N?,but the excessive amount of Al lowers the purity of the product,and the purity is the highest when the amount of Al is 1.05 mol.Ti₂Al?C,N?has typical MAX phase ternary ceramic morphology and the grain is a nanosheet layered structure.At the fracture surface,the stress caused by the external force causes a relative slip between the crystal grains or the crystal grains to cause the kink,and also breaks the weak bond in the structure to cause the nano monolayer to fall off.In the reaction,Al melting promotes the reaction of Ti?s?and g-C₃N₄?s?to form Ti?C,N??s?,Ti?s?and Al?l?to form TiAl?s?during the reaction cooling process.Finally,Ti?C,N??s?and TiAl?s?are reacted as intermediates to form Ti₂Al?C,N??s?.The study of the layered growth mechanism of Ti₂Al?C,N?solid solution shows that the Ti₂Al?C,N?grains grow in a two-dimensional growth mechanism and grow in a step-like growth mode;the Ti₂Al?C,N?large grain layers has an inward lateral spreading mode;the presence of small impurity particles hinders the lateral spreading of the Ti₂Al?C,N?layer.The Ti₂Al?C,N?powder was used as the research object,and the isothermal temperature oxidation experiment was carried out in the air atmosphere.Basic oxidation is complete when oxidizing to 900°C at 400°C.In the oxidation process,Al is more likely to combine with O to form oxides than Ti.When O diffuses inward,C and N diffuse outward in the form of gas.The final products of oxidation are rutile TiO₂ and?-Al₂O₃.The oxide film has a certain protective effect on the oxidation of the powder,which also indicates that Ti₂Al?C,N?has good antioxidant capacity and has certain application prospects.